sys/kern/kern_fork.c

root/sys/kern/kern_fork.c
/*-
 * SPDX-License-Identifier: BSD-3-Clause
 *
 * Copyright (c) 1982, 1986, 1989, 1991, 1993
 *      The Regents of the University of California.  All rights reserved.
 * (c) UNIX System Laboratories, Inc.
 * All or some portions of this file are derived from material licensed
 * to the University of California by American Telephone and Telegraph
 * Co. or Unix System Laboratories, Inc. and are reproduced herein with
 * the permission of UNIX System Laboratories, Inc.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#include "opt_ktrace.h"
#include "opt_kstack_pages.h"

#define EXTERR_CATEGORY EXTERR_CAT_FORK
#include <sys/systm.h>
#include <sys/acct.h>
#include <sys/bitstring.h>
#include <sys/eventhandler.h>
#include <sys/exterrvar.h>
#include <sys/fcntl.h>
#include <sys/filedesc.h>
#include <sys/jail.h>
#include <sys/kernel.h>
#include <sys/kthread.h>
#include <sys/ktr.h>
#include <sys/ktrace.h>
#include <sys/sysctl.h>
#include <sys/lock.h>
#include <sys/malloc.h>
#include <sys/msan.h>
#include <sys/mutex.h>
#include <sys/priv.h>
#include <sys/proc.h>
#include <sys/procdesc.h>
#include <sys/ptrace.h>
#include <sys/racct.h>
#include <sys/resourcevar.h>
#include <sys/sched.h>
#include <sys/sdt.h>
#include <sys/signalvar.h>
#include <sys/sx.h>
#include <sys/syscall.h>
#include <sys/syscallsubr.h>
#include <sys/sysent.h>
#include <sys/sysproto.h>
#include <sys/vmmeter.h>
#include <sys/vnode.h>
#include <sys/unistd.h>

#include <security/audit/audit.h>
#include <security/mac/mac_framework.h>

#include <vm/vm.h>
#include <vm/pmap.h>
#include <vm/vm_map.h>
#include <vm/vm_extern.h>
#include <vm/uma.h>

#ifdef KDTRACE_HOOKS
#include <sys/dtrace_bsd.h>
dtrace_fork_func_t      dtrace_fasttrap_fork;
#endif

SDT_PROVIDER_DECLARE(proc);
SDT_PROBE_DEFINE3(proc, , , create, "struct proc *", "struct proc *", "int");

#ifndef _SYS_SYSPROTO_H_
struct fork_args {
        int     dummy;
};
#endif

/* ARGSUSED */
int
sys_fork(struct thread *td, struct fork_args *uap)
{
        struct fork_req fr;
        int error, pid;

        bzero(&fr, sizeof(fr));
        fr.fr_flags = RFFDG | RFPROC;
        fr.fr_pidp = &pid;
        error = fork1(td, &fr);
        if (error == 0) {
                td->td_retval[0] = pid;
                td->td_retval[1] = 0;
        }
        return (error);
}

/* ARGUSED */
int
sys_pdfork(struct thread *td, struct pdfork_args *uap)
{
        struct fork_req fr;
        int error, fd, pid;

        bzero(&fr, sizeof(fr));
        fr.fr_flags = RFFDG | RFPROC | RFPROCDESC;
        fr.fr_pidp = &pid;
        fr.fr_pd_fd = &fd;
        fr.fr_pd_flags = uap->flags;
        AUDIT_ARG_FFLAGS(uap->flags);
        /*
         * It is necessary to return fd by reference because 0 is a valid file
         * descriptor number, and the child needs to be able to distinguish
         * itself from the parent using the return value.
         */
        error = fork1(td, &fr);
        if (error == 0) {
                td->td_retval[0] = pid;
                td->td_retval[1] = 0;
                error = copyout(&fd, uap->fdp, sizeof(fd));
        }
        return (error);
}

/* ARGSUSED */
int
sys_vfork(struct thread *td, struct vfork_args *uap)
{
        struct fork_req fr;
        int error, pid;

        bzero(&fr, sizeof(fr));
        fr.fr_flags = RFFDG | RFPROC | RFPPWAIT | RFMEM;
        fr.fr_pidp = &pid;
        error = fork1(td, &fr);
        if (error == 0) {
                td->td_retval[0] = pid;
                td->td_retval[1] = 0;
        }
        return (error);
}

int
sys_rfork(struct thread *td, struct rfork_args *uap)
{
        struct fork_req fr;
        int error, pid;

        /* Don't allow kernel-only flags. */
        if ((uap->flags & RFKERNELONLY) != 0)
                return (EXTERROR(EINVAL, "Kernel-only flags %#jx", uap->flags));
        /* RFSPAWN must not appear with others */
        if ((uap->flags & RFSPAWN) != 0 && uap->flags != RFSPAWN)
                return (EXTERROR(EINVAL, "RFSPAWN must be the only flag %#jx",
                    uap->flags));

        AUDIT_ARG_FFLAGS(uap->flags);
        bzero(&fr, sizeof(fr));
        if ((uap->flags & RFSPAWN) != 0) {
                fr.fr_flags = RFFDG | RFPROC | RFPPWAIT | RFMEM;
                fr.fr_flags2 = FR2_DROPSIG_CAUGHT;
        } else {
                fr.fr_flags = uap->flags;
        }
        fr.fr_pidp = &pid;
        error = fork1(td, &fr);
        if (error == 0) {
                td->td_retval[0] = pid;
                td->td_retval[1] = 0;
        }
        return (error);
}

int
sys_pdrfork(struct thread *td, struct pdrfork_args *uap)
{
        struct fork_req fr;
        int error, fd, pid;

        bzero(&fr, sizeof(fr));
        fd = -1;

