kern_fork.c

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    1 /*-
    2  * Copyright (c) 1982, 1986, 1989, 1991, 1993
    3  *      The Regents of the University of California.  All rights reserved.
    4  * (c) UNIX System Laboratories, Inc.
    5  * All or some portions of this file are derived from material licensed
    6  * to the University of California by American Telephone and Telegraph
    7  * Co. or Unix System Laboratories, Inc. and are reproduced herein with
    8  * the permission of UNIX System Laboratories, Inc.
    9  *
   10  * Redistribution and use in source and binary forms, with or without
   11  * modification, are permitted provided that the following conditions
   12  * are met:
   13  * 1. Redistributions of source code must retain the above copyright
   14  *    notice, this list of conditions and the following disclaimer.
   15  * 2. Redistributions in binary form must reproduce the above copyright
   16  *    notice, this list of conditions and the following disclaimer in the
   17  *    documentation and/or other materials provided with the distribution.
   18  * 4. Neither the name of the University nor the names of its contributors
   19  *    may be used to endorse or promote products derived from this software
   20  *    without specific prior written permission.
   21  *
   22  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
   23  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   24  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   25  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
   26  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   27  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   28  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   29  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   30  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   31  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   32  * SUCH DAMAGE.
   33  *
   34  *      @(#)kern_fork.c 8.6 (Berkeley) 4/8/94
   35  */
   36 
   37 #include <sys/cdefs.h>
   38 __FBSDID("$FreeBSD$");
   39 
   40 #include "opt_kdtrace.h"
   41 #include "opt_ktrace.h"
   42 #include "opt_kstack_pages.h"
   43 #include "opt_procdesc.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, kernel, , create, "struct proc *",
   94     "struct proc *", "int");
   95 
   96 #ifndef _SYS_SYSPROTO_H_
   97 struct fork_args {
   98         int     dummy;
   99 };
  100 #endif
  101 
  102 /* ARGSUSED */
  103 int
  104 sys_fork(struct thread *td, struct fork_args *uap)
  105 {
  106         int error;
  107         struct proc *p2;
  108 
  109         error = fork1(td, RFFDG | RFPROC, 0, &p2, NULL, 0);
  110         if (error == 0) {
  111                 td->td_retval[0] = p2->p_pid;
  112                 td->td_retval[1] = 0;
  113         }
  114         return (error);
  115 }
  116 
  117 /* ARGUSED */
  118 int
  119 sys_pdfork(td, uap)
  120         struct thread *td;
  121         struct pdfork_args *uap;
  122 {
  123 #ifdef PROCDESC
  124         int error, fd;
  125         struct proc *p2;
  126 
  127         /*
  128          * It is necessary to return fd by reference because 0 is a valid file
  129          * descriptor number, and the child needs to be able to distinguish
  130          * itself from the parent using the return value.
  131          */
  132         error = fork1(td, RFFDG | RFPROC | RFPROCDESC, 0, &p2,
  133             &fd, uap->flags);
  134         if (error == 0) {
  135                 td->td_retval[0] = p2->p_pid;
  136                 td->td_retval[1] = 0;
  137                 error = copyout(&fd, uap->fdp, sizeof(fd));
  138         }
  139         return (error);
  140 #else
  141         return (ENOSYS);
  142 #endif
  143 }
  144 
  145 /* ARGSUSED */
  146 int
  147 sys_vfork(struct thread *td, struct vfork_args *uap)
  148 {
  149         int error, flags;
  150         struct proc *p2;
  151 
  152 #ifdef XEN
  153         flags = RFFDG | RFPROC; /* validate that this is still an issue */
  154 #else
  155         flags = RFFDG | RFPROC | RFPPWAIT | RFMEM;
  156 #endif          
  157         error = fork1(td, flags, 0, &p2, NULL, 0);
  158         if (error == 0) {
  159                 td->td_retval[0] = p2->p_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 proc *p2;
  169         int error;
  170 
  171         /* Don't allow kernel-only flags. */
  172         if ((uap->flags & RFKERNELONLY) != 0)
  173                 return (EINVAL);
  174 
  175         AUDIT_ARG_FFLAGS(uap->flags);
  176         error = fork1(td, uap->flags, 0, &p2, NULL, 0);
  177         if (error == 0) {
  178                 td->td_retval[0] = p2 ? p2->p_pid : 0;
  179                 td->td_retval[1] = 0;
  180         }
  181         return (error);
  182 }
  183 
  184 int     nprocs = 1;             /* process 0 */
  185 int     lastpid = 0;
  186 SYSCTL_INT(_kern, OID_AUTO, lastpid, CTLFLAG_RD, &lastpid, 0, 
  187     "Last used PID");
  188 
  189 /*
  190  * Random component to lastpid generation.  We mix in a random factor to make
  191  * it a little harder to predict.  We sanity check the modulus value to avoid
  192  * doing it in critical paths.  Don't let it be too small or we pointlessly
  193  * waste randomness entropy, and don't let it be impossibly large.  Using a
  194  * modulus that is too big causes a LOT more process table scans and slows
  195  * down fork processing as the pidchecked caching is defeated.
