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_fork.c

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    1 /*-
    2  * SPDX-License-Identifier: BSD-3-Clause
    3  *
    4  * Copyright (c) 1982, 1986, 1989, 1991, 1993
    5  *      The Regents of the University of California.  All rights reserved.
    6  * (c) UNIX System Laboratories, Inc.
    7  * All or some portions of this file are derived from material licensed
    8  * to the University of California by American Telephone and Telegraph
    9  * Co. or Unix System Laboratories, Inc. and are reproduced herein with
   10  * the permission of UNIX System Laboratories, Inc.
   11  *
   12  * Redistribution and use in source and binary forms, with or without
   13  * modification, are permitted provided that the following conditions
   14  * are met:
   15  * 1. Redistributions of source code must retain the above copyright
   16  *    notice, this list of conditions and the following disclaimer.
   17  * 2. Redistributions in binary form must reproduce the above copyright
   18  *    notice, this list of conditions and the following disclaimer in the
   19  *    documentation and/or other materials provided with the distribution.
   20  * 3. Neither the name of the University nor the names of its contributors
   21  *    may be used to endorse or promote products derived from this software
   22  *    without specific prior written permission.
   23  *
   24  * THIS SOFTWARE IS PROVIDED BY THE REGENTS 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 REGENTS 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  *      @(#)kern_fork.c 8.6 (Berkeley) 4/8/94
   37  */
   38 
   39 #include <sys/cdefs.h>
   40 __FBSDID("$FreeBSD$");
   41 
   42 #include "opt_ktrace.h"
   43 #include "opt_kstack_pages.h"
   44 
   45 #include <sys/param.h>
   46 #include <sys/systm.h>
   47 #include <sys/sysproto.h>
   48 #include <sys/eventhandler.h>
   49 #include <sys/fcntl.h>
   50 #include <sys/filedesc.h>
   51 #include <sys/jail.h>
   52 #include <sys/kernel.h>
   53 #include <sys/kthread.h>
   54 #include <sys/sysctl.h>
   55 #include <sys/lock.h>
   56 #include <sys/malloc.h>
   57 #include <sys/mutex.h>
   58 #include <sys/priv.h>
   59 #include <sys/proc.h>
   60 #include <sys/procdesc.h>
   61 #include <sys/pioctl.h>
   62 #include <sys/ptrace.h>
   63 #include <sys/racct.h>
   64 #include <sys/resourcevar.h>
   65 #include <sys/sched.h>
   66 #include <sys/syscall.h>
   67 #include <sys/vmmeter.h>
   68 #include <sys/vnode.h>
   69 #include <sys/acct.h>
   70 #include <sys/ktr.h>
   71 #include <sys/ktrace.h>
   72 #include <sys/unistd.h>
   73 #include <sys/sdt.h>
   74 #include <sys/sx.h>
   75 #include <sys/sysent.h>
   76 #include <sys/signalvar.h>
   77 
   78 #include <security/audit/audit.h>
   79 #include <security/mac/mac_framework.h>
   80 
   81 #include <vm/vm.h>
   82 #include <vm/pmap.h>
   83 #include <vm/vm_map.h>
   84 #include <vm/vm_extern.h>
   85 #include <vm/uma.h>
   86 
   87 #ifdef KDTRACE_HOOKS
   88 #include <sys/dtrace_bsd.h>
   89 dtrace_fork_func_t      dtrace_fasttrap_fork;
   90 #endif
   91 
   92 SDT_PROVIDER_DECLARE(proc);
   93 SDT_PROBE_DEFINE3(proc, , , create, "struct proc *", "struct proc *", "int");
   94 
   95 #ifndef _SYS_SYSPROTO_H_
   96 struct fork_args {
   97         int     dummy;
   98 };
   99 #endif
  100 
  101 EVENTHANDLER_LIST_DECLARE(process_fork);
  102 
  103 /* ARGSUSED */
  104 int
  105 sys_fork(struct thread *td, struct fork_args *uap)
  106 {
  107         struct fork_req fr;
  108         int error, pid;
  109 
  110         bzero(&fr, sizeof(fr));
  111         fr.fr_flags = RFFDG | RFPROC;
  112         fr.fr_pidp = &pid;
  113         error = fork1(td, &fr);
  114         if (error == 0) {
  115                 td->td_retval[0] = pid;
  116                 td->td_retval[1] = 0;
  117         }
  118         return (error);
  119 }
  120 
  121 /* ARGUSED */
  122 int
  123 sys_pdfork(struct thread *td, struct pdfork_args *uap)
  124 {
  125         struct fork_req fr;
  126         int error, fd, pid;
  127 
  128         bzero(&fr, sizeof(fr));
  129         fr.fr_flags = RFFDG | RFPROC | RFPROCDESC;
  130         fr.fr_pidp = &pid;
  131         fr.fr_pd_fd = &fd;
  132         fr.fr_pd_flags = uap->flags;
  133         /*
  134          * It is necessary to return fd by reference because 0 is a valid file
  135          * descriptor number, and the child needs to be able to distinguish
  136          * itself from the parent using the return value.
