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

     /*-
      * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
      *
      * Copyright (c) 2009, 2016 Robert N. M. Watson
      * All rights reserved.
      *
      * This software was developed at the University of Cambridge Computer
      * Laboratory with support from a grant from Google, Inc.
      *
     * Portions of this software were developed by BAE Systems, the University of
     * Cambridge Computer Laboratory, and Memorial University under DARPA/AFRL
     * contract FA8650-15-C-7558 ("CADETS"), as part of the DARPA Transparent
     * Computing (TC) research program.
     *
     * 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.
     *
     * THIS SOFTWARE IS PROVIDED BY THE AUTHOR 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 AUTHOR 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.
     */
    
    /*-
     * FreeBSD process descriptor facility.
     *
     * Some processes are represented by a file descriptor, which will be used in
     * preference to signaling and pids for the purposes of process management,
     * and is, in effect, a form of capability.  When a process descriptor is
     * used with a process, it ceases to be visible to certain traditional UNIX
     * process facilities, such as waitpid(2).
     *
     * Some semantics:
     *
     * - At most one process descriptor will exist for any process, although
     *   references to that descriptor may be held from many processes (or even
     *   be in flight between processes over a local domain socket).
     * - Last close on the process descriptor will terminate the process using
     *   SIGKILL and reparent it to init so that there's a process to reap it
     *   when it's done exiting.
     * - If the process exits before the descriptor is closed, it will not
     *   generate SIGCHLD on termination, or be picked up by waitpid().
     * - The pdkill(2) system call may be used to deliver a signal to the process
     *   using its process descriptor.
     * - The pdwait4(2) system call may be used to block (or not) on a process
     *   descriptor to collect termination information.
     *
     * Open questions:
     *
     * - How to handle ptrace(2)?
     * - Will we want to add a pidtoprocdesc(2) system call to allow process
     *   descriptors to be created for processes without pdfork(2)?
     */
    
    #include <sys/cdefs.h>
    __FBSDID("$FreeBSD$");
    
    #include <sys/param.h>
    #include <sys/capsicum.h>
    #include <sys/fcntl.h>
    #include <sys/file.h>
    #include <sys/filedesc.h>
    #include <sys/kernel.h>
    #include <sys/lock.h>
    #include <sys/mutex.h>
    #include <sys/poll.h>
    #include <sys/proc.h>
    #include <sys/procdesc.h>
    #include <sys/resourcevar.h>
    #include <sys/stat.h>
    #include <sys/sysproto.h>
    #include <sys/sysctl.h>
    #include <sys/systm.h>
    #include <sys/ucred.h>
    #include <sys/user.h>
    
    #include <security/audit/audit.h>
    
    #include <vm/uma.h>
    
    FEATURE(process_descriptors, "Process Descriptors");
    
    static uma_zone_t procdesc_zone;
    
    static fo_poll_t        procdesc_poll;
    static fo_kqfilter_t    procdesc_kqfilter;
   static fo_stat_t        procdesc_stat;
   static fo_close_t       procdesc_close;
   static fo_fill_kinfo_t  procdesc_fill_kinfo;
   
   static struct fileops procdesc_ops = {
           .fo_read = invfo_rdwr,
           .fo_write = invfo_rdwr,
           .fo_truncate = invfo_truncate,
           .fo_ioctl = invfo_ioctl,
           .fo_poll = procdesc_poll,
           .fo_kqfilter = procdesc_kqfilter,
           .fo_stat = procdesc_stat,
           .fo_close = procdesc_close,
           .fo_chmod = invfo_chmod,
           .fo_chown = invfo_chown,
           .fo_sendfile = invfo_sendfile,
           .fo_fill_kinfo = procdesc_fill_kinfo,
           .fo_flags = DFLAG_PASSABLE,
   };
   
   /*
    * Initialize with VFS so that process descriptors are available along with
    * other file descriptor types.  As long as it runs before init(8) starts,
    * there shouldn't be a problem.
    */
   static void
   procdesc_init(void *dummy __unused)
   {
   
           procdesc_zone = uma_zcreate("procdesc", sizeof(struct procdesc),
               NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, 0);
           if (procdesc_zone == NULL)
                   panic("procdesc_init: procdesc_zone not initialized");
   }
   SYSINIT(vfs, SI_SUB_VFS, SI_ORDER_ANY, procdesc_init, NULL);
   
