FreeBSD/Linux Kernel Cross Reference
sys/kern/kern_prot.c

     /*-
      * SPDX-License-Identifier: BSD-3-Clause
      *
      * Copyright (c) 1982, 1986, 1989, 1990, 1991, 1993
      *      The Regents of the University of California.
      * (c) UNIX System Laboratories, Inc.
      * Copyright (c) 2000-2001 Robert N. M. Watson.
      * All rights reserved.
      *
     * All or some portions of this file are derived from material licensed
     * to the University of California by American Telephone and Telegraph
     * Co. or Unix System Laboratories, Inc. and are reproduced herein with
     * the permission of UNIX System Laboratories, Inc.
     *
     * Redistribution and use in source and binary forms, with or without
     * modification, are permitted provided that the following conditions
     * are met:
     * 1. Redistributions of source code must retain the above copyright
     *    notice, this list of conditions and the following disclaimer.
     * 2. Redistributions in binary form must reproduce the above copyright
     *    notice, this list of conditions and the following disclaimer in the
     *    documentation and/or other materials provided with the distribution.
     * 3. Neither the name of the University nor the names of its contributors
     *    may be used to endorse or promote products derived from this software
     *    without specific prior written permission.
     *
     * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
     * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
     * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
     * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
     * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
     * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     * SUCH DAMAGE.
     *
     *      @(#)kern_prot.c 8.6 (Berkeley) 1/21/94
     */
    
    /*
     * System calls related to processes and protection
     */
    
    #include <sys/cdefs.h>
    __FBSDID("$FreeBSD$");
    
    #include "opt_inet.h"
    #include "opt_inet6.h"
    
    #include <sys/param.h>
    #include <sys/systm.h>
    #include <sys/acct.h>
    #include <sys/kdb.h>
    #include <sys/kernel.h>
    #include <sys/lock.h>
    #include <sys/loginclass.h>
    #include <sys/malloc.h>
    #include <sys/mutex.h>
    #include <sys/refcount.h>
    #include <sys/sx.h>
    #include <sys/priv.h>
    #include <sys/proc.h>
    #include <sys/sysent.h>
    #include <sys/sysproto.h>
    #include <sys/jail.h>
    #include <sys/racct.h>
    #include <sys/rctl.h>
    #include <sys/resourcevar.h>
    #include <sys/socket.h>
    #include <sys/socketvar.h>
    #include <sys/syscallsubr.h>
    #include <sys/sysctl.h>
    
    #ifdef REGRESSION
    FEATURE(regression,
        "Kernel support for interfaces necessary for regression testing (SECURITY RISK!)");
    #endif
    
    #include <security/audit/audit.h>
    #include <security/mac/mac_framework.h>
    
    static MALLOC_DEFINE(M_CRED, "cred", "credentials");
    
    SYSCTL_NODE(_security, OID_AUTO, bsd, CTLFLAG_RW | CTLFLAG_MPSAFE, 0,
        "BSD security policy");
    
    static void crfree_final(struct ucred *cr);
    static void crsetgroups_locked(struct ucred *cr, int ngrp,
        gid_t *groups);
    
    #ifndef _SYS_SYSPROTO_H_
    struct getpid_args {
            int     dummy;
    };
    #endif
    /* ARGSUSED */
    int
   sys_getpid(struct thread *td, struct getpid_args *uap)
   {
           struct proc *p = td->td_proc;
   
           td->td_retval[0] = p->p_pid;
   #if defined(COMPAT_43)
           if (SV_PROC_FLAG(p, SV_AOUT))
                   td->td_retval[1] = kern_getppid(td);
   #endif
           return (0);
   }
   
   #ifndef _SYS_SYSPROTO_H_
   struct getppid_args {
           int     dummy;
   };
   #endif
   /* ARGSUSED */
   int
   sys_getppid(struct thread *td, struct getppid_args *uap)
   {
   
           td->td_retval[0] = kern_getppid(td);
           return (0);
   }
   
   int
   kern_getppid(struct thread *td)
   {
           struct proc *p = td->td_proc;
   
           return (p->p_oppid);
   }
   
   /*
    * Get process group ID; note that POSIX getpgrp takes no parameter.
    */
   #ifndef _SYS_SYSPROTO_H_
   struct getpgrp_args {
           int     dummy;
   };
   #endif
   int
   sys_getpgrp(struct thread *td, struct getpgrp_args *uap)
   {
           struct proc *p = td->td_proc;
   
           PROC_LOCK(p);
           td->td_retval[0] = p->p_pgrp->pg_id;
           PROC_UNLOCK(p);
           return (0);
   }
   
   /* Get an arbitrary pid's process group id */
   #ifndef _SYS_SYSPROTO_H_
   struct getpgid_args {
           pid_t   pid;
   };
   #endif
   int
   sys_getpgid(struct thread *td, struct getpgid_args *uap)
   {
           struct proc *p;
           int error;
   
           if (uap->pid == 0) {
                   p = td->td_proc;
                   PROC_LOCK(p);
           } else {
                   p = pfind(uap->pid);
                   if (p == NULL)
                           return (ESRCH);
                   error = p_cansee(td, p);
                   if (error) {
                           PROC_UNLOCK(p);
                           return (error);
                   }
           }
           td->td_retval[0] = p->p_pgrp->pg_id;
           PROC_UNLOCK(p);
           return (0);
   }
   
   /*
    * Get an arbitrary pid's session id.
    */
   #ifndef _SYS_SYSPROTO_H_
   struct getsid_args {
           pid_t   pid;
   };
   #endif
   int
   sys_getsid(struct thread *td, struct getsid_args *uap)
   {
   
           return (kern_getsid(td, uap->pid));
   }
   
   int
   kern_getsid(struct thread *td, pid_t pid)
   {
           struct proc *p;
           int error;
   
           if (pid == 0) {
                   p = td->td_proc;
                   PROC_LOCK(p);
           } else {
                   p = pfind(pid);
                   if (p == NULL)
                           return (ESRCH);
                   error = p_cansee(td, p);
                   if (error) {
                           PROC_UNLOCK(p);
                           return (error);
                   }
           }
           td->td_retval[0] = p->p_session->s_sid;
           PROC_UNLOCK(p);
           return (0);
   }
   
   #ifndef _SYS_SYSPROTO_H_
   struct getuid_args {
           int     dummy;
   };
   #endif
   /* ARGSUSED */
   int
   sys_getuid(struct thread *td, struct getuid_args *uap)
   {
   
           td->td_retval[0] = td->td_ucred->cr_ruid;
   #if defined(COMPAT_43)
           td->td_retval[1] = td->td_ucred->cr_uid;
   #endif
           return (0);
   }
   
   #ifndef _SYS_SYSPROTO_H_
   struct geteuid_args {
           int     dummy;
   };
   #endif
   /* ARGSUSED */
   int
   sys_geteuid(struct thread *td, struct geteuid_args *uap)
   {
   
           td->td_retval[0] = td->td_ucred->cr_uid;
           return (0);
   }
   
   #ifndef _SYS_SYSPROTO_H_
   struct getgid_args {
           int     dummy;
   };
   #endif
   /* ARGSUSED */
   int
   sys_getgid(struct thread *td, struct getgid_args *uap)
   {
   
           td->td_retval[0] = td->td_ucred->cr_rgid;
   #if defined(COMPAT_43)
           td->td_retval[1] = td->td_ucred->cr_groups[0];
   #endif
           return (0);
   }
   
   /*
    * Get effective group ID.  The "egid" is groups[0], and could be obtained
    * via getgroups.  This syscall exists because it is somewhat painful to do
    * correctly in a library function.
    */
   #ifndef _SYS_SYSPROTO_H_
   struct getegid_args {
           int     dummy;
   };
   #endif
   /* ARGSUSED */
   int
   sys_getegid(struct thread *td, struct getegid_args *uap)
   {
   
           td->td_retval[0] = td->td_ucred->cr_groups[0];
           return (0);
   }
   
   #ifndef _SYS_SYSPROTO_H_
   struct getgroups_args {
           int     gidsetsize;
           gid_t   *gidset;
   };
   #endif
   int
   sys_getgroups(struct thread *td, struct getgroups_args *uap)
   {
           struct ucred *cred;
           int ngrp, error;
   
           cred = td->td_ucred;
           ngrp = cred->cr_ngroups;
   
           if (uap->gidsetsize == 0) {
                   error = 0;
                   goto out;
           }
           if (uap->gidsetsize < ngrp)
                   return (EINVAL);
   
           error = copyout(cred->cr_groups, uap->gidset, ngrp * sizeof(gid_t));
   out:
           td->td_retval[0] = ngrp;
           return (error);
   }
   
