/*      $NetBSD: kern_fork.c,v 1.234 2026/01/04 01:33:56 riastradh Exp $        */

/*-
 * Copyright (c) 1999, 2001, 2004, 2006, 2007, 2008, 2019
 *     The NetBSD Foundation, Inc.
 * All rights reserved.
 *
 * This code is derived from software contributed to The NetBSD Foundation
 * by Jason R. Thorpe of the Numerical Aerospace Simulation Facility,
 * NASA Ames Research Center, by Charles M. Hannum, and by Andrew Doran.
 *
 * 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.
 *
 * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. 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 FOUNDATION 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.
 */

/*
 * 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.
 *
 *      @(#)kern_fork.c 8.8 (Berkeley) 2/14/95
 */

#include <sys/cdefs.h>
__KERNEL_RCSID(0, "$NetBSD: kern_fork.c,v 1.234 2026/01/04 01:33:56 riastradh Exp $");

#include "opt_ktrace.h"
#include "opt_dtrace.h"

#include <sys/param.h>
#include <sys/types.h>

#include <sys/acct.h>
#include <sys/atomic.h>
#include <sys/file.h>
#include <sys/filedesc.h>
#include <sys/kauth.h>
#include <sys/kernel.h>
#include <sys/ktrace.h>
#include <sys/mount.h>
#include <sys/pool.h>
#include <sys/proc.h>
#include <sys/ptrace.h>
#include <sys/ras.h>
#include <sys/resourcevar.h>
#include <sys/sched.h>
#include <sys/sdt.h>
#include <sys/signalvar.h>
#include <sys/syscall.h>
#include <sys/syscallargs.h>
#include <sys/systm.h>
#include <sys/uidinfo.h>
#include <sys/vnode.h>

/*
 * DTrace SDT provider definitions
 */
SDT_PROVIDER_DECLARE(proc);
SDT_PROBE_DEFINE3(proc, kernel, , create,
    "struct proc *", /* new process */
    "struct proc *", /* parent process */
    "int" /* flags */);

u_int   nprocs __cacheline_aligned = 1;         /* process 0 */

/*
 * Number of ticks to sleep if fork() would fail due to process hitting
 * limits. Exported in milliseconds to userland via sysctl.
 */
int     forkfsleep = 0;

int
sys_fork(struct lwp *l, const void *v, register_t *retval)
{

        return fork1(l, 0, SIGCHLD, NULL, 0, NULL, NULL, retval);
}

/*
 * vfork(2) system call compatible with 4.4BSD (i.e. BSD with Mach VM).
 * Address space is not shared, but parent is blocked until child exit.
 */
int
sys_vfork(struct lwp *l, const void *v, register_t *retval)
{

        return fork1(l, FORK_PPWAIT, SIGCHLD, NULL, 0, NULL, NULL,
            retval);
}

/*
 * New vfork(2) system call for NetBSD, which implements original 3BSD vfork(2)
 * semantics.  Address space is shared, and parent is blocked until child exit.
 */
int
sys___vfork14(struct lwp *l, const void *v, register_t *retval)
{

        return fork1(l, FORK_PPWAIT|FORK_SHAREVM, SIGCHLD, NULL, 0,
            NULL, NULL, retval);
}

/*
 * Linux-compatible __clone(2) system call.
 */
int
sys___clone(struct lwp *l, const struct sys___clone_args *uap,
    register_t *retval)
{
        /* {
                syscallarg(int) flags;
                syscallarg(void *) stack;
        } */
        int flags, sig;

        /*
         * We don't support the CLONE_PTRACE flag.
         */
        if (SCARG(uap, flags) & CLONE_PTRACE)
                return SET_ERROR(EINVAL);

        /*
         * Linux enforces CLONE_VM with CLONE_SIGHAND, do same.
         */
        if (SCARG(uap, flags) & CLONE_SIGHAND
            && (SCARG(uap, flags) & CLONE_VM) == 0)
                return SET_ERROR(EINVAL);

        flags = 0;

        if (SCARG(uap, flags) & CLONE_VM)
                flags |= FORK_SHAREVM;
        if (SCARG(uap, flags) & CLONE_FS)
                flags |= FORK_SHARECWD;
        if (SCARG(uap, flags) & CLONE_FILES)
                flags |= FORK_SHAREFILES;
        if (SCARG(uap, flags) & CLONE_SIGHAND)
                flags |= FORK_SHARESIGS;
        if (SCARG(uap, flags) & CLONE_VFORK)
                flags |= FORK_PPWAIT;

        sig = SCARG(uap, flags) & CLONE_CSIGNAL;
        if (sig < 0 || sig >= _NSIG)
                return SET_ERROR(EINVAL);