   /*
    * Return a locked process given a process descriptor, or ESRCH if it has
    * died.
    */
   int
   procdesc_find(struct thread *td, int fd, cap_rights_t *rightsp,
       struct proc **p)
   {
           struct procdesc *pd;
           struct file *fp;
           int error;
   
           error = fget(td, fd, rightsp, &fp);
           if (error)
                   return (error);
           if (fp->f_type != DTYPE_PROCDESC) {
                   error = EBADF;
                   goto out;
           }
           pd = fp->f_data;
           sx_slock(&proctree_lock);
           if (pd->pd_proc != NULL) {
                   *p = pd->pd_proc;
                   PROC_LOCK(*p);
           } else
                   error = ESRCH;
           sx_sunlock(&proctree_lock);
   out:
           fdrop(fp, td);
           return (error);
   }
   
   /*
    * Function to be used by procstat(1) sysctls when returning procdesc
    * information.
    */
   pid_t
   procdesc_pid(struct file *fp_procdesc)
   {
           struct procdesc *pd;
   
           KASSERT(fp_procdesc->f_type == DTYPE_PROCDESC,
              ("procdesc_pid: !procdesc"));
   
           pd = fp_procdesc->f_data;
           return (pd->pd_pid);
   }
   
   /*
    * Retrieve the PID associated with a process descriptor.
    */
   int
   kern_pdgetpid(struct thread *td, int fd, cap_rights_t *rightsp, pid_t *pidp)
   {
           struct file *fp;
           int error;
   
           error = fget(td, fd, rightsp, &fp);
           if (error)
                   return (error);
           if (fp->f_type != DTYPE_PROCDESC) {
                   error = EBADF;
                   goto out;
           }
           *pidp = procdesc_pid(fp);
   out:
           fdrop(fp, td);
           return (error);
   }
   
   /*
    * System call to return the pid of a process given its process descriptor.
    */
   int
   sys_pdgetpid(struct thread *td, struct pdgetpid_args *uap)
   {
           pid_t pid;
           int error;
   
           AUDIT_ARG_FD(uap->fd);
           error = kern_pdgetpid(td, uap->fd, &cap_pdgetpid_rights, &pid);
           if (error == 0)
                   error = copyout(&pid, uap->pidp, sizeof(pid));
           return (error);
   }
   
   /*
    * When a new process is forked by pdfork(), a file descriptor is allocated
    * by the fork code first, then the process is forked, and then we get a
    * chance to set up the process descriptor.  Failure is not permitted at this
    * point, so procdesc_new() must succeed.
    */
   void
   procdesc_new(struct proc *p, int flags)
   {
           struct procdesc *pd;
   
           pd = uma_zalloc(procdesc_zone, M_WAITOK | M_ZERO);
           pd->pd_proc = p;
           pd->pd_pid = p->p_pid;
           p->p_procdesc = pd;
           pd->pd_flags = 0;
           if (flags & PD_DAEMON)
                   pd->pd_flags |= PDF_DAEMON;
           PROCDESC_LOCK_INIT(pd);
           knlist_init_mtx(&pd->pd_selinfo.si_note, &pd->pd_lock);
   
           /*
            * Process descriptors start out with two references: one from their
            * struct file, and the other from their struct proc.
            */
           refcount_init(&pd->pd_refcount, 2);
   }
   
   /*
    * Create a new process decriptor for the process that refers to it.
    */
   int
   procdesc_falloc(struct thread *td, struct file **resultfp, int *resultfd,
       int flags, struct filecaps *fcaps)
   {
           int fflags;
   
           fflags = 0;
           if (flags & PD_CLOEXEC)
                   fflags = O_CLOEXEC;
   
           return (falloc_caps(td, resultfp, resultfd, fflags, fcaps));
   }
   
   /*
    * Initialize a file with a process descriptor.
    */
   void
   procdesc_finit(struct procdesc *pdp, struct file *fp)
   {
   
           finit(fp, FREAD | FWRITE, DTYPE_PROCDESC, pdp, &procdesc_ops);
   }
   
   static void
   procdesc_free(struct procdesc *pd)
   {
   
           /*
            * When the last reference is released, we assert that the descriptor
            * has been closed, but not that the process has exited, as we will
            * detach the descriptor before the process dies if the descript is
            * closed, as we can't wait synchronously.
            */
           if (refcount_release(&pd->pd_refcount)) {
                   KASSERT(pd->pd_proc == NULL,
                       ("procdesc_free: pd_proc != NULL"));
                   KASSERT((pd->pd_flags & PDF_CLOSED),
                       ("procdesc_free: !PDF_CLOSED"));
   
                   knlist_destroy(&pd->pd_selinfo.si_note);
                   PROCDESC_LOCK_DESTROY(pd);
                   uma_zfree(procdesc_zone, pd);
           }
   }
   