  196  */
  197 static int randompid = 0;
  198 
  199 static int
  200 sysctl_kern_randompid(SYSCTL_HANDLER_ARGS)
  201 {
  202         int error, pid;
  203 
  204         error = sysctl_wire_old_buffer(req, sizeof(int));
  205         if (error != 0)
  206                 return(error);
  207         sx_xlock(&allproc_lock);
  208         pid = randompid;
  209         error = sysctl_handle_int(oidp, &pid, 0, req);
  210         if (error == 0 && req->newptr != NULL) {
  211                 if (pid < 0 || pid > pid_max - 100)     /* out of range */
  212                         pid = pid_max - 100;
  213                 else if (pid < 2)                       /* NOP */
  214                         pid = 0;
  215                 else if (pid < 100)                     /* Make it reasonable */
  216                         pid = 100;
  217                 randompid = pid;
  218         }
  219         sx_xunlock(&allproc_lock);
  220         return (error);
  221 }
  222 
  223 SYSCTL_PROC(_kern, OID_AUTO, randompid, CTLTYPE_INT|CTLFLAG_RW,
  224     0, 0, sysctl_kern_randompid, "I", "Random PID modulus");
  225 
  226 static int
  227 fork_findpid(int flags)
  228 {
  229         struct proc *p;
  230         int trypid;
  231         static int pidchecked = 0;
  232 
  233         /*
  234          * Requires allproc_lock in order to iterate over the list
  235          * of processes, and proctree_lock to access p_pgrp.
  236          */
  237         sx_assert(&allproc_lock, SX_LOCKED);
  238         sx_assert(&proctree_lock, SX_LOCKED);
  239 
  240         /*
  241          * Find an unused process ID.  We remember a range of unused IDs
  242          * ready to use (from lastpid+1 through pidchecked-1).
  243          *
  244          * If RFHIGHPID is set (used during system boot), do not allocate
  245          * low-numbered pids.
  246          */
  247         trypid = lastpid + 1;
  248         if (flags & RFHIGHPID) {
  249                 if (trypid < 10)
  250                         trypid = 10;
  251         } else {
  252                 if (randompid)
  253                         trypid += arc4random() % randompid;
  254         }
  255 retry:
  256         /*
  257          * If the process ID prototype has wrapped around,
  258          * restart somewhat above 0, as the low-numbered procs
  259          * tend to include daemons that don't exit.
  260          */
  261         if (trypid >= pid_max) {
  262                 trypid = trypid % pid_max;
  263                 if (trypid < 100)
  264                         trypid += 100;
  265                 pidchecked = 0;
  266         }
  267         if (trypid >= pidchecked) {
  268                 int doingzomb = 0;
  269 
  270                 pidchecked = PID_MAX;
  271                 /*
  272                  * Scan the active and zombie procs to check whether this pid
  273                  * is in use.  Remember the lowest pid that's greater
  274                  * than trypid, so we can avoid checking for a while.
  275                  */
  276                 p = LIST_FIRST(&allproc);
  277 again:
  278                 for (; p != NULL; p = LIST_NEXT(p, p_list)) {
  279                         while (p->p_pid == trypid ||
  280                             (p->p_pgrp != NULL &&
  281                             (p->p_pgrp->pg_id == trypid ||
  282                             (p->p_session != NULL &&
  283                             p->p_session->s_sid == trypid)))) {
  284                                 trypid++;
  285                                 if (trypid >= pidchecked)
  286                                         goto retry;
  287                         }
  288                         if (p->p_pid > trypid && pidchecked > p->p_pid)
  289                                 pidchecked = p->p_pid;
  290                         if (p->p_pgrp != NULL) {
  291                                 if (p->p_pgrp->pg_id > trypid &&
  292                                     pidchecked > p->p_pgrp->pg_id)
  293                                         pidchecked = p->p_pgrp->pg_id;
  294                                 if (p->p_session != NULL &&
  295                                     p->p_session->s_sid > trypid &&
  296                                     pidchecked > p->p_session->s_sid)
  297                                         pidchecked = p->p_session->s_sid;
  298                         }
  299                 }
  300                 if (!doingzomb) {
  301                         doingzomb = 1;
  302                         p = LIST_FIRST(&zombproc);
  303                         goto again;
  304                 }
  305         }
  306 
  307         /*
  308          * RFHIGHPID does not mess with the lastpid counter during boot.
  309          */
  310         if (flags & RFHIGHPID)
  311                 pidchecked = 0;
  312         else
  313                 lastpid = trypid;
  314 
  315         return (trypid);
  316 }
  317 
  318 static int
  319 fork_norfproc(struct thread *td, int flags)
  320 {
  321         int error;
  322         struct proc *p1;
  323 
  324         KASSERT((flags & RFPROC) == 0,
  325             ("fork_norfproc called with RFPROC set"));
  326         p1 = td->td_proc;
  327 
  328         if (((p1->p_flag & (P_HADTHREADS|P_SYSTEM)) == P_HADTHREADS) &&
  329             (flags & (RFCFDG | RFFDG))) {
  330                 PROC_LOCK(p1);
  331                 if (thread_single(SINGLE_BOUNDARY)) {
  332                         PROC_UNLOCK(p1);
  333                         return (ERESTART);
  334                 }
  335                 PROC_UNLOCK(p1);
  336         }
  337 
  338         error = vm_forkproc(td, NULL, NULL, NULL, flags);
  339         if (error)
  340                 goto fail;
  341 
  342         /*
  343          * Close all file descriptors.