        AUDIT_ARG_FFLAGS(uap->pdflags);
        AUDIT_ARG_CMD(uap->rfflags);

        if ((uap->rfflags & (RFSTOPPED | RFHIGHPID)) != 0)
                return (EXTERROR(EINVAL,
                    "Kernel-only flags %#jx", uap->rfflags));

        /* RFSPAWN must not appear with others */
        if ((uap->rfflags & RFSPAWN) != 0) {
                if (uap->rfflags != RFSPAWN)
                        return (EXTERROR(EINVAL,
                            "RFSPAWN must be the only flag %#jx",
                            uap->rfflags));
                fr.fr_flags = RFFDG | RFPROC | RFPPWAIT | RFMEM | RFPROCDESC;
                fr.fr_flags2 = FR2_DROPSIG_CAUGHT;
        } else {
                if ((uap->rfflags & (RFPROC | RFPROCDESC)) !=
                    (RFPROC | RFPROCDESC)) {
                        return (EXTERROR(EINVAL,
                            "RFPROC|RFPROCDESC required %#jx", uap->rfflags));
                }
                fr.fr_flags = uap->rfflags;
        }

        fr.fr_pidp = &pid;
        fr.fr_pd_fd = &fd;
        fr.fr_pd_flags = uap->pdflags;
        error = fork1(td, &fr);
        if (error == 0) {
                td->td_retval[0] = pid;
                td->td_retval[1] = 0;
                if ((fr.fr_flags & (RFPROC | RFPROCDESC)) ==
                    (RFPROC | RFPROCDESC) || uap->rfflags == RFSPAWN)
                        error = copyout(&fd, uap->fdp, sizeof(fd));
        }
        return (error);
}

int __exclusive_cache_line      nprocs = 1;             /* process 0 */
int     lastpid = 0;
SYSCTL_INT(_kern, OID_AUTO, lastpid, CTLFLAG_RD, &lastpid, 0,
    "Last used PID");

/*
 * Random component to lastpid generation.  We mix in a random factor to make
 * it a little harder to predict.  We sanity check the modulus value to avoid
 * doing it in critical paths.  Don't let it be too small or we pointlessly
 * waste randomness entropy, and don't let it be impossibly large.  Using a
 * modulus that is too big causes a LOT more process table scans and slows
 * down fork processing as the pidchecked caching is defeated.
 */
static int randompid = 0;

static int
sysctl_kern_randompid(SYSCTL_HANDLER_ARGS)
{
        int error, pid;

        error = sysctl_wire_old_buffer(req, sizeof(int));
        if (error != 0)
                return(error);
        sx_xlock(&allproc_lock);
        pid = randompid;
        error = sysctl_handle_int(oidp, &pid, 0, req);
        if (error == 0 && req->newptr != NULL) {
                if (pid == 0)
                        randompid = 0;
                else if (pid == 1)
                        /* generate a random PID modulus between 100 and 1123 */
                        randompid = 100 + arc4random() % 1024;
                else if (pid < 0 || pid > pid_max - 100)
                        /* out of range */
                        randompid = pid_max - 100;
                else if (pid < 100)
                        /* Make it reasonable */
                        randompid = 100;
                else
                        randompid = pid;
        }
        sx_xunlock(&allproc_lock);
        return (error);
}

SYSCTL_PROC(_kern, OID_AUTO, randompid,
    CTLTYPE_INT | CTLFLAG_RW | CTLFLAG_MPSAFE, 0, 0,
    sysctl_kern_randompid, "I",
    "Random PID modulus. Special values: 0: disable, 1: choose random value");

extern bitstr_t proc_id_pidmap;
extern bitstr_t proc_id_grpidmap;
extern bitstr_t proc_id_sessidmap;
extern bitstr_t proc_id_reapmap;

/*
 * Find an unused process ID
 *
 * If RFHIGHPID is set (used during system boot), do not allocate
 * low-numbered pids.
 */
static int
fork_findpid(int flags)
{
        pid_t result;
        int trypid, random;

        /*
         * Avoid calling arc4random with procid_lock held.
         */
        random = 0;
        if (__predict_false(randompid))
                random = arc4random() % randompid;

        mtx_lock(&procid_lock);

        trypid = lastpid + 1;
        if (flags & RFHIGHPID) {
                if (trypid < 10)
                        trypid = 10;
        } else {
                trypid += random;
        }
retry:
        if (trypid >= pid_max)
                trypid = 2;

        bit_ffc_at(&proc_id_pidmap, trypid, pid_max, &result);
        if (result == -1) {
                KASSERT(trypid != 2, ("unexpectedly ran out of IDs"));
                trypid = 2;
                goto retry;
        }
        if (bit_test(&proc_id_grpidmap, result) ||
            bit_test(&proc_id_sessidmap, result) ||
            bit_test(&proc_id_reapmap, result)) {
                trypid = result + 1;
                goto retry;
        }

        /*
         * RFHIGHPID does not mess with the lastpid counter during boot.
         */
        if ((flags & RFHIGHPID) == 0)
                lastpid = result;

        bit_set(&proc_id_pidmap, result);
        mtx_unlock(&procid_lock);

        return (result);
}

static int
fork_norfproc(struct thread *td, int flags)
{
        struct proc *p1;
        int error;

        KASSERT((flags & RFPROC) == 0,
            ("fork_norfproc called with RFPROC set"));
        p1 = td->td_proc;

