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  * - Will we want to add a pidtoprocdesc(2) system call to allow process
   64  *   descriptors to be created for processes without pdfork(2)?
   65  */
   66 
   67 #include <sys/cdefs.h>
   68 __FBSDID("$FreeBSD$");
   69 
   70 #include <sys/param.h>
   71 #include <sys/capsicum.h>
   72 #include <sys/fcntl.h>
   73 #include <sys/file.h>
   74 #include <sys/filedesc.h>
   75 #include <sys/kernel.h>
   76 #include <sys/lock.h>
   77 #include <sys/mutex.h>
   78 #include <sys/poll.h>
   79 #include <sys/proc.h>
   80 #include <sys/procdesc.h>
   81 #include <sys/resourcevar.h>
   82 #include <sys/stat.h>
   83 #include <sys/sysproto.h>
   84 #include <sys/sysctl.h>
   85 #include <sys/systm.h>
   86 #include <sys/ucred.h>
   87 #include <sys/user.h>
   88 
   89 #include <security/audit/audit.h>
   90 
   91 #include <vm/uma.h>
   92 
   93 FEATURE(process_descriptors, "Process Descriptors");
   94 
   95 MALLOC_DEFINE(M_PROCDESC, "procdesc", "process descriptors");
   96 
   97 static fo_poll_t        procdesc_poll;
   98 static fo_kqfilter_t    procdesc_kqfilter;
   99 static fo_stat_t        procdesc_stat;
  100 static fo_close_t       procdesc_close;
  101 static fo_fill_kinfo_t  procdesc_fill_kinfo;
  102 
  103 static struct fileops procdesc_ops = {
  104         .fo_read = invfo_rdwr,
  105         .fo_write = invfo_rdwr,
  106         .fo_truncate = invfo_truncate,
  107         .fo_ioctl = invfo_ioctl,
  108         .fo_poll = procdesc_poll,
  109         .fo_kqfilter = procdesc_kqfilter,
  110         .fo_stat = procdesc_stat,
  111         .fo_close = procdesc_close,
  112         .fo_chmod = invfo_chmod,
  113         .fo_chown = invfo_chown,
  114         .fo_sendfile = invfo_sendfile,
  115         .fo_fill_kinfo = procdesc_fill_kinfo,
  116         .fo_flags = DFLAG_PASSABLE,
  117 };
  118 
  119 /*
  120  * Return a locked process given a process descriptor, or ESRCH if it has
  121  * died.
  122  */
  123 int
  124 procdesc_find(struct thread *td, int fd, cap_rights_t *rightsp,
  125     struct proc **p)
  126 {
  127         struct procdesc *pd;
  128         struct file *fp;
  129         int error;
  130 
  131         error = fget(td, fd, rightsp, &fp);
  132         if (error)
  133                 return (error);
  134         if (fp->f_type != DTYPE_PROCDESC) {
  135                 error = EBADF;
  136                 goto out;
  137         }
  138         pd = fp->f_data;
  139         sx_slock(&proctree_lock);
  140         if (pd->pd_proc != NULL) {
  141                 *p = pd->pd_proc;
  142                 PROC_LOCK(*p);
  143         } else
  144                 error = ESRCH;
  145         sx_sunlock(&proctree_lock);
  146 out:
  147         fdrop(fp, td);
  148         return (error);
  149 }
  150 
  151 /*
  152  * Function to be used by procstat(1) sysctls when returning procdesc
  153  * information.
  154  */
  155 pid_t
  156 procdesc_pid(struct file *fp_procdesc)
  157 {
  158         struct procdesc *pd;
  159 
  160         KASSERT(fp_procdesc->f_type == DTYPE_PROCDESC,
  161            ("procdesc_pid: !procdesc"));
  162 
  163         pd = fp_procdesc->f_data;
  164         return (pd->pd_pid);
  165 }
  166 
  167 /*
  168  * Retrieve the PID associated with a process descriptor.
  169  */
  170 int
  171 kern_pdgetpid(struct thread *td, int fd, cap_rights_t *rightsp, pid_t *pidp)
  172 {
  173         struct file *fp;
  174         int error;
  175 
  176         error = fget(td, fd, rightsp, &fp);
  177         if (error)
  178                 return (error);
  179         if (fp->f_type != DTYPE_PROCDESC) {
  180                 error = EBADF;
  181                 goto out;
  182         }
  183         *pidp = procdesc_pid(fp);
  184 out:
  185         fdrop(fp, td);
  186         return (error);
  187 }
  188 
  189 /*
  190  * System call to return the pid of a process given its process descriptor.