  344          */
  345         if (flags & RFCFDG) {
  346                 struct filedesc *fdtmp;
  347                 fdtmp = fdinit(td->td_proc->p_fd);
  348                 fdfree(td);
  349                 p1->p_fd = fdtmp;
  350         }
  351 
  352         /*
  353          * Unshare file descriptors (from parent).
  354          */
  355         if (flags & RFFDG) 
  356                 fdunshare(p1, td);
  357 
  358 fail:
  359         if (((p1->p_flag & (P_HADTHREADS|P_SYSTEM)) == P_HADTHREADS) &&
  360             (flags & (RFCFDG | RFFDG))) {
  361                 PROC_LOCK(p1);
  362                 thread_single_end();
  363                 PROC_UNLOCK(p1);
  364         }
  365         return (error);
  366 }
  367 
  368 static void
  369 do_fork(struct thread *td, int flags, struct proc *p2, struct thread *td2,
  370     struct vmspace *vm2, int pdflags)
  371 {
  372         struct proc *p1, *pptr;
  373         int p2_held, trypid;
  374         struct filedesc *fd;
  375         struct filedesc_to_leader *fdtol;
  376         struct sigacts *newsigacts;
  377 
  378         sx_assert(&proctree_lock, SX_SLOCKED);
  379         sx_assert(&allproc_lock, SX_XLOCKED);
  380 
  381         p2_held = 0;
  382         p1 = td->td_proc;
  383 
  384         /*
  385          * Increment the nprocs resource before blocking can occur.  There
  386          * are hard-limits as to the number of processes that can run.
  387          */
  388         nprocs++;
  389 
  390         trypid = fork_findpid(flags);
  391 
  392         sx_sunlock(&proctree_lock);
  393 
  394         p2->p_state = PRS_NEW;          /* protect against others */
  395         p2->p_pid = trypid;
  396         AUDIT_ARG_PID(p2->p_pid);
  397         LIST_INSERT_HEAD(&allproc, p2, p_list);
  398         LIST_INSERT_HEAD(PIDHASH(p2->p_pid), p2, p_hash);
  399         tidhash_add(td2);
  400         PROC_LOCK(p2);
  401         PROC_LOCK(p1);
  402 
  403         sx_xunlock(&allproc_lock);
  404 
  405         bcopy(&p1->p_startcopy, &p2->p_startcopy,
  406             __rangeof(struct proc, p_startcopy, p_endcopy));
  407         pargs_hold(p2->p_args);
  408         PROC_UNLOCK(p1);
  409 
  410         bzero(&p2->p_startzero,
  411             __rangeof(struct proc, p_startzero, p_endzero));
  412         p2->p_treeflag = 0;
  413 
  414         p2->p_ucred = crhold(td->td_ucred);
  415 
  416         /* Tell the prison that we exist. */
  417         prison_proc_hold(p2->p_ucred->cr_prison);
  418 
  419         PROC_UNLOCK(p2);
  420 
  421         /*
  422          * Malloc things while we don't hold any locks.
  423          */
  424         if (flags & RFSIGSHARE)
  425                 newsigacts = NULL;
  426         else
  427                 newsigacts = sigacts_alloc();
  428 
  429         /*
  430          * Copy filedesc.
  431          */
  432         if (flags & RFCFDG) {
  433                 fd = fdinit(p1->p_fd);
  434                 fdtol = NULL;
  435         } else if (flags & RFFDG) {
  436                 fd = fdcopy(p1->p_fd);
  437                 fdtol = NULL;
  438         } else {
  439                 fd = fdshare(p1->p_fd);
  440                 if (p1->p_fdtol == NULL)
  441                         p1->p_fdtol = filedesc_to_leader_alloc(NULL, NULL,
  442                             p1->p_leader);
  443                 if ((flags & RFTHREAD) != 0) {
  444                         /*
  445                          * Shared file descriptor table, and shared
  446                          * process leaders.
  447                          */
  448                         fdtol = p1->p_fdtol;
  449                         FILEDESC_XLOCK(p1->p_fd);
  450                         fdtol->fdl_refcount++;
  451                         FILEDESC_XUNLOCK(p1->p_fd);
  452                 } else {
  453                         /* 
  454                          * Shared file descriptor table, and different
  455                          * process leaders.
  456                          */
  457                         fdtol = filedesc_to_leader_alloc(p1->p_fdtol,
  458                             p1->p_fd, p2);
  459                 }
  460         }
  461         /*
  462          * Make a proc table entry for the new process.
  463          * Start by zeroing the section of proc that is zero-initialized,
  464          * then copy the section that is copied directly from the parent.