   #ifndef _SYS_SYSPROTO_H_
   struct setsid_args {
           int     dummy;
   };
   #endif
   /* ARGSUSED */
   int
   sys_setsid(struct thread *td, struct setsid_args *uap)
   {
           struct pgrp *pgrp;
           int error;
           struct proc *p = td->td_proc;
           struct pgrp *newpgrp;
           struct session *newsess;
   
           error = 0;
           pgrp = NULL;
   
           newpgrp = uma_zalloc(pgrp_zone, M_WAITOK);
           newsess = malloc(sizeof(struct session), M_SESSION, M_WAITOK | M_ZERO);
   
           sx_xlock(&proctree_lock);
   
           if (p->p_pgid == p->p_pid || (pgrp = pgfind(p->p_pid)) != NULL) {
                   if (pgrp != NULL)
                           PGRP_UNLOCK(pgrp);
                   error = EPERM;
           } else {
                   (void)enterpgrp(p, p->p_pid, newpgrp, newsess);
                   td->td_retval[0] = p->p_pid;
                   newpgrp = NULL;
                   newsess = NULL;
           }
   
           sx_xunlock(&proctree_lock);
   
           uma_zfree(pgrp_zone, newpgrp);
           free(newsess, M_SESSION);
   
           return (error);
   }
   
   /*
    * set process group (setpgid/old setpgrp)
    *
    * caller does setpgid(targpid, targpgid)
    *
    * pid must be caller or child of caller (ESRCH)
    * if a child
    *      pid must be in same session (EPERM)
    *      pid can't have done an exec (EACCES)
    * if pgid != pid
    *      there must exist some pid in same session having pgid (EPERM)
    * pid must not be session leader (EPERM)
    */
   #ifndef _SYS_SYSPROTO_H_
   struct setpgid_args {
           int     pid;            /* target process id */
           int     pgid;           /* target pgrp id */
   };
   #endif
   /* ARGSUSED */
   int
   sys_setpgid(struct thread *td, struct setpgid_args *uap)
   {
           struct proc *curp = td->td_proc;
           struct proc *targp;     /* target process */
           struct pgrp *pgrp;      /* target pgrp */
           int error;
           struct pgrp *newpgrp;
   
           if (uap->pgid < 0)
                   return (EINVAL);
   
           error = 0;
   
           newpgrp = uma_zalloc(pgrp_zone, M_WAITOK);
   
           sx_xlock(&proctree_lock);
           if (uap->pid != 0 && uap->pid != curp->p_pid) {
                   if ((targp = pfind(uap->pid)) == NULL) {
                           error = ESRCH;
                           goto done;
                   }
                   if (!inferior(targp)) {
                           PROC_UNLOCK(targp);
                           error = ESRCH;
                           goto done;
                   }
                   if ((error = p_cansee(td, targp))) {
                           PROC_UNLOCK(targp);
                           goto done;
                   }
                   if (targp->p_pgrp == NULL ||
                       targp->p_session != curp->p_session) {
                           PROC_UNLOCK(targp);
                           error = EPERM;
                           goto done;
                   }
                   if (targp->p_flag & P_EXEC) {
                           PROC_UNLOCK(targp);
                           error = EACCES;
                           goto done;
                   }
                   PROC_UNLOCK(targp);
           } else
                   targp = curp;
           if (SESS_LEADER(targp)) {
                   error = EPERM;
                   goto done;
           }
           if (uap->pgid == 0)
                   uap->pgid = targp->p_pid;
           if ((pgrp = pgfind(uap->pgid)) == NULL) {
                   if (uap->pgid == targp->p_pid) {
                           error = enterpgrp(targp, uap->pgid, newpgrp,
                               NULL);
                           if (error == 0)
                                   newpgrp = NULL;
                   } else
                           error = EPERM;
           } else {
                   if (pgrp == targp->p_pgrp) {
                           PGRP_UNLOCK(pgrp);
                           goto done;
                   }
                   if (pgrp->pg_id != targp->p_pid &&
                       pgrp->pg_session != curp->p_session) {
                           PGRP_UNLOCK(pgrp);
                           error = EPERM;
                           goto done;
                   }
                   PGRP_UNLOCK(pgrp);
                   error = enterthispgrp(targp, pgrp);
           }
   done:
           sx_xunlock(&proctree_lock);
           KASSERT((error == 0) || (newpgrp != NULL),
               ("setpgid failed and newpgrp is NULL"));
           uma_zfree(pgrp_zone, newpgrp);
           return (error);
   }
   
   /*
    * Use the clause in B.4.2.2 that allows setuid/setgid to be 4.2/4.3BSD
    * compatible.  It says that setting the uid/gid to euid/egid is a special
    * case of "appropriate privilege".  Once the rules are expanded out, this
    * basically means that setuid(nnn) sets all three id's, in all permitted
    * cases unless _POSIX_SAVED_IDS is enabled.  In that case, setuid(getuid())
    * does not set the saved id - this is dangerous for traditional BSD
    * programs.  For this reason, we *really* do not want to set
    * _POSIX_SAVED_IDS and do not want to clear POSIX_APPENDIX_B_4_2_2.
    */
   #define POSIX_APPENDIX_B_4_2_2
   
   #ifndef _SYS_SYSPROTO_H_
   struct setuid_args {
           uid_t   uid;
   };
   #endif
   /* ARGSUSED */
   int
   sys_setuid(struct thread *td, struct setuid_args *uap)
   {
           struct proc *p = td->td_proc;
           struct ucred *newcred, *oldcred;
           uid_t uid;
           struct uidinfo *uip;
           int error;
   
           uid = uap->uid;
           AUDIT_ARG_UID(uid);
           newcred = crget();
           uip = uifind(uid);
           PROC_LOCK(p);
           /*
            * Copy credentials so other references do not see our changes.
            */
           oldcred = crcopysafe(p, newcred);
   
   #ifdef MAC
           error = mac_cred_check_setuid(oldcred, uid);
           if (error)
                   goto fail;
   #endif
   
           /*
            * See if we have "permission" by POSIX 1003.1 rules.
            *
            * Note that setuid(geteuid()) is a special case of
            * "appropriate privileges" in appendix B.4.2.2.  We need
            * to use this clause to be compatible with traditional BSD
            * semantics.  Basically, it means that "setuid(xx)" sets all
            * three id's (assuming you have privs).
            *
            * Notes on the logic.  We do things in three steps.
            * 1: We determine if the euid is going to change, and do EPERM
            *    right away.  We unconditionally change the euid later if this
            *    test is satisfied, simplifying that part of the logic.
            * 2: We determine if the real and/or saved uids are going to
            *    change.  Determined by compile options.
            * 3: Change euid last. (after tests in #2 for "appropriate privs")
            */
           if (uid != oldcred->cr_ruid &&          /* allow setuid(getuid()) */
   #ifdef _POSIX_SAVED_IDS
               uid != oldcred->cr_svuid &&         /* allow setuid(saved gid) */
   #endif
   #ifdef POSIX_APPENDIX_B_4_2_2   /* Use BSD-compat clause from B.4.2.2 */
               uid != oldcred->cr_uid &&           /* allow setuid(geteuid()) */
   #endif
               (error = priv_check_cred(oldcred, PRIV_CRED_SETUID)) != 0)
                   goto fail;
   
   #ifdef _POSIX_SAVED_IDS
           /*
            * Do we have "appropriate privileges" (are we root or uid == euid)
            * If so, we are changing the real uid and/or saved uid.
            */
           if (
   #ifdef POSIX_APPENDIX_B_4_2_2   /* Use the clause from B.4.2.2 */
               uid == oldcred->cr_uid ||
   #endif
               /* We are using privs. */
               priv_check_cred(oldcred, PRIV_CRED_SETUID) == 0)
   #endif
           {
                   /*
                    * Set the real uid and transfer proc count to new user.
                    */
                   if (uid != oldcred->cr_ruid) {
                           change_ruid(newcred, uip);
                           setsugid(p);
                   }
                   /*
                    * Set saved uid
                    *
                    * XXX always set saved uid even if not _POSIX_SAVED_IDS, as
                    * the security of seteuid() depends on it.  B.4.2.2 says it
                    * is important that we should do this.
                    */
                   if (uid != oldcred->cr_svuid) {
                           change_svuid(newcred, uid);
                           setsugid(p);
                   }
           }
   
           /*
            * In all permitted cases, we are changing the euid.
            */
           if (uid != oldcred->cr_uid) {
                   change_euid(newcred, uip);
                   setsugid(p);
           }
           proc_set_cred(p, newcred);
   #ifdef RACCT
           racct_proc_ucred_changed(p, oldcred, newcred);
           crhold(newcred);
   #endif
           PROC_UNLOCK(p);
   #ifdef RCTL
           rctl_proc_ucred_changed(p, newcred);
           crfree(newcred);
   #endif
           uifree(uip);
           crfree(oldcred);
           return (0);
   
   fail:
           PROC_UNLOCK(p);
           uifree(uip);
           crfree(newcred);
           return (error);
   }
   
   #ifndef _SYS_SYSPROTO_H_
   struct seteuid_args {
           uid_t   euid;
   };
   #endif
   /* ARGSUSED */
   int
   sys_seteuid(struct thread *td, struct seteuid_args *uap)
   {
           struct proc *p = td->td_proc;
           struct ucred *newcred, *oldcred;
           uid_t euid;
           struct uidinfo *euip;
           int error;
   
           euid = uap->euid;
           AUDIT_ARG_EUID(euid);
           newcred = crget();
           euip = uifind(euid);
           PROC_LOCK(p);
           /*
            * Copy credentials so other references do not see our changes.
            */
           oldcred = crcopysafe(p, newcred);
   
   #ifdef MAC
           error = mac_cred_check_seteuid(oldcred, euid);
           if (error)
                   goto fail;
   #endif
   
           if (euid != oldcred->cr_ruid &&         /* allow seteuid(getuid()) */
               euid != oldcred->cr_svuid &&        /* allow seteuid(saved uid) */
               (error = priv_check_cred(oldcred, PRIV_CRED_SETEUID)) != 0)
                   goto fail;
   
           /*
            * Everything's okay, do it.
            */
           if (oldcred->cr_uid != euid) {
                   change_euid(newcred, euip);
                   setsugid(p);
           }
           proc_set_cred(p, newcred);
           PROC_UNLOCK(p);
           uifree(euip);
           crfree(oldcred);
           return (0);
   
   fail:
           PROC_UNLOCK(p);
           uifree(euip);
           crfree(newcred);
           return (error);
   }
   
   #ifndef _SYS_SYSPROTO_H_
   struct setgid_args {
           gid_t   gid;
   };
   #endif
   /* ARGSUSED */
   int
   sys_setgid(struct thread *td, struct setgid_args *uap)
   {
           struct proc *p = td->td_proc;
           struct ucred *newcred, *oldcred;
           gid_t gid;
           int error;
   
           gid = uap->gid;
           AUDIT_ARG_GID(gid);
           newcred = crget();
           PROC_LOCK(p);
           oldcred = crcopysafe(p, newcred);
   