  191  */
  192 int
  193 sys_pdgetpid(struct thread *td, struct pdgetpid_args *uap)
  194 {
  195         pid_t pid;
  196         int error;
  197 
  198         AUDIT_ARG_FD(uap->fd);
  199         error = kern_pdgetpid(td, uap->fd, &cap_pdgetpid_rights, &pid);
  200         if (error == 0)
  201                 error = copyout(&pid, uap->pidp, sizeof(pid));
  202         return (error);
  203 }
  204 
  205 /*
  206  * When a new process is forked by pdfork(), a file descriptor is allocated
  207  * by the fork code first, then the process is forked, and then we get a
  208  * chance to set up the process descriptor.  Failure is not permitted at this
  209  * point, so procdesc_new() must succeed.
  210  */
  211 void
  212 procdesc_new(struct proc *p, int flags)
  213 {
  214         struct procdesc *pd;
  215 
  216         pd = malloc(sizeof(*pd), M_PROCDESC, M_WAITOK | M_ZERO);
  217         pd->pd_proc = p;
  218         pd->pd_pid = p->p_pid;
  219         p->p_procdesc = pd;
  220         pd->pd_flags = 0;
  221         if (flags & PD_DAEMON)
  222                 pd->pd_flags |= PDF_DAEMON;
  223         PROCDESC_LOCK_INIT(pd);
  224         knlist_init_mtx(&pd->pd_selinfo.si_note, &pd->pd_lock);
  225 
  226         /*
  227          * Process descriptors start out with two references: one from their
  228          * struct file, and the other from their struct proc.
  229          */
  230         refcount_init(&pd->pd_refcount, 2);
  231 }
  232 
  233 /*
  234  * Create a new process decriptor for the process that refers to it.
  235  */
  236 int
  237 procdesc_falloc(struct thread *td, struct file **resultfp, int *resultfd,
  238     int flags, struct filecaps *fcaps)
  239 {
  240         int fflags;
  241 
  242         fflags = 0;
  243         if (flags & PD_CLOEXEC)
  244                 fflags = O_CLOEXEC;
  245 
  246         return (falloc_caps(td, resultfp, resultfd, fflags, fcaps));
  247 }
  248 
  249 /*
  250  * Initialize a file with a process descriptor.
  251  */
  252 void
  253 procdesc_finit(struct procdesc *pdp, struct file *fp)
  254 {
  255 
  256         finit(fp, FREAD | FWRITE, DTYPE_PROCDESC, pdp, &procdesc_ops);
  257 }
  258 
  259 static void
  260 procdesc_free(struct procdesc *pd)
  261 {
  262 
  263         /*
  264          * When the last reference is released, we assert that the descriptor
  265          * has been closed, but not that the process has exited, as we will
  266          * detach the descriptor before the process dies if the descript is
  267          * closed, as we can't wait synchronously.
  268          */
  269         if (refcount_release(&pd->pd_refcount)) {
  270                 KASSERT(pd->pd_proc == NULL,
  271                     ("procdesc_free: pd_proc != NULL"));
  272                 KASSERT((pd->pd_flags & PDF_CLOSED),
  273                     ("procdesc_free: !PDF_CLOSED"));
  274 
  275                 knlist_destroy(&pd->pd_selinfo.si_note);
  276                 PROCDESC_LOCK_DESTROY(pd);
  277                 free(pd, M_PROCDESC);
  278         }
  279 }
  280 
  281 /*
  282  * procdesc_exit() - notify a process descriptor that its process is exiting.
  283  * We use the proctree_lock to ensure that process exit either happens
  284  * strictly before or strictly after a concurrent call to procdesc_close().
  285  */
  286 int
  287 procdesc_exit(struct proc *p)
  288 {
  289         struct procdesc *pd;
  290 
  291         sx_assert(&proctree_lock, SA_XLOCKED);
  292         PROC_LOCK_ASSERT(p, MA_OWNED);
  293         KASSERT(p->p_procdesc != NULL, ("procdesc_exit: p_procdesc NULL"));
  294 
  295         pd = p->p_procdesc;
  296 
  297         PROCDESC_LOCK(pd);
  298         KASSERT((pd->pd_flags & PDF_CLOSED) == 0 || p->p_pptr == p->p_reaper,
  299             ("procdesc_exit: closed && parent not reaper"));
  300 
  301         pd->pd_flags |= PDF_EXITED;
  302         pd->pd_xstat = KW_EXITCODE(p->p_xexit, p->p_xsig);
  303 
  304         /*
  305          * If the process descriptor has been closed, then we have nothing
  306          * to do; return 1 so that init will get SIGCHLD and do the reaping.
  307          * Clean up the procdesc now rather than letting it happen during
  308          * that reap.
