The Design and Implementation of the FreeBSD Operating System, Second Edition
Now available: The Design and Implementation of the FreeBSD Operating System (Second Edition)


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

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    1 /*
    2  * Copyright (c) 1989, 1993
    3  *      The Regents of the University of California.  All rights reserved.
    4  *
    5  * Redistribution and use in source and binary forms, with or without
    6  * modification, are permitted provided that the following conditions
    7  * are met:
    8  * 1. Redistributions of source code must retain the above copyright
    9  *    notice, this list of conditions and the following disclaimer.
   10  * 2. Redistributions in binary form must reproduce the above copyright
   11  *    notice, this list of conditions and the following disclaimer in the
   12  *    documentation and/or other materials provided with the distribution.
   13  * 3. Neither the name of the University nor the names of its contributors
   14  *    may be used to endorse or promote products derived from this software
   15  *    without specific prior written permission.
   16  *
   17  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
   18  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   19  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   20  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
   21  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   22  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   23  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   24  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   25  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   26  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   27  * SUCH DAMAGE.
   28  *
   29  *      @(#)kern_ktrace.c       8.2 (Berkeley) 9/23/93
   30  * $FreeBSD: src/sys/kern/kern_ktrace.c,v 1.35.2.6 2002/07/05 22:36:38 darrenr Exp $
   31  */
   32 
   33 #include "opt_ktrace.h"
   34 
   35 #include <sys/param.h>
   36 #include <sys/systm.h>
   37 #include <sys/sysproto.h>
   38 #include <sys/kernel.h>
   39 #include <sys/proc.h>
   40 #include <sys/fcntl.h>
   41 #include <sys/lock.h>
   42 #include <sys/nlookup.h>
   43 #include <sys/vnode.h>
   44 #include <sys/ktrace.h>
   45 #include <sys/malloc.h>
   46 #include <sys/syslog.h>
   47 #include <sys/sysent.h>
   48 
   49 #include <vm/vm_zone.h>
   50 
   51 #include <sys/mplock2.h>
   52 
   53 static MALLOC_DEFINE(M_KTRACE, "KTRACE", "KTRACE");
   54 
   55 #ifdef KTRACE
   56 static void ktrgetheader (struct ktr_header *kth, int type);
   57 static struct ktr_syscall *ktrgetsyscall(struct ktr_header *kth,
   58                                 struct ktr_syscall *ktp_cache, int narg);
   59 static void ktrputsyscall(struct ktr_syscall *ktp_cache,
   60                                 struct ktr_syscall *ktp);
   61 static void ktrwrite (struct lwp *, struct ktr_header *, struct uio *);
   62 static int ktrcanset (struct thread *,struct proc *);
   63 static int ktrsetchildren (struct thread *, struct proc *,
   64                                 int, int, ktrace_node_t);
   65 static int ktrops (struct thread *,struct proc *,int,int, ktrace_node_t);
   66 
   67 /*
   68  * MPSAFE
   69  */
   70 static
   71 void
   72 ktrgetheader(struct ktr_header *kth, int type)
   73 {
   74         thread_t td = curthread;
   75         struct proc *p = td->td_proc;
   76         struct lwp *lp = td->td_lwp;
   77 
   78         kth->ktr_type = type;
   79         /* XXX threaded flag is a hack at the moment */
   80         kth->ktr_flags = (p->p_nthreads > 1) ? KTRH_THREADED : 0;
   81         kth->ktr_flags |= KTRH_CPUID_ENCODE(td->td_gd->gd_cpuid);
   82         /*microtime(&kth->ktr_time); set in ktrwrite */
   83         kth->ktr_pid = p->p_pid;
   84         kth->ktr_tid = lp->lwp_tid;
   85         bcopy(p->p_comm, kth->ktr_comm, MAXCOMLEN + 1);
   86 }
   87 
   88 static
   89 struct ktr_syscall *
   90 ktrgetsyscall(struct ktr_header *kth, struct ktr_syscall *ktp_cache, int narg)
   91 {
   92         size_t len;
   93 
   94         len = offsetof(struct ktr_syscall, ktr_args[narg]);
   95         if (len > sizeof(*ktp_cache))
   96                 ktp_cache = kmalloc(len, M_KTRACE, M_WAITOK);
   97         kth->ktr_buf = (caddr_t)ktp_cache;
   98         kth->ktr_len = (int)len;
   99         return (ktp_cache);
  100 }
  101 
  102 static
  103 void
  104 ktrputsyscall(struct ktr_syscall *ktp_cache, struct ktr_syscall *ktp)
  105 {
  106         if (ktp != ktp_cache)
  107                 kfree(ktp, M_KTRACE);
  108 }
  109 
  110 void
  111 ktrsyscall(struct lwp *lp, int code, int narg, register_t args[])
  112 {
  113         struct ktr_header kth;
  114         struct ktr_syscall ktp_cache;
  115         struct ktr_syscall *ktp;
  116         register_t *argp;
  117         int i;
  118 
  119         /*
  120          * Setting the active bit prevents a ktrace recursion from the
  121          * ktracing op itself.