   #ifdef MAC
           error = mac_cred_check_setgid(oldcred, gid);
           if (error)
                   goto fail;
   #endif
   
           /*
            * See if we have "permission" by POSIX 1003.1 rules.
            *
            * Note that setgid(getegid()) is a special case of
            * "appropriate privileges" in appendix B.4.2.2.  We need
            * to use this clause to be compatible with traditional BSD
            * semantics.  Basically, it means that "setgid(xx)" sets all
            * three id's (assuming you have privs).
            *
            * For notes on the logic here, see setuid() above.
            */
           if (gid != oldcred->cr_rgid &&          /* allow setgid(getgid()) */
   #ifdef _POSIX_SAVED_IDS
               gid != oldcred->cr_svgid &&         /* allow setgid(saved gid) */
   #endif
   #ifdef POSIX_APPENDIX_B_4_2_2   /* Use BSD-compat clause from B.4.2.2 */
               gid != oldcred->cr_groups[0] && /* allow setgid(getegid()) */
   #endif
               (error = priv_check_cred(oldcred, PRIV_CRED_SETGID)) != 0)
                   goto fail;
   
   #ifdef _POSIX_SAVED_IDS
           /*
            * Do we have "appropriate privileges" (are we root or gid == egid)
            * If so, we are changing the real uid and saved gid.
            */
           if (
   #ifdef POSIX_APPENDIX_B_4_2_2   /* use the clause from B.4.2.2 */
               gid == oldcred->cr_groups[0] ||
   #endif
               /* We are using privs. */
               priv_check_cred(oldcred, PRIV_CRED_SETGID) == 0)
   #endif
           {
                   /*
                    * Set real gid
                    */
                   if (oldcred->cr_rgid != gid) {
                           change_rgid(newcred, gid);
                           setsugid(p);
                   }
                   /*
                    * Set saved gid
                    *
                    * XXX always set saved gid even if not _POSIX_SAVED_IDS, as
                    * the security of setegid() depends on it.  B.4.2.2 says it
                    * is important that we should do this.
                    */
                   if (oldcred->cr_svgid != gid) {
                           change_svgid(newcred, gid);
                           setsugid(p);
                   }
           }
           /*
            * In all cases permitted cases, we are changing the egid.
            * Copy credentials so other references do not see our changes.
            */
           if (oldcred->cr_groups[0] != gid) {
                   change_egid(newcred, gid);
                   setsugid(p);
           }
           proc_set_cred(p, newcred);
           PROC_UNLOCK(p);
           crfree(oldcred);
           return (0);
   
   fail:
           PROC_UNLOCK(p);
           crfree(newcred);
           return (error);
   }
   
   #ifndef _SYS_SYSPROTO_H_
   struct setegid_args {
           gid_t   egid;
   };
   #endif
   /* ARGSUSED */
   int
   sys_setegid(struct thread *td, struct setegid_args *uap)
   {
           struct proc *p = td->td_proc;
           struct ucred *newcred, *oldcred;
           gid_t egid;
           int error;
   
           egid = uap->egid;
           AUDIT_ARG_EGID(egid);
           newcred = crget();
           PROC_LOCK(p);
           oldcred = crcopysafe(p, newcred);
   
   #ifdef MAC
           error = mac_cred_check_setegid(oldcred, egid);
           if (error)
                   goto fail;
   #endif
   
           if (egid != oldcred->cr_rgid &&         /* allow setegid(getgid()) */
               egid != oldcred->cr_svgid &&        /* allow setegid(saved gid) */
               (error = priv_check_cred(oldcred, PRIV_CRED_SETEGID)) != 0)
                   goto fail;
   
           if (oldcred->cr_groups[0] != egid) {
                   change_egid(newcred, egid);
                   setsugid(p);
           }
           proc_set_cred(p, newcred);
           PROC_UNLOCK(p);
           crfree(oldcred);
           return (0);
   
   fail:
           PROC_UNLOCK(p);
           crfree(newcred);
           return (error);
   }
   
   #ifndef _SYS_SYSPROTO_H_
   struct setgroups_args {
           int     gidsetsize;
           gid_t   *gidset;
   };
   #endif
   /* ARGSUSED */
   int
   sys_setgroups(struct thread *td, struct setgroups_args *uap)
   {
           gid_t smallgroups[XU_NGROUPS];
           gid_t *groups;
           int gidsetsize, error;
   
           gidsetsize = uap->gidsetsize;
           if (gidsetsize > ngroups_max + 1 || gidsetsize < 0)
                   return (EINVAL);
   
           if (gidsetsize > XU_NGROUPS)
                   groups = malloc(gidsetsize * sizeof(gid_t), M_TEMP, M_WAITOK);
           else
                   groups = smallgroups;
   
           error = copyin(uap->gidset, groups, gidsetsize * sizeof(gid_t));
           if (error == 0)
                   error = kern_setgroups(td, gidsetsize, groups);
   
           if (gidsetsize > XU_NGROUPS)
                   free(groups, M_TEMP);
           return (error);
   }
   
   int
   kern_setgroups(struct thread *td, u_int ngrp, gid_t *groups)
   {
           struct proc *p = td->td_proc;
           struct ucred *newcred, *oldcred;
           int error;
   
           MPASS(ngrp <= ngroups_max + 1);
           AUDIT_ARG_GROUPSET(groups, ngrp);
           newcred = crget();
           crextend(newcred, ngrp);
           PROC_LOCK(p);
           oldcred = crcopysafe(p, newcred);
   
   #ifdef MAC
           error = mac_cred_check_setgroups(oldcred, ngrp, groups);
           if (error)
                   goto fail;
   #endif
   
           error = priv_check_cred(oldcred, PRIV_CRED_SETGROUPS);
           if (error)
                   goto fail;
   
           if (ngrp == 0) {
                   /*
                    * setgroups(0, NULL) is a legitimate way of clearing the
                    * groups vector on non-BSD systems (which generally do not
                    * have the egid in the groups[0]).  We risk security holes
                    * when running non-BSD software if we do not do the same.
                    */
                   newcred->cr_ngroups = 1;
           } else {
                   crsetgroups_locked(newcred, ngrp, groups);
           }
           setsugid(p);
           proc_set_cred(p, newcred);
           PROC_UNLOCK(p);
           crfree(oldcred);
           return (0);
   
   fail:
           PROC_UNLOCK(p);
           crfree(newcred);
           return (error);
   }
   
   #ifndef _SYS_SYSPROTO_H_
   struct setreuid_args {
           uid_t   ruid;
           uid_t   euid;
   };
   #endif
   /* ARGSUSED */
   int
   sys_setreuid(struct thread *td, struct setreuid_args *uap)
   {
           struct proc *p = td->td_proc;
           struct ucred *newcred, *oldcred;
           uid_t euid, ruid;
           struct uidinfo *euip, *ruip;
           int error;
   
           euid = uap->euid;
           ruid = uap->ruid;
           AUDIT_ARG_EUID(euid);
           AUDIT_ARG_RUID(ruid);
           newcred = crget();
           euip = uifind(euid);
           ruip = uifind(ruid);
           PROC_LOCK(p);
           oldcred = crcopysafe(p, newcred);
   
   #ifdef MAC
           error = mac_cred_check_setreuid(oldcred, ruid, euid);
           if (error)
                   goto fail;
   #endif
   
           if (((ruid != (uid_t)-1 && ruid != oldcred->cr_ruid &&
                 ruid != oldcred->cr_svuid) ||
                (euid != (uid_t)-1 && euid != oldcred->cr_uid &&
                 euid != oldcred->cr_ruid && euid != oldcred->cr_svuid)) &&
               (error = priv_check_cred(oldcred, PRIV_CRED_SETREUID)) != 0)
                   goto fail;
   
           if (euid != (uid_t)-1 && oldcred->cr_uid != euid) {
                   change_euid(newcred, euip);
                   setsugid(p);
           }
           if (ruid != (uid_t)-1 && oldcred->cr_ruid != ruid) {
                   change_ruid(newcred, ruip);
                   setsugid(p);
           }
           if ((ruid != (uid_t)-1 || newcred->cr_uid != newcred->cr_ruid) &&
               newcred->cr_svuid != newcred->cr_uid) {
                   change_svuid(newcred, newcred->cr_uid);
                   setsugid(p);
           }
           proc_set_cred(p, newcred);
   #ifdef RACCT
           racct_proc_ucred_changed(p, oldcred, newcred);
           crhold(newcred);
   #endif
           PROC_UNLOCK(p);
   #ifdef RCTL
           rctl_proc_ucred_changed(p, newcred);
           crfree(newcred);
   #endif
           uifree(ruip);
           uifree(euip);
           crfree(oldcred);
           return (0);
   
   fail:
           PROC_UNLOCK(p);
           uifree(ruip);
           uifree(euip);
           crfree(newcred);
           return (error);
   }
   
   #ifndef _SYS_SYSPROTO_H_
   struct setregid_args {
           gid_t   rgid;
           gid_t   egid;
   };
   #endif
   /* ARGSUSED */
   int
   sys_setregid(struct thread *td, struct setregid_args *uap)
   {
           struct proc *p = td->td_proc;
           struct ucred *newcred, *oldcred;
           gid_t egid, rgid;
           int error;
   
           egid = uap->egid;
           rgid = uap->rgid;
           AUDIT_ARG_EGID(egid);
           AUDIT_ARG_RGID(rgid);
           newcred = crget();
           PROC_LOCK(p);
           oldcred = crcopysafe(p, newcred);
   