        /*
         * Quiesce other threads if necessary.  If RFMEM is not specified we
         * must ensure that other threads do not concurrently create a second
         * process sharing the vmspace, see vmspace_unshare().
         */
        if ((p1->p_flag & (P_HADTHREADS | P_SYSTEM)) == P_HADTHREADS &&
            ((flags & (RFCFDG | RFFDG)) != 0 || (flags & RFMEM) == 0)) {
                PROC_LOCK(p1);
                if (thread_single(p1, SINGLE_BOUNDARY)) {
                        PROC_UNLOCK(p1);
                        return (ERESTART);
                }
                PROC_UNLOCK(p1);
        }

        error = vm_forkproc(td, NULL, NULL, NULL, flags);
        if (error != 0)
                goto fail;

        /*
         * Close all file descriptors.
         */
        if ((flags & RFCFDG) != 0) {
                struct filedesc *fdtmp;
                struct pwddesc *pdtmp;

                pdtmp = pdinit(td->td_proc->p_pd, false);
                fdtmp = fdinit();
                pdescfree(td);
                fdescfree(td);
                p1->p_fd = fdtmp;
                p1->p_pd = pdtmp;
        }

        /*
         * Unshare file descriptors (from parent).
         */
        if ((flags & RFFDG) != 0) {
                fdunshare(td);
                pdunshare(td);
        }

fail:
        if ((p1->p_flag & (P_HADTHREADS | P_SYSTEM)) == P_HADTHREADS &&
            ((flags & (RFCFDG | RFFDG)) != 0 || (flags & RFMEM) == 0)) {
                PROC_LOCK(p1);
                thread_single_end(p1, SINGLE_BOUNDARY);
                PROC_UNLOCK(p1);
        }
        return (error);
}

static void
do_fork(struct thread *td, struct fork_req *fr, struct proc *p2, struct thread *td2,
    struct vmspace *vm2, struct file *fp_procdesc)
{
        struct proc *p1, *pptr;
        struct filedesc *fd;
        struct filedesc_to_leader *fdtol;
        struct pwddesc *pd;
        struct sigacts *newsigacts;

        p1 = td->td_proc;

        PROC_LOCK(p1);
        bcopy(&p1->p_startcopy, &p2->p_startcopy,
            __rangeof(struct proc, p_startcopy, p_endcopy));
        pargs_hold(p2->p_args);
        PROC_UNLOCK(p1);

        bzero(&p2->p_startzero,
            __rangeof(struct proc, p_startzero, p_endzero));

        /* Tell the prison that we exist. */
        prison_proc_hold(p2->p_ucred->cr_prison);

        p2->p_state = PRS_NEW;          /* protect against others */
        p2->p_pid = fork_findpid(fr->fr_flags);
        AUDIT_ARG_PID(p2->p_pid);
        TSFORK(p2->p_pid, p1->p_pid);

        sx_xlock(&allproc_lock);
        LIST_INSERT_HEAD(&allproc, p2, p_list);
        allproc_gen++;
        prison_proc_link(p2->p_ucred->cr_prison, p2);
        sx_xunlock(&allproc_lock);

        sx_xlock(PIDHASHLOCK(p2->p_pid));
        LIST_INSERT_HEAD(PIDHASH(p2->p_pid), p2, p_hash);
        sx_xunlock(PIDHASHLOCK(p2->p_pid));

        tidhash_add(td2);

        /*
         * Malloc things while we don't hold any locks.
         */
        if (fr->fr_flags & RFSIGSHARE)
                newsigacts = NULL;
        else
                newsigacts = sigacts_alloc();

        /*
         * Copy filedesc.
         */
        if (fr->fr_flags & RFCFDG) {
                pd = pdinit(p1->p_pd, false);
                fd = fdinit();
                fdtol = NULL;
        } else if (fr->fr_flags & RFFDG) {
                if (fr->fr_flags2 & FR2_SHARE_PATHS)
                        pd = pdshare(p1->p_pd);
                else
                        pd = pdcopy(p1->p_pd);
                fd = fdcopy(p1->p_fd, p2);
                fdtol = NULL;
        } else {
                if (fr->fr_flags2 & FR2_SHARE_PATHS)
                        pd = pdcopy(p1->p_pd);
                else
                        pd = pdshare(p1->p_pd);
                fd = fdshare(p1->p_fd);
                if (p1->p_fdtol == NULL)
                        p1->p_fdtol = filedesc_to_leader_alloc(NULL, NULL,
                            p1->p_leader);
                if ((fr->fr_flags & RFTHREAD) != 0) {
                        /*
                         * Shared file descriptor table, and shared
                         * process leaders.
                         */
                        fdtol = filedesc_to_leader_share(p1->p_fdtol, p1->p_fd);
                } else {
                        /*
                         * Shared file descriptor table, and different
                         * process leaders.
                         */
                        fdtol = filedesc_to_leader_alloc(p1->p_fdtol,
                            p1->p_fd, p2);
                }
        }
        /*
         * Make a proc table entry for the new process.
         * Start by zeroing the section of proc that is zero-initialized,
         * then copy the section that is copied directly from the parent.
         */

        PROC_LOCK(p2);
        PROC_LOCK(p1);

        bzero(&td2->td_startzero,
            __rangeof(struct thread, td_startzero, td_endzero));

        bcopy(&td->td_startcopy, &td2->td_startcopy,
            __rangeof(struct thread, td_startcopy, td_endcopy));

        bcopy(&p2->p_comm, &td2->td_name, sizeof(td2->td_name));
        td2->td_sigstk = td->td_sigstk;
        td2->td_flags = TDF_INMEM;
        td2->td_lend_user_pri = PRI_MAX;