  137          */
  138         error = fork1(td, &fr);
  139         if (error == 0) {
  140                 td->td_retval[0] = pid;
  141                 td->td_retval[1] = 0;
  142                 error = copyout(&fd, uap->fdp, sizeof(fd));
  143         }
  144         return (error);
  145 }
  146 
  147 /* ARGSUSED */
  148 int
  149 sys_vfork(struct thread *td, struct vfork_args *uap)
  150 {
  151         struct fork_req fr;
  152         int error, pid;
  153 
  154         bzero(&fr, sizeof(fr));
  155         fr.fr_flags = RFFDG | RFPROC | RFPPWAIT | RFMEM;
  156         fr.fr_pidp = &pid;
  157         error = fork1(td, &fr);
  158         if (error == 0) {
  159                 td->td_retval[0] = pid;
  160                 td->td_retval[1] = 0;
  161         }
  162         return (error);
  163 }
  164 
  165 int
  166 sys_rfork(struct thread *td, struct rfork_args *uap)
  167 {
  168         struct fork_req fr;
  169         int error, pid;
  170 
  171         /* Don't allow kernel-only flags. */
  172         if ((uap->flags & RFKERNELONLY) != 0)
  173                 return (EINVAL);
  174         /* RFSPAWN must not appear with others */
  175         if ((uap->flags & RFSPAWN) != 0 && uap->flags != RFSPAWN)
  176                 return (EINVAL);
  177 
  178         AUDIT_ARG_FFLAGS(uap->flags);
  179         bzero(&fr, sizeof(fr));
  180         if ((uap->flags & RFSPAWN) != 0) {
  181                 fr.fr_flags = RFFDG | RFPROC | RFPPWAIT | RFMEM;
  182                 fr.fr_flags2 = FR2_DROPSIG_CAUGHT;
  183         } else {
  184                 fr.fr_flags = uap->flags;
  185         }
  186         fr.fr_pidp = &pid;
  187         error = fork1(td, &fr);
  188         if (error == 0) {
  189                 td->td_retval[0] = pid;
  190                 td->td_retval[1] = 0;
  191         }
  192         return (error);
  193 }
  194 
  195 int     nprocs = 1;             /* process 0 */
  196 int     lastpid = 0;
  197 SYSCTL_INT(_kern, OID_AUTO, lastpid, CTLFLAG_RD, &lastpid, 0,
  198     "Last used PID");
  199 
  200 /*
  201  * Random component to lastpid generation.  We mix in a random factor to make
  202  * it a little harder to predict.  We sanity check the modulus value to avoid
  203  * doing it in critical paths.  Don't let it be too small or we pointlessly
  204  * waste randomness entropy, and don't let it be impossibly large.  Using a
  205  * modulus that is too big causes a LOT more process table scans and slows
  206  * down fork processing as the pidchecked caching is defeated.
  207  */
  208 static int randompid = 0;
  209 
  210 static int
  211 sysctl_kern_randompid(SYSCTL_HANDLER_ARGS)
  212 {
  213         int error, pid;
  214 
  215         error = sysctl_wire_old_buffer(req, sizeof(int));
  216         if (error != 0)
  217                 return(error);
  218         sx_xlock(&allproc_lock);
  219         pid = randompid;
  220         error = sysctl_handle_int(oidp, &pid, 0, req);
  221         if (error == 0 && req->newptr != NULL) {
  222                 if (pid == 0)
  223                         randompid = 0;
  224                 else if (pid == 1)
  225                         /* generate a random PID modulus between 100 and 1123 */
  226                         randompid = 100 + arc4random() % 1024;
  227                 else if (pid < 0 || pid > pid_max - 100)
  228                         /* out of range */
  229                         randompid = pid_max - 100;
  230                 else if (pid < 100)
  231                         /* Make it reasonable */
  232                         randompid = 100;
  233                 else
  234                         randompid = pid;
  235         }
  236         sx_xunlock(&allproc_lock);
  237         return (error);
  238 }
  239 
  240 SYSCTL_PROC(_kern, OID_AUTO, randompid, CTLTYPE_INT|CTLFLAG_RW,
  241     0, 0, sysctl_kern_randompid, "I", "Random PID modulus. Special values: 0: disable, 1: choose random value");
  242 
  243 static int
  244 fork_findpid(int flags)
  245 {
  246         struct proc *p;
  247         int trypid;
  248         static int pidchecked = 0;
  249 
  250         /*
  251          * Requires allproc_lock in order to iterate over the list
  252          * of processes, and proctree_lock to access p_pgrp.
  253          */
  254         sx_assert(&allproc_lock, SX_LOCKED);
  255         sx_assert(&proctree_lock, SX_LOCKED);
  256 
  257         /*
  258          * Find an unused process ID.  We remember a range of unused IDs
  259          * ready to use (from lastpid+1 through pidchecked-1).
  260          *
  261          * If RFHIGHPID is set (used during system boot), do not allocate
  262          * low-numbered pids.
  263          */
  264         trypid = lastpid + 1;
  265         if (flags & RFHIGHPID) {
  266                 if (trypid < 10)
  267                         trypid = 10;
  268         } else {
  269                 if (randompid)
  270                         trypid += arc4random() % randompid;
  271         }
  272 retry:
  273         /*
  274          * If the process ID prototype has wrapped around,
  275          * restart somewhat above 0, as the low-numbered procs
  276          * tend to include daemons that don't exit.
  277          */
  278         if (trypid >= pid_max) {
  279                 trypid = trypid % pid_max;
  280                 if (trypid < 100)
  281                         trypid += 100;
  282                 pidchecked = 0;
  283         }
  284         if (trypid >= pidchecked) {
  285                 int doingzomb = 0;
  286 
  287                 pidchecked = PID_MAX;
  288                 /*
  289                  * Scan the active and zombie procs to check whether this pid
  290                  * is in use.  Remember the lowest pid that's greater
  291                  * than trypid, so we can avoid checking for a while.
  292                  *
  293                  * Avoid reuse of the process group id, session id or
  294                  * the reaper subtree id.  Note that for process group
  295                  * and sessions, the amount of reserved pids is
  296                  * limited by process limit.  For the subtree ids, the
  297                  * id is kept reserved only while there is a
  298                  * non-reaped process in the subtree, so amount of
  299                  * reserved pids is limited by process limit times
  300                  * two.