   #ifdef MAC
           error = mac_cred_check_setregid(oldcred, rgid, egid);
           if (error)
                   goto fail;
   #endif
   
           if (((rgid != (gid_t)-1 && rgid != oldcred->cr_rgid &&
               rgid != oldcred->cr_svgid) ||
                (egid != (gid_t)-1 && egid != oldcred->cr_groups[0] &&
                egid != oldcred->cr_rgid && egid != oldcred->cr_svgid)) &&
               (error = priv_check_cred(oldcred, PRIV_CRED_SETREGID)) != 0)
                   goto fail;
   
           if (egid != (gid_t)-1 && oldcred->cr_groups[0] != egid) {
                   change_egid(newcred, egid);
                   setsugid(p);
           }
           if (rgid != (gid_t)-1 && oldcred->cr_rgid != rgid) {
                   change_rgid(newcred, rgid);
                   setsugid(p);
           }
           if ((rgid != (gid_t)-1 || newcred->cr_groups[0] != newcred->cr_rgid) &&
               newcred->cr_svgid != newcred->cr_groups[0]) {
                   change_svgid(newcred, newcred->cr_groups[0]);
                   setsugid(p);
           }
           proc_set_cred(p, newcred);
           PROC_UNLOCK(p);
           crfree(oldcred);
           return (0);
   
   fail:
          PROC_UNLOCK(p);
          crfree(newcred);
          return (error);
  }
  
  /*
   * setresuid(ruid, euid, suid) is like setreuid except control over the saved
   * uid is explicit.
   */
  #ifndef _SYS_SYSPROTO_H_
  struct setresuid_args {
          uid_t   ruid;
          uid_t   euid;
          uid_t   suid;
  };
  #endif
  /* ARGSUSED */
  int
  sys_setresuid(struct thread *td, struct setresuid_args *uap)
  {
          struct proc *p = td->td_proc;
          struct ucred *newcred, *oldcred;
          uid_t euid, ruid, suid;
          struct uidinfo *euip, *ruip;
          int error;
  
          euid = uap->euid;
          ruid = uap->ruid;
          suid = uap->suid;
          AUDIT_ARG_EUID(euid);
          AUDIT_ARG_RUID(ruid);
          AUDIT_ARG_SUID(suid);
          newcred = crget();
          euip = uifind(euid);
          ruip = uifind(ruid);
          PROC_LOCK(p);
          oldcred = crcopysafe(p, newcred);
  
  #ifdef MAC
          error = mac_cred_check_setresuid(oldcred, ruid, euid, suid);
          if (error)
                  goto fail;
  #endif
  
          if (((ruid != (uid_t)-1 && ruid != oldcred->cr_ruid &&
               ruid != oldcred->cr_svuid &&
                ruid != oldcred->cr_uid) ||
               (euid != (uid_t)-1 && euid != oldcred->cr_ruid &&
              euid != oldcred->cr_svuid &&
                euid != oldcred->cr_uid) ||
               (suid != (uid_t)-1 && suid != oldcred->cr_ruid &&
              suid != oldcred->cr_svuid &&
                suid != oldcred->cr_uid)) &&
              (error = priv_check_cred(oldcred, PRIV_CRED_SETRESUID)) != 0)
                  goto fail;
  
          if (euid != (uid_t)-1 && oldcred->cr_uid != euid) {
                  change_euid(newcred, euip);
                  setsugid(p);
          }
          if (ruid != (uid_t)-1 && oldcred->cr_ruid != ruid) {
                  change_ruid(newcred, ruip);
                  setsugid(p);
          }
          if (suid != (uid_t)-1 && oldcred->cr_svuid != suid) {
                  change_svuid(newcred, suid);
                  setsugid(p);
          }
          proc_set_cred(p, newcred);
  #ifdef RACCT
          racct_proc_ucred_changed(p, oldcred, newcred);
          crhold(newcred);
  #endif
          PROC_UNLOCK(p);
  #ifdef RCTL
          rctl_proc_ucred_changed(p, newcred);
          crfree(newcred);
  #endif
          uifree(ruip);
          uifree(euip);
          crfree(oldcred);
          return (0);
  
  fail:
          PROC_UNLOCK(p);
          uifree(ruip);
          uifree(euip);
          crfree(newcred);
          return (error);
  
  }
  
  /*
   * setresgid(rgid, egid, sgid) is like setregid except control over the saved
   * gid is explicit.
   */
  #ifndef _SYS_SYSPROTO_H_
  struct setresgid_args {
          gid_t   rgid;
          gid_t   egid;
          gid_t   sgid;
  };
  #endif
  /* ARGSUSED */
  int
  sys_setresgid(struct thread *td, struct setresgid_args *uap)
  {
          struct proc *p = td->td_proc;
          struct ucred *newcred, *oldcred;
          gid_t egid, rgid, sgid;
          int error;
  
          egid = uap->egid;
          rgid = uap->rgid;
          sgid = uap->sgid;
          AUDIT_ARG_EGID(egid);
          AUDIT_ARG_RGID(rgid);
          AUDIT_ARG_SGID(sgid);
          newcred = crget();
          PROC_LOCK(p);
          oldcred = crcopysafe(p, newcred);
  
  #ifdef MAC
          error = mac_cred_check_setresgid(oldcred, rgid, egid, sgid);
          if (error)
                  goto fail;
  #endif
  
          if (((rgid != (gid_t)-1 && rgid != oldcred->cr_rgid &&
                rgid != oldcred->cr_svgid &&
                rgid != oldcred->cr_groups[0]) ||
               (egid != (gid_t)-1 && egid != oldcred->cr_rgid &&
                egid != oldcred->cr_svgid &&
                egid != oldcred->cr_groups[0]) ||
               (sgid != (gid_t)-1 && sgid != oldcred->cr_rgid &&
                sgid != oldcred->cr_svgid &&
                sgid != oldcred->cr_groups[0])) &&
              (error = priv_check_cred(oldcred, PRIV_CRED_SETRESGID)) != 0)
                  goto fail;
  
          if (egid != (gid_t)-1 && oldcred->cr_groups[0] != egid) {
                  change_egid(newcred, egid);
                  setsugid(p);
          }
          if (rgid != (gid_t)-1 && oldcred->cr_rgid != rgid) {
                  change_rgid(newcred, rgid);
                  setsugid(p);
          }
          if (sgid != (gid_t)-1 && oldcred->cr_svgid != sgid) {
                  change_svgid(newcred, sgid);
                  setsugid(p);
          }
          proc_set_cred(p, newcred);
          PROC_UNLOCK(p);
          crfree(oldcred);
          return (0);
  
  fail:
          PROC_UNLOCK(p);
          crfree(newcred);
          return (error);
  }
  
  #ifndef _SYS_SYSPROTO_H_
  struct getresuid_args {
          uid_t   *ruid;
          uid_t   *euid;
          uid_t   *suid;
  };
  #endif
  /* ARGSUSED */
  int
  sys_getresuid(struct thread *td, struct getresuid_args *uap)
  {
          struct ucred *cred;
          int error1 = 0, error2 = 0, error3 = 0;
  
          cred = td->td_ucred;
          if (uap->ruid)
                  error1 = copyout(&cred->cr_ruid,
                      uap->ruid, sizeof(cred->cr_ruid));
          if (uap->euid)
                  error2 = copyout(&cred->cr_uid,
                      uap->euid, sizeof(cred->cr_uid));
          if (uap->suid)
                  error3 = copyout(&cred->cr_svuid,
                      uap->suid, sizeof(cred->cr_svuid));
          return (error1 ? error1 : error2 ? error2 : error3);
  }
  
  #ifndef _SYS_SYSPROTO_H_
  struct getresgid_args {
          gid_t   *rgid;
          gid_t   *egid;
          gid_t   *sgid;
  };
  #endif
  /* ARGSUSED */
  int
  sys_getresgid(struct thread *td, struct getresgid_args *uap)
  {
          struct ucred *cred;
          int error1 = 0, error2 = 0, error3 = 0;
  
          cred = td->td_ucred;
          if (uap->rgid)
                  error1 = copyout(&cred->cr_rgid,
                      uap->rgid, sizeof(cred->cr_rgid));
          if (uap->egid)
                  error2 = copyout(&cred->cr_groups[0],
                      uap->egid, sizeof(cred->cr_groups[0]));
          if (uap->sgid)
                  error3 = copyout(&cred->cr_svgid,
                      uap->sgid, sizeof(cred->cr_svgid));
          return (error1 ? error1 : error2 ? error2 : error3);
  }
  
  #ifndef _SYS_SYSPROTO_H_
  struct issetugid_args {
          int dummy;
  };
  #endif
  /* ARGSUSED */
  int
  sys_issetugid(struct thread *td, struct issetugid_args *uap)
  {
          struct proc *p = td->td_proc;
  
          /*
           * Note: OpenBSD sets a P_SUGIDEXEC flag set at execve() time,
           * we use P_SUGID because we consider changing the owners as
           * "tainting" as well.
           * This is significant for procs that start as root and "become"
           * a user without an exec - programs cannot know *everything*
           * that libc *might* have put in their data segment.
           */
          td->td_retval[0] = (p->p_flag & P_SUGID) ? 1 : 0;
          return (0);
  }
  
  int
  sys___setugid(struct thread *td, struct __setugid_args *uap)
  {
  #ifdef REGRESSION
          struct proc *p;
  
          p = td->td_proc;
          switch (uap->flag) {
          case 0:
                  PROC_LOCK(p);
                  p->p_flag &= ~P_SUGID;
                  PROC_UNLOCK(p);
                  return (0);
          case 1:
                  PROC_LOCK(p);
                  p->p_flag |= P_SUGID;
                  PROC_UNLOCK(p);
                  return (0);
          default:
                  return (EINVAL);
          }
  #else /* !REGRESSION */
  
          return (ENOSYS);
  #endif /* REGRESSION */
  }
  
  /*
   * Check if gid is a member of the group set.
   */
  int
  groupmember(gid_t gid, struct ucred *cred)
  {
          int l;
          int h;
          int m;
  
          if (cred->cr_groups[0] == gid)
                  return(1);
  