#ifdef VIMAGE
        td2->td_vnet = NULL;
        td2->td_vnet_lpush = NULL;
#endif

        /*
         * Allow the scheduler to initialize the child.
         */
        thread_lock(td);
        sched_fork(td, td2);
        /*
         * Request AST to check for TDP_RFPPWAIT.  Do it here
         * to avoid calling thread_lock() again.
         */
        if ((fr->fr_flags & RFPPWAIT) != 0)
                ast_sched_locked(td, TDA_VFORK);
        thread_unlock(td);

        /*
         * Duplicate sub-structures as needed.
         * Increase reference counts on shared objects.
         */
        p2->p_flag = P_INMEM;
        p2->p_flag2 = p1->p_flag2 & (P2_ASLR_DISABLE | P2_ASLR_ENABLE |
            P2_ASLR_IGNSTART | P2_NOTRACE | P2_NOTRACE_EXEC |
            P2_PROTMAX_ENABLE | P2_PROTMAX_DISABLE | P2_TRAPCAP |
            P2_STKGAP_DISABLE | P2_STKGAP_DISABLE_EXEC | P2_NO_NEW_PRIVS |
            P2_WXORX_DISABLE | P2_WXORX_ENABLE_EXEC | P2_LOGSIGEXIT_CTL |
            P2_LOGSIGEXIT_ENABLE);
        p2->p_swtick = ticks;
        if (p1->p_flag & P_PROFIL)
                startprofclock(p2);

        if (fr->fr_flags & RFSIGSHARE) {
                p2->p_sigacts = sigacts_hold(p1->p_sigacts);
        } else {
                sigacts_copy(newsigacts, p1->p_sigacts);
                p2->p_sigacts = newsigacts;
                if ((fr->fr_flags2 & (FR2_DROPSIG_CAUGHT | FR2_KPROC)) != 0) {
                        mtx_lock(&p2->p_sigacts->ps_mtx);
                        if ((fr->fr_flags2 & FR2_DROPSIG_CAUGHT) != 0)
                                sig_drop_caught(p2);
                        if ((fr->fr_flags2 & FR2_KPROC) != 0)
                                p2->p_sigacts->ps_flag |= PS_NOCLDWAIT;
                        mtx_unlock(&p2->p_sigacts->ps_mtx);
                }
        }

        if (fr->fr_flags & RFTSIGZMB)
                p2->p_sigparent = RFTSIGNUM(fr->fr_flags);
        else if (fr->fr_flags & RFLINUXTHPN)
                p2->p_sigparent = SIGUSR1;
        else
                p2->p_sigparent = SIGCHLD;

        if ((fr->fr_flags2 & FR2_KPROC) != 0) {
                p2->p_flag |= P_SYSTEM | P_KPROC;
                td2->td_pflags |= TDP_KTHREAD;
        }

        p2->p_textvp = p1->p_textvp;
        p2->p_textdvp = p1->p_textdvp;
        p2->p_fd = fd;
        p2->p_fdtol = fdtol;
        p2->p_pd = pd;

        if (p1->p_flag2 & P2_INHERIT_PROTECTED) {
                p2->p_flag |= P_PROTECTED;
                p2->p_flag2 |= P2_INHERIT_PROTECTED;
        }

        /*
         * p_limit is copy-on-write.  Bump its refcount.
         */
        lim_fork(p1, p2);

        thread_cow_get_proc(td2, p2);

        pstats_fork(p1->p_stats, p2->p_stats);

        PROC_UNLOCK(p1);
        PROC_UNLOCK(p2);

        /*
         * Bump references to the text vnode and directory, and copy
         * the hardlink name.
         */
        if (p2->p_textvp != NULL)
                vrefact(p2->p_textvp);
        if (p2->p_textdvp != NULL)
                vrefact(p2->p_textdvp);
        p2->p_binname = p1->p_binname == NULL ? NULL :
            strdup(p1->p_binname, M_PARGS);

        /*
         * Set up linkage for kernel based threading.
         */
        if ((fr->fr_flags & RFTHREAD) != 0) {
                mtx_lock(&ppeers_lock);
                p2->p_peers = p1->p_peers;
                p1->p_peers = p2;
                p2->p_leader = p1->p_leader;
                mtx_unlock(&ppeers_lock);
                PROC_LOCK(p1->p_leader);
                if ((p1->p_leader->p_flag & P_WEXIT) != 0) {
                        PROC_UNLOCK(p1->p_leader);
                        /*
                         * The task leader is exiting, so process p1 is
                         * going to be killed shortly.  Since p1 obviously
                         * isn't dead yet, we know that the leader is either
                         * sending SIGKILL's to all the processes in this
                         * task or is sleeping waiting for all the peers to
                         * exit.  We let p1 complete the fork, but we need
                         * to go ahead and kill the new process p2 since
                         * the task leader may not get a chance to send
                         * SIGKILL to it.  We leave it on the list so that
                         * the task leader will wait for this new process
                         * to commit suicide.
                         */
                        PROC_LOCK(p2);
                        kern_psignal(p2, SIGKILL);
                        PROC_UNLOCK(p2);
                } else
                        PROC_UNLOCK(p1->p_leader);
        } else {
                p2->p_peers = NULL;
                p2->p_leader = p2;
        }

        sx_xlock(&proctree_lock);
        PGRP_LOCK(p1->p_pgrp);
        PROC_LOCK(p2);
        PROC_LOCK(p1);