  465          */
  466 
  467         PROC_LOCK(p2);
  468         PROC_LOCK(p1);
  469 
  470         bzero(&td2->td_startzero,
  471             __rangeof(struct thread, td_startzero, td_endzero));
  472 
  473         bcopy(&td->td_startcopy, &td2->td_startcopy,
  474             __rangeof(struct thread, td_startcopy, td_endcopy));
  475 
  476         bcopy(&p2->p_comm, &td2->td_name, sizeof(td2->td_name));
  477         td2->td_sigstk = td->td_sigstk;
  478         td2->td_sigmask = td->td_sigmask;
  479         td2->td_flags = TDF_INMEM;
  480         td2->td_lend_user_pri = PRI_MAX;
  481         td2->td_dbg_sc_code = td->td_dbg_sc_code;
  482         td2->td_dbg_sc_narg = td->td_dbg_sc_narg;
  483 
  484 #ifdef VIMAGE
  485         td2->td_vnet = NULL;
  486         td2->td_vnet_lpush = NULL;
  487 #endif
  488 
  489         /*
  490          * Allow the scheduler to initialize the child.
  491          */
  492         thread_lock(td);
  493         sched_fork(td, td2);
  494         thread_unlock(td);
  495 
  496         /*
  497          * Duplicate sub-structures as needed.
  498          * Increase reference counts on shared objects.
  499          */
  500         p2->p_flag = P_INMEM;
  501         p2->p_flag2 = 0;
  502         p2->p_swtick = ticks;
  503         if (p1->p_flag & P_PROFIL)
  504                 startprofclock(p2);
  505         td2->td_ucred = crhold(p2->p_ucred);
  506 
  507         if (flags & RFSIGSHARE) {
  508                 p2->p_sigacts = sigacts_hold(p1->p_sigacts);
  509         } else {
  510                 sigacts_copy(newsigacts, p1->p_sigacts);
  511                 p2->p_sigacts = newsigacts;
  512         }
  513 
  514         if (flags & RFTSIGZMB)
  515                 p2->p_sigparent = RFTSIGNUM(flags);
  516         else if (flags & RFLINUXTHPN)
  517                 p2->p_sigparent = SIGUSR1;
  518         else
  519                 p2->p_sigparent = SIGCHLD;
  520 
  521         p2->p_textvp = p1->p_textvp;
  522         p2->p_fd = fd;
  523         p2->p_fdtol = fdtol;
  524 
  525         if (p1->p_flag2 & P2_INHERIT_PROTECTED) {
  526                 p2->p_flag |= P_PROTECTED;
  527                 p2->p_flag2 |= P2_INHERIT_PROTECTED;
  528         }
  529 
  530         /*
  531          * p_limit is copy-on-write.  Bump its refcount.
  532          */
  533         lim_fork(p1, p2);
  534 
  535         pstats_fork(p1->p_stats, p2->p_stats);
  536 
  537         PROC_UNLOCK(p1);
  538         PROC_UNLOCK(p2);
  539 
  540         /* Bump references to the text vnode (for procfs). */
  541         if (p2->p_textvp)
  542                 vref(p2->p_textvp);
  543 
  544         /*
  545          * Set up linkage for kernel based threading.
  546          */
  547         if ((flags & RFTHREAD) != 0) {
  548                 mtx_lock(&ppeers_lock);
  549                 p2->p_peers = p1->p_peers;
  550                 p1->p_peers = p2;
  551                 p2->p_leader = p1->p_leader;
  552                 mtx_unlock(&ppeers_lock);
  553                 PROC_LOCK(p1->p_leader);
  554                 if ((p1->p_leader->p_flag & P_WEXIT) != 0) {
  555                         PROC_UNLOCK(p1->p_leader);
  556                         /*
  557                          * The task leader is exiting, so process p1 is
  558                          * going to be killed shortly.  Since p1 obviously
  559                          * isn't dead yet, we know that the leader is either
  560                          * sending SIGKILL's to all the processes in this
  561                          * task or is sleeping waiting for all the peers to
  562                          * exit.  We let p1 complete the fork, but we need
  563                          * to go ahead and kill the new process p2 since
  564                          * the task leader may not get a chance to send
  565                          * SIGKILL to it.  We leave it on the list so that
  566                          * the task leader will wait for this new process
  567                          * to commit suicide.
  568                          */
  569                         PROC_LOCK(p2);
  570                         kern_psignal(p2, SIGKILL);
  571                         PROC_UNLOCK(p2);
  572                 } else
  573                         PROC_UNLOCK(p1->p_leader);
  574         } else {
  575                 p2->p_peers = NULL;
  576                 p2->p_leader = p2;
  577         }
  578 
  579         sx_xlock(&proctree_lock);
  580         PGRP_LOCK(p1->p_pgrp);
  581         PROC_LOCK(p2);
  582         PROC_LOCK(p1);
  583 
  584         /*
  585          * Preserve some more flags in subprocess.  P_PROFIL has already
  586          * been preserved.