  122          */
  123         lp->lwp_traceflag |= KTRFAC_ACTIVE;
  124         ktrgetheader(&kth, KTR_SYSCALL);
  125 
  126         ktp = ktrgetsyscall(&kth, &ktp_cache, narg);
  127         ktp->ktr_code = code;
  128         ktp->ktr_narg = narg;
  129         argp = &ktp->ktr_args[0];
  130         for (i = 0; i < narg; i++)
  131                 *argp++ = args[i];
  132         ktrwrite(lp, &kth, NULL);
  133 
  134         ktrputsyscall(&ktp_cache, ktp);
  135         lp->lwp_traceflag &= ~KTRFAC_ACTIVE;
  136 }
  137 
  138 void
  139 ktrsysret(struct lwp *lp, int code, int error, register_t retval)
  140 {
  141         struct ktr_header kth;
  142         struct ktr_sysret ktp;
  143 
  144         lp->lwp_traceflag |= KTRFAC_ACTIVE;
  145         ktrgetheader(&kth, KTR_SYSRET);
  146 
  147         ktp.ktr_code = code;
  148         ktp.ktr_error = error;
  149         if (error == 0)
  150                 ktp.ktr_retval = retval;                /* what about val2 ? */
  151         else
  152                 ktp.ktr_retval = 0;
  153 
  154         kth.ktr_buf = (caddr_t)&ktp;
  155         kth.ktr_len = (int)sizeof(struct ktr_sysret);
  156 
  157         ktrwrite(lp, &kth, NULL);
  158         lp->lwp_traceflag &= ~KTRFAC_ACTIVE;
  159 }
  160 
  161 void
  162 ktrnamei(struct lwp *lp, char *path)
  163 {
  164         struct ktr_header kth;
  165 
  166         lp->lwp_traceflag |= KTRFAC_ACTIVE;
  167         ktrgetheader(&kth, KTR_NAMEI);
  168 
  169         kth.ktr_len = (int)strlen(path);
  170         kth.ktr_buf = path;
  171 
  172         ktrwrite(lp, &kth, NULL);
  173         lp->lwp_traceflag &= ~KTRFAC_ACTIVE;
  174 }
  175 
  176 void
  177 ktrgenio(struct lwp *lp, int fd, enum uio_rw rw, struct uio *uio, int error)
  178 {
  179         struct ktr_header kth;
  180         struct ktr_genio ktg;
  181 
  182         if (error)
  183                 return;
  184         lp->lwp_traceflag |= KTRFAC_ACTIVE;
  185         ktrgetheader(&kth, KTR_GENIO);
  186 
  187         ktg.ktr_fd = fd;
  188         ktg.ktr_rw = rw;
  189         kth.ktr_buf = (caddr_t)&ktg;
  190         kth.ktr_len = (int)sizeof(struct ktr_genio);
  191         uio->uio_offset = 0;
  192         uio->uio_rw = UIO_WRITE;
  193 
  194         ktrwrite(lp, &kth, uio);
  195         lp->lwp_traceflag &= ~KTRFAC_ACTIVE;
  196 }
  197 
  198 void
  199 ktrpsig(struct lwp *lp, int sig, sig_t action, sigset_t *mask, int code)
  200 {
  201         struct ktr_header kth;
  202         struct ktr_psig kp;
  203 
  204         lp->lwp_traceflag |= KTRFAC_ACTIVE;
  205         ktrgetheader(&kth, KTR_PSIG);
  206 
  207         kp.signo = (char)sig;
  208         kp.action = action;
  209         kp.mask = *mask;
  210         kp.code = code;
  211         kth.ktr_buf = (caddr_t)&kp;
  212         kth.ktr_len = (int)sizeof(struct ktr_psig);
  213 
  214         ktrwrite(lp, &kth, NULL);
  215         lp->lwp_traceflag &= ~KTRFAC_ACTIVE;
  216 }
  217 
  218 void
  219 ktrcsw(struct lwp *lp, int out, int user)
  220 {
  221         struct ktr_header kth;
  222         struct ktr_csw kc;
  223 
  224         lp->lwp_traceflag |= KTRFAC_ACTIVE;
  225         ktrgetheader(&kth, KTR_CSW);
  226 
  227         kc.out = out;
  228         kc.user = user;
  229         kth.ktr_buf = (caddr_t)&kc;
  230         kth.ktr_len = (int)sizeof(struct ktr_csw);
  231 
  232         ktrwrite(lp, &kth, NULL);
  233         lp->lwp_traceflag &= ~KTRFAC_ACTIVE;
  234 }
  235 #endif
  236 
  237 /* Interface and common routines */
  238 
  239 #ifdef KTRACE
  240 /*
  241  * ktrace system call
  242  */
  243 struct ktrace_clear_info {
  244         ktrace_node_t tracenode;
  245         int rootclear;
  246         int error;
  247 };
  248 
  249 static int ktrace_clear_callback(struct proc *p, void *data);
  250 
  251 #endif
  252 
  253 /*
  254  * MPALMOSTSAFE
  255  */
  256 int
  257 sys_ktrace(struct ktrace_args *uap)
  258 {
  259 #ifdef KTRACE
  260         struct ktrace_clear_info info;
  261         struct thread *td = curthread;
  262         struct proc *curp = td->td_proc;
  263         struct proc *p;
  264         struct pgrp *pg;
  265         int facs = uap->facs & ~KTRFAC_ROOT;
  266         int ops = KTROP(uap->ops);
  267         int descend = uap->ops & KTRFLAG_DESCEND;
  268         int ret = 0;
  269         int error = 0;
  270         struct nlookupdata nd;
  271         ktrace_node_t tracenode = NULL;
  272 
  273         get_mplock();
  274         curp->p_traceflag |= KTRFAC_ACTIVE;
  275         if (ops != KTROP_CLEAR) {
  276                 /*
  277                  * an operation which requires a file argument.
  278                  */
  279                 error = nlookup_init(&nd, uap->fname, 
  280                                         UIO_USERSPACE, NLC_LOCKVP);
  281                 if (error == 0)
  282                         error = vn_open(&nd, NULL, FREAD|FWRITE|O_NOFOLLOW, 0);
  283                 if (error == 0 && nd.nl_open_vp->v_type != VREG)
  284                         error = EACCES;
  285                 if (error) {
  286                         curp->p_traceflag &= ~KTRFAC_ACTIVE;
  287                         nlookup_done(&nd);
  288                         goto done;
  289                 }
  290                 tracenode = kmalloc(sizeof(struct ktrace_node), M_KTRACE,
  291                                     M_WAITOK | M_ZERO);
  292                 tracenode->kn_vp = nd.nl_open_vp;
  293                 tracenode->kn_refs = 1;
  294                 nd.nl_open_vp = NULL;
  295                 nlookup_done(&nd);
  296                 vn_unlock(tracenode->kn_vp);
  297         }
  298         /*
  299          * Clear all uses of the tracefile.  Not the most efficient operation
  300          * in the world.
  301          */
  302         if (ops == KTROP_CLEARFILE) {
  303                 info.tracenode = tracenode;
  304                 info.error = 0;
  305                 info.rootclear = 0;
  306                 allproc_scan(ktrace_clear_callback, &info);
  307                 error = info.error;
  308                 goto done;
  309         }
  310         /*
  311          * need something to (un)trace (XXX - why is this here?)
  312          */
  313         if (!facs) {
  314                 error = EINVAL;
  315                 goto done;
  316         }
  317         /*
  318          * do it
  319          */
  320         if (uap->pid < 0) {
  321                 /*
  322                  * By process group.  Process group is referenced, preventing
  323                  * disposal.
  324                  */
  325                 pg = pgfind(-uap->pid);
  326                 if (pg == NULL) {
  327                         error = ESRCH;
  328                         goto done;
  329                 }
  330                 lwkt_gettoken(&pg->pg_token);
  331                 LIST_FOREACH(p, &pg->pg_members, p_pglist) {
  332                         PHOLD(p);
  333                         if (descend)
  334                                 ret |= ktrsetchildren(td, p, ops, facs, tracenode);
  335                         else
  336                                 ret |= ktrops(td, p, ops, facs, tracenode);
  337                         PRELE(p);
  338                 }
  339                 lwkt_reltoken(&pg->pg_token);
  340                 pgrel(pg);
  341         } else {
  342                 /*
  343                  * by pid
  344                  */
  345                 p = pfind(uap->pid);
  346                 if (p == NULL) {
  347                         error = ESRCH;
  348                         goto done;
  349                 }
  350                 if (descend)
  351                         ret |= ktrsetchildren(td, p, ops, facs, tracenode);
  352                 else
  353                         ret |= ktrops(td, p, ops, facs, tracenode);
  354                 PRELE(p);
  355         }
  356         if (!ret)
  357                 error = EPERM;
  358 done:
  359         if (tracenode)
  360                 ktrdestroy(&tracenode);
  361         curp->p_traceflag &= ~KTRFAC_ACTIVE;
  362         rel_mplock();
  363         return (error);
  364 #else
  365         return ENOSYS;
  366 #endif
  367 }
  368 
  369 #ifdef KTRACE
  370 
  371 /*
  372  * NOTE: NOT MPSAFE (yet)
  373  */
  374 static int
  375 ktrace_clear_callback(struct proc *p, void *data)
  376 {
  377         struct ktrace_clear_info *info = data;
  378 
  379         if (p->p_tracenode) {
  380                 if (info->rootclear) {
  381                         if (p->p_tracenode == info->tracenode) {
  382                                 ktrdestroy(&p->p_tracenode);
  383                                 p->p_traceflag = 0;
  384                         }
  385                 } else {
  386                         if (p->p_tracenode->kn_vp == info->tracenode->kn_vp) {
  387                                 if (ktrcanset(curthread, p)) {
  388                                         ktrdestroy(&p->p_tracenode);
  389                                         p->p_traceflag = 0;
  390                                 } else {
  391                                         info->error = EPERM;
  392                                 }
  393                         }
  394                 }
  395         }
  396         return(0);
  397 }
  398 
  399 #endif
  400 
  401 /*
  402  * utrace system call
  403  *
  404  * MPALMOSTSAFE
  405  */
  406 int
  407 sys_utrace(struct utrace_args *uap)
  408 {
  409 #ifdef KTRACE
  410         struct ktr_header kth;
  411         struct thread *td = curthread;  /* XXX */
  412         char cp_cache[64];
  413         caddr_t cp;
  414 
  415         if (!KTRPOINT(td, KTR_USER))
  416                 return (0);
  417         if (uap->len > KTR_USER_MAXLEN)
  418                 return (EINVAL);
  419         td->td_lwp->lwp_traceflag |= KTRFAC_ACTIVE;
  420         ktrgetheader(&kth, KTR_USER);
  421         if (uap->len <= sizeof(cp_cache))
  422                 cp = cp_cache;
  423         else
  424                 cp = kmalloc(uap->len, M_KTRACE, M_WAITOK);
  425 
  426         if (!copyin(uap->addr, cp, uap->len)) {
  427                 kth.ktr_buf = cp;
  428                 kth.ktr_len = uap->len;
  429                 ktrwrite(td->td_lwp, &kth, NULL);
  430         }
  431         if (cp != cp_cache)
  432                 kfree(cp, M_KTRACE);
  433         td->td_lwp->lwp_traceflag &= ~KTRFAC_ACTIVE;
  434 
  435         return (0);
  436 #else
  437         return (ENOSYS);
  438 #endif
  439 }
  440 
  441 void
  442 ktrdestroy(struct ktrace_node **tracenodep)
  443 {
  444         ktrace_node_t tracenode;
  445 
  446         if ((tracenode = *tracenodep) != NULL) {
  447                 *tracenodep = NULL;
  448                 KKASSERT(tracenode->kn_refs > 0);
  449                 if (atomic_fetchadd_int(&tracenode->kn_refs, -1) == 1) {
  450                         vn_close(tracenode->kn_vp, FREAD|FWRITE);
  451                         tracenode->kn_vp = NULL;
  452                         kfree(tracenode, M_KTRACE);
  453                 }
  454         }
  455 }
  456 
  457 /*
  458  * This allows a process to inherit a ref on a tracenode and is also used
  459  * as a temporary ref to prevent a tracenode from being destroyed out from
  460  * under an active operation.
  461  */
  462 ktrace_node_t
  463 ktrinherit(ktrace_node_t tracenode)
  464 {
  465         if (tracenode) {
  466                 KKASSERT(tracenode->kn_refs > 0);
  467                 atomic_add_int(&tracenode->kn_refs, 1);
  468         }
  469         return(tracenode);
  470 }
  471 
  472 #ifdef KTRACE
  473 static int
  474 ktrops(struct thread *td, struct proc *p, int ops, int facs,
  475        ktrace_node_t tracenode)
  476 {
  477         ktrace_node_t oldnode;
  478 
  479         if (!ktrcanset(td, p))
  480                 return (0);
  481         if (ops == KTROP_SET) {
  482                 if ((oldnode = p->p_tracenode) != tracenode) {
  483                         p->p_tracenode = ktrinherit(tracenode);
  484                         ktrdestroy(&oldnode);
  485                 }
  486                 p->p_traceflag |= facs;
  487                 if (td->td_ucred->cr_uid == 0)
  488                         p->p_traceflag |= KTRFAC_ROOT;
  489         } else {
  490                 /* KTROP_CLEAR */
  491                 if (((p->p_traceflag &= ~facs) & KTRFAC_MASK) == 0) {
  492                         /* no more tracing */
  493                         p->p_traceflag = 0;
  494                         ktrdestroy(&p->p_tracenode);
  495                 }
  496         }
  497 
  498         return (1);
  499 }
  500 
  501 static int
  502 ktrsetchildren(struct thread *td, struct proc *top, int ops, int facs,
  503                ktrace_node_t tracenode)
  504 {
  505         struct proc *p;
  506         struct proc *np;
  507         int ret = 0;
  508 
  509         p = top;
  510         PHOLD(p);
  511         lwkt_gettoken(&p->p_token);
  512 
  513         for (;;) {
  514                 ret |= ktrops(td, p, ops, facs, tracenode);
  515 
  516                 /*
  517                  * If this process has children, descend to them next,
  518                  * otherwise do any siblings, and if done with this level,
  519                  * follow back up the tree (but not past top).
  520                  */
  521                 if ((np = LIST_FIRST(&p->p_children)) != NULL) {
  522                         PHOLD(np);
  523                 }
  524                 while (np == NULL) {
  525                         if (p == top)
  526                                 break;
  527                         if ((np = LIST_NEXT(p, p_sibling)) != NULL) {
  528                                 PHOLD(np);
  529                                 break;
  530                         }
  531 
  532                         /*
  533                          * recurse up to parent, set p in our inner
  534                          * loop when doing this.  np can be NULL if
  535                          * we race a reparenting to init (thus 'top'
  536                          * is skipped past and never encountered).
  537                          */
  538                         np = p->p_pptr;
  539                         if (np == NULL)
  540                                 break;
  541                         PHOLD(np);
  542                         lwkt_reltoken(&p->p_token);
  543                         PRELE(p);
  544                         p = np;
  545                         lwkt_gettoken(&p->p_token);
  546                         np = NULL;
  547                 }
  548                 lwkt_reltoken(&p->p_token);
  549                 PRELE(p);
  550                 p = np;
  551                 if (p == NULL)
  552                         break;
  553                 /* Already held, but we need the token too */
  554                 lwkt_gettoken(&p->p_token);
  555         }
  556         return (ret);
  557 }
  558 
  559 static void
  560 ktrwrite(struct lwp *lp, struct ktr_header *kth, struct uio *uio)
  561 {
  562         struct ktrace_clear_info info;
  563         struct uio auio;
  564         struct iovec aiov[2];
  565         int error;
  566         ktrace_node_t tracenode;
  567 
  568         /*
  569          * We have to ref our tracenode to prevent it from being ripped out
  570          * from under us while we are trying to use it.   p_tracenode can
  571          * go away at any time if another process gets a write error.
