/* $NetBSD: kern_fork.c,v 1.230 2023/02/25 08:22:00 skrll 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 __KERNEL_RCSID(0, "$NetBSD: kern_fork.c,v 1.230 2023/02/25 08:22:00 skrll Exp $"); #include "opt_ktrace.h" #include "opt_dtrace.h" #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include /* * 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 miliseconds 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); }