  309          */
  310         if (pd->pd_flags & PDF_CLOSED) {
  311                 PROCDESC_UNLOCK(pd);
  312                 pd->pd_proc = NULL;
  313                 p->p_procdesc = NULL;
  314                 procdesc_free(pd);
  315                 return (1);
  316         }
  317         if (pd->pd_flags & PDF_SELECTED) {
  318                 pd->pd_flags &= ~PDF_SELECTED;
  319                 selwakeup(&pd->pd_selinfo);
  320         }
  321         KNOTE_LOCKED(&pd->pd_selinfo.si_note, NOTE_EXIT);
  322         PROCDESC_UNLOCK(pd);
  323         return (0);
  324 }
  325 
  326 /*
  327  * When a process descriptor is reaped, perhaps as a result of close() or
  328  * pdwait4(), release the process's reference on the process descriptor.
  329  */
  330 void
  331 procdesc_reap(struct proc *p)
  332 {
  333         struct procdesc *pd;
  334 
  335         sx_assert(&proctree_lock, SA_XLOCKED);
  336         KASSERT(p->p_procdesc != NULL, ("procdesc_reap: p_procdesc == NULL"));
  337 
  338         pd = p->p_procdesc;
  339         pd->pd_proc = NULL;
  340         p->p_procdesc = NULL;
  341         procdesc_free(pd);
  342 }
  343 
  344 /*
  345  * procdesc_close() - last close on a process descriptor.  If the process is
  346  * still running, terminate with SIGKILL (unless PDF_DAEMON is set) and let
  347  * its reaper clean up the mess; if not, we have to clean up the zombie
  348  * ourselves.
  349  */
  350 static int
  351 procdesc_close(struct file *fp, struct thread *td)
  352 {
  353         struct procdesc *pd;
  354         struct proc *p;
  355 
  356         KASSERT(fp->f_type == DTYPE_PROCDESC, ("procdesc_close: !procdesc"));
  357 
  358         pd = fp->f_data;
  359         fp->f_ops = &badfileops;
  360         fp->f_data = NULL;
  361 
  362         sx_xlock(&proctree_lock);
  363         PROCDESC_LOCK(pd);
  364         pd->pd_flags |= PDF_CLOSED;
  365         PROCDESC_UNLOCK(pd);
  366         p = pd->pd_proc;
  367         if (p == NULL) {
  368                 /*
  369                  * This is the case where process' exit status was already
  370                  * collected and procdesc_reap() was already called.
  371                  */
  372                 sx_xunlock(&proctree_lock);
  373         } else {
  374                 PROC_LOCK(p);
  375                 AUDIT_ARG_PROCESS(p);
  376                 if (p->p_state == PRS_ZOMBIE) {
  377                         /*
  378                          * If the process is already dead and just awaiting
  379                          * reaping, do that now.  This will release the
  380                          * process's reference to the process descriptor when it
  381                          * calls back into procdesc_reap().
  382                          */
  383                         proc_reap(curthread, p, NULL, 0);
  384                 } else {
  385                         /*
  386                          * If the process is not yet dead, we need to kill it,
  387                          * but we can't wait around synchronously for it to go
  388                          * away, as that path leads to madness (and deadlocks).
  389                          * First, detach the process from its descriptor so that
  390                          * its exit status will be reported normally.
  391                          */
  392                         pd->pd_proc = NULL;
  393                         p->p_procdesc = NULL;
  394                         procdesc_free(pd);
  395 
  396                         /*
  397                          * Next, reparent it to its reaper (usually init(8)) so
  398                          * that there's someone to pick up the pieces; finally,
  399                          * terminate with prejudice.
  400                          */
  401                         p->p_sigparent = SIGCHLD;
  402                         if ((p->p_flag & P_TRACED) == 0) {
  403                                 proc_reparent(p, p->p_reaper, true);
  404                         } else {
  405                                 proc_clear_orphan(p);
  406                                 p->p_oppid = p->p_reaper->p_pid;
  407                                 proc_add_orphan(p, p->p_reaper);
  408                         }
  409                         if ((pd->pd_flags & PDF_DAEMON) == 0)
  410                                 kern_psignal(p, SIGKILL);
  411                         PROC_UNLOCK(p);
  412                         sx_xunlock(&proctree_lock);
  413                 }
  414         }
  415 
  416         /*
  417          * Release the file descriptor's reference on the process descriptor.