  301                  */
  302                 p = LIST_FIRST(&allproc);
  303 again:
  304                 for (; p != NULL; p = LIST_NEXT(p, p_list)) {
  305                         while (p->p_pid == trypid ||
  306                             p->p_reapsubtree == trypid ||
  307                             (p->p_pgrp != NULL &&
  308                             (p->p_pgrp->pg_id == trypid ||
  309                             (p->p_session != NULL &&
  310                             p->p_session->s_sid == trypid)))) {
  311                                 trypid++;
  312                                 if (trypid >= pidchecked)
  313                                         goto retry;
  314                         }
  315                         if (p->p_pid > trypid && pidchecked > p->p_pid)
  316                                 pidchecked = p->p_pid;
  317                         if (p->p_pgrp != NULL) {
  318                                 if (p->p_pgrp->pg_id > trypid &&
  319                                     pidchecked > p->p_pgrp->pg_id)
  320                                         pidchecked = p->p_pgrp->pg_id;
  321                                 if (p->p_session != NULL &&
  322                                     p->p_session->s_sid > trypid &&
  323                                     pidchecked > p->p_session->s_sid)
  324                                         pidchecked = p->p_session->s_sid;
  325                         }
  326                 }
  327                 if (!doingzomb) {
  328                         doingzomb = 1;
  329                         p = LIST_FIRST(&zombproc);
  330                         goto again;
  331                 }
  332         }
  333 
  334         /*
  335          * RFHIGHPID does not mess with the lastpid counter during boot.
  336          */
  337         if (flags & RFHIGHPID)
  338                 pidchecked = 0;
  339         else
  340                 lastpid = trypid;
  341 
  342         return (trypid);
  343 }
  344 
  345 static int
  346 fork_norfproc(struct thread *td, int flags)
  347 {
  348         int error;
  349         struct proc *p1;
  350 
  351         KASSERT((flags & RFPROC) == 0,
  352             ("fork_norfproc called with RFPROC set"));
  353         p1 = td->td_proc;
  354 
  355         if (((p1->p_flag & (P_HADTHREADS|P_SYSTEM)) == P_HADTHREADS) &&
  356             (flags & (RFCFDG | RFFDG))) {
  357                 PROC_LOCK(p1);
  358                 if (thread_single(p1, SINGLE_BOUNDARY)) {
  359                         PROC_UNLOCK(p1);
  360                         return (ERESTART);
  361                 }
  362                 PROC_UNLOCK(p1);
  363         }
  364 
  365         error = vm_forkproc(td, NULL, NULL, NULL, flags);
  366         if (error)
  367                 goto fail;
  368 
  369         /*
  370          * Close all file descriptors.
  371          */
  372         if (flags & RFCFDG) {
  373                 struct filedesc *fdtmp;
  374                 fdtmp = fdinit(td->td_proc->p_fd, false);
  375                 fdescfree(td);
  376                 p1->p_fd = fdtmp;
  377         }
  378 
  379         /*
  380          * Unshare file descriptors (from parent).
  381          */
  382         if (flags & RFFDG)
  383                 fdunshare(td);
  384 
  385 fail:
  386         if (((p1->p_flag & (P_HADTHREADS|P_SYSTEM)) == P_HADTHREADS) &&
  387             (flags & (RFCFDG | RFFDG))) {
  388                 PROC_LOCK(p1);
  389                 thread_single_end(p1, SINGLE_BOUNDARY);
  390                 PROC_UNLOCK(p1);
  391         }
  392         return (error);
  393 }
  394 
  395 static void
  396 do_fork(struct thread *td, struct fork_req *fr, struct proc *p2, struct thread *td2,
  397     struct vmspace *vm2, struct file *fp_procdesc)
  398 {
  399         struct proc *p1, *pptr;
  400         int trypid;
  401         struct filedesc *fd;
  402         struct filedesc_to_leader *fdtol;
  403         struct sigacts *newsigacts;
  404 
  405         sx_assert(&proctree_lock, SX_LOCKED);
  406         sx_assert(&allproc_lock, SX_XLOCKED);
  407 
  408         p1 = td->td_proc;
  409 
  410         trypid = fork_findpid(fr->fr_flags);
  411 
  412         p2->p_state = PRS_NEW;          /* protect against others */
  413         p2->p_pid = trypid;
  414         AUDIT_ARG_PID(p2->p_pid);
  415         LIST_INSERT_HEAD(&allproc, p2, p_list);
  416         allproc_gen++;
  417         LIST_INSERT_HEAD(PIDHASH(p2->p_pid), p2, p_hash);
  418         PROC_LOCK(p2);
  419         PROC_LOCK(p1);
  420 
  421         sx_xunlock(&allproc_lock);
  422         sx_xunlock(&proctree_lock);
  423 
  424         bcopy(&p1->p_startcopy, &p2->p_startcopy,
  425             __rangeof(struct proc, p_startcopy, p_endcopy));
  426         p2->p_fctl0 = p1->p_fctl0;
  427         pargs_hold(p2->p_args);
  428 
  429         PROC_UNLOCK(p1);
  430 
  431         bzero(&p2->p_startzero,
  432             __rangeof(struct proc, p_startzero, p_endzero));
  433 
  434         /* Tell the prison that we exist. */
  435         prison_proc_hold(p2->p_ucred->cr_prison);
  436 
  437         PROC_UNLOCK(p2);
  438 
  439         tidhash_add(td2);
  440 
  441         /*
  442          * Malloc things while we don't hold any locks.
  443          */
  444         if (fr->fr_flags & RFSIGSHARE)
  445                 newsigacts = NULL;
  446         else
  447                 newsigacts = sigacts_alloc();
  448 
  449         /*
  450          * Copy filedesc.
  451          */
  452         if (fr->fr_flags & RFCFDG) {
  453                 fd = fdinit(p1->p_fd, false);
  454                 fdtol = NULL;
  455         } else if (fr->fr_flags & RFFDG) {
  456                 fd = fdcopy(p1->p_fd);
  457                 fdtol = NULL;
  458         } else {
  459                 fd = fdshare(p1->p_fd);
  460                 if (p1->p_fdtol == NULL)
  461                         p1->p_fdtol = filedesc_to_leader_alloc(NULL, NULL,
  462                             p1->p_leader);
  463                 if ((fr->fr_flags & RFTHREAD) != 0) {
  464                         /*
  465                          * Shared file descriptor table, and shared
  466                          * process leaders.