   /*
    * procdesc_exit() - notify a process descriptor that its process is exiting.
    * We use the proctree_lock to ensure that process exit either happens
    * strictly before or strictly after a concurrent call to procdesc_close().
    */
   int
   procdesc_exit(struct proc *p)
   {
           struct procdesc *pd;
   
           sx_assert(&proctree_lock, SA_XLOCKED);
           PROC_LOCK_ASSERT(p, MA_OWNED);
           KASSERT(p->p_procdesc != NULL, ("procdesc_exit: p_procdesc NULL"));
   
           pd = p->p_procdesc;
   
           PROCDESC_LOCK(pd);
           KASSERT((pd->pd_flags & PDF_CLOSED) == 0 || p->p_pptr == p->p_reaper,
               ("procdesc_exit: closed && parent not reaper"));
   
           pd->pd_flags |= PDF_EXITED;
           pd->pd_xstat = KW_EXITCODE(p->p_xexit, p->p_xsig);
   
           /*
            * If the process descriptor has been closed, then we have nothing
            * to do; return 1 so that init will get SIGCHLD and do the reaping.
            * Clean up the procdesc now rather than letting it happen during
            * that reap.
            */
           if (pd->pd_flags & PDF_CLOSED) {
                   PROCDESC_UNLOCK(pd);
                   pd->pd_proc = NULL;
                   p->p_procdesc = NULL;
                   procdesc_free(pd);
                   return (1);
           }
           if (pd->pd_flags & PDF_SELECTED) {
                   pd->pd_flags &= ~PDF_SELECTED;
                   selwakeup(&pd->pd_selinfo);
           }
           KNOTE_LOCKED(&pd->pd_selinfo.si_note, NOTE_EXIT);
           PROCDESC_UNLOCK(pd);
           return (0);
   }
   
   /*
    * When a process descriptor is reaped, perhaps as a result of close() or
    * pdwait4(), release the process's reference on the process descriptor.
    */
   void
   procdesc_reap(struct proc *p)
   {
           struct procdesc *pd;
   
           sx_assert(&proctree_lock, SA_XLOCKED);
           KASSERT(p->p_procdesc != NULL, ("procdesc_reap: p_procdesc == NULL"));
   
           pd = p->p_procdesc;
           pd->pd_proc = NULL;
           p->p_procdesc = NULL;
           procdesc_free(pd);
   }
   
   /*
    * procdesc_close() - last close on a process descriptor.  If the process is
    * still running, terminate with SIGKILL (unless PDF_DAEMON is set) and let
    * its reaper clean up the mess; if not, we have to clean up the zombie
    * ourselves.
    */
   static int
   procdesc_close(struct file *fp, struct thread *td)
   {
           struct procdesc *pd;
           struct proc *p;
   
           KASSERT(fp->f_type == DTYPE_PROCDESC, ("procdesc_close: !procdesc"));
   
           pd = fp->f_data;
           fp->f_ops = &badfileops;
           fp->f_data = NULL;
   
           sx_xlock(&proctree_lock);
           PROCDESC_LOCK(pd);
           pd->pd_flags |= PDF_CLOSED;
           PROCDESC_UNLOCK(pd);
           p = pd->pd_proc;
           if (p == NULL) {
                   /*
                    * This is the case where process' exit status was already
                    * collected and procdesc_reap() was already called.
                    */
                   sx_xunlock(&proctree_lock);
           } else {
                   PROC_LOCK(p);
                   AUDIT_ARG_PROCESS(p);
                   if (p->p_state == PRS_ZOMBIE) {
                           /*
                            * If the process is already dead and just awaiting
                            * reaping, do that now.  This will release the
                            * process's reference to the process descriptor when it
                            * calls back into procdesc_reap().
                            */
                           proc_reap(curthread, p, NULL, 0);
                   } else {
                           /*
                            * If the process is not yet dead, we need to kill it,
                            * but we can't wait around synchronously for it to go
                            * away, as that path leads to madness (and deadlocks).
                            * First, detach the process from its descriptor so that
                            * its exit status will be reported normally.
                            */
                           pd->pd_proc = NULL;
                           p->p_procdesc = NULL;
                           procdesc_free(pd);
   
                           /*
                            * Next, reparent it to its reaper (usually init(8)) so
                            * that there's someone to pick up the pieces; finally,
                            * terminate with prejudice.
                            */
                           p->p_sigparent = SIGCHLD;
                           if ((p->p_flag & P_TRACED) == 0) {
                                   proc_reparent(p, p->p_reaper, true);
                           } else {
                                   proc_clear_orphan(p);
                                   p->p_oppid = p->p_reaper->p_pid;
                                   proc_add_orphan(p, p->p_reaper);
                           }
                           if ((pd->pd_flags & PDF_DAEMON) == 0)
                                   kern_psignal(p, SIGKILL);
                           PROC_UNLOCK(p);
                           sx_xunlock(&proctree_lock);
                   }
           }
   