          /*
           * If gid was not our primary group, perform a binary search
           * of the supplemental groups.  This is possible because we
           * sort the groups in crsetgroups().
           */
          l = 1;
          h = cred->cr_ngroups;
          while (l < h) {
                  m = l + ((h - l) / 2);
                  if (cred->cr_groups[m] < gid)
                          l = m + 1; 
                  else
                          h = m; 
          }
          if ((l < cred->cr_ngroups) && (cred->cr_groups[l] == gid))
                  return (1);
  
          return (0);
  }
  
  /*
   * Test the active securelevel against a given level.  securelevel_gt()
   * implements (securelevel > level).  securelevel_ge() implements
   * (securelevel >= level).  Note that the logic is inverted -- these
   * functions return EPERM on "success" and 0 on "failure".
   *
   * Due to care taken when setting the securelevel, we know that no jail will
   * be less secure that its parent (or the physical system), so it is sufficient
   * to test the current jail only.
   *
   * XXXRW: Possibly since this has to do with privilege, it should move to
   * kern_priv.c.
   */
  int
  securelevel_gt(struct ucred *cr, int level)
  {
  
          return (cr->cr_prison->pr_securelevel > level ? EPERM : 0);
  }
  
  int
  securelevel_ge(struct ucred *cr, int level)
  {
  
          return (cr->cr_prison->pr_securelevel >= level ? EPERM : 0);
  }
  
  /*
   * 'see_other_uids' determines whether or not visibility of processes
   * and sockets with credentials holding different real uids is possible
   * using a variety of system MIBs.
   * XXX: data declarations should be together near the beginning of the file.
   */
  static int      see_other_uids = 1;
  SYSCTL_INT(_security_bsd, OID_AUTO, see_other_uids, CTLFLAG_RW,
      &see_other_uids, 0,
      "Unprivileged processes may see subjects/objects with different real uid");
  
  /*-
   * Determine if u1 "can see" the subject specified by u2, according to the
   * 'see_other_uids' policy.
   * Returns: 0 for permitted, ESRCH otherwise
   * Locks: none
   * References: *u1 and *u2 must not change during the call
   *             u1 may equal u2, in which case only one reference is required
   */
  int
  cr_canseeotheruids(struct ucred *u1, struct ucred *u2)
  {
  
          if (!see_other_uids && u1->cr_ruid != u2->cr_ruid) {
                  if (priv_check_cred(u1, PRIV_SEEOTHERUIDS) != 0)
                          return (ESRCH);
          }
          return (0);
  }
  
  /*
   * 'see_other_gids' determines whether or not visibility of processes
   * and sockets with credentials holding different real gids is possible
   * using a variety of system MIBs.
   * XXX: data declarations should be together near the beginning of the file.
   */
  static int      see_other_gids = 1;
  SYSCTL_INT(_security_bsd, OID_AUTO, see_other_gids, CTLFLAG_RW,
      &see_other_gids, 0,
      "Unprivileged processes may see subjects/objects with different real gid");
  
  /*
   * Determine if u1 can "see" the subject specified by u2, according to the
   * 'see_other_gids' policy.
   * Returns: 0 for permitted, ESRCH otherwise
   * Locks: none
   * References: *u1 and *u2 must not change during the call
   *             u1 may equal u2, in which case only one reference is required
   */
  int
  cr_canseeothergids(struct ucred *u1, struct ucred *u2)
  {
          int i, match;
  
          if (!see_other_gids) {
                  match = 0;
                  for (i = 0; i < u1->cr_ngroups; i++) {
                          if (groupmember(u1->cr_groups[i], u2))
                                  match = 1;
                          if (match)
                                  break;
                  }
                  if (!match) {
                          if (priv_check_cred(u1, PRIV_SEEOTHERGIDS) != 0)
                                  return (ESRCH);
                  }
          }
          return (0);
  }
  
  /*
   * 'see_jail_proc' determines whether or not visibility of processes and
   * sockets with credentials holding different jail ids is possible using a
   * variety of system MIBs.
   *
   * XXX: data declarations should be together near the beginning of the file.
   */
  
  static int      see_jail_proc = 1;
  SYSCTL_INT(_security_bsd, OID_AUTO, see_jail_proc, CTLFLAG_RW,
      &see_jail_proc, 0,
      "Unprivileged processes may see subjects/objects with different jail ids");
  
  /*-
   * Determine if u1 "can see" the subject specified by u2, according to the
   * 'see_jail_proc' policy.
   * Returns: 0 for permitted, ESRCH otherwise
   * Locks: none
   * References: *u1 and *u2 must not change during the call
   *             u1 may equal u2, in which case only one reference is required
   */
  int
  cr_canseejailproc(struct ucred *u1, struct ucred *u2)
  {
          if (u1->cr_uid == 0)
                  return (0);
          return (!see_jail_proc && u1->cr_prison != u2->cr_prison ? ESRCH : 0);
  }
  
  /*-
   * Determine if u1 "can see" the subject specified by u2.
   * Returns: 0 for permitted, an errno value otherwise
   * Locks: none
   * References: *u1 and *u2 must not change during the call
   *             u1 may equal u2, in which case only one reference is required
   */
  int
  cr_cansee(struct ucred *u1, struct ucred *u2)
  {
          int error;
  
          if ((error = prison_check(u1, u2)))
                  return (error);
  #ifdef MAC
          if ((error = mac_cred_check_visible(u1, u2)))
                  return (error);
  #endif
          if ((error = cr_canseeotheruids(u1, u2)))
                  return (error);
          if ((error = cr_canseeothergids(u1, u2)))
                  return (error);
          if ((error = cr_canseejailproc(u1, u2)))
                  return (error);
          return (0);
  }
  
  /*-
   * Determine if td "can see" the subject specified by p.
   * Returns: 0 for permitted, an errno value otherwise
   * Locks: Sufficient locks to protect p->p_ucred must be held.  td really
   *        should be curthread.
   * References: td and p must be valid for the lifetime of the call
   */
  int
  p_cansee(struct thread *td, struct proc *p)
  {
  
          /* Wrap cr_cansee() for all functionality. */
          KASSERT(td == curthread, ("%s: td not curthread", __func__));
          PROC_LOCK_ASSERT(p, MA_OWNED);
          return (cr_cansee(td->td_ucred, p->p_ucred));
  }
  
  /*
   * 'conservative_signals' prevents the delivery of a broad class of
   * signals by unprivileged processes to processes that have changed their
   * credentials since the last invocation of execve().  This can prevent
   * the leakage of cached information or retained privileges as a result
   * of a common class of signal-related vulnerabilities.  However, this
   * may interfere with some applications that expect to be able to
   * deliver these signals to peer processes after having given up
   * privilege.
   */
  static int      conservative_signals = 1;
  SYSCTL_INT(_security_bsd, OID_AUTO, conservative_signals, CTLFLAG_RW,
      &conservative_signals, 0, "Unprivileged processes prevented from "
      "sending certain signals to processes whose credentials have changed");
  /*-
   * Determine whether cred may deliver the specified signal to proc.
   * Returns: 0 for permitted, an errno value otherwise.
   * Locks: A lock must be held for proc.
   * References: cred and proc must be valid for the lifetime of the call.
   */
  int
  cr_cansignal(struct ucred *cred, struct proc *proc, int signum)
  {
          int error;
  
          PROC_LOCK_ASSERT(proc, MA_OWNED);
          /*
           * Jail semantics limit the scope of signalling to proc in the
           * same jail as cred, if cred is in jail.
           */
          error = prison_check(cred, proc->p_ucred);
          if (error)
                  return (error);
  #ifdef MAC
          if ((error = mac_proc_check_signal(cred, proc, signum)))
                  return (error);
  #endif
          if ((error = cr_canseeotheruids(cred, proc->p_ucred)))
                  return (error);
          if ((error = cr_canseeothergids(cred, proc->p_ucred)))
                  return (error);
  
          /*
           * UNIX signal semantics depend on the status of the P_SUGID
           * bit on the target process.  If the bit is set, then additional
           * restrictions are placed on the set of available signals.
           */
          if (conservative_signals && (proc->p_flag & P_SUGID)) {
                  switch (signum) {
                  case 0:
                  case SIGKILL:
                  case SIGINT:
                  case SIGTERM:
                  case SIGALRM:
                  case SIGSTOP:
                  case SIGTTIN:
                  case SIGTTOU:
                  case SIGTSTP:
                  case SIGHUP:
                  case SIGUSR1:
                  case SIGUSR2:
                          /*
                           * Generally, permit job and terminal control
                           * signals.
                           */
                          break;
                  default:
                          /* Not permitted without privilege. */
                          error = priv_check_cred(cred, PRIV_SIGNAL_SUGID);
                          if (error)
                                  return (error);
                  }
          }
  
          /*
           * Generally, the target credential's ruid or svuid must match the
           * subject credential's ruid or euid.
           */
          if (cred->cr_ruid != proc->p_ucred->cr_ruid &&
              cred->cr_ruid != proc->p_ucred->cr_svuid &&
              cred->cr_uid != proc->p_ucred->cr_ruid &&
              cred->cr_uid != proc->p_ucred->cr_svuid) {
                  error = priv_check_cred(cred, PRIV_SIGNAL_DIFFCRED);
                  if (error)
                          return (error);
          }
  
          return (0);
  }
  
  /*-
   * Determine whether td may deliver the specified signal to p.
   * Returns: 0 for permitted, an errno value otherwise
   * Locks: Sufficient locks to protect various components of td and p
   *        must be held.  td must be curthread, and a lock must be
   *        held for p.
   * References: td and p must be valid for the lifetime of the call
   */
  int
  p_cansignal(struct thread *td, struct proc *p, int signum)
  {
  
          KASSERT(td == curthread, ("%s: td not curthread", __func__));
          PROC_LOCK_ASSERT(p, MA_OWNED);
          if (td->td_proc == p)
                  return (0);
  