        /*
         * Linux doesn't have close-on-fork yet, so we don't
         * know what they will do combining CLONE_FILES with
         * close-on-fork (which are not really compatible).
         * This might need to be changed in the future (another
         * option would be to just disable FORK_SHAREFILES)
         */
        if ((flags & FORK_SHAREFILES) != 0) {
                if (l->l_fd != NULL && l->l_fd->fd_foclose)
                        return SET_ERROR(EINVAL);
        }

        /*
         * Note that the Linux API does not provide a portable way of
         * specifying the stack area; the caller must know if the stack
         * grows up or down.  So, we pass a stack size of 0, so that the
         * code that makes this adjustment is a noop.
         */
        return fork1(l, flags, sig, SCARG(uap, stack), 0,
            NULL, NULL, retval);
}

/*
 * Print the 'table full' message once per 10 seconds.
 */
static struct timeval fork_tfmrate = { 10, 0 };

/*
 * Check if a process is traced and shall inform about FORK events.
 */
static inline bool
tracefork(struct proc *p, int flags)
{

        return (p->p_slflag & (PSL_TRACEFORK|PSL_TRACED)) ==
            (PSL_TRACEFORK|PSL_TRACED) && (flags & FORK_PPWAIT) == 0;
}

/*
 * Check if a process is traced and shall inform about VFORK events.
 */
static inline bool
tracevfork(struct proc *p, int flags)
{

        return (p->p_slflag & (PSL_TRACEVFORK|PSL_TRACED)) ==
            (PSL_TRACEVFORK|PSL_TRACED) && (flags & FORK_PPWAIT) != 0;
}

/*
 * Check if a process is traced and shall inform about VFORK_DONE events.
 */
static inline bool
tracevforkdone(struct proc *p, int flags)
{

        return (p->p_slflag & (PSL_TRACEVFORK_DONE|PSL_TRACED)) ==
            (PSL_TRACEVFORK_DONE|PSL_TRACED) && (flags & FORK_PPWAIT);
}

/*
 * General fork call.  Note that another LWP in the process may call exec()
 * or exit() while we are forking.  It's safe to continue here, because
 * neither operation will complete until all LWPs have exited the process.
 */
int
fork1(struct lwp *l1, int flags, int exitsig, void *stack, size_t stacksize,
    void (*func)(void *), void *arg, register_t *retval)
{
        struct proc     *p1, *p2, *parent;
        struct plimit   *p1_lim;
        uid_t           uid;
        struct lwp      *l2;
        int             count;
        vaddr_t         uaddr;
        int             tnprocs;
        int             error = 0;

        p1 = l1->l_proc;
        uid = kauth_cred_getuid(l1->l_cred);
        tnprocs = atomic_inc_uint_nv(&nprocs);

        /*
         * Although process entries are dynamically created, we still keep
         * a global limit on the maximum number we will create.
         */
        if (__predict_false(tnprocs >= maxproc))
                error = -1;
        else
                error = kauth_authorize_process(l1->l_cred,
                    KAUTH_PROCESS_FORK, p1, KAUTH_ARG(tnprocs), NULL, NULL);

        if (error) {
                static struct timeval lasttfm;
                atomic_dec_uint(&nprocs);
                if (ratecheck(&lasttfm, &fork_tfmrate))
                        tablefull("proc", "increase kern.maxproc or NPROC");
                if (forkfsleep)
                        kpause("forkmx", false, forkfsleep, NULL);
                return SET_ERROR(EAGAIN);
        }

        /*
         * Enforce limits.
         */
        count = chgproccnt(uid, 1);
        if (__predict_false(count > p1->p_rlimit[RLIMIT_NPROC].rlim_cur)) {
                if (kauth_authorize_process(l1->l_cred, KAUTH_PROCESS_RLIMIT,
                    p1, KAUTH_ARG(KAUTH_REQ_PROCESS_RLIMIT_BYPASS),
                    &p1->p_rlimit[RLIMIT_NPROC], KAUTH_ARG(RLIMIT_NPROC)) != 0) {
                        (void)chgproccnt(uid, -1);
                        atomic_dec_uint(&nprocs);
                        if (forkfsleep)
                                kpause("forkulim", false, forkfsleep, NULL);
                        return SET_ERROR(EAGAIN);
                }
        }