  587          */
  588         p2->p_flag |= p1->p_flag & P_SUGID;
  589         td2->td_pflags |= td->td_pflags & TDP_ALTSTACK;
  590         SESS_LOCK(p1->p_session);
  591         if (p1->p_session->s_ttyvp != NULL && p1->p_flag & P_CONTROLT)
  592                 p2->p_flag |= P_CONTROLT;
  593         SESS_UNLOCK(p1->p_session);
  594         if (flags & RFPPWAIT)
  595                 p2->p_flag |= P_PPWAIT;
  596 
  597         p2->p_pgrp = p1->p_pgrp;
  598         LIST_INSERT_AFTER(p1, p2, p_pglist);
  599         PGRP_UNLOCK(p1->p_pgrp);
  600         LIST_INIT(&p2->p_children);
  601         LIST_INIT(&p2->p_orphans);
  602 
  603         callout_init_mtx(&p2->p_itcallout, &p2->p_mtx, 0);
  604 
  605         /*
  606          * If PF_FORK is set, the child process inherits the
  607          * procfs ioctl flags from its parent.
  608          */
  609         if (p1->p_pfsflags & PF_FORK) {
  610                 p2->p_stops = p1->p_stops;
  611                 p2->p_pfsflags = p1->p_pfsflags;
  612         }
  613 
  614         /*
  615          * This begins the section where we must prevent the parent
  616          * from being swapped.
  617          */
  618         _PHOLD(p1);
  619         PROC_UNLOCK(p1);
  620 
  621         /*
  622          * Attach the new process to its parent.
  623          *
  624          * If RFNOWAIT is set, the newly created process becomes a child
  625          * of init.  This effectively disassociates the child from the
  626          * parent.
  627          */
  628         if (flags & RFNOWAIT)
  629                 pptr = initproc;
  630         else
  631                 pptr = p1;
  632         p2->p_pptr = pptr;
  633         LIST_INSERT_HEAD(&pptr->p_children, p2, p_sibling);
  634         sx_xunlock(&proctree_lock);
  635 
  636         /* Inform accounting that we have forked. */
  637         p2->p_acflag = AFORK;
  638         PROC_UNLOCK(p2);
  639 
  640 #ifdef KTRACE
  641         ktrprocfork(p1, p2);
  642 #endif
  643 
  644         /*
  645          * Finish creating the child process.  It will return via a different
  646          * execution path later.  (ie: directly into user mode)
  647          */
  648         vm_forkproc(td, p2, td2, vm2, flags);
  649 
  650         if (flags == (RFFDG | RFPROC)) {
  651                 PCPU_INC(cnt.v_forks);
  652                 PCPU_ADD(cnt.v_forkpages, p2->p_vmspace->vm_dsize +
  653                     p2->p_vmspace->vm_ssize);
  654         } else if (flags == (RFFDG | RFPROC | RFPPWAIT | RFMEM)) {
  655                 PCPU_INC(cnt.v_vforks);
  656                 PCPU_ADD(cnt.v_vforkpages, p2->p_vmspace->vm_dsize +
  657                     p2->p_vmspace->vm_ssize);
  658         } else if (p1 == &proc0) {
  659                 PCPU_INC(cnt.v_kthreads);
  660                 PCPU_ADD(cnt.v_kthreadpages, p2->p_vmspace->vm_dsize +
  661                     p2->p_vmspace->vm_ssize);
  662         } else {
  663                 PCPU_INC(cnt.v_rforks);
  664                 PCPU_ADD(cnt.v_rforkpages, p2->p_vmspace->vm_dsize +
  665                     p2->p_vmspace->vm_ssize);
  666         }
  667 
  668 #ifdef PROCDESC
  669         /*
  670          * Associate the process descriptor with the process before anything
  671          * can happen that might cause that process to need the descriptor.
  672          * However, don't do this until after fork(2) can no longer fail.
  673          */
  674         if (flags & RFPROCDESC)
  675                 procdesc_new(p2, pdflags);
  676 #endif
  677 
  678         /*
  679          * Both processes are set up, now check if any loadable modules want
  680          * to adjust anything.
  681          */
  682         EVENTHANDLER_INVOKE(process_fork, p1, p2, flags);
  683 
  684         /*
  685          * Set the child start time and mark the process as being complete.
  686          */
  687         PROC_LOCK(p2);
  688         PROC_LOCK(p1);
  689         microuptime(&p2->p_stats->p_start);
  690         PROC_SLOCK(p2);
  691         p2->p_state = PRS_NORMAL;
  692         PROC_SUNLOCK(p2);
  693 
  694 #ifdef KDTRACE_HOOKS
  695         /*
  696          * Tell the DTrace fasttrap provider about the new process so that any
  697          * tracepoints inherited from the parent can be removed. We have to do
  698          * this only after p_state is PRS_NORMAL since the fasttrap module will
  699          * use pfind() later on.
  700          */
  701         if ((flags & RFMEM) == 0 && dtrace_fasttrap_fork)
  702                 dtrace_fasttrap_fork(p1, p2);
  703 #endif
  704         if ((p1->p_flag & (P_TRACED | P_FOLLOWFORK)) == (P_TRACED |
  705             P_FOLLOWFORK)) {
  706                 /*
  707                  * Arrange for debugger to receive the fork event.
