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NetBSD/sys/kern/kern_fork.c

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/* $NetBSD: kern_fork.c,v 1.231 2024/05/14 19:00:44 andvar 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 1.231 2024/05/14 19:00:44 andvar Exp $");
#include "opt_ktrace.h"
#include "opt_dtrace.h"
#include <sys/param.h>
#include <sys/systm.h>
#include <sys/filedesc.h>
#include <sys/kernel.h>
#include <sys/pool.h>
#include <sys/mount.h>
#include <sys/proc.h>
#include <sys/ras.h>
#include <sys/resourcevar.h>
#include <sys/vnode.h>
#include <sys/file.h>
#include <sys/acct.h>
#include <sys/ktrace.h>
#include <sys/sched.h>
#include <sys/signalvar.h>
#include <sys/syscall.h>
#include <sys/kauth.h>
#include <sys/atomic.h>
#include <sys/syscallargs.h>
#include <sys/uidinfo.h>
#include <sys/sdt.h>
#include <sys/ptrace.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 EINVAL;
/*
* Linux enforces CLONE_VM with CLONE_SIGHAND, do same.
*/
if (SCARG(uap, flags) & CLONE_SIGHAND
&& (SCARG(uap, flags) & CLONE_VM) == 0)
return 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 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 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 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 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 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);
}
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