  418          */
  419         procdesc_free(pd);
  420         return (0);
  421 }
  422 
  423 static int
  424 procdesc_poll(struct file *fp, int events, struct ucred *active_cred,
  425     struct thread *td)
  426 {
  427         struct procdesc *pd;
  428         int revents;
  429 
  430         revents = 0;
  431         pd = fp->f_data;
  432         PROCDESC_LOCK(pd);
  433         if (pd->pd_flags & PDF_EXITED)
  434                 revents |= POLLHUP;
  435         if (revents == 0) {
  436                 selrecord(td, &pd->pd_selinfo);
  437                 pd->pd_flags |= PDF_SELECTED;
  438         }
  439         PROCDESC_UNLOCK(pd);
  440         return (revents);
  441 }
  442 
  443 static void
  444 procdesc_kqops_detach(struct knote *kn)
  445 {
  446         struct procdesc *pd;
  447 
  448         pd = kn->kn_fp->f_data;
  449         knlist_remove(&pd->pd_selinfo.si_note, kn, 0);
  450 }
  451 
  452 static int
  453 procdesc_kqops_event(struct knote *kn, long hint)
  454 {
  455         struct procdesc *pd;
  456         u_int event;
  457 
  458         pd = kn->kn_fp->f_data;
  459         if (hint == 0) {
  460                 /*
  461                  * Initial test after registration. Generate a NOTE_EXIT in
  462                  * case the process already terminated before registration.
  463                  */
  464                 event = pd->pd_flags & PDF_EXITED ? NOTE_EXIT : 0;
  465         } else {
  466                 /* Mask off extra data. */
  467                 event = (u_int)hint & NOTE_PCTRLMASK;
  468         }
  469 
  470         /* If the user is interested in this event, record it. */
  471         if (kn->kn_sfflags & event)
  472                 kn->kn_fflags |= event;
  473 
  474         /* Process is gone, so flag the event as finished. */
  475         if (event == NOTE_EXIT) {
  476                 kn->kn_flags |= EV_EOF | EV_ONESHOT;
  477                 if (kn->kn_fflags & NOTE_EXIT)
  478                         kn->kn_data = pd->pd_xstat;
  479                 if (kn->kn_fflags == 0)
  480                         kn->kn_flags |= EV_DROP;
  481                 return (1);
  482         }
  483 
  484         return (kn->kn_fflags != 0);
  485 }
  486 
  487 static struct filterops procdesc_kqops = {
  488         .f_isfd = 1,
  489         .f_detach = procdesc_kqops_detach,
  490         .f_event = procdesc_kqops_event,
  491 };
  492 
  493 static int
  494 procdesc_kqfilter(struct file *fp, struct knote *kn)
  495 {
  496         struct procdesc *pd;
  497 
  498         pd = fp->f_data;
  499         switch (kn->kn_filter) {
  500         case EVFILT_PROCDESC:
  501                 kn->kn_fop = &procdesc_kqops;
  502                 kn->kn_flags |= EV_CLEAR;
  503                 knlist_add(&pd->pd_selinfo.si_note, kn, 0);
  504                 return (0);
  505         default:
  506                 return (EINVAL);
  507         }
  508 }
  509 
  510 static int
  511 procdesc_stat(struct file *fp, struct stat *sb, struct ucred *active_cred)
  512 {
  513         struct procdesc *pd;
  514         struct timeval pstart, boottime;
  515 
  516         /*
  517          * XXXRW: Perhaps we should cache some more information from the
  518          * process so that we can return it reliably here even after it has
  519          * died.  For example, caching its credential data.
  520          */
  521         bzero(sb, sizeof(*sb));
  522         pd = fp->f_data;
  523         sx_slock(&proctree_lock);
  524         if (pd->pd_proc != NULL) {
  525                 PROC_LOCK(pd->pd_proc);
  526                 AUDIT_ARG_PROCESS(pd->pd_proc);
  527 
  528                 /* Set birth and [acm] times to process start time. */
  529                 pstart = pd->pd_proc->p_stats->p_start;
  530                 getboottime(&boottime);
  531                 timevaladd(&pstart, &boottime);
  532                 TIMEVAL_TO_TIMESPEC(&pstart, &sb->st_birthtim);
  533                 sb->st_atim = sb->st_birthtim;
  534                 sb->st_ctim = sb->st_birthtim;
  535                 sb->st_mtim = sb->st_birthtim;
  536                 if (pd->pd_proc->p_state != PRS_ZOMBIE)
  537                         sb->st_mode = S_IFREG | S_IRWXU;
  538                 else
  539                         sb->st_mode = S_IFREG;
  540                 sb->st_uid = pd->pd_proc->p_ucred->cr_ruid;
  541                 sb->st_gid = pd->pd_proc->p_ucred->cr_rgid;
  542                 PROC_UNLOCK(pd->pd_proc);
  543         } else
  544                 sb->st_mode = S_IFREG;
  545         sx_sunlock(&proctree_lock);
  546         return (0);
  547 }
  548 
  549 static int
  550 procdesc_fill_kinfo(struct file *fp, struct kinfo_file *kif,
  551     struct filedesc *fdp)
  552 {
  553         struct procdesc *pdp;
  554 
  555         kif->kf_type = KF_TYPE_PROCDESC;
  556         pdp = fp->f_data;
  557         kif->kf_un.kf_proc.kf_pid = pdp->pd_pid;
  558         return (0);
  559 }

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