        /*
         * Preserve some more flags in subprocess.  P_PROFIL has already
         * been preserved.
         */
        p2->p_flag |= p1->p_flag & P_SUGID;
        td2->td_pflags |= td->td_pflags & (TDP_ALTSTACK | TDP_SIGFASTBLOCK);
        td2->td_pflags2 |= td->td_pflags2 & TDP2_UEXTERR;
        if (p1->p_flag & P_CONTROLT) {
                SESS_LOCK(p1->p_session);
                if (p1->p_session->s_ttyvp != NULL)
                        p2->p_flag |= P_CONTROLT;
                SESS_UNLOCK(p1->p_session);
        }
        if (fr->fr_flags & RFPPWAIT)
                p2->p_flag |= P_PPWAIT;

        p2->p_pgrp = p1->p_pgrp;
        LIST_INSERT_AFTER(p1, p2, p_pglist);
        PGRP_UNLOCK(p1->p_pgrp);
        LIST_INIT(&p2->p_children);
        LIST_INIT(&p2->p_orphans);

        callout_init_mtx(&p2->p_itcallout, &p2->p_mtx, 0);

        PROC_UNLOCK(p1);

        /*
         * Attach the new process to its parent.
         *
         * If RFNOWAIT is set, the newly created process becomes a child
         * of init.  This effectively disassociates the child from the
         * parent.
         */
        if ((fr->fr_flags & RFNOWAIT) != 0) {
                pptr = p1->p_reaper;
                p2->p_reaper = pptr;
        } else {
                p2->p_reaper = (p1->p_treeflag & P_TREE_REAPER) != 0 ?
                    p1 : p1->p_reaper;
                pptr = p1;
        }
        p2->p_pptr = pptr;
        p2->p_oppid = pptr->p_pid;
        LIST_INSERT_HEAD(&pptr->p_children, p2, p_sibling);
        LIST_INIT(&p2->p_reaplist);
        LIST_INSERT_HEAD(&p2->p_reaper->p_reaplist, p2, p_reapsibling);
        if (p2->p_reaper == p1 && p1 != initproc) {
                p2->p_reapsubtree = p2->p_pid;
                proc_id_set_cond(PROC_ID_REAP, p2->p_pid);
        } else {
                /*
                 * Explicitly copy this field under the proctree lock, as it
                 * might have changed since the bulk copying of the parent's
                 * fields.
                 */
                p2->p_reapsubtree = p1->p_reapsubtree;
        }
        sx_xunlock(&proctree_lock);

        /* Inform accounting that we have forked. */
        p2->p_acflag = AFORK;
        PROC_UNLOCK(p2);

#ifdef KTRACE
        ktrprocfork(p1, p2);
#endif

        /*
         * Finish creating the child process.  It will return via a different
         * execution path later.  (ie: directly into user mode)
         */
        vm_forkproc(td, p2, td2, vm2, fr->fr_flags);

        if (fr->fr_flags == (RFFDG | RFPROC)) {
                VM_CNT_INC(v_forks);
                VM_CNT_ADD(v_forkpages, p2->p_vmspace->vm_dsize +
                    p2->p_vmspace->vm_ssize);
        } else if (fr->fr_flags == (RFFDG | RFPROC | RFPPWAIT | RFMEM)) {
                VM_CNT_INC(v_vforks);
                VM_CNT_ADD(v_vforkpages, p2->p_vmspace->vm_dsize +
                    p2->p_vmspace->vm_ssize);
        } else if (p1 == &proc0) {
                VM_CNT_INC(v_kthreads);
                VM_CNT_ADD(v_kthreadpages, p2->p_vmspace->vm_dsize +
                    p2->p_vmspace->vm_ssize);
        } else {
                VM_CNT_INC(v_rforks);
                VM_CNT_ADD(v_rforkpages, p2->p_vmspace->vm_dsize +
                    p2->p_vmspace->vm_ssize);
        }

        /*
         * Associate the process descriptor with the process before anything
         * can happen that might cause that process to need the descriptor.
         * However, don't do this until after fork(2) can no longer fail.
         */
        if (fr->fr_flags & RFPROCDESC)
                procdesc_new(p2, fr->fr_pd_flags);

        /*
         * Both processes are set up, now check if any loadable modules want
         * to adjust anything.
         */
        EVENTHANDLER_DIRECT_INVOKE(process_fork, p1, p2, fr->fr_flags);

        /*
         * Set the child start time and mark the process as being complete.
         */
        PROC_LOCK(p2);
        PROC_LOCK(p1);
        microuptime(&p2->p_stats->p_start);
        PROC_SLOCK(p2);
        p2->p_state = PRS_NORMAL;
        PROC_SUNLOCK(p2);

#ifdef KDTRACE_HOOKS
        /*
         * Tell the DTrace fasttrap provider about the new process so that any
         * tracepoints inherited from the parent can be removed. We have to do
         * this only after p_state is PRS_NORMAL since the fasttrap module will
         * use pfind() later on.
         */
        if ((fr->fr_flags & RFMEM) == 0 && dtrace_fasttrap_fork)
                dtrace_fasttrap_fork(p1, p2);
#endif
        if (fr->fr_flags & RFPPWAIT) {
                td->td_pflags |= TDP_RFPPWAIT;
                td->td_rfppwait_p = p2;
                td->td_dbgflags |= TDB_VFORK;
        }
        PROC_UNLOCK(p2);

        /*
         * Tell any interested parties about the new process.
         */
        knote_fork(p1->p_klist, p2->p_pid);

        PROC_UNLOCK(p1);
        SDT_PROBE3(proc, , , create, p2, p1, fr->fr_flags);

        if (fr->fr_flags & RFPROCDESC) {
                procdesc_finit(p2->p_procdesc, fp_procdesc);
                fdrop(fp_procdesc, td);
        }