          /*
           * UNIX signalling semantics require that processes in the same
           * session always be able to deliver SIGCONT to one another,
           * overriding the remaining protections.
           */
          /* XXX: This will require an additional lock of some sort. */
          if (signum == SIGCONT && td->td_proc->p_session == p->p_session)
                  return (0);
          /*
           * Some compat layers use SIGTHR and higher signals for
           * communication between different kernel threads of the same
           * process, so that they expect that it's always possible to
           * deliver them, even for suid applications where cr_cansignal() can
           * deny such ability for security consideration.  It should be
           * pretty safe to do since the only way to create two processes
           * with the same p_leader is via rfork(2).
           */
          if (td->td_proc->p_leader != NULL && signum >= SIGTHR &&
              signum < SIGTHR + 4 && td->td_proc->p_leader == p->p_leader)
                  return (0);
  
          return (cr_cansignal(td->td_ucred, p, signum));
  }
  
  /*-
   * Determine whether td may reschedule p.
   * Returns: 0 for permitted, an errno value otherwise
   * Locks: Sufficient locks to protect various components of td and p
   *        must be held.  td must be curthread, and a lock must
   *        be held for p.
   * References: td and p must be valid for the lifetime of the call
   */
  int
  p_cansched(struct thread *td, struct proc *p)
  {
          int error;
  
          KASSERT(td == curthread, ("%s: td not curthread", __func__));
          PROC_LOCK_ASSERT(p, MA_OWNED);
          if (td->td_proc == p)
                  return (0);
          if ((error = prison_check(td->td_ucred, p->p_ucred)))
                  return (error);
  #ifdef MAC
          if ((error = mac_proc_check_sched(td->td_ucred, p)))
                  return (error);
  #endif
          if ((error = cr_canseeotheruids(td->td_ucred, p->p_ucred)))
                  return (error);
          if ((error = cr_canseeothergids(td->td_ucred, p->p_ucred)))
                  return (error);
          if (td->td_ucred->cr_ruid != p->p_ucred->cr_ruid &&
              td->td_ucred->cr_uid != p->p_ucred->cr_ruid) {
                  error = priv_check(td, PRIV_SCHED_DIFFCRED);
                  if (error)
                          return (error);
          }
          return (0);
  }
  
  /*
   * Handle getting or setting the prison's unprivileged_proc_debug
   * value.
   */
  static int
  sysctl_unprivileged_proc_debug(SYSCTL_HANDLER_ARGS)
  {
          int error, val;
  
          val = prison_allow(req->td->td_ucred, PR_ALLOW_UNPRIV_DEBUG);
          error = sysctl_handle_int(oidp, &val, 0, req);
          if (error != 0 || req->newptr == NULL)
                  return (error);
          if (val != 0 && val != 1)
                  return (EINVAL);
          prison_set_allow(req->td->td_ucred, PR_ALLOW_UNPRIV_DEBUG, val);
          return (0);
  }
  
  /*
   * The 'unprivileged_proc_debug' flag may be used to disable a variety of
   * unprivileged inter-process debugging services, including some procfs
   * functionality, ptrace(), and ktrace().  In the past, inter-process
   * debugging has been involved in a variety of security problems, and sites
   * not requiring the service might choose to disable it when hardening
   * systems.
   */
  SYSCTL_PROC(_security_bsd, OID_AUTO, unprivileged_proc_debug,
      CTLTYPE_INT | CTLFLAG_RW | CTLFLAG_PRISON | CTLFLAG_SECURE |
      CTLFLAG_MPSAFE, 0, 0, sysctl_unprivileged_proc_debug, "I",
      "Unprivileged processes may use process debugging facilities");
  
  /*-
   * Determine whether td may debug p.
   * Returns: 0 for permitted, an errno value otherwise
   * Locks: Sufficient locks to protect various components of td and p
   *        must be held.  td must be curthread, and a lock must
   *        be held for p.
   * References: td and p must be valid for the lifetime of the call
   */
  int
  p_candebug(struct thread *td, struct proc *p)
  {
          int credentialchanged, error, grpsubset, i, uidsubset;
  
          KASSERT(td == curthread, ("%s: td not curthread", __func__));
          PROC_LOCK_ASSERT(p, MA_OWNED);
          if ((error = priv_check(td, PRIV_DEBUG_UNPRIV)))
                  return (error);
          if (td->td_proc == p)
                  return (0);
          if ((error = prison_check(td->td_ucred, p->p_ucred)))
                  return (error);
  #ifdef MAC
          if ((error = mac_proc_check_debug(td->td_ucred, p)))
                  return (error);
  #endif
          if ((error = cr_canseeotheruids(td->td_ucred, p->p_ucred)))
                  return (error);
          if ((error = cr_canseeothergids(td->td_ucred, p->p_ucred)))
                  return (error);
  
          /*
           * Is p's group set a subset of td's effective group set?  This
           * includes p's egid, group access list, rgid, and svgid.
           */
          grpsubset = 1;
          for (i = 0; i < p->p_ucred->cr_ngroups; i++) {
                  if (!groupmember(p->p_ucred->cr_groups[i], td->td_ucred)) {
                          grpsubset = 0;
                          break;
                  }
          }
          grpsubset = grpsubset &&
              groupmember(p->p_ucred->cr_rgid, td->td_ucred) &&
              groupmember(p->p_ucred->cr_svgid, td->td_ucred);
  
          /*
           * Are the uids present in p's credential equal to td's
           * effective uid?  This includes p's euid, svuid, and ruid.
           */
          uidsubset = (td->td_ucred->cr_uid == p->p_ucred->cr_uid &&
              td->td_ucred->cr_uid == p->p_ucred->cr_svuid &&
              td->td_ucred->cr_uid == p->p_ucred->cr_ruid);
  
          /*
           * Has the credential of the process changed since the last exec()?
           */
          credentialchanged = (p->p_flag & P_SUGID);
  
          /*
           * If p's gids aren't a subset, or the uids aren't a subset,
           * or the credential has changed, require appropriate privilege
           * for td to debug p.
           */
          if (!grpsubset || !uidsubset) {
                  error = priv_check(td, PRIV_DEBUG_DIFFCRED);
                  if (error)
                          return (error);
          }
  
          if (credentialchanged) {
                  error = priv_check(td, PRIV_DEBUG_SUGID);
                  if (error)
                          return (error);
          }
  
          /* Can't trace init when securelevel > 0. */
          if (p == initproc) {
                  error = securelevel_gt(td->td_ucred, 0);
                  if (error)
                          return (error);
          }
  
          /*
           * Can't trace a process that's currently exec'ing.
           *
           * XXX: Note, this is not a security policy decision, it's a
           * basic correctness/functionality decision.  Therefore, this check
           * should be moved to the caller's of p_candebug().
           */
          if ((p->p_flag & P_INEXEC) != 0)
                  return (EBUSY);
  
          /* Denied explicitely */
          if ((p->p_flag2 & P2_NOTRACE) != 0) {
                  error = priv_check(td, PRIV_DEBUG_DENIED);
                  if (error != 0)
                          return (error);
          }
  
          return (0);
  }
  
  /*-
   * Determine whether the subject represented by cred can "see" a socket.
   * Returns: 0 for permitted, ENOENT otherwise.
   */
  int
  cr_canseesocket(struct ucred *cred, struct socket *so)
  {
          int error;
  
          error = prison_check(cred, so->so_cred);
          if (error)
                  return (ENOENT);
  #ifdef MAC
          error = mac_socket_check_visible(cred, so);
          if (error)
                  return (error);
  #endif
          if (cr_canseeotheruids(cred, so->so_cred))
                  return (ENOENT);
          if (cr_canseeothergids(cred, so->so_cred))
                  return (ENOENT);
  
          return (0);
  }
  
  /*-
   * Determine whether td can wait for the exit of p.
   * Returns: 0 for permitted, an errno value otherwise
   * Locks: Sufficient locks to protect various components of td and p
   *        must be held.  td must be curthread, and a lock must
   *        be held for p.
   * References: td and p must be valid for the lifetime of the call
  
   */
  int
  p_canwait(struct thread *td, struct proc *p)
  {
          int error;
  
          KASSERT(td == curthread, ("%s: td not curthread", __func__));
          PROC_LOCK_ASSERT(p, MA_OWNED);
          if ((error = prison_check(td->td_ucred, p->p_ucred)))
                  return (error);
  #ifdef MAC
          if ((error = mac_proc_check_wait(td->td_ucred, p)))
                  return (error);
  #endif
  #if 0
          /* XXXMAC: This could have odd effects on some shells. */
          if ((error = cr_canseeotheruids(td->td_ucred, p->p_ucred)))
                  return (error);
  #endif
  
          return (0);
  }
  
  /*
   * Credential management.
   *
   * struct ucred objects are rarely allocated but gain and lose references all
   * the time (e.g., on struct file alloc/dealloc) turning refcount updates into
   * a significant source of cache-line ping ponging. Common cases are worked
   * around by modifying thread-local counter instead if the cred to operate on
   * matches td_realucred.
   *
   * The counter is split into 2 parts:
   * - cr_users -- total count of all struct proc and struct thread objects
   *   which have given cred in p_ucred and td_ucred respectively
   * - cr_ref -- the actual ref count, only valid if cr_users == 0
   *
   * If users == 0 then cr_ref behaves similarly to refcount(9), in particular if
   * the count reaches 0 the object is freeable.
   * If users > 0 and curthread->td_realucred == cred, then updates are performed
   * against td_ucredref.
   * In other cases updates are performed against cr_ref.
   *
   * Changing td_realucred into something else decrements cr_users and transfers
   * accumulated updates.
   */
  struct ucred *
  crcowget(struct ucred *cr)
  {
  
          mtx_lock(&cr->cr_mtx);
          KASSERT(cr->cr_users > 0, ("%s: users %d not > 0 on cred %p",
              __func__, cr->cr_users, cr));
          cr->cr_users++;
          cr->cr_ref++;
          mtx_unlock(&cr->cr_mtx);
          return (cr);
  }
  
  static struct ucred *
  crunuse(struct thread *td)
  {
          struct ucred *cr, *crold;
  