  467                          */
  468                         fdtol = p1->p_fdtol;
  469                         FILEDESC_XLOCK(p1->p_fd);
  470                         fdtol->fdl_refcount++;
  471                         FILEDESC_XUNLOCK(p1->p_fd);
  472                 } else {
  473                         /*
  474                          * Shared file descriptor table, and different
  475                          * process leaders.
  476                          */
  477                         fdtol = filedesc_to_leader_alloc(p1->p_fdtol,
  478                             p1->p_fd, p2);
  479                 }
  480         }
  481         /*
  482          * Make a proc table entry for the new process.
  483          * Start by zeroing the section of proc that is zero-initialized,
  484          * then copy the section that is copied directly from the parent.
  485          */
  486 
  487         PROC_LOCK(p2);
  488         PROC_LOCK(p1);
  489 
  490         bzero(&td2->td_startzero,
  491             __rangeof(struct thread, td_startzero, td_endzero));
  492         td2->td_pflags2 = 0;
  493         td2->td_errno = 0;
  494 
  495         bcopy(&td->td_startcopy, &td2->td_startcopy,
  496             __rangeof(struct thread, td_startcopy, td_endcopy));
  497 
  498         bcopy(&p2->p_comm, &td2->td_name, sizeof(td2->td_name));
  499         td2->td_sigstk = td->td_sigstk;
  500         td2->td_flags = TDF_INMEM;
  501         td2->td_lend_user_pri = PRI_MAX;
  502 
  503 #ifdef VIMAGE
  504         td2->td_vnet = NULL;
  505         td2->td_vnet_lpush = NULL;
  506 #endif
  507 
  508         /*
  509          * Allow the scheduler to initialize the child.
  510          */
  511         thread_lock(td);
  512         sched_fork(td, td2);
  513         thread_unlock(td);
  514 
  515         /*
  516          * Duplicate sub-structures as needed.
  517          * Increase reference counts on shared objects.
  518          */
  519         p2->p_flag = P_INMEM;
  520         p2->p_flag2 = p1->p_flag2 & (P2_ASLR_DISABLE | P2_ASLR_ENABLE |
  521             P2_ASLR_IGNSTART | P2_NOTRACE | P2_NOTRACE_EXEC |
  522             P2_TRAPCAP |
  523             P2_STKGAP_DISABLE | P2_STKGAP_DISABLE_EXEC);
  524         p2->p_swtick = ticks;
  525         if (p1->p_flag & P_PROFIL)
  526                 startprofclock(p2);
  527 
  528         if (fr->fr_flags & RFSIGSHARE) {
  529                 p2->p_sigacts = sigacts_hold(p1->p_sigacts);
  530         } else {
  531                 sigacts_copy(newsigacts, p1->p_sigacts);
  532                 p2->p_sigacts = newsigacts;
  533                 if ((fr->fr_flags2 & FR2_DROPSIG_CAUGHT) != 0) {
  534                         mtx_lock(&p2->p_sigacts->ps_mtx);
  535                         sig_drop_caught(p2);
  536                         mtx_unlock(&p2->p_sigacts->ps_mtx);
  537                 }
  538         }
  539 
  540         if (fr->fr_flags & RFTSIGZMB)
  541                 p2->p_sigparent = RFTSIGNUM(fr->fr_flags);
  542         else if (fr->fr_flags & RFLINUXTHPN)
  543                 p2->p_sigparent = SIGUSR1;
  544         else
  545                 p2->p_sigparent = SIGCHLD;
  546 
  547         p2->p_textvp = p1->p_textvp;
  548         p2->p_fd = fd;
  549         p2->p_fdtol = fdtol;
  550 
  551         if (p1->p_flag2 & P2_INHERIT_PROTECTED) {
  552                 p2->p_flag |= P_PROTECTED;
  553                 p2->p_flag2 |= P2_INHERIT_PROTECTED;
  554         }
  555 
  556         /*
  557          * p_limit is copy-on-write.  Bump its refcount.
  558          */
  559         lim_fork(p1, p2);
  560 
  561         thread_cow_get_proc(td2, p2);
  562 
  563         pstats_fork(p1->p_stats, p2->p_stats);
  564 
  565         PROC_UNLOCK(p1);
  566         PROC_UNLOCK(p2);
  567 
  568         /* Bump references to the text vnode (for procfs). */
  569         if (p2->p_textvp)
  570                 vrefact(p2->p_textvp);
  571 
  572         /*
  573          * Set up linkage for kernel based threading.
  574          */
  575         if ((fr->fr_flags & RFTHREAD) != 0) {
  576                 mtx_lock(&ppeers_lock);
  577                 p2->p_peers = p1->p_peers;
  578                 p1->p_peers = p2;
  579                 p2->p_leader = p1->p_leader;
  580                 mtx_unlock(&ppeers_lock);
  581                 PROC_LOCK(p1->p_leader);
  582                 if ((p1->p_leader->p_flag & P_WEXIT) != 0) {
  583                         PROC_UNLOCK(p1->p_leader);
  584                         /*
  585                          * The task leader is exiting, so process p1 is
  586                          * going to be killed shortly.  Since p1 obviously
  587                          * isn't dead yet, we know that the leader is either
  588                          * sending SIGKILL's to all the processes in this
  589                          * task or is sleeping waiting for all the peers to
  590                          * exit.  We let p1 complete the fork, but we need
  591                          * to go ahead and kill the new process p2 since
  592                          * the task leader may not get a chance to send
  593                          * SIGKILL to it.  We leave it on the list so that
  594                          * the task leader will wait for this new process
  595                          * to commit suicide.