           /*
            * Release the file descriptor's reference on the process descriptor.
            */
           procdesc_free(pd);
           return (0);
   }
   
   static int
   procdesc_poll(struct file *fp, int events, struct ucred *active_cred,
       struct thread *td)
   {
           struct procdesc *pd;
           int revents;
   
           revents = 0;
           pd = fp->f_data;
           PROCDESC_LOCK(pd);
           if (pd->pd_flags & PDF_EXITED)
                   revents |= POLLHUP;
           if (revents == 0) {
                   selrecord(td, &pd->pd_selinfo);
                   pd->pd_flags |= PDF_SELECTED;
           }
           PROCDESC_UNLOCK(pd);
           return (revents);
   }
   
   static void
   procdesc_kqops_detach(struct knote *kn)
   {
           struct procdesc *pd;
   
           pd = kn->kn_fp->f_data;
           knlist_remove(&pd->pd_selinfo.si_note, kn, 0);
   }
   
   static int
   procdesc_kqops_event(struct knote *kn, long hint)
   {
           struct procdesc *pd;
           u_int event;
   
           pd = kn->kn_fp->f_data;
           if (hint == 0) {
                   /*
                    * Initial test after registration. Generate a NOTE_EXIT in
                    * case the process already terminated before registration.
                    */
                   event = pd->pd_flags & PDF_EXITED ? NOTE_EXIT : 0;
           } else {
                   /* Mask off extra data. */
                   event = (u_int)hint & NOTE_PCTRLMASK;
           }
   
           /* If the user is interested in this event, record it. */
           if (kn->kn_sfflags & event)
                   kn->kn_fflags |= event;
   
           /* Process is gone, so flag the event as finished. */
           if (event == NOTE_EXIT) {
                   kn->kn_flags |= EV_EOF | EV_ONESHOT;
                   if (kn->kn_fflags & NOTE_EXIT)
                           kn->kn_data = pd->pd_xstat;
                   if (kn->kn_fflags == 0)
                           kn->kn_flags |= EV_DROP;
                   return (1);
           }
   
           return (kn->kn_fflags != 0);
   }
   
   static struct filterops procdesc_kqops = {
           .f_isfd = 1,
           .f_detach = procdesc_kqops_detach,
           .f_event = procdesc_kqops_event,
   };
   
   static int
   procdesc_kqfilter(struct file *fp, struct knote *kn)
   {
           struct procdesc *pd;
   
           pd = fp->f_data;
           switch (kn->kn_filter) {
           case EVFILT_PROCDESC:
                   kn->kn_fop = &procdesc_kqops;
                   kn->kn_flags |= EV_CLEAR;
                   knlist_add(&pd->pd_selinfo.si_note, kn, 0);
                   return (0);
           default:
                   return (EINVAL);
           }
   }
   
   static int
   procdesc_stat(struct file *fp, struct stat *sb, struct ucred *active_cred,
       struct thread *td)
   {
           struct procdesc *pd;
           struct timeval pstart, boottime;
   
           /*
            * XXXRW: Perhaps we should cache some more information from the
            * process so that we can return it reliably here even after it has
            * died.  For example, caching its credential data.
            */
           bzero(sb, sizeof(*sb));
           pd = fp->f_data;
           sx_slock(&proctree_lock);
           if (pd->pd_proc != NULL) {
                   PROC_LOCK(pd->pd_proc);
                   AUDIT_ARG_PROCESS(pd->pd_proc);
   
                   /* Set birth and [acm] times to process start time. */
                   pstart = pd->pd_proc->p_stats->p_start;
                   getboottime(&boottime);
                   timevaladd(&pstart, &boottime);
                   TIMEVAL_TO_TIMESPEC(&pstart, &sb->st_birthtim);
                   sb->st_atim = sb->st_birthtim;
                   sb->st_ctim = sb->st_birthtim;
                   sb->st_mtim = sb->st_birthtim;
                   if (pd->pd_proc->p_state != PRS_ZOMBIE)
                           sb->st_mode = S_IFREG | S_IRWXU;
                   else
                           sb->st_mode = S_IFREG;
                   sb->st_uid = pd->pd_proc->p_ucred->cr_ruid;
                   sb->st_gid = pd->pd_proc->p_ucred->cr_rgid;
                   PROC_UNLOCK(pd->pd_proc);
           } else
                   sb->st_mode = S_IFREG;
           sx_sunlock(&proctree_lock);
           return (0);
   }
   
   static int
   procdesc_fill_kinfo(struct file *fp, struct kinfo_file *kif,
       struct filedesc *fdp)
   {
           struct procdesc *pdp;
   
           kif->kf_type = KF_TYPE_PROCDESC;
           pdp = fp->f_data;
           kif->kf_un.kf_proc.kf_pid = pdp->pd_pid;
           return (0);
   }

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