          MPASS(td->td_realucred == td->td_ucred);
          cr = td->td_realucred;
          mtx_lock(&cr->cr_mtx);
          cr->cr_ref += td->td_ucredref;
          td->td_ucredref = 0;
          KASSERT(cr->cr_users > 0, ("%s: users %d not > 0 on cred %p",
              __func__, cr->cr_users, cr));
          cr->cr_users--;
          if (cr->cr_users == 0) {
                  KASSERT(cr->cr_ref > 0, ("%s: ref %d not > 0 on cred %p",
                      __func__, cr->cr_ref, cr));
                  crold = cr;
          } else {
                  cr->cr_ref--;
                  crold = NULL;
          }
          mtx_unlock(&cr->cr_mtx);
          td->td_realucred = NULL;
          return (crold);
  }
  
  static void
  crunusebatch(struct ucred *cr, int users, int ref)
  {
  
          KASSERT(users > 0, ("%s: passed users %d not > 0 ; cred %p",
              __func__, users, cr));
          mtx_lock(&cr->cr_mtx);
          KASSERT(cr->cr_users >= users, ("%s: users %d not > %d on cred %p",
              __func__, cr->cr_users, users, cr));
          cr->cr_users -= users;
          cr->cr_ref += ref;
          cr->cr_ref -= users;
          if (cr->cr_users > 0) {
                  mtx_unlock(&cr->cr_mtx);
                  return;
          }
          KASSERT(cr->cr_ref >= 0, ("%s: ref %d not >= 0 on cred %p",
              __func__, cr->cr_ref, cr));
          if (cr->cr_ref > 0) {
                  mtx_unlock(&cr->cr_mtx);
                  return;
          }
          crfree_final(cr);
  }
  
  void
  crcowfree(struct thread *td)
  {
          struct ucred *cr;
  
          cr = crunuse(td);
          if (cr != NULL)
                  crfree(cr);
  }
  
  struct ucred *
  crcowsync(void)
  {
          struct thread *td;
          struct proc *p;
          struct ucred *crnew, *crold;
  
          td = curthread;
          p = td->td_proc;
          PROC_LOCK_ASSERT(p, MA_OWNED);
  
          MPASS(td->td_realucred == td->td_ucred);
          if (td->td_realucred == p->p_ucred)
                  return (NULL);
  
          crnew = crcowget(p->p_ucred);
          crold = crunuse(td);
          td->td_realucred = crnew;
          td->td_ucred = td->td_realucred;
          return (crold);
  }
  
  /*
   * Batching.
   */
  void
  credbatch_add(struct credbatch *crb, struct thread *td)
  {
          struct ucred *cr;
  
          MPASS(td->td_realucred != NULL);
          MPASS(td->td_realucred == td->td_ucred);
          MPASS(td->td_state == TDS_INACTIVE);
          cr = td->td_realucred;
          KASSERT(cr->cr_users > 0, ("%s: users %d not > 0 on cred %p",
              __func__, cr->cr_users, cr));
          if (crb->cred != cr) {
                  if (crb->users > 0) {
                          MPASS(crb->cred != NULL);
                          crunusebatch(crb->cred, crb->users, crb->ref);
                          crb->users = 0;
                          crb->ref = 0;
                  }
          }
          crb->cred = cr;
          crb->users++;
          crb->ref += td->td_ucredref;
          td->td_ucredref = 0;
          td->td_realucred = NULL;
  }
  
  void
  credbatch_final(struct credbatch *crb)
  {
  
          MPASS(crb->cred != NULL);
          MPASS(crb->users > 0);
          crunusebatch(crb->cred, crb->users, crb->ref);
  }
  
  /*
   * Allocate a zeroed cred structure.
   */
  struct ucred *
  crget(void)
  {
          struct ucred *cr;
  
          cr = malloc(sizeof(*cr), M_CRED, M_WAITOK | M_ZERO);
          mtx_init(&cr->cr_mtx, "cred", NULL, MTX_DEF);
          cr->cr_ref = 1;
  #ifdef AUDIT
          audit_cred_init(cr);
  #endif
  #ifdef MAC
          mac_cred_init(cr);
  #endif
          cr->cr_groups = cr->cr_smallgroups;
          cr->cr_agroups =
              sizeof(cr->cr_smallgroups) / sizeof(cr->cr_smallgroups[0]);
          return (cr);
  }
  
  /*
   * Claim another reference to a ucred structure.
   */
  struct ucred *
  crhold(struct ucred *cr)
  {
          struct thread *td;
  
          td = curthread;
          if (__predict_true(td->td_realucred == cr)) {
                  KASSERT(cr->cr_users > 0, ("%s: users %d not > 0 on cred %p",
                      __func__, cr->cr_users, cr));
                  td->td_ucredref++;
                  return (cr);
          }
          mtx_lock(&cr->cr_mtx);
          cr->cr_ref++;
          mtx_unlock(&cr->cr_mtx);
          return (cr);
  }
  
  /*
   * Free a cred structure.  Throws away space when ref count gets to 0.
   */
  void
  crfree(struct ucred *cr)
  {
          struct thread *td;
  
          td = curthread;
          if (__predict_true(td->td_realucred == cr)) {
                  KASSERT(cr->cr_users > 0, ("%s: users %d not > 0 on cred %p",
                      __func__, cr->cr_users, cr));
                  td->td_ucredref--;
                  return;
          }
          mtx_lock(&cr->cr_mtx);
          KASSERT(cr->cr_users >= 0, ("%s: users %d not >= 0 on cred %p",
              __func__, cr->cr_users, cr));
          cr->cr_ref--;
          if (cr->cr_users > 0) {
                  mtx_unlock(&cr->cr_mtx);
                  return;
          }
          KASSERT(cr->cr_ref >= 0, ("%s: ref %d not >= 0 on cred %p",
              __func__, cr->cr_ref, cr));
          if (cr->cr_ref > 0) {
                  mtx_unlock(&cr->cr_mtx);
                  return;
          }
          crfree_final(cr);
  }
  
  static void
  crfree_final(struct ucred *cr)
  {
  
          KASSERT(cr->cr_users == 0, ("%s: users %d not == 0 on cred %p",
              __func__, cr->cr_users, cr));
          KASSERT(cr->cr_ref == 0, ("%s: ref %d not == 0 on cred %p",
              __func__, cr->cr_ref, cr));
  
          /*
           * Some callers of crget(), such as nfs_statfs(), allocate a temporary
           * credential, but don't allocate a uidinfo structure.
           */
          if (cr->cr_uidinfo != NULL)
                  uifree(cr->cr_uidinfo);
          if (cr->cr_ruidinfo != NULL)
                  uifree(cr->cr_ruidinfo);
          if (cr->cr_prison != NULL)
                  prison_free(cr->cr_prison);
          if (cr->cr_loginclass != NULL)
                  loginclass_free(cr->cr_loginclass);
  #ifdef AUDIT
          audit_cred_destroy(cr);
  #endif
  #ifdef MAC
          mac_cred_destroy(cr);
  #endif
          mtx_destroy(&cr->cr_mtx);
          if (cr->cr_groups != cr->cr_smallgroups)
                  free(cr->cr_groups, M_CRED);
          free(cr, M_CRED);
  }
  
  /*
   * Copy a ucred's contents from a template.  Does not block.
   */
  void
  crcopy(struct ucred *dest, struct ucred *src)
  {
  
          KASSERT(dest->cr_ref == 1, ("crcopy of shared ucred"));
          bcopy(&src->cr_startcopy, &dest->cr_startcopy,
              (unsigned)((caddr_t)&src->cr_endcopy -
                  (caddr_t)&src->cr_startcopy));
          crsetgroups(dest, src->cr_ngroups, src->cr_groups);
          uihold(dest->cr_uidinfo);
          uihold(dest->cr_ruidinfo);
          prison_hold(dest->cr_prison);
          loginclass_hold(dest->cr_loginclass);
  #ifdef AUDIT
          audit_cred_copy(src, dest);
  #endif
  #ifdef MAC
          mac_cred_copy(src, dest);
  #endif
  }
  
  /*
   * Dup cred struct to a new held one.
   */
  struct ucred *
  crdup(struct ucred *cr)
  {
          struct ucred *newcr;
  
          newcr = crget();
          crcopy(newcr, cr);
          return (newcr);
  }
  
  /*
   * Fill in a struct xucred based on a struct ucred.
   */
  void
  cru2x(struct ucred *cr, struct xucred *xcr)
  {
          int ngroups;
  
          bzero(xcr, sizeof(*xcr));
          xcr->cr_version = XUCRED_VERSION;
          xcr->cr_uid = cr->cr_uid;
  
          ngroups = MIN(cr->cr_ngroups, XU_NGROUPS);
          xcr->cr_ngroups = ngroups;
          bcopy(cr->cr_groups, xcr->cr_groups,
              ngroups * sizeof(*cr->cr_groups));
  }
  
  void
  cru2xt(struct thread *td, struct xucred *xcr)
  {
  
          cru2x(td->td_ucred, xcr);
          xcr->cr_pid = td->td_proc->p_pid;
  }
  
  /*
   * Set initial process credentials.
   * Callers are responsible for providing the reference for provided credentials.
   */
  void
  proc_set_cred_init(struct proc *p, struct ucred *newcred)
  {
  
          p->p_ucred = crcowget(newcred);
  }
  
  /*
   * Change process credentials.
   * Callers are responsible for providing the reference for passed credentials
   * and for freeing old ones.
   *
   * Process has to be locked except when it does not have credentials (as it
   * should not be visible just yet) or when newcred is NULL (as this can be
   * only used when the process is about to be freed, at which point it should
   * not be visible anymore).
   */
  void
  proc_set_cred(struct proc *p, struct ucred *newcred)
  {
          struct ucred *cr;
  
          cr = p->p_ucred;
          MPASS(cr != NULL);
          PROC_LOCK_ASSERT(p, MA_OWNED);
          KASSERT(newcred->cr_users == 0, ("%s: users %d not 0 on cred %p",
              __func__, newcred->cr_users, newcred));
          mtx_lock(&cr->cr_mtx);
          KASSERT(cr->cr_users > 0, ("%s: users %d not > 0 on cred %p",
              __func__, cr->cr_users, cr));
          cr->cr_users--;
          mtx_unlock(&cr->cr_mtx);
          p->p_ucred = newcred;
          newcred->cr_users = 1;
          PROC_UPDATE_COW(p);
  }
  
  void
  proc_unset_cred(struct proc *p)
  {
          struct ucred *cr;
  
