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71e2a681f1
The __clone_internal returns the error on errno. Checked on x86_64-linux-gnu.
439 lines
14 KiB
C
439 lines
14 KiB
C
/* POSIX spawn interface. Linux version.
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Copyright (C) 2016-2022 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<https://www.gnu.org/licenses/>. */
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#include <internal-signals.h>
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#include <ldsodefs.h>
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#include <local-setxid.h>
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#include <not-cancel.h>
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#include <paths.h>
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#include <shlib-compat.h>
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#include <spawn.h>
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#include <spawn_int.h>
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#include <sysdep.h>
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#include <sys/resource.h>
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#include <clone_internal.h>
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/* The Linux implementation of posix_spawn{p} uses the clone syscall directly
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with CLONE_VM and CLONE_VFORK flags and an allocated stack. The new stack
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and start function solves most the vfork limitation (possible parent
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clobber due stack spilling). The remaining issue are:
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1. That no signal handlers must run in child context, to avoid corrupting
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parent's state.
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2. The parent must ensure child's stack freeing.
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3. Child must synchronize with parent to enforce 2. and to possible
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return execv issues.
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The first issue is solved by blocking all signals in child, even
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the NPTL-internal ones (SIGCANCEL and SIGSETXID). The second and
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third issue is done by a stack allocation in parent, and by using a
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field in struct spawn_args where the child can write an error
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code. CLONE_VFORK ensures that the parent does not run until the
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child has either exec'ed successfully or exited. */
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/* The Unix standard contains a long explanation of the way to signal
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an error after the fork() was successful. Since no new wait status
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was wanted there is no way to signal an error using one of the
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available methods. The committee chose to signal an error by a
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normal program exit with the exit code 127. */
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#define SPAWN_ERROR 127
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struct posix_spawn_args
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{
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sigset_t oldmask;
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const char *file;
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int (*exec) (const char *, char *const *, char *const *);
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const posix_spawn_file_actions_t *fa;
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const posix_spawnattr_t *restrict attr;
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char *const *argv;
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ptrdiff_t argc;
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char *const *envp;
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int xflags;
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int err;
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};
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/* Older version requires that shell script without shebang definition
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to be called explicitly using /bin/sh (_PATH_BSHELL). */
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static void
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maybe_script_execute (struct posix_spawn_args *args)
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{
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if (SHLIB_COMPAT (libc, GLIBC_2_2, GLIBC_2_15)
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&& (args->xflags & SPAWN_XFLAGS_TRY_SHELL) && errno == ENOEXEC)
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{
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char *const *argv = args->argv;
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ptrdiff_t argc = args->argc;
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/* Construct an argument list for the shell. */
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char *new_argv[argc + 2];
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new_argv[0] = (char *) _PATH_BSHELL;
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new_argv[1] = (char *) args->file;
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if (argc > 1)
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memcpy (new_argv + 2, argv + 1, argc * sizeof (char *));
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else
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new_argv[2] = NULL;
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/* Execute the shell. */
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args->exec (new_argv[0], new_argv, args->envp);
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}
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}
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/* Function used in the clone call to setup the signals mask, posix_spawn
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attributes, and file actions. It run on its own stack (provided by the
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posix_spawn call). */
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static int
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__spawni_child (void *arguments)
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{
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struct posix_spawn_args *args = arguments;
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const posix_spawnattr_t *restrict attr = args->attr;
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const posix_spawn_file_actions_t *file_actions = args->fa;
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/* The child must ensure that no signal handler are enabled because it shared
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memory with parent, so the signal disposition must be either SIG_DFL or
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SIG_IGN. It does by iterating over all signals and although it could
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possibly be more optimized (by tracking which signal potentially have a
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signal handler), it might requires system specific solutions (since the
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sigset_t data type can be very different on different architectures). */
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struct sigaction sa;
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memset (&sa, '\0', sizeof (sa));
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sigset_t hset;
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__sigprocmask (SIG_BLOCK, 0, &hset);
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for (int sig = 1; sig < _NSIG; ++sig)
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{
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if ((attr->__flags & POSIX_SPAWN_SETSIGDEF)
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&& __sigismember (&attr->__sd, sig))
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{
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sa.sa_handler = SIG_DFL;
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}
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else if (__sigismember (&hset, sig))
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{
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if (__is_internal_signal (sig))
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sa.sa_handler = SIG_IGN;
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else
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{
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__libc_sigaction (sig, 0, &sa);
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if (sa.sa_handler == SIG_IGN)
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continue;
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sa.sa_handler = SIG_DFL;
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}
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}
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else
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continue;
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__libc_sigaction (sig, &sa, 0);
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}
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#ifdef _POSIX_PRIORITY_SCHEDULING
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/* Set the scheduling algorithm and parameters. */
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if ((attr->__flags & (POSIX_SPAWN_SETSCHEDPARAM | POSIX_SPAWN_SETSCHEDULER))
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== POSIX_SPAWN_SETSCHEDPARAM)
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{
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if (__sched_setparam (0, &attr->__sp) == -1)
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goto fail;
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}
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else if ((attr->__flags & POSIX_SPAWN_SETSCHEDULER) != 0)
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{
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if (__sched_setscheduler (0, attr->__policy, &attr->__sp) == -1)
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goto fail;
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}
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#endif
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if ((attr->__flags & POSIX_SPAWN_SETSID) != 0
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&& __setsid () < 0)
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goto fail;
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/* Set the process group ID. */
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if ((attr->__flags & POSIX_SPAWN_SETPGROUP) != 0
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&& __setpgid (0, attr->__pgrp) != 0)
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goto fail;
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/* Set the effective user and group IDs. */
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if ((attr->__flags & POSIX_SPAWN_RESETIDS) != 0
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&& (local_seteuid (__getuid ()) != 0
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|| local_setegid (__getgid ()) != 0))
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goto fail;
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/* Execute the file actions. */
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if (file_actions != 0)
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{
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int cnt;
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struct rlimit64 fdlimit;
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bool have_fdlimit = false;
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for (cnt = 0; cnt < file_actions->__used; ++cnt)
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{
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struct __spawn_action *action = &file_actions->__actions[cnt];
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switch (action->tag)
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{
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case spawn_do_close:
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if (__close_nocancel (action->action.close_action.fd) != 0)
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{
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if (!have_fdlimit)
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{
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__getrlimit64 (RLIMIT_NOFILE, &fdlimit);
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have_fdlimit = true;
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}
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/* Signal errors only for file descriptors out of range. */
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if (action->action.close_action.fd < 0
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|| action->action.close_action.fd >= fdlimit.rlim_cur)
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goto fail;
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}
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break;
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case spawn_do_open:
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{
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/* POSIX states that if fