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/sys_procdesc.c

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    1 /*-
    2  * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
    3  *
    4  * Copyright (c) 2009, 2016 Robert N. M. Watson
    5  * All rights reserved.
    6  *
    7  * This software was developed at the University of Cambridge Computer
    8  * Laboratory with support from a grant from Google, Inc.
    9  *
   10  * Portions of this software were developed by BAE Systems, the University of
   11  * Cambridge Computer Laboratory, and Memorial University under DARPA/AFRL
   12  * contract FA8650-15-C-7558 ("CADETS"), as part of the DARPA Transparent
   13  * Computing (TC) research program.
   14  *
   15  * Redistribution and use in source and binary forms, with or without
   16  * modification, are permitted provided that the following conditions
   17  * are met:
   18  * 1. Redistributions of source code must retain the above copyright
   19  *    notice, this list of conditions and the following disclaimer.
   20  * 2. Redistributions in binary form must reproduce the above copyright
   21  *    notice, this list of conditions and the following disclaimer in the
   22  *    documentation and/or other materials provided with the distribution.
   23  *
   24  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
   25  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   26  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   27  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
   28  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   29  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   30  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   31  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   32  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   33  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   34  * SUCH DAMAGE.
   35  */
   36 
   37 /*-
   38  * FreeBSD process descriptor facility.
   39  *
   40  * Some processes are represented by a file descriptor, which will be used in
   41  * preference to signaling and pids for the purposes of process management,
   42  * and is, in effect, a form of capability.  When a process descriptor is
   43  * used with a process, it ceases to be visible to certain traditional UNIX
   44  * process facilities, such as waitpid(2).
   45  *
   46  * Some semantics:
   47  *
   48  * - At most one process descriptor will exist for any process, although
   49  *   references to that descriptor may be held from many processes (or even
   50  *   be in flight between processes over a local domain socket).
   51  * - Last close on the process descriptor will terminate the process using
   52  *   SIGKILL and reparent it to init so that there's a process to reap it
   53  *   when it's done exiting.
   54  * - If the process exits before the descriptor is closed, it will not
   55  *   generate SIGCHLD on termination, or be picked up by waitpid().
   56  * - The pdkill(2) system call may be used to deliver a signal to the process
   57  *   using its process descriptor.
   58  * - The pdwait4(2) system call may be used to block (or not) on a process
   59  *   descriptor to collect termination information.
   60  *
   61  * Open questions:
   62  *
   63  * - How to handle ptrace(2)?
   64  * - Will we want to add a pidtoprocdesc(2) system call to allow process
   65  *   descriptors to be created for processes without pdfork(2)?
   66  */
   67 
   68 #include <sys/cdefs.h>
   69 __FBSDID("$FreeBSD: releng/12.0/sys/kern/sys_procdesc.c 339390 2018-10-16 20:06:56Z markj $");
   70 
   71 #include <sys/param.h>
   72 #include <sys/capsicum.h>
   73 #include <sys/fcntl.h>
   74 #include <sys/file.h>
   75 #include <sys/filedesc.h>
   76 #include <sys/kernel.h>
   77 #include <sys/lock.h>
   78 #include <sys/mutex.h>
   79 #include <sys/poll.h>
   80 #include <sys/proc.h>
   81 #include <sys/procdesc.h>
   82 #include <sys/resourcevar.h>
   83 #include <sys/stat.h>
   84 #include <sys/sysproto.h>
   85 #include <sys/sysctl.h>
   86 #include <sys/systm.h>
   87 #include <sys/ucred.h>
   88 #include <sys/user.h>
   89 
   90 #include <security/audit/audit.h>
   91 
   92 #include <vm/uma.h>
   93 
   94 FEATURE(process_descriptors, "Process Descriptors");
   95 
   96 static uma_zone_t procdesc_zone;
   97 
   98 static fo_poll_t        procdesc_poll;
   99 static fo_kqfilter_t    procdesc_kqfilter;
  100 static fo_stat_t        procdesc_stat;
  101 static fo_close_t       procdesc_close;
  102 static fo_fill_kinfo_t  procdesc_fill_kinfo;
  103 
  104 static struct fileops procdesc_ops = {
  105         .fo_read = invfo_rdwr,
  106         .fo_write = invfo_rdwr,
  107         .fo_truncate = invfo_truncate,
  108         .fo_ioctl = invfo_ioctl,
  109         .fo_poll = procdesc_poll,
  110         .fo_kqfilter = procdesc_kqfilter,
  111         .fo_stat = procdesc_stat,
  112         .fo_close = procdesc_close,
  113         .fo_chmod = invfo_chmod,
  114         .fo_chown = invfo_chown,
  115         .fo_sendfile = invfo_sendfile,
  116         .fo_fill_kinfo = procdesc_fill_kinfo,
  117         .fo_flags = DFLAG_PASSABLE,
  118 };
  119 
  120 /*
  121  * Initialize with VFS so that process descriptors are available along with
  122  * other file descriptor types.  As long as it runs before init(8) starts,
  123  * there shouldn't be a problem.
  124  */
  125 static void
  126 procdesc_init(void *dummy __unused)
  127 {
  128 
  129         procdesc_zone = uma_zcreate("procdesc", sizeof(struct procdesc),
  130             NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, 0);
  131         if (procdesc_zone == NULL)
  132                 panic("procdesc_init: procdesc_zone not initialized");
  133 }
  134 SYSINIT(vfs, SI_SUB_VFS, SI_ORDER_ANY, procdesc_init, NULL);
  135 
  136 /*
  137  * Return a locked process given a process descriptor, or ESRCH if it has
  138  * died.
  139  */
  140 int
  141 procdesc_find(struct thread *td, int fd, cap_rights_t *rightsp,
  142     struct proc **p)
  143 {
  144         struct procdesc *pd;
  145         struct file *fp;
  146         int error;
  147 
  148         error = fget(td, fd, rightsp, &fp);
  149         if (error)
  150                 return (error);
  151         if (fp->f_type != DTYPE_PROCDESC) {
  152                 error = EBADF;
  153                 goto out;
  154         }
  155         pd = fp->f_data;
  156         sx_slock(&proctree_lock);
  157         if (pd->pd_proc != NULL) {
  158                 *p = pd->pd_proc;
  159                 PROC_LOCK(*p);
  160         } else
  161                 error = ESRCH;
  162         sx_sunlock(&proctree_lock);
  163 out:
  164         fdrop(fp, td);
  165         return (error);
  166 }
  167 
  168 /*
  169  * Function to be used by procstat(1) sysctls when returning procdesc
  170  * information.
  171  */
  172 pid_t
  173 procdesc_pid(struct file *fp_procdesc)
  174 {
  175         struct procdesc *pd;
  176 
  177         KASSERT(fp_procdesc->f_type == DTYPE_PROCDESC,
  178            ("procdesc_pid: !procdesc"));
  179 
  180         pd = fp_procdesc->f_data;
  181         return (pd->pd_pid);
  182 }
  183 
  184 /*
  185  * Retrieve the PID associated with a process descriptor.
  186  */
  187 int
  188 kern_pdgetpid(struct thread *td, int fd, cap_rights_t *rightsp, pid_t *pidp)
  189 {
  190         struct file *fp;
  191         int error;
  192 
  193         error = fget(td, fd, rightsp, &fp);
  194         if (error)
  195                 return (error);
  196         if (fp->f_type != DTYPE_PROCDESC) {
  197                 error = EBADF;
  198                 goto out;
  199         }
  200         *pidp = procdesc_pid(fp);
  201 out:
  202         fdrop(fp, td);
  203         return (error);
  204 }
  205 
  206 /*
  207  * System call to return the pid of a process given its process descriptor.
  208  */
  209 int
  210 sys_pdgetpid(struct thread *td, struct pdgetpid_args *uap)
  211 {
  212         pid_t pid;
  213         int error;
  214 
  215         AUDIT_ARG_FD(uap->fd);
  216         error = kern_pdgetpid(td, uap->fd, &cap_pdgetpid_rights, &pid);
  217         if (error == 0)
  218                 error = copyout(&pid, uap->pidp, sizeof(pid));
  219         return (error);
  220 }
  221 
  222 /*
  223  * When a new process is forked by pdfork(), a file descriptor is allocated
  224  * by the fork code first, then the process is forked, and then we get a
  225  * chance to set up the process descriptor.  Failure is not permitted at this
  226  * point, so procdesc_new() must succeed.
  227  */
  228 void
  229 procdesc_new(struct proc *p, int flags)
  230 {
  231         struct procdesc *pd;
  232 
  233         pd = uma_zalloc(procdesc_zone, M_WAITOK | M_ZERO);
  234         pd->pd_proc = p;
  235         pd->pd_pid = p->p_pid;
  236         p->p_procdesc = pd;
  237         pd->pd_flags = 0;
  238         if (flags & PD_DAEMON)
  239                 pd->pd_flags |= PDF_DAEMON;
  240         PROCDESC_LOCK_INIT(pd);
  241         knlist_init_mtx(&pd->pd_selinfo.si_note, &pd->pd_lock);
  242 
  243         /*
  244          * Process descriptors start out with two references: one from their
  245          * struct file, and the other from their struct proc.
  246          */
  247         refcount_init(&pd->pd_refcount, 2);
  248 }
  249 
  250 /*
  251  * Create a new process decriptor for the process that refers to it.
  252  */
  253 int
  254 procdesc_falloc(struct thread *td, struct file **resultfp, int *resultfd,
  255     int flags, struct filecaps *fcaps)
  256 {
  257         int fflags;
  258 
  259         fflags = 0;
  260         if (flags & PD_CLOEXEC)
  261                 fflags = O_CLOEXEC;
  262 
  263         return (falloc_caps(td, resultfp, resultfd, fflags, fcaps));
  264 }
  265 
  266 /*
  267  * Initialize a file with a process descriptor.
  268  */
  269 void
  270 procdesc_finit(struct procdesc *pdp, struct file *fp)
  271 {
  272 
  273         finit(fp, FREAD | FWRITE, DTYPE_PROCDESC, pdp, &procdesc_ops);
  274 }
  275 
  276 static void
  277 procdesc_free(struct procdesc *pd)
  278 {
  279 
  280         /*
  281          * When the last reference is released, we assert that the descriptor
  282          * has been closed, but not that the process has exited, as we will
  283          * detach the descriptor before the process dies if the descript is
  284          * closed, as we can't wait synchronously.
  285          */
  286         if (refcount_release(&pd->pd_refcount)) {
  287                 KASSERT(pd->pd_proc == NULL,
  288                     ("procdesc_free: pd_proc != NULL"));
  289                 KASSERT((pd->pd_flags & PDF_CLOSED),
  290                     ("procdesc_free: !PDF_CLOSED"));
  291 
  292                 knlist_destroy(&pd->pd_selinfo.si_note);
  293                 PROCDESC_LOCK_DESTROY(pd);
  294                 uma_zfree(procdesc_zone, pd);
  295         }
  296 }
  297 
  298 /*
  299  * procdesc_exit() - notify a process descriptor that its process is exiting.
  300  * We use the proctree_lock to ensure that process exit either happens
  301  * strictly before or strictly after a concurrent call to procdesc_close().
  302  */
  303 int
  304 procdesc_exit(struct proc *p)
  305 {
  306         struct procdesc *pd;
  307 
  308         sx_assert(&proctree_lock, SA_XLOCKED);
  309         PROC_LOCK_ASSERT(p, MA_OWNED);
  310         KASSERT(p->p_procdesc != NULL, ("procdesc_exit: p_procdesc NULL"));
  311 
  312         pd = p->p_procdesc;
  313 
  314         PROCDESC_LOCK(pd);
  315         KASSERT((pd->pd_flags & PDF_CLOSED) == 0 || p->p_pptr == p->p_reaper,
  316             ("procdesc_exit: closed && parent not reaper"));
  317 
  318         pd->pd_flags |= PDF_EXITED;
  319         pd->pd_xstat = KW_EXITCODE(p->p_xexit, p->p_xsig);
  320 
  321         /*
  322          * If the process descriptor has been closed, then we have nothing
  323          * to do; return 1 so that init will get SIGCHLD and do the reaping.
  324          * Clean up the procdesc now rather than letting it happen during
  325          * that reap.
  326          */
  327         if (pd->pd_flags & PDF_CLOSED) {
  328                 PROCDESC_UNLOCK(pd);
  329                 pd->pd_proc = NULL;
  330                 p->p_procdesc = NULL;
  331                 procdesc_free(pd);
  332                 return (1);
  333         }
  334         if (pd->pd_flags & PDF_SELECTED) {
  335                 pd->pd_flags &= ~PDF_SELECTED;
  336                 selwakeup(&pd->pd_selinfo);
  337         }
  338         KNOTE_LOCKED(&pd->pd_selinfo.si_note, NOTE_EXIT);
  339         PROCDESC_UNLOCK(pd);
  340         return (0);
  341 }
  342 
  343 /*
  344  * When a process descriptor is reaped, perhaps as a result of close() or
  345  * pdwait4(), release the process's reference on the process descriptor.
  346  */
  347 void
  348 procdesc_reap(struct proc *p)
  349 {
  350         struct procdesc *pd;
  351 
  352         sx_assert(&proctree_lock, SA_XLOCKED);
  353         KASSERT(p->p_procdesc != NULL, ("procdesc_reap: p_procdesc == NULL"));
  354 
  355         pd = p->p_procdesc;
  356         pd->pd_proc = NULL;
  357         p->p_procdesc = NULL;
  358         procdesc_free(pd);
  359 }
  360 
  361 /*
  362  * procdesc_close() - last close on a process descriptor.  If the process is
  363  * still running, terminate with SIGKILL (unless PDF_DAEMON is set) and let
  364  * its reaper clean up the mess; if not, we have to clean up the zombie
  365  * ourselves.
  366  */
  367 static int
  368 procdesc_close(struct file *fp, struct thread *td)
  369 {
  370         struct procdesc *pd;
  371         struct proc *p;
  372 
  373         KASSERT(fp->f_type == DTYPE_PROCDESC, ("procdesc_close: !procdesc"));
  374 
  375         pd = fp->f_data;
  376         fp->f_ops = &badfileops;
  377         fp->f_data = NULL;
  378 
  379         sx_xlock(&proctree_lock);
  380         PROCDESC_LOCK(pd);
  381         pd->pd_flags |= PDF_CLOSED;
  382         PROCDESC_UNLOCK(pd);
  383         p = pd->pd_proc;
  384         if (p == NULL) {
  385                 /*
  386                  * This is the case where process' exit status was already
  387                  * collected and procdesc_reap() was already called.
  388                  */
  389                 sx_xunlock(&proctree_lock);
  390         } else {
  391                 PROC_LOCK(p);
  392                 AUDIT_ARG_PROCESS(p);
  393                 if (p->p_state == PRS_ZOMBIE) {
  394                         /*
  395                          * If the process is already dead and just awaiting
  396                          * reaping, do that now.  This will release the
  397                          * process's reference to the process descriptor when it
  398                          * calls back into procdesc_reap().
  399                          */
  400                         proc_reap(curthread, p, NULL, 0);
  401                 } else {
  402                         /*
  403                          * If the process is not yet dead, we need to kill it,
  404                          * but we can't wait around synchronously for it to go
  405                          * away, as that path leads to madness (and deadlocks).
  406                          * First, detach the process from its descriptor so that
  407                          * its exit status will be reported normally.
  408                          */
  409                         pd->pd_proc = NULL;
  410                         p->p_procdesc = NULL;
  411                         procdesc_free(pd);
  412 
  413                         /*
  414                          * Next, reparent it to its reaper (usually init(8)) so
  415                          * that there's someone to pick up the pieces; finally,
  416                          * terminate with prejudice.
  417                          */
  418                         p->p_sigparent = SIGCHLD;
  419                         proc_reparent(p, p->p_reaper);
  420                         if ((pd->pd_flags & PDF_DAEMON) == 0)
  421                                 kern_psignal(p, SIGKILL);
  422                         PROC_UNLOCK(p);
  423                         sx_xunlock(&proctree_lock);
  424                 }
  425         }
  426 
  427         /*
  428          * Release the file descriptor's reference on the process descriptor.
  429          */
  430         procdesc_free(pd);
  431         return (0);
  432 }
  433 
  434 static int
  435 procdesc_poll(struct file *fp, int events, struct ucred *active_cred,
  436     struct thread *td)
  437 {
  438         struct procdesc *pd;
  439         int revents;
  440 
  441         revents = 0;
  442         pd = fp->f_data;
  443         PROCDESC_LOCK(pd);
  444         if (pd->pd_flags & PDF_EXITED)
  445                 revents |= POLLHUP;
  446         if (revents == 0) {
  447                 selrecord(td, &pd->pd_selinfo);
  448                 pd->pd_flags |= PDF_SELECTED;
  449         }
  450         PROCDESC_UNLOCK(pd);
  451         return (revents);
  452 }
  453 
  454 static void
  455 procdesc_kqops_detach(struct knote *kn)
  456 {
  457         struct procdesc *pd;
  458 
  459         pd = kn->kn_fp->f_data;
  460         knlist_remove(&pd->pd_selinfo.si_note, kn, 0);
  461 }
  462 
  463 static int
  464 procdesc_kqops_event(struct knote *kn, long hint)
  465 {
  466         struct procdesc *pd;
  467         u_int event;
  468 
  469         pd = kn->kn_fp->f_data;
  470         if (hint == 0) {
  471                 /*
  472                  * Initial test after registration. Generate a NOTE_EXIT in
  473                  * case the process already terminated before registration.