          MPASS(p->p_state == PRS_ZOMBIE || p->p_state == PRS_NEW);
          cr = p->p_ucred;
          p->p_ucred = NULL;
          KASSERT(cr->cr_users > 0, ("%s: users %d not > 0 on cred %p",
              __func__, cr->cr_users, cr));
          mtx_lock(&cr->cr_mtx);
          cr->cr_users--;
          if (cr->cr_users == 0)
                  KASSERT(cr->cr_ref > 0, ("%s: ref %d not > 0 on cred %p",
                      __func__, cr->cr_ref, cr));
          mtx_unlock(&cr->cr_mtx);
          crfree(cr);
  }
  
  struct ucred *
  crcopysafe(struct proc *p, struct ucred *cr)
  {
          struct ucred *oldcred;
          int groups;
  
          PROC_LOCK_ASSERT(p, MA_OWNED);
  
          oldcred = p->p_ucred;
          while (cr->cr_agroups < oldcred->cr_agroups) {
                  groups = oldcred->cr_agroups;
                  PROC_UNLOCK(p);
                  crextend(cr, groups);
                  PROC_LOCK(p);
                  oldcred = p->p_ucred;
          }
          crcopy(cr, oldcred);
  
          return (oldcred);
  }
  
  /*
   * Extend the passed in credential to hold n items.
   */
  void
  crextend(struct ucred *cr, int n)
  {
          int cnt;
  
          /* Truncate? */
          if (n <= cr->cr_agroups)
                  return;
  
          /*
           * We extend by 2 each time since we're using a power of two
           * allocator until we need enough groups to fill a page.
           * Once we're allocating multiple pages, only allocate as many
           * as we actually need.  The case of processes needing a
           * non-power of two number of pages seems more likely than
           * a real world process that adds thousands of groups one at a
           * time.
           */
          if ( n < PAGE_SIZE / sizeof(gid_t) ) {
                  if (cr->cr_agroups == 0)
                          cnt = MAX(1, MINALLOCSIZE / sizeof(gid_t));
                  else
                          cnt = cr->cr_agroups * 2;
  
                  while (cnt < n)
                          cnt *= 2;
          } else
                  cnt = roundup2(n, PAGE_SIZE / sizeof(gid_t));
  
          /* Free the old array. */
          if (cr->cr_groups != cr->cr_smallgroups)
                  free(cr->cr_groups, M_CRED);
  
          cr->cr_groups = malloc(cnt * sizeof(gid_t), M_CRED, M_WAITOK | M_ZERO);
          cr->cr_agroups = cnt;
  }
  
  /*
   * Copy groups in to a credential, preserving any necessary invariants.
   * Currently this includes the sorting of all supplemental gids.
   * crextend() must have been called before hand to ensure sufficient
   * space is available.
   */
  static void
  crsetgroups_locked(struct ucred *cr, int ngrp, gid_t *groups)
  {
          int i;
          int j;
          gid_t g;
  
          KASSERT(cr->cr_agroups >= ngrp, ("cr_ngroups is too small"));
  
          bcopy(groups, cr->cr_groups, ngrp * sizeof(gid_t));
          cr->cr_ngroups = ngrp;
  
          /*
           * Sort all groups except cr_groups[0] to allow groupmember to
           * perform a binary search.
           *
           * XXX: If large numbers of groups become common this should
           * be replaced with shell sort like linux uses or possibly
           * heap sort.
           */
          for (i = 2; i < ngrp; i++) {
                  g = cr->cr_groups[i];
                  for (j = i-1; j >= 1 && g < cr->cr_groups[j]; j--)
                          cr->cr_groups[j + 1] = cr->cr_groups[j];
                  cr->cr_groups[j + 1] = g;
          }
  }
  
  /*
   * Copy groups in to a credential after expanding it if required.
   * Truncate the list to (ngroups_max + 1) if it is too large.
   */
  void
  crsetgroups(struct ucred *cr, int ngrp, gid_t *groups)
  {
  
          if (ngrp > ngroups_max + 1)
                  ngrp = ngroups_max + 1;
  
          crextend(cr, ngrp);
          crsetgroups_locked(cr, ngrp, groups);
  }
  
  /*
   * Get login name, if available.
   */
  #ifndef _SYS_SYSPROTO_H_
  struct getlogin_args {
          char    *namebuf;
          u_int   namelen;
  };
  #endif
  /* ARGSUSED */
  int
  sys_getlogin(struct thread *td, struct getlogin_args *uap)
  {
          char login[MAXLOGNAME];
          struct proc *p = td->td_proc;
          size_t len;
  
          if (uap->namelen > MAXLOGNAME)
                  uap->namelen = MAXLOGNAME;
          PROC_LOCK(p);
          SESS_LOCK(p->p_session);
          len = strlcpy(login, p->p_session->s_login, uap->namelen) + 1;
          SESS_UNLOCK(p->p_session);
          PROC_UNLOCK(p);
          if (len > uap->namelen)
                  return (ERANGE);
          return (copyout(login, uap->namebuf, len));
  }
  
  /*
   * Set login name.
   */
  #ifndef _SYS_SYSPROTO_H_
  struct setlogin_args {
          char    *namebuf;
  };
  #endif
  /* ARGSUSED */
  int
  sys_setlogin(struct thread *td, struct setlogin_args *uap)
  {
          struct proc *p = td->td_proc;
          int error;
          char logintmp[MAXLOGNAME];
  
          CTASSERT(sizeof(p->p_session->s_login) >= sizeof(logintmp));
  
          error = priv_check(td, PRIV_PROC_SETLOGIN);
          if (error)
                  return (error);
          error = copyinstr(uap->namebuf, logintmp, sizeof(logintmp), NULL);
          if (error != 0) {
                  if (error == ENAMETOOLONG)
                          error = EINVAL;
                  return (error);
          }
          AUDIT_ARG_LOGIN(logintmp);
          PROC_LOCK(p);
          SESS_LOCK(p->p_session);
          strcpy(p->p_session->s_login, logintmp);
          SESS_UNLOCK(p->p_session);
          PROC_UNLOCK(p);
          return (0);
  }
  
  void
  setsugid(struct proc *p)
  {
  
          PROC_LOCK_ASSERT(p, MA_OWNED);
          p->p_flag |= P_SUGID;
  }
  
  /*-
   * Change a process's effective uid.
   * Side effects: newcred->cr_uid and newcred->cr_uidinfo will be modified.
   * References: newcred must be an exclusive credential reference for the
   *             duration of the call.
   */
  void
  change_euid(struct ucred *newcred, struct uidinfo *euip)
  {
  
          newcred->cr_uid = euip->ui_uid;
          uihold(euip);
          uifree(newcred->cr_uidinfo);
          newcred->cr_uidinfo = euip;
  }
  
  /*-
   * Change a process's effective gid.
   * Side effects: newcred->cr_gid will be modified.
   * References: newcred must be an exclusive credential reference for the
   *             duration of the call.
   */
  void
  change_egid(struct ucred *newcred, gid_t egid)
  {
  
          newcred->cr_groups[0] = egid;
  }
  
  /*-
   * Change a process's real uid.
   * Side effects: newcred->cr_ruid will be updated, newcred->cr_ruidinfo
   *               will be updated, and the old and new cr_ruidinfo proc
   *               counts will be updated.
   * References: newcred must be an exclusive credential reference for the
   *             duration of the call.
   */
  void
  change_ruid(struct ucred *newcred, struct uidinfo *ruip)
  {
  
          (void)chgproccnt(newcred->cr_ruidinfo, -1, 0);
          newcred->cr_ruid = ruip->ui_uid;
          uihold(ruip);
          uifree(newcred->cr_ruidinfo);
          newcred->cr_ruidinfo = ruip;
          (void)chgproccnt(newcred->cr_ruidinfo, 1, 0);
  }
  
  /*-
   * Change a process's real gid.
   * Side effects: newcred->cr_rgid will be updated.
   * References: newcred must be an exclusive credential reference for the
   *             duration of the call.
   */
  void
  change_rgid(struct ucred *newcred, gid_t rgid)
  {
  
          newcred->cr_rgid = rgid;
  }
  
  /*-
   * Change a process's saved uid.
   * Side effects: newcred->cr_svuid will be updated.
   * References: newcred must be an exclusive credential reference for the
   *             duration of the call.
   */
  void
  change_svuid(struct ucred *newcred, uid_t svuid)
  {
  
          newcred->cr_svuid = svuid;
  }
  
  /*-
   * Change a process's saved gid.
   * Side effects: newcred->cr_svgid will be updated.
   * References: newcred must be an exclusive credential reference for the
   *             duration of the call.
   */
  void
  change_svgid(struct ucred *newcred, gid_t svgid)
  {
  
          newcred->cr_svgid = svgid;
  }

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