  596                          */
  597                         PROC_LOCK(p2);
  598                         kern_psignal(p2, SIGKILL);
  599                         PROC_UNLOCK(p2);
  600                 } else
  601                         PROC_UNLOCK(p1->p_leader);
  602         } else {
  603                 p2->p_peers = NULL;
  604                 p2->p_leader = p2;
  605         }
  606 
  607         sx_xlock(&proctree_lock);
  608         PGRP_LOCK(p1->p_pgrp);
  609         PROC_LOCK(p2);
  610         PROC_LOCK(p1);
  611 
  612         /*
  613          * Preserve some more flags in subprocess.  P_PROFIL has already
  614          * been preserved.
  615          */
  616         p2->p_flag |= p1->p_flag & P_SUGID;
  617         td2->td_pflags |= (td->td_pflags & TDP_ALTSTACK) | TDP_FORKING;
  618         SESS_LOCK(p1->p_session);
  619         if (p1->p_session->s_ttyvp != NULL && p1->p_flag & P_CONTROLT)
  620                 p2->p_flag |= P_CONTROLT;
  621         SESS_UNLOCK(p1->p_session);
  622         if (fr->fr_flags & RFPPWAIT)
  623                 p2->p_flag |= P_PPWAIT;
  624 
  625         p2->p_pgrp = p1->p_pgrp;
  626         LIST_INSERT_AFTER(p1, p2, p_pglist);
  627         PGRP_UNLOCK(p1->p_pgrp);
  628         LIST_INIT(&p2->p_children);
  629         LIST_INIT(&p2->p_orphans);
  630 
  631         callout_init_mtx(&p2->p_itcallout, &p2->p_mtx, 0);
  632 
  633         /*
  634          * If PF_FORK is set, the child process inherits the
  635          * procfs ioctl flags from its parent.
  636          */
  637         if (p1->p_pfsflags & PF_FORK) {
  638                 p2->p_stops = p1->p_stops;
  639                 p2->p_pfsflags = p1->p_pfsflags;
  640         }
  641 
  642         /*
  643          * This begins the section where we must prevent the parent
  644          * from being swapped.
  645          */
  646         _PHOLD(p1);
  647         PROC_UNLOCK(p1);
  648 
  649         /*
  650          * Attach the new process to its parent.
  651          *
  652          * If RFNOWAIT is set, the newly created process becomes a child
  653          * of init.  This effectively disassociates the child from the
  654          * parent.
  655          */
  656         if ((fr->fr_flags & RFNOWAIT) != 0) {
  657                 pptr = p1->p_reaper;
  658                 p2->p_reaper = pptr;
  659         } else {
  660                 p2->p_reaper = (p1->p_treeflag & P_TREE_REAPER) != 0 ?
  661                     p1 : p1->p_reaper;
  662                 pptr = p1;
  663         }
  664         p2->p_pptr = pptr;
  665         p2->p_oppid = pptr->p_pid;
  666         LIST_INSERT_HEAD(&pptr->p_children, p2, p_sibling);
  667         LIST_INIT(&p2->p_reaplist);
  668         LIST_INSERT_HEAD(&p2->p_reaper->p_reaplist, p2, p_reapsibling);
  669         if (p2->p_reaper == p1)
  670                 p2->p_reapsubtree = p2->p_pid;
  671         sx_xunlock(&proctree_lock);
  672 
  673         /* Inform accounting that we have forked. */
  674         p2->p_acflag = AFORK;
  675         PROC_UNLOCK(p2);
  676 
  677 #ifdef KTRACE
  678         ktrprocfork(p1, p2);
  679 #endif
  680 
  681         /*
  682          * Finish creating the child process.  It will return via a different
  683          * execution path later.  (ie: directly into user mode)
  684          */
  685         vm_forkproc(td, p2, td2, vm2, fr->fr_flags);
  686 
  687         if (fr->fr_flags == (RFFDG | RFPROC)) {
  688                 VM_CNT_INC(v_forks);
  689                 VM_CNT_ADD(v_forkpages, p2->p_vmspace->vm_dsize +
  690                     p2->p_vmspace->vm_ssize);
  691         } else if (fr->fr_flags == (RFFDG | RFPROC | RFPPWAIT | RFMEM)) {
  692                 VM_CNT_INC(v_vforks);
  693                 VM_CNT_ADD(v_vforkpages, p2->p_vmspace->vm_dsize +
  694                     p2->p_vmspace->vm_ssize);
  695         } else if (p1 == &proc0) {
  696                 VM_CNT_INC(v_kthreads);
  697                 VM_CNT_ADD(v_kthreadpages, p2->p_vmspace->vm_dsize +
  698                     p2->p_vmspace->vm_ssize);
  699         } else {
  700                 VM_CNT_INC(v_rforks);
  701                 VM_CNT_ADD(v_rforkpages, p2->p_vmspace->vm_dsize +
  702                     p2->p_vmspace->vm_ssize);
  703         }
  704 
  705         /*
  706          * Associate the process descriptor with the process before anything
  707          * can happen that might cause that process to need the descriptor.
  708          * However, don't do this until after fork(2) can no longer fail.
  709          */
  710         if (fr->fr_flags & RFPROCDESC)
  711                 procdesc_new(p2, fr->fr_pd_flags);
  712 
  713         /*
  714          * Both processes are set up, now check if any loadable modules want
  715          * to adjust anything.
  716          */
  717         EVENTHANDLER_DIRECT_INVOKE(process_fork, p1, p2, fr->fr_flags);
  718 
  719         /*
  720          * Set the child start time and mark the process as being complete.
  721          */
  722         PROC_LOCK(p2);
  723         PROC_LOCK(p1);
  724         microuptime(&p2->p_stats->p_start);
  725         PROC_SLOCK(p2);
  726         p2->p_state = PRS_NORMAL;
  727         PROC_SUNLOCK(p2);
  728 
  729 #ifdef KDTRACE_HOOKS
  730         /*
  731          * Tell the DTrace fasttrap provider about the new process so that any
  732          * tracepoints inherited from the parent can be removed. We have to do
  733          * this only after p_state is PRS_NORMAL since the fasttrap module will
  734          * use pfind() later on.