        /*
         * Allocate virtual address space for the U-area now, while it
         * is still easy to abort the fork operation if we're out of
         * kernel virtual address space.
         */
        uaddr = uvm_uarea_alloc();
        if (__predict_false(uaddr == 0)) {
                (void)chgproccnt(uid, -1);
                atomic_dec_uint(&nprocs);
                return SET_ERROR(ENOMEM);
        }

        /* Allocate new proc. */
        p2 = proc_alloc();
        if (p2 == NULL) {
                /* We were unable to allocate a process ID. */
                uvm_uarea_free(uaddr);
                mutex_enter(p1->p_lock);
                uid = kauth_cred_getuid(p1->p_cred);
                (void)chgproccnt(uid, -1);
                mutex_exit(p1->p_lock);
                atomic_dec_uint(&nprocs);
                return SET_ERROR(EAGAIN);
        }

        /*
         * We are now committed to the fork.  From here on, we may
         * block on resources, but resource allocation may NOT fail.
         */

        /*
         * 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.
         */
        memset(&p2->p_startzero, 0,
            (unsigned) ((char *)&p2->p_endzero - (char *)&p2->p_startzero));
        memcpy(&p2->p_startcopy, &p1->p_startcopy,
            (unsigned) ((char *)&p2->p_endcopy - (char *)&p2->p_startcopy));

        TAILQ_INIT(&p2->p_sigpend.sp_info);

        LIST_INIT(&p2->p_lwps);
        LIST_INIT(&p2->p_sigwaiters);

        /*
         * Duplicate sub-structures as needed.
         * Increase reference counts on shared objects.
         * Inherit flags we want to keep.  The flags related to SIGCHLD
         * handling are important in order to keep a consistent behaviour
         * for the child after the fork.  If we are a 32-bit process, the
         * child will be too.
         */
        p2->p_flag =
            p1->p_flag & (PK_SUGID | PK_NOCLDWAIT | PK_CLDSIGIGN | PK_32);
        p2->p_emul = p1->p_emul;
        p2->p_execsw = p1->p_execsw;

        if (flags & FORK_SYSTEM) {
                /*
                 * Mark it as a system process.  Set P_NOCLDWAIT so that
                 * children are reparented to init(8) when they exit.
                 * init(8) can easily wait them out for us.
                 */
                p2->p_flag |= (PK_SYSTEM | PK_NOCLDWAIT);
        }

        mutex_init(&p2->p_stmutex, MUTEX_DEFAULT, IPL_HIGH);
        mutex_init(&p2->p_auxlock, MUTEX_DEFAULT, IPL_NONE);
        rw_init(&p2->p_reflock);
        cv_init(&p2->p_waitcv, "wait");
        cv_init(&p2->p_lwpcv, "lwpwait");

        /*
         * Share a lock between the processes if they are to share signal
         * state: we must synchronize access to it.
         */
        if (flags & FORK_SHARESIGS) {
                p2->p_lock = p1->p_lock;
                mutex_obj_hold(p1->p_lock);
        } else
                p2->p_lock = mutex_obj_alloc(MUTEX_DEFAULT, IPL_NONE);

        kauth_proc_fork(p1, p2);

        p2->p_raslist = NULL;
#if defined(__HAVE_RAS)
        ras_fork(p1, p2);
#endif

        /* bump references to the text vnode (for procfs) */
        p2->p_textvp = p1->p_textvp;
        if (p2->p_textvp)
                vref(p2->p_textvp);
        if (p1->p_path)
                p2->p_path = kmem_strdupsize(p1->p_path, NULL, KM_SLEEP);
        else
                p2->p_path = NULL;

        if (flags & FORK_SHAREFILES)
                fd_share(p2);
        else if (flags & FORK_CLEANFILES)
                p2->p_fd = fd_init(NULL);
        else
                p2->p_fd = fd_copy();