        /*
         * Speculative check for PTRACE_FORK. PTRACE_FORK is not
         * synced with forks in progress so it is OK if we miss it
         * if being set atm.
         */
        if ((p1->p_ptevents & PTRACE_FORK) != 0) {
                sx_xlock(&proctree_lock);
                PROC_LOCK(p2);

                /*
                 * p1->p_ptevents & p1->p_pptr are protected by both
                 * process and proctree locks for modifications,
                 * so owning proctree_lock allows the race-free read.
                 */
                if ((p1->p_ptevents & PTRACE_FORK) != 0) {
                        /*
                         * Arrange for debugger to receive the fork event.
                         *
                         * We can report PL_FLAG_FORKED regardless of
                         * P_FOLLOWFORK settings, but it does not make a sense
                         * for runaway child.
                         */
                        td->td_dbgflags |= TDB_FORK;
                        td->td_dbg_forked = p2->p_pid;
                        td2->td_dbgflags |= TDB_STOPATFORK;
                        proc_set_traced(p2, true);
                        CTR2(KTR_PTRACE,
                            "do_fork: attaching to new child pid %d: oppid %d",
                            p2->p_pid, p2->p_oppid);
                        proc_reparent(p2, p1->p_pptr, false);
                }
                PROC_UNLOCK(p2);
                sx_xunlock(&proctree_lock);
        }

        /*
         * Activate procdesc NOTE_FORK after we attached the debugger
         * to the child.  This guarantees that a debugger which does
         * kevent() on the process descriptor to get notifications of
         * fork events, can properly observe the child right after the
         * notification fired.
         */
        procdesc_fork(p1, p2->p_pid);

        racct_proc_fork_done(p2);

        if ((fr->fr_flags & RFSTOPPED) == 0) {
                if (fr->fr_pidp != NULL)
                        *fr->fr_pidp = p2->p_pid;
                /*
                 * If RFSTOPPED not requested, make child runnable and
                 * add to run queue.
                 */
                thread_lock(td2);
                TD_SET_CAN_RUN(td2);
                sched_add(td2, SRQ_BORING);
        } else {
                *fr->fr_procp = p2;
        }
}

static void
ast_vfork(struct thread *td, int tda __unused)
{
        struct proc *p, *p2;

        MPASS(td->td_pflags & TDP_RFPPWAIT);

        p = td->td_proc;
        /*
         * Preserve synchronization semantics of vfork.  If
         * waiting for child to exec or exit, fork set
         * P_PPWAIT on child, and there we sleep on our proc
         * (in case of exit).
         *
         * Do it after the ptracestop() above is finished, to
         * not block our debugger until child execs or exits
         * to finish vfork wait.
         */
        td->td_pflags &= ~TDP_RFPPWAIT;
        p2 = td->td_rfppwait_p;
again:
        PROC_LOCK(p2);
        while (p2->p_flag & P_PPWAIT) {
                PROC_LOCK(p);
                if (thread_suspend_check_needed()) {
                        PROC_UNLOCK(p2);
                        thread_suspend_check(0);
                        PROC_UNLOCK(p);
                        goto again;
                } else {
                        PROC_UNLOCK(p);
                }
                cv_timedwait(&p2->p_pwait, &p2->p_mtx, hz);
        }
        PROC_UNLOCK(p2);

        if (td->td_dbgflags & TDB_VFORK) {
                PROC_LOCK(p);
                if (p->p_ptevents & PTRACE_VFORK)
                        ptracestop(td, SIGTRAP, NULL);
                td->td_dbgflags &= ~TDB_VFORK;
                PROC_UNLOCK(p);
        }
}

int
fork1(struct thread *td, struct fork_req *fr)
{
        struct proc *p1, *newproc;
        struct thread *td2;
        struct vmspace *vm2;
        struct ucred *cred;
        struct file *fp_procdesc;
        struct pgrp *pg;
        vm_ooffset_t mem_charged;
        int error, nprocs_new;
        static int curfail;
        static struct timeval lastfail;
        int flags, pages;
        bool killsx_locked, singlethreaded;

        flags = fr->fr_flags;
        pages = fr->fr_pages;

        if ((flags & RFSTOPPED) != 0)
                MPASS(fr->fr_procp != NULL && fr->fr_pidp == NULL);
        else
                MPASS(fr->fr_procp == NULL);

        if ((flags & ~(RFFLAGS | RFTSIGFLAGS(RFTSIGMASK))) != 0)
                return (EXTERROR(EINVAL,
                    "Undef or unimplemented flags %#jx", flags));

        if ((flags & RFTSIGFLAGS(RFTSIGMASK)) != 0 && (flags & RFTSIGZMB) == 0)
                return (EXTERROR(EINVAL,
                    "Signal value requires RFTSIGZMB", flags));

        if ((flags & (RFFDG | RFCFDG)) == (RFFDG | RFCFDG))
                return (EXTERROR(EINVAL, "Can not copy and clear"));

        if ((flags & RFTSIGZMB) != 0 && (u_int)RFTSIGNUM(flags) > _SIG_MAXSIG)
                return (EXTERROR(EINVAL, "Invalid signal", RFTSIGNUM(flags)));

        if ((flags & RFPROCDESC) != 0) {
                if ((flags & RFPROC) == 0)
                        return (EXTERROR(EINVAL,
            "Can not not create a process yet get a process descriptor"));

                if (fr->fr_pd_fd == NULL)
                        return (EXTERROR(EINVAL,
                    "Must provide a place to put a procdesc if creating one"));

                if ((fr->fr_pd_flags & ~PD_ALLOWED_AT_FORK) != 0)
                        return (EXTERROR(EINVAL,
                            "Invallid pdflags at fork %#jx", fr->fr_pd_flags));
        }

        p1 = td->td_proc;