  708                  *
  709                  * We can report PL_FLAG_FORKED regardless of
  710                  * P_FOLLOWFORK settings, but it does not make a sense
  711                  * for runaway child.
  712                  */
  713                 td->td_dbgflags |= TDB_FORK;
  714                 td->td_dbg_forked = p2->p_pid;
  715                 td2->td_dbgflags |= TDB_STOPATFORK;
  716                 _PHOLD(p2);
  717                 p2_held = 1;
  718         }
  719         if (flags & RFPPWAIT) {
  720                 td->td_pflags |= TDP_RFPPWAIT;
  721                 td->td_rfppwait_p = p2;
  722         }
  723         PROC_UNLOCK(p2);
  724         if ((flags & RFSTOPPED) == 0) {
  725                 /*
  726                  * If RFSTOPPED not requested, make child runnable and
  727                  * add to run queue.
  728                  */
  729                 thread_lock(td2);
  730                 TD_SET_CAN_RUN(td2);
  731                 sched_add(td2, SRQ_BORING);
  732                 thread_unlock(td2);
  733         }
  734 
  735         /*
  736          * Now can be swapped.
  737          */
  738         _PRELE(p1);
  739         PROC_UNLOCK(p1);
  740 
  741         /*
  742          * Tell any interested parties about the new process.
  743          */
  744         knote_fork(&p1->p_klist, p2->p_pid);
  745         SDT_PROBE3(proc, kernel, , create, p2, p1, flags);
  746 
  747         /*
  748          * Wait until debugger is attached to child.
  749          */
  750         PROC_LOCK(p2);
  751         while ((td2->td_dbgflags & TDB_STOPATFORK) != 0)
  752                 cv_wait(&p2->p_dbgwait, &p2->p_mtx);
  753         if (p2_held)
  754                 _PRELE(p2);
  755         PROC_UNLOCK(p2);
  756 }
  757 
  758 int
  759 fork1(struct thread *td, int flags, int pages, struct proc **procp,
  760     int *procdescp, int pdflags)
  761 {
  762         struct proc *p1;
  763         struct proc *newproc;
  764         int ok;
  765         struct thread *td2;
  766         struct vmspace *vm2;
  767         vm_ooffset_t mem_charged;
  768         int error;
  769         static int curfail;
  770         static struct timeval lastfail;
  771 #ifdef PROCDESC
  772         struct file *fp_procdesc = NULL;
  773 #endif
  774 
  775         /* Check for the undefined or unimplemented flags. */
  776         if ((flags & ~(RFFLAGS | RFTSIGFLAGS(RFTSIGMASK))) != 0)
  777                 return (EINVAL);
  778 
  779         /* Signal value requires RFTSIGZMB. */
  780         if ((flags & RFTSIGFLAGS(RFTSIGMASK)) != 0 && (flags & RFTSIGZMB) == 0)
  781                 return (EINVAL);
  782 
  783         /* Can't copy and clear. */
  784         if ((flags & (RFFDG|RFCFDG)) == (RFFDG|RFCFDG))
  785                 return (EINVAL);
  786 
  787         /* Check the validity of the signal number. */
  788         if ((flags & RFTSIGZMB) != 0 && (u_int)RFTSIGNUM(flags) > _SIG_MAXSIG)
  789                 return (EINVAL);
  790 
  791 #ifdef PROCDESC
  792         if ((flags & RFPROCDESC) != 0) {
  793                 /* Can't not create a process yet get a process descriptor. */
  794                 if ((flags & RFPROC) == 0)
  795                         return (EINVAL);
  796 
  797                 /* Must provide a place to put a procdesc if creating one. */
  798                 if (procdescp == NULL)
  799                         return (EINVAL);
  800         }
  801 #endif
  802 
  803         p1 = td->td_proc;
  804 
  805         /*
  806          * Here we don't create a new process, but we divorce
  807          * certain parts of a process from itself.
  808          */
  809         if ((flags & RFPROC) == 0) {
  810                 *procp = NULL;
  811                 return (fork_norfproc(td, flags));
  812         }
  813 
  814 #ifdef PROCDESC
  815         /*
  816          * If required, create a process descriptor in the parent first; we
  817          * will abandon it if something goes wrong. We don't finit() until
  818          * later.