  735          */
  736         if ((fr->fr_flags & RFMEM) == 0 && dtrace_fasttrap_fork)
  737                 dtrace_fasttrap_fork(p1, p2);
  738 #endif
  739         /*
  740          * Hold the process so that it cannot exit after we make it runnable,
  741          * but before we wait for the debugger.
  742          */
  743         _PHOLD(p2);
  744         if (fr->fr_flags & RFPPWAIT) {
  745                 td->td_pflags |= TDP_RFPPWAIT;
  746                 td->td_rfppwait_p = p2;
  747                 td->td_dbgflags |= TDB_VFORK;
  748         }
  749         PROC_UNLOCK(p2);
  750 
  751         /*
  752          * Now can be swapped.
  753          */
  754         _PRELE(p1);
  755         PROC_UNLOCK(p1);
  756 
  757         /*
  758          * Tell any interested parties about the new process.
  759          */
  760         knote_fork(p1->p_klist, p2->p_pid);
  761         SDT_PROBE3(proc, , , create, p2, p1, fr->fr_flags);
  762 
  763         if (fr->fr_flags & RFPROCDESC) {
  764                 procdesc_finit(p2->p_procdesc, fp_procdesc);
  765                 fdrop(fp_procdesc, td);
  766         }
  767         
  768         /*
  769          * Speculative check for PTRACE_FORK. PTRACE_FORK is not
  770          * synced with forks in progress so it is OK if we miss it
  771          * if being set atm.
  772          */
  773         if ((p1->p_ptevents & PTRACE_FORK) != 0) {
  774                 sx_xlock(&proctree_lock);
  775                 PROC_LOCK(p2);
  776                 
  777                 /*
  778                  * p1->p_ptevents & p1->p_pptr are protected by both
  779                  * process and proctree locks for modifications,
  780                  * so owning proctree_lock allows the race-free read.
  781                  */
  782                 if ((p1->p_ptevents & PTRACE_FORK) != 0) {
  783                         /*
  784                          * Arrange for debugger to receive the fork event.
  785                          *
  786                          * We can report PL_FLAG_FORKED regardless of
  787                          * P_FOLLOWFORK settings, but it does not make a sense
  788                          * for runaway child.
  789                          */
  790                         td->td_dbgflags |= TDB_FORK;
  791                         td->td_dbg_forked = p2->p_pid;
  792                         td2->td_dbgflags |= TDB_STOPATFORK;
  793                         proc_set_traced(p2, true);
  794                         CTR2(KTR_PTRACE,
  795                             "do_fork: attaching to new child pid %d: oppid %d",
  796                             p2->p_pid, p2->p_oppid);
  797                         proc_reparent(p2, p1->p_pptr, false);
  798                 }
  799                 PROC_UNLOCK(p2);
  800                 sx_xunlock(&proctree_lock);
  801         }
  802         
  803         if ((fr->fr_flags & RFSTOPPED) == 0) {
  804                 /*
  805                  * If RFSTOPPED not requested, make child runnable and
  806                  * add to run queue.
  807                  */
  808                 thread_lock(td2);
  809                 TD_SET_CAN_RUN(td2);
  810                 sched_add(td2, SRQ_BORING);
  811                 thread_unlock(td2);
  812                 if (fr->fr_pidp != NULL)
  813                         *fr->fr_pidp = p2->p_pid;
  814         } else {
  815                 *fr->fr_procp = p2;
  816         }
  817 
  818         PROC_LOCK(p2);
  819         _PRELE(p2);
  820         racct_proc_fork_done(p2);
  821         PROC_UNLOCK(p2);
  822 }
  823 
  824 int
  825 fork1(struct thread *td, struct fork_req *fr)
  826 {
  827         struct proc *p1, *newproc;
  828         struct thread *td2;
  829         struct vmspace *vm2;
  830         struct file *fp_procdesc;
  831         vm_ooffset_t mem_charged;
  832         int error, nprocs_new, ok;
  833         static int curfail;
  834         static struct timeval lastfail;
  835         int flags, pages;
  836 
  837         flags = fr->fr_flags;
  838         pages = fr->fr_pages;
  839 
  840         if ((flags & RFSTOPPED) != 0)
  841                 MPASS(fr->fr_procp != NULL && fr->fr_pidp == NULL);
  842         else
  843                 MPASS(fr->fr_procp == NULL);
  844 
  845         /* Check for the undefined or unimplemented flags. */
  846         if ((flags & ~(RFFLAGS | RFTSIGFLAGS(RFTSIGMASK))) != 0)
  847                 return (EINVAL);
  848 
  849         /* Signal value requires RFTSIGZMB. */
  850         if ((flags & RFTSIGFLAGS(RFTSIGMASK)) != 0 && (flags & RFTSIGZMB) == 0)
  851                 return (EINVAL);
  852 
  853         /* Can't copy and clear. */
  854         if ((flags & (RFFDG|RFCFDG)) == (RFFDG|RFCFDG))
  855                 return (EINVAL);
  856 
  857         /* Check the validity of the signal number. */
  858         if ((flags & RFTSIGZMB) != 0 && (u_int)RFTSIGNUM(flags) > _SIG_MAXSIG)
  859                 return (EINVAL);
  860 
  861         if ((flags & RFPROCDESC) != 0) {
  862                 /* Can't not create a process yet get a process descriptor. */
  863                 if ((flags & RFPROC) == 0)
  864                         return (EINVAL);
  865 
  866                 /* Must provide a place to put a procdesc if creating one. */
  867                 if (fr->fr_pd_fd == NULL)
  868                         return (EINVAL);
  869 
  870                 /* Check if we are using supported flags. */
  871                 if ((fr->fr_pd_flags & ~PD_ALLOWED_AT_FORK) != 0)
  872                         return (EINVAL);
  873         }
  874 
  875         p1 = td->td_proc;
  876 
  877         /*
  878          * Here we don't create a new process, but we divorce
  879          * certain parts of a process from itself.