        /* XXX racy */
        p2->p_mqueue_cnt = p1->p_mqueue_cnt;

        if (flags & FORK_SHARECWD)
                cwdshare(p2);
        else
                p2->p_cwdi = cwdinit();

        /*
         * Note: p_limit (rlimit stuff) is copy-on-write, so normally
         * we just need increase pl_refcnt.
         */
        p1_lim = p1->p_limit;
        if (!p1_lim->pl_writeable) {
                lim_addref(p1_lim);
                p2->p_limit = p1_lim;
        } else {
                p2->p_limit = lim_copy(p1_lim);
        }

        if (flags & FORK_PPWAIT) {
                /* Mark ourselves as waiting for a child. */
                p2->p_lflag = PL_PPWAIT;
                l1->l_vforkwaiting = true;
                p2->p_vforklwp = l1;
        } else {
                p2->p_lflag = 0;
                l1->l_vforkwaiting = false;
        }
        p2->p_sflag = 0;
        p2->p_slflag = 0;
        parent = (flags & FORK_NOWAIT) ? initproc : p1;
        p2->p_pptr = parent;
        p2->p_ppid = parent->p_pid;
        LIST_INIT(&p2->p_children);

        p2->p_aio = NULL;

#ifdef KTRACE
        /*
         * Copy traceflag and tracefile if enabled.
         * If not inherited, these were zeroed above.
         */
        if (p1->p_traceflag & KTRFAC_INHERIT) {
                mutex_enter(&ktrace_lock);
                p2->p_traceflag = p1->p_traceflag;
                if ((p2->p_tracep = p1->p_tracep) != NULL)
                        ktradref(p2);
                mutex_exit(&ktrace_lock);
        }
#endif

        /*
         * Create signal actions for the child process.
         */
        p2->p_sigacts = sigactsinit(p1, flags & FORK_SHARESIGS);
        mutex_enter(p1->p_lock);
        p2->p_sflag |=
            (p1->p_sflag & (PS_STOPFORK | PS_STOPEXEC | PS_NOCLDSTOP));
        sched_proc_fork(p1, p2);
        mutex_exit(p1->p_lock);

        p2->p_stflag = p1->p_stflag;

        /*
         * p_stats.
         * Copy parts of p_stats, and zero out the rest.
         */
        p2->p_stats = pstatscopy(p1->p_stats);

        /*
         * Set up the new process address space.
         */
        uvm_proc_fork(p1, p2, (flags & FORK_SHAREVM) ? true : false);

        /*
         * Finish creating the child process.
         * It will return through a different path later.
         */
        lwp_create(l1, p2, uaddr, (flags & FORK_PPWAIT) ? LWP_VFORK : 0,
            stack, stacksize, (func != NULL) ? func : child_return, arg, &l2,
            l1->l_class, &l1->l_sigmask, &l1->l_sigstk);

        /*
         * Inherit l_private from the parent.
         * Note that we cannot use lwp_setprivate() here since that
         * also sets the CPU TLS register, which is incorrect if the
         * process has changed that without letting the kernel know.
         */
        l2->l_private = l1->l_private;

        /*
         * If emulation has a process fork hook, call it now.
         */
        if (p2->p_emul->e_proc_fork)
                (*p2->p_emul->e_proc_fork)(p2, l1, flags);

        /*
         * ...and finally, any other random fork hooks that subsystems
         * might have registered.
         */
        doforkhooks(p2, p1);

        SDT_PROBE(proc, kernel, , create, p2, p1, flags, 0, 0);

        /*
         * It's now safe for the scheduler and other processes to see the
         * child process.
         */
        mutex_enter(&proc_lock);

        if (p1->p_session->s_ttyvp != NULL && p1->p_lflag & PL_CONTROLT)
                p2->p_lflag |= PL_CONTROLT;

        LIST_INSERT_HEAD(&parent->p_children, p2, p_sibling);
        p2->p_exitsig = exitsig;                /* signal for parent on exit */

        /*
         * Trace fork(2) and vfork(2)-like events on demand in a debugger.
         */
        if (tracefork(p1, flags) || tracevfork(p1, flags)) {
                proc_changeparent(p2, p1->p_pptr);
                SET(p2->p_slflag, PSL_TRACEDCHILD);
        }

        p2->p_oppid = p1->p_pid; /* Remember the original parent id. */

        LIST_INSERT_AFTER(p1, p2, p_pglist);
        LIST_INSERT_HEAD(&allproc, p2, p_list);

        p2->p_trace_enabled = trace_is_enabled(p2);
#ifdef __HAVE_SYSCALL_INTERN
        (*p2->p_emul->e_syscall_intern)(p2);
#endif