        /*
         * Here we don't create a new process, but we divorce
         * certain parts of a process from itself.
         */
        if ((flags & RFPROC) == 0) {
                if (fr->fr_procp != NULL)
                        *fr->fr_procp = NULL;
                else if (fr->fr_pidp != NULL)
                        *fr->fr_pidp = 0;
                return (fork_norfproc(td, flags));
        }

        fp_procdesc = NULL;
        newproc = NULL;
        vm2 = NULL;
        killsx_locked = false;
        singlethreaded = false;

        /*
         * Increment the nprocs resource before allocations occur.
         * Although process entries are dynamically created, we still
         * keep a global limit on the maximum number we will
         * create. There are hard-limits as to the number of processes
         * that can run, established by the KVA and memory usage for
         * the process data.
         *
         * Don't allow a nonprivileged user to use the last ten
         * processes; don't let root exceed the limit.
         */
        nprocs_new = atomic_fetchadd_int(&nprocs, 1) + 1;
        if (nprocs_new >= maxproc - 10) {
                if (priv_check_cred(td->td_ucred, PRIV_MAXPROC) != 0 ||
                    nprocs_new >= maxproc) {
                        error = EAGAIN;
                        sx_xlock(&allproc_lock);
                        if (ppsratecheck(&lastfail, &curfail, 1)) {
                                printf("maxproc limit exceeded by uid %u "
                                    "(pid %d); see tuning(7) and "
                                    "login.conf(5)\n",
                                    td->td_ucred->cr_ruid, p1->p_pid);
                        }
                        sx_xunlock(&allproc_lock);
                        goto fail2;
                }
        }

        /*
         * If we are possibly multi-threaded, and there is a process
         * sending a signal to our group right now, ensure that our
         * other threads cannot be chosen for the signal queueing.
         * Otherwise, this might delay signal action, and make the new
         * child escape the signaling.
         */
        pg = p1->p_pgrp;
        if (p1->p_numthreads > 1) {
                if (sx_try_slock(&pg->pg_killsx) != 0) {
                        killsx_locked = true;
                } else {
                        PROC_LOCK(p1);
                        if (thread_single(p1, SINGLE_BOUNDARY)) {
                                PROC_UNLOCK(p1);
                                error = ERESTART;
                                goto fail2;
                        }
                        PROC_UNLOCK(p1);
                        singlethreaded = true;
                }
        }

        /*
         * Atomically check for signals and block processes from sending
         * a signal to our process group until the child is visible.
         */
        if (!killsx_locked && sx_slock_sig(&pg->pg_killsx) != 0) {
                error = ERESTART;
                goto fail2;
        }
        if (__predict_false(p1->p_pgrp != pg || sig_intr() != 0)) {
                /*
                 * Either the process was moved to other process
                 * group, or there is pending signal.  sx_slock_sig()
                 * does not check for signals if not sleeping for the
                 * lock.
                 */
                sx_sunlock(&pg->pg_killsx);
                killsx_locked = false;
                error = ERESTART;
                goto fail2;
        } else {
                killsx_locked = true;
        }

        /*
         * If required, create a process descriptor in the parent first; we
         * will abandon it if something goes wrong. We don't finit() until
         * later.
         */
        if (flags & RFPROCDESC) {
                error = procdesc_falloc(td, &fp_procdesc, fr->fr_pd_fd,
                    fr->fr_pd_flags, fr->fr_pd_fcaps);
                if (error != 0)
                        goto fail2;
                AUDIT_ARG_FD(*fr->fr_pd_fd);
        }

        mem_charged = 0;
        if (pages == 0)
                pages = kstack_pages;
        /* Allocate new proc. */
        newproc = uma_zalloc(proc_zone, M_WAITOK);
        PROC_TREE_REF(newproc);
        td2 = FIRST_THREAD_IN_PROC(newproc);
        if (td2 == NULL) {
                td2 = thread_alloc(pages);
                if (td2 == NULL) {
                        error = ENOMEM;
                        goto fail2;
                }
                proc_linkup(newproc, td2);
        } else {
                error = thread_recycle(td2, pages);
                if (error != 0)
                        goto fail2;
        }

        if ((flags & RFMEM) == 0) {
                vm2 = vmspace_fork(p1->p_vmspace, &mem_charged);
                if (vm2 == NULL) {
                        error = ENOMEM;
                        goto fail2;
                }
                if (!swap_reserve(mem_charged)) {
                        /*
                         * The swap reservation failed. The accounting
                         * from the entries of the copied vm2 will be
                         * subtracted in vmspace_free(), so force the
                         * reservation there.
                         */
                        swap_reserve_force(mem_charged);
                        error = ENOMEM;
                        goto fail2;
                }
        } else
                vm2 = NULL;

        /*
         * XXX: This is ugly; when we copy resource usage, we need to bump
         *      per-cred resource counters.
         */
        newproc->p_ucred = crcowget(td->td_ucred);

        /*
         * Initialize resource accounting for the child process.
         */
        error = racct_proc_fork(p1, newproc);
        if (error != 0) {
                error = EAGAIN;
                goto fail1;
        }