  819          */
  820         if (flags & RFPROCDESC) {
  821                 error = falloc(td, &fp_procdesc, procdescp, 0);
  822                 if (error != 0)
  823                         return (error);
  824         }
  825 #endif
  826 
  827         mem_charged = 0;
  828         vm2 = NULL;
  829         if (pages == 0)
  830                 pages = KSTACK_PAGES;
  831         /* Allocate new proc. */
  832         newproc = uma_zalloc(proc_zone, M_WAITOK);
  833         td2 = FIRST_THREAD_IN_PROC(newproc);
  834         if (td2 == NULL) {
  835                 td2 = thread_alloc(pages);
  836                 if (td2 == NULL) {
  837                         error = ENOMEM;
  838                         goto fail1;
  839                 }
  840                 proc_linkup(newproc, td2);
  841         } else {
  842                 if (td2->td_kstack == 0 || td2->td_kstack_pages != pages) {
  843                         if (td2->td_kstack != 0)
  844                                 vm_thread_dispose(td2);
  845                         if (!thread_alloc_stack(td2, pages)) {
  846                                 error = ENOMEM;
  847                                 goto fail1;
  848                         }
  849                 }
  850         }
  851 
  852         if ((flags & RFMEM) == 0) {
  853                 vm2 = vmspace_fork(p1->p_vmspace, &mem_charged);
  854                 if (vm2 == NULL) {
  855                         error = ENOMEM;
  856                         goto fail1;
  857                 }
  858                 if (!swap_reserve(mem_charged)) {
  859                         /*
  860                          * The swap reservation failed. The accounting
  861                          * from the entries of the copied vm2 will be
  862                          * substracted in vmspace_free(), so force the
  863                          * reservation there.
  864                          */
  865                         swap_reserve_force(mem_charged);
  866                         error = ENOMEM;
  867                         goto fail1;
  868                 }
  869         } else
  870                 vm2 = NULL;
  871 
  872         /*
  873          * XXX: This is ugly; when we copy resource usage, we need to bump
  874          *      per-cred resource counters.
  875          */
  876         newproc->p_ucred = p1->p_ucred;
  877 
  878         /*
  879          * Initialize resource accounting for the child process.
  880          */
  881         error = racct_proc_fork(p1, newproc);
  882         if (error != 0) {
  883                 error = EAGAIN;
  884                 goto fail1;
  885         }
  886 
  887 #ifdef MAC
  888         mac_proc_init(newproc);
  889 #endif
  890         knlist_init_mtx(&newproc->p_klist, &newproc->p_mtx);
  891         STAILQ_INIT(&newproc->p_ktr);
  892 
  893         /* We have to lock the process tree while we look for a pid. */
  894         sx_slock(&proctree_lock);
  895 
  896         /*
  897          * Although process entries are dynamically created, we still keep
  898          * a global limit on the maximum number we will create.  Don't allow
  899          * a nonprivileged user to use the last ten processes; don't let root
  900          * exceed the limit. The variable nprocs is the current number of
  901          * processes, maxproc is the limit.
  902          */
  903         sx_xlock(&allproc_lock);
  904         if ((nprocs >= maxproc - 10 && priv_check_cred(td->td_ucred,
  905             PRIV_MAXPROC, 0) != 0) || nprocs >= maxproc) {
  906                 error = EAGAIN;
  907                 goto fail;
  908         }
  909 
  910         /*
  911          * Increment the count of procs running with this uid. Don't allow
  912          * a nonprivileged user to exceed their current limit.
  913          *
  914          * XXXRW: Can we avoid privilege here if it's not needed?
  915          */
  916         error = priv_check_cred(td->td_ucred, PRIV_PROC_LIMIT, 0);
  917         if (error == 0)
  918                 ok = chgproccnt(td->td_ucred->cr_ruidinfo, 1, 0);
  919         else {
  920                 PROC_LOCK(p1);
  921                 ok = chgproccnt(td->td_ucred->cr_ruidinfo, 1,
  922                     lim_cur(p1, RLIMIT_NPROC));
  923                 PROC_UNLOCK(p1);
  924         }
  925         if (ok) {
  926                 do_fork(td, flags, newproc, td2, vm2, pdflags);
  927 
  928                 /*
  929                  * Return child proc pointer to parent.
  930                  */
  931                 *procp = newproc;
  932 #ifdef PROCDESC
  933                 if (flags & RFPROCDESC)
  934                         procdesc_finit(newproc->p_procdesc, fp_procdesc);
  935 #endif
  936                 racct_proc_fork_done(newproc);
  937                 return (0);
  938         }
  939 
  940         error = EAGAIN;
  941 fail:
  942         sx_sunlock(&proctree_lock);
  943         if (ppsratecheck(&lastfail, &curfail, 1))
  944                 printf("maxproc limit exceeded by uid %u (pid %d); see tuning(7) and login.conf(5)\n",
  945                     td->td_ucred->cr_ruid, p1->p_pid);
  946         sx_xunlock(&allproc_lock);
  947 #ifdef MAC
  948         mac_proc_destroy(newproc);
  949 #endif
  950         racct_proc_exit(newproc);
  951 fail1:
  952         if (vm2 != NULL)
  953                 vmspace_free(vm2);
  954         uma_zfree(proc_zone, newproc);
  955 #ifdef PROCDESC
  956         if (((flags & RFPROCDESC) != 0) && (fp_procdesc != NULL))
  957                 fdrop(fp_procdesc, td);
  958 #endif
  959         pause("fork", hz / 2);
  960         return (error);
  961 }
  962 
  963 /*
  964  * Handle the return of a child process from fork1().  This function
  965  * is called from the MD fork_trampoline() entry point.