        /*
         * Update stats now that we know the fork was successful.
         */
        KPREEMPT_DISABLE(l1);
        CPU_COUNT(CPU_COUNT_FORKS, 1);
        if (flags & FORK_PPWAIT)
                CPU_COUNT(CPU_COUNT_FORKS_PPWAIT, 1);
        if (flags & FORK_SHAREVM)
                CPU_COUNT(CPU_COUNT_FORKS_SHAREVM, 1);
        KPREEMPT_ENABLE(l1);

        if (ktrpoint(KTR_EMUL))
                p2->p_traceflag |= KTRFAC_TRC_EMUL;

        /*
         * Notify any interested parties about the new process.
         */
        if (!SLIST_EMPTY(&p1->p_klist)) {
                mutex_exit(&proc_lock);
                knote_proc_fork(p1, p2);
                mutex_enter(&proc_lock);
        }

        /*
         * Make child runnable, set start time, and add to run queue except
         * if the parent requested the child to start in SSTOP state.
         */
        mutex_enter(p2->p_lock);

        /*
         * Start profiling.
         */
        if ((p2->p_stflag & PST_PROFIL) != 0) {
                mutex_spin_enter(&p2->p_stmutex);
                startprofclock(p2);
                mutex_spin_exit(&p2->p_stmutex);
        }

        getmicrotime(&p2->p_stats->p_start);
        p2->p_acflag = AFORK;
        lwp_lock(l2);
        KASSERT(p2->p_nrlwps == 1);
        KASSERT(l2->l_stat == LSIDL);
        if (p2->p_sflag & PS_STOPFORK) {
                p2->p_nrlwps = 0;
                p2->p_stat = SSTOP;
                p2->p_waited = 0;
                p1->p_nstopchild++;
                l2->l_stat = LSSTOP;
                KASSERT(l2->l_wchan == NULL);
                lwp_unlock(l2);
        } else {
                p2->p_nrlwps = 1;
                p2->p_stat = SACTIVE;
                setrunnable(l2);
                /* LWP now unlocked */
        }

        /*
         * Return child pid to parent process,
         * marking us as parent via retval[1].
         */
        if (retval != NULL) {
                retval[0] = p2->p_pid;
                retval[1] = 0;
        }

        mutex_exit(p2->p_lock);

        /*
         * Let the parent know that we are tracing its child.
         */
        if (tracefork(p1, flags) || tracevfork(p1, flags)) {
                mutex_enter(p1->p_lock);
                eventswitch(TRAP_CHLD,
                    tracefork(p1, flags) ? PTRACE_FORK : PTRACE_VFORK,
                    retval[0]);
                mutex_enter(&proc_lock);
        }

        /*
         * Preserve synchronization semantics of vfork.  If waiting for
         * child to exec or exit, sleep until it clears p_vforkwaiting.
         */
        while (l1->l_vforkwaiting)
                cv_wait(&l1->l_waitcv, &proc_lock);

        /*
         * Let the parent know that we are tracing its child.
         */
        if (tracevforkdone(p1, flags)) {
                mutex_enter(p1->p_lock);
                eventswitch(TRAP_CHLD, PTRACE_VFORK_DONE, retval[0]);
        } else
                mutex_exit(&proc_lock);

        return 0;
}

/*
 * MI code executed in each newly spawned process before returning to userland.
 */
void
child_return(void *arg)
{
        struct lwp *l = curlwp;
        struct proc *p = l->l_proc;

        if ((p->p_slflag & (PSL_TRACED|PSL_TRACEDCHILD)) ==
            (PSL_TRACED|PSL_TRACEDCHILD)) {
                eventswitchchild(p, TRAP_CHLD,
                    ISSET(p->p_lflag, PL_PPWAIT) ? PTRACE_VFORK : PTRACE_FORK);
        }

        md_child_return(l);

        /*
         * Return SYS_fork for all fork types, including vfork(2) and clone(2).
         *
         * This approach simplifies the code and avoids extra locking.
         */
        ktrsysret(SYS_fork, 0, 0);
}