#ifdef MAC
        mac_proc_init(newproc);
#endif

        /*
         * Increment the count of procs running with this uid. Don't allow
         * a nonprivileged user to exceed their current limit.
         */
        cred = td->td_ucred;
        if (!chgproccnt(cred->cr_ruidinfo, 1, lim_cur(td, RLIMIT_NPROC))) {
                if (priv_check_cred(cred, PRIV_PROC_LIMIT) != 0)
                        goto fail0;
                chgproccnt(cred->cr_ruidinfo, 1, 0);
        }

        newproc->p_klist = knlist_alloc(&newproc->p_mtx);

        do_fork(td, fr, newproc, td2, vm2, fp_procdesc);
        error = 0;
        goto cleanup;
fail0:
        error = EAGAIN;
#ifdef MAC
        mac_proc_destroy(newproc);
#endif
        racct_proc_exit(newproc);
fail1:
        proc_unset_cred(newproc, false);
fail2:
        if (vm2 != NULL)
                vmspace_free(vm2);
        if (newproc != NULL)
                PROC_TREE_UNREF(newproc);
        if ((flags & RFPROCDESC) != 0 && fp_procdesc != NULL) {
                fdclose(td, fp_procdesc, *fr->fr_pd_fd);
                fdrop(fp_procdesc, td);
        }
        atomic_add_int(&nprocs, -1);
cleanup:
        if (killsx_locked)
                sx_sunlock(&pg->pg_killsx);
        if (singlethreaded) {
                PROC_LOCK(p1);
                thread_single_end(p1, SINGLE_BOUNDARY);
                PROC_UNLOCK(p1);
        }
        if (error != 0)
                pause("fork", hz / 2);
        return (error);
}

/*
 * Handle the return of a child process from fork1().  This function
 * is called from the MD fork_trampoline() entry point.
 */
void
fork_exit(void (*callout)(void *, struct trapframe *), void *arg,
    struct trapframe *frame)
{
        struct proc *p;
        struct thread *td;
        struct thread *dtd;

        kmsan_mark(frame, sizeof(*frame), KMSAN_STATE_INITED);

        td = curthread;
        p = td->td_proc;
        KASSERT(p->p_state == PRS_NORMAL, ("executing process is still new"));

        CTR4(KTR_PROC, "fork_exit: new thread %p (td_sched %p, pid %d, %s)",
            td, td_get_sched(td), p->p_pid, td->td_name);

        sched_fork_exit(td);

        /*
         * Processes normally resume in mi_switch() after being
         * cpu_switch()'ed to, but when children start up they arrive here
         * instead, so we must do much the same things as mi_switch() would.
         */
        if ((dtd = PCPU_GET(deadthread))) {
                PCPU_SET(deadthread, NULL);
                thread_stash(dtd);
        }
        thread_unlock(td);

        /*
         * cpu_fork_kthread_handler intercepts this function call to
         * have this call a non-return function to stay in kernel mode.
         * initproc has its own fork handler, but it does return.
         */
        KASSERT(callout != NULL, ("NULL callout in fork_exit"));
        callout(arg, frame);

        /*
         * Check if a kernel thread misbehaved and returned from its main
         * function.
         */
        if (p->p_flag & P_KPROC) {
                printf("Kernel thread \"%s\" (pid %d) exited prematurely.\n",
                    td->td_name, p->p_pid);
                kthread_exit();
        }
        mtx_assert(&Giant, MA_NOTOWNED);

        /*
         * Now going to return to userland.
         */

        if (p->p_sysent->sv_schedtail != NULL)
                (p->p_sysent->sv_schedtail)(td);

        userret(td, frame);
}

/*
 * Simplified back end of syscall(), used when returning from fork()
 * directly into user mode.  This function is passed in to fork_exit()
 * as the first parameter and is called when returning to a new
 * userland process.
 */
void
fork_return(struct thread *td, struct trapframe *frame)
{
        struct proc *p;

        p = td->td_proc;
        if (td->td_dbgflags & TDB_STOPATFORK) {
                PROC_LOCK(p);
                if ((p->p_flag & P_TRACED) != 0) {
                        /*
                         * Inform the debugger if one is still present.
                         */
                        td->td_dbgflags |= TDB_CHILD | TDB_SCX | TDB_FSTP;
                        ptracestop(td, SIGSTOP, NULL);
                        td->td_dbgflags &= ~(TDB_CHILD | TDB_SCX);
                } else {
                        /*
                         * ... otherwise clear the request.
                         */
                        td->td_dbgflags &= ~TDB_STOPATFORK;
                }
                PROC_UNLOCK(p);
        } else if (p->p_flag & P_TRACED) {
                /*
                 * This is the start of a new thread in a traced
                 * process.  Report a system call exit event.
                 */
                PROC_LOCK(p);
                td->td_dbgflags |= TDB_SCX;
                if ((p->p_ptevents & PTRACE_SCX) != 0 ||
                    (td->td_dbgflags & TDB_BORN) != 0)
                        ptracestop(td, SIGTRAP, NULL);
                td->td_dbgflags &= ~(TDB_SCX | TDB_BORN);
                PROC_UNLOCK(p);
        }

        /*
         * If the prison was killed mid-fork, die along with it.
         */
        if (!prison_isalive(td->td_ucred->cr_prison))
                kern_exit(td, 0, SIGKILL);

#ifdef KTRACE
        if (KTRPOINT(td, KTR_SYSRET))
                ktrsysret(td->td_sa.code, 0, 0);
#endif
}

static void
fork_init(void *arg __unused)
{
        ast_register(TDA_VFORK, ASTR_ASTF_REQUIRED | ASTR_TDP, TDP_RFPPWAIT,
            ast_vfork);
}
SYSINIT(fork, SI_SUB_INTRINSIC, SI_ORDER_ANY, fork_init, NULL);
FreeBSD