  966  */
  967 void
  968 fork_exit(void (*callout)(void *, struct trapframe *), void *arg,
  969     struct trapframe *frame)
  970 {
  971         struct proc *p;
  972         struct thread *td;
  973         struct thread *dtd;
  974 
  975         td = curthread;
  976         p = td->td_proc;
  977         KASSERT(p->p_state == PRS_NORMAL, ("executing process is still new"));
  978 
  979         CTR4(KTR_PROC, "fork_exit: new thread %p (td_sched %p, pid %d, %s)",
  980                 td, td->td_sched, p->p_pid, td->td_name);
  981 
  982         sched_fork_exit(td);
  983         /*
  984         * Processes normally resume in mi_switch() after being
  985         * cpu_switch()'ed to, but when children start up they arrive here
  986         * instead, so we must do much the same things as mi_switch() would.
  987         */
  988         if ((dtd = PCPU_GET(deadthread))) {
  989                 PCPU_SET(deadthread, NULL);
  990                 thread_stash(dtd);
  991         }
  992         thread_unlock(td);
  993 
  994         /*
  995          * cpu_set_fork_handler intercepts this function call to
  996          * have this call a non-return function to stay in kernel mode.
  997          * initproc has its own fork handler, but it does return.
  998          */
  999         KASSERT(callout != NULL, ("NULL callout in fork_exit"));
 1000         callout(arg, frame);
 1001 
 1002         /*
 1003          * Check if a kernel thread misbehaved and returned from its main
 1004          * function.
 1005          */
 1006         if (p->p_flag & P_KTHREAD) {
 1007                 printf("Kernel thread \"%s\" (pid %d) exited prematurely.\n",
 1008                     td->td_name, p->p_pid);
 1009                 kthread_exit();
 1010         }
 1011         mtx_assert(&Giant, MA_NOTOWNED);
 1012 
 1013         if (p->p_sysent->sv_schedtail != NULL)
 1014                 (p->p_sysent->sv_schedtail)(td);
 1015 }
 1016 
 1017 /*
 1018  * Simplified back end of syscall(), used when returning from fork()
 1019  * directly into user mode.  Giant is not held on entry, and must not
 1020  * be held on return.  This function is passed in to fork_exit() as the
 1021  * first parameter and is called when returning to a new userland process.
 1022  */
 1023 void
 1024 fork_return(struct thread *td, struct trapframe *frame)
 1025 {
 1026         struct proc *p, *dbg;
 1027 
 1028         p = td->td_proc;
 1029         if (td->td_dbgflags & TDB_STOPATFORK) {
 1030                 sx_xlock(&proctree_lock);
 1031                 PROC_LOCK(p);
 1032                 if ((p->p_pptr->p_flag & (P_TRACED | P_FOLLOWFORK)) ==
 1033                     (P_TRACED | P_FOLLOWFORK)) {
 1034                         /*
 1035                          * If debugger still wants auto-attach for the
 1036                          * parent's children, do it now.
 1037                          */
 1038                         dbg = p->p_pptr->p_pptr;
 1039                         p->p_flag |= P_TRACED;
 1040                         p->p_oppid = p->p_pptr->p_pid;
 1041                         CTR2(KTR_PTRACE,
 1042                     "fork_return: attaching to new child pid %d: oppid %d",
 1043                             p->p_pid, p->p_oppid);
 1044                         proc_reparent(p, dbg);
 1045                         sx_xunlock(&proctree_lock);
 1046                         td->td_dbgflags |= TDB_CHILD | TDB_SCX;
 1047                         ptracestop(td, SIGSTOP);
 1048                         td->td_dbgflags &= ~(TDB_CHILD | TDB_SCX);
 1049                 } else {
 1050                         /*
 1051                          * ... otherwise clear the request.
 1052                          */
 1053                         sx_xunlock(&proctree_lock);
 1054                         td->td_dbgflags &= ~TDB_STOPATFORK;
 1055                         cv_broadcast(&p->p_dbgwait);
 1056                 }
 1057                 PROC_UNLOCK(p);
 1058         } else if (p->p_flag & P_TRACED) {
 1059                 /*
 1060                  * This is the start of a new thread in a traced
 1061                  * process.  Report a system call exit event.
 1062                  */
 1063                 PROC_LOCK(p);
 1064                 td->td_dbgflags |= TDB_SCX;
 1065                 _STOPEVENT(p, S_SCX, td->td_dbg_sc_code);
 1066                 if ((p->p_stops & S_PT_SCX) != 0)
 1067                         ptracestop(td, SIGTRAP);
 1068                 td->td_dbgflags &= ~TDB_SCX;
 1069                 PROC_UNLOCK(p);
 1070         }
 1071 
 1072         userret(td, frame);
 1073 
 1074 #ifdef KTRACE
 1075         if (KTRPOINT(td, KTR_SYSRET))
 1076                 ktrsysret(SYS_fork, 0, 0);
 1077 #endif
 1078         mtx_assert(&Giant, MA_NOTOWNED);
 1079 }
Cache object: c5174f55c53b29f20dddf91a3a13d661
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FreeBSD/Linux Kernel Cross Reference sys/kern/kern_fork.c

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