  474                  */
  475                 event = pd->pd_flags & PDF_EXITED ? NOTE_EXIT : 0;
  476         } else {
  477                 /* Mask off extra data. */
  478                 event = (u_int)hint & NOTE_PCTRLMASK;
  479         }
  480 
  481         /* If the user is interested in this event, record it. */
  482         if (kn->kn_sfflags & event)
  483                 kn->kn_fflags |= event;
  484 
  485         /* Process is gone, so flag the event as finished. */
  486         if (event == NOTE_EXIT) {
  487                 kn->kn_flags |= EV_EOF | EV_ONESHOT;
  488                 if (kn->kn_fflags & NOTE_EXIT)
  489                         kn->kn_data = pd->pd_xstat;
  490                 if (kn->kn_fflags == 0)
  491                         kn->kn_flags |= EV_DROP;
  492                 return (1);
  493         }
  494 
  495         return (kn->kn_fflags != 0);
  496 }
  497 
  498 static struct filterops procdesc_kqops = {
  499         .f_isfd = 1,
  500         .f_detach = procdesc_kqops_detach,
  501         .f_event = procdesc_kqops_event,
  502 };
  503 
  504 static int
  505 procdesc_kqfilter(struct file *fp, struct knote *kn)
  506 {
  507         struct procdesc *pd;
  508 
  509         pd = fp->f_data;
  510         switch (kn->kn_filter) {
  511         case EVFILT_PROCDESC:
  512                 kn->kn_fop = &procdesc_kqops;
  513                 kn->kn_flags |= EV_CLEAR;
  514                 knlist_add(&pd->pd_selinfo.si_note, kn, 0);
  515                 return (0);
  516         default:
  517                 return (EINVAL);
  518         }
  519 }
  520 
  521 static int
  522 procdesc_stat(struct file *fp, struct stat *sb, struct ucred *active_cred,
  523     struct thread *td)
  524 {
  525         struct procdesc *pd;
  526         struct timeval pstart, boottime;
  527 
  528         /*
  529          * XXXRW: Perhaps we should cache some more information from the
  530          * process so that we can return it reliably here even after it has
  531          * died.  For example, caching its credential data.
  532          */
  533         bzero(sb, sizeof(*sb));
  534         pd = fp->f_data;
  535         sx_slock(&proctree_lock);
  536         if (pd->pd_proc != NULL) {
  537                 PROC_LOCK(pd->pd_proc);
  538                 AUDIT_ARG_PROCESS(pd->pd_proc);
  539 
  540                 /* Set birth and [acm] times to process start time. */
  541                 pstart = pd->pd_proc->p_stats->p_start;
  542                 getboottime(&boottime);
  543                 timevaladd(&pstart, &boottime);
  544                 TIMEVAL_TO_TIMESPEC(&pstart, &sb->st_birthtim);
  545                 sb->st_atim = sb->st_birthtim;
  546                 sb->st_ctim = sb->st_birthtim;
  547                 sb->st_mtim = sb->st_birthtim;
  548                 if (pd->pd_proc->p_state != PRS_ZOMBIE)
  549                         sb->st_mode = S_IFREG | S_IRWXU;
  550                 else
  551                         sb->st_mode = S_IFREG;
  552                 sb->st_uid = pd->pd_proc->p_ucred->cr_ruid;
  553                 sb->st_gid = pd->pd_proc->p_ucred->cr_rgid;
  554                 PROC_UNLOCK(pd->pd_proc);
  555         } else
  556                 sb->st_mode = S_IFREG;
  557         sx_sunlock(&proctree_lock);
  558         return (0);
  559 }
  560 
  561 static int
  562 procdesc_fill_kinfo(struct file *fp, struct kinfo_file *kif,
  563     struct filedesc *fdp)
  564 {
  565         struct procdesc *pdp;
  566 
  567         kif->kf_type = KF_TYPE_PROCDESC;
  568         pdp = fp->f_data;
  569         kif->kf_un.kf_proc.kf_pid = pdp->pd_pid;
  570         return (0);
  571 }

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