  572          *
  573          * XXX not MP safe
  574          */
  575         if (lp->lwp_proc->p_tracenode == NULL)
  576                 return;
  577         tracenode = ktrinherit(lp->lwp_proc->p_tracenode);
  578         auio.uio_iov = &aiov[0];
  579         auio.uio_offset = 0;
  580         auio.uio_segflg = UIO_SYSSPACE;
  581         auio.uio_rw = UIO_WRITE;
  582         aiov[0].iov_base = (caddr_t)kth;
  583         aiov[0].iov_len = sizeof(struct ktr_header);
  584         auio.uio_resid = sizeof(struct ktr_header);
  585         auio.uio_iovcnt = 1;
  586         auio.uio_td = curthread;
  587         if (kth->ktr_len > 0) {
  588                 auio.uio_iovcnt++;
  589                 aiov[1].iov_base = kth->ktr_buf;
  590                 aiov[1].iov_len = kth->ktr_len;
  591                 auio.uio_resid += kth->ktr_len;
  592                 if (uio != NULL)
  593                         kth->ktr_len += uio->uio_resid;
  594         }
  595 
  596         /*
  597          * NOTE: Must set timestamp after obtaining lock to ensure no
  598          *       timestamp reversals in the output file.
  599          */
  600         vn_lock(tracenode->kn_vp, LK_EXCLUSIVE | LK_RETRY);
  601         microtime(&kth->ktr_time);
  602         error = VOP_WRITE(tracenode->kn_vp, &auio,
  603                           IO_UNIT | IO_APPEND, lp->lwp_thread->td_ucred);
  604         if (error == 0 && uio != NULL) {
  605                 error = VOP_WRITE(tracenode->kn_vp, uio,
  606                               IO_UNIT | IO_APPEND, lp->lwp_thread->td_ucred);
  607         }
  608         vn_unlock(tracenode->kn_vp);
  609         if (error) {
  610                 /*
  611                  * If an error occured, give up tracing on all processes
  612                  * using this tracenode.  This is not MP safe but is
  613                  * blocking-safe.
  614                  */
  615                 log(LOG_NOTICE,
  616                     "ktrace write failed, errno %d, tracing stopped\n", error);
  617                 info.tracenode = tracenode;
  618                 info.error = 0;
  619                 info.rootclear = 1;
  620                 allproc_scan(ktrace_clear_callback, &info);
  621         }
  622         ktrdestroy(&tracenode);
  623 }
  624 
  625 /*
  626  * Return true if caller has permission to set the ktracing state
  627  * of target.  Essentially, the target can't possess any
  628  * more permissions than the caller.  KTRFAC_ROOT signifies that
  629  * root previously set the tracing status on the target process, and
  630  * so, only root may further change it.
  631  *
  632  * TODO: check groups.  use caller effective gid.
  633  */
  634 static int
  635 ktrcanset(struct thread *calltd, struct proc *targetp)
  636 {
  637         struct ucred *caller = calltd->td_ucred;
  638         struct ucred *target = targetp->p_ucred;
  639 
  640         if (!PRISON_CHECK(caller, target))
  641                 return (0);
  642         if ((caller->cr_uid == target->cr_ruid &&
  643              target->cr_ruid == target->cr_svuid &&
  644              caller->cr_rgid == target->cr_rgid &&      /* XXX */
  645              target->cr_rgid == target->cr_svgid &&
  646              (targetp->p_traceflag & KTRFAC_ROOT) == 0 &&
  647              (targetp->p_flags & P_SUGID) == 0) ||
  648              caller->cr_uid == 0)
  649                 return (1);
  650 
  651         return (0);
  652 }
  653 
  654 #endif /* KTRACE */

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