  880          */
  881         if ((flags & RFPROC) == 0) {
  882                 if (fr->fr_procp != NULL)
  883                         *fr->fr_procp = NULL;
  884                 else if (fr->fr_pidp != NULL)
  885                         *fr->fr_pidp = 0;
  886                 return (fork_norfproc(td, flags));
  887         }
  888 
  889         fp_procdesc = NULL;
  890         newproc = NULL;
  891         vm2 = NULL;
  892 
  893         /*
  894          * Increment the nprocs resource before allocations occur.
  895          * Although process entries are dynamically created, we still
  896          * keep a global limit on the maximum number we will
  897          * create. There are hard-limits as to the number of processes
  898          * that can run, established by the KVA and memory usage for
  899          * the process data.
  900          *
  901          * Don't allow a nonprivileged user to use the last ten
  902          * processes; don't let root exceed the limit.
  903          */
  904         nprocs_new = atomic_fetchadd_int(&nprocs, 1) + 1;
  905         if (nprocs_new >= maxproc - 10) {
  906                 if (priv_check_cred(td->td_ucred, PRIV_MAXPROC, 0) != 0 ||
  907                     nprocs_new >= maxproc) {
  908                         error = EAGAIN;
  909                         sx_xlock(&allproc_lock);
  910                         if (ppsratecheck(&lastfail, &curfail, 1)) {
  911                                 printf("maxproc limit exceeded by uid %u "
  912                                     "(pid %d); see tuning(7) and "
  913                                     "login.conf(5)\n",
  914                                     td->td_ucred->cr_ruid, p1->p_pid);
  915                         }
  916                         sx_xunlock(&allproc_lock);
  917                         goto fail2;
  918                 }
  919         }
  920 
  921         /*
  922          * If required, create a process descriptor in the parent first; we
  923          * will abandon it if something goes wrong. We don't finit() until
  924          * later.
  925          */
  926         if (flags & RFPROCDESC) {
  927                 error = procdesc_falloc(td, &fp_procdesc, fr->fr_pd_fd,
  928                     fr->fr_pd_flags, fr->fr_pd_fcaps);
  929                 if (error != 0)
  930                         goto fail2;
  931         }
  932 
  933         mem_charged = 0;
  934         if (pages == 0)
  935                 pages = kstack_pages;
  936         /* Allocate new proc. */
  937         newproc = uma_zalloc(proc_zone, M_WAITOK);
  938         td2 = FIRST_THREAD_IN_PROC(newproc);
  939         if (td2 == NULL) {
  940                 td2 = thread_alloc(pages);
  941                 if (td2 == NULL) {
  942                         error = ENOMEM;
  943                         goto fail2;
  944                 }
  945                 proc_linkup(newproc, td2);
  946         } else {
  947                 if (td2->td_kstack == 0 || td2->td_kstack_pages != pages) {
  948                         if (td2->td_kstack != 0)
  949                                 vm_thread_dispose(td2);
  950                         if (!thread_alloc_stack(td2, pages)) {
  951                                 error = ENOMEM;
  952                                 goto fail2;
  953                         }
  954                 }
  955         }
  956 
  957         if ((flags & RFMEM) == 0) {
  958                 vm2 = vmspace_fork(p1->p_vmspace, &mem_charged);
  959                 if (vm2 == NULL) {
  960                         error = ENOMEM;
  961                         goto fail2;
  962                 }
  963                 if (!swap_reserve(mem_charged)) {
  964                         /*
  965                          * The swap reservation failed. The accounting
  966                          * from the entries of the copied vm2 will be
  967                          * subtracted in vmspace_free(), so force the
  968                          * reservation there.
  969                          */
  970                         swap_reserve_force(mem_charged);
  971                         error = ENOMEM;
  972                         goto fail2;
  973                 }
  974         } else
  975                 vm2 = NULL;
  976 
  977         /*
  978          * XXX: This is ugly; when we copy resource usage, we need to bump
  979          *      per-cred resource counters.
  980          */
  981         proc_set_cred_init(newproc, crhold(td->td_ucred));
  982 
  983         /*
  984          * Initialize resource accounting for the child process.
  985          */
  986         error = racct_proc_fork(p1, newproc);
  987         if (error != 0) {
  988                 error = EAGAIN;
  989                 goto fail1;
  990         }
  991 
  992 #ifdef MAC
  993         mac_proc_init(newproc);
  994 #endif
  995         newproc->p_klist = knlist_alloc(&newproc->p_mtx);
  996         STAILQ_INIT(&newproc->p_ktr);
  997 
  998         /* We have to lock the process tree while we look for a pid. */
  999         sx_xlock(&proctree_lock);
 1000         sx_xlock(&allproc_lock);
 1001 
 1002         /*
 1003          * Increment the count of procs running with this uid. Don't allow
 1004          * a nonprivileged user to exceed their current limit.
 1005          *
 1006          * XXXRW: Can we avoid privilege here if it's not needed?
 1007          */
 1008         error = priv_check_cred(td->td_ucred, PRIV_PROC_LIMIT, 0);
 1009         if (error == 0)
 1010                 ok = chgproccnt(td->td_ucred->cr_ruidinfo, 1, 0);
 1011         else {
 1012                 ok = chgproccnt(td->td_ucred->cr_ruidinfo, 1,
 1013                     lim_cur(td, RLIMIT_NPROC));
 1014         }
 1015         if (ok) {
 1016                 do_fork(td, fr, newproc, td2, vm2, fp_procdesc);
 1017                 return (0);
 1018         }
 1019 
 1020         error = EAGAIN;
 1021         sx_xunlock(&allproc_lock);
 1022         sx_xunlock(&proctree_lock);
 1023 #ifdef MAC
 1024         mac_proc_destroy(newproc);
 1025 #endif
 1026         racct_proc_exit(newproc);
 1027 fail1:
 1028         crfree(newproc->p_ucred);
 1029         newproc->p_ucred = NULL;
 1030 fail2:
 1031         if (vm2 != NULL)
 1032                 vmspace_free(vm2);
 1033         uma_zfree(proc_zone, newproc);
 1034         if ((flags & RFPROCDESC) != 0 && fp_procdesc != NULL) {
 1035                 fdclose(td, fp_procdesc, *fr->fr_pd_fd);
 1036                 fdrop(fp_procdesc, td);
 1037         }
 1038         atomic_add_int(&nprocs, -1);
 1039         pause("fork", hz / 2);
 1040         return (error);
 1041 }
 1042 
 1043 /*
 1044  * Handle the return of a child process from fork1().  This function
 1045  * is called from the MD fork_trampoline() entry point.
 1046  */
 1047 void
 1048 fork_exit(void (*callout)(void *, struct trapframe *), void *arg,
 1049     struct trapframe *frame)
 1050 {
 1051         struct proc *p;
 1052         struct thread *td;
 1053         struct thread *dtd;
 1054 
 1055         td = curthread;
 1056         p = td->td_proc;
 1057         KASSERT(p->p_state == PRS_NORMAL, ("executing process is still new"));
 1058 
 1059         CTR4(KTR_PROC, "fork_exit: new thread %p (td_sched %p, pid %d, %s)",
 1060             td, td_get_sched(td), p->p_pid, td->td_name);
 1061 
 1062         sched_fork_exit(td);
 1063         /*
 1064         * Processes normally resume in mi_switch() after being
 1065         * cpu_switch()'ed to, but when children start up they arrive here
 1066         * instead, so we must do much the same things as mi_switch() would.
 1067         */
 1068         if ((dtd = PCPU_GET(deadthread))) {
 1069                 PCPU_SET(deadthread, NULL);
 1070                 thread_stash(dtd);
 1071         }
 1072         thread_unlock(td);
 1073 
 1074         /*
 1075          * cpu_fork_kthread_handler intercepts this function call to
 1076          * have this call a non-return function to stay in kernel mode.
 1077          * initproc has its own fork handler, but it does return.
 1078          */
 1079         KASSERT(callout != NULL, ("NULL callout in fork_exit"));
 1080         callout(arg, frame);
 1081 
 1082         /*
 1083          * Check if a kernel thread misbehaved and returned from its main
 1084          * function.
 1085          */
 1086         if (p->p_flag & P_KPROC) {
 1087                 printf("Kernel thread \"%s\" (pid %d) exited prematurely.\n",
 1088                     td->td_name, p->p_pid);
 1089                 kthread_exit();
 1090         }
 1091         mtx_assert(&Giant, MA_NOTOWNED);
 1092 
 1093         if (p->p_sysent->sv_schedtail != NULL)
 1094                 (p->p_sysent->sv_schedtail)(td);
 1095         td->td_pflags &= ~TDP_FORKING;
 1096 }
 1097 
 1098 /*
 1099  * Simplified back end of syscall(), used when returning from fork()
 1100  * directly into user mode.  This function is passed in to fork_exit()
 1101  * as the first parameter and is called when returning to a new
 1102  * userland process.
 1103  */
 1104 void
 1105 fork_return(struct thread *td, struct trapframe *frame)
 1106 {
 1107         struct proc *p;
 1108 
 1109         p = td->td_proc;
 1110         if (td->td_dbgflags & TDB_STOPATFORK) {
 1111                 PROC_LOCK(p);
 1112                 if ((p->p_flag & P_TRACED) != 0) {
 1113                         /*
 1114                          * Inform the debugger if one is still present.
 1115                          */
 1116                         td->td_dbgflags |= TDB_CHILD | TDB_SCX | TDB_FSTP;
 1117                         ptracestop(td, SIGSTOP, NULL);
 1118                         td->td_dbgflags &= ~(TDB_CHILD | TDB_SCX);
 1119                 } else {
 1120                         /*
 1121                          * ... otherwise clear the request.
 1122                          */
 1123                         td->td_dbgflags &= ~TDB_STOPATFORK;
 1124                 }
 1125                 PROC_UNLOCK(p);
 1126         } else if (p->p_flag & P_TRACED || td->td_dbgflags & TDB_BORN) {
 1127                 /*
 1128                  * This is the start of a new thread in a traced
 1129                  * process.  Report a system call exit event.
 1130                  */
 1131                 PROC_LOCK(p);
 1132                 td->td_dbgflags |= TDB_SCX;
 1133                 _STOPEVENT(p, S_SCX, td->td_sa.code);
 1134                 if ((p->p_ptevents & PTRACE_SCX) != 0 ||
 1135                     (td->td_dbgflags & TDB_BORN) != 0)
 1136                         ptracestop(td, SIGTRAP, NULL);
 1137                 td->td_dbgflags &= ~(TDB_SCX | TDB_BORN);
 1138                 PROC_UNLOCK(p);
 1139         }
 1140 
 1141         /*
 1142          * If the prison was killed mid-fork, die along with it.
 1143          */
 1144         if (td->td_ucred->cr_prison->pr_flags & PR_REMOVE)
 1145                 exit1(td, 0, SIGKILL);
 1146 
 1147         userret(td, frame);
 1148 
 1149 #ifdef KTRACE
 1150         if (KTRPOINT(td, KTR_SYSRET))
 1151                 ktrsysret(SYS_fork, 0, 0);
 1152 #endif
 1153 }

Cache object: addbd6f910b1c219d8d99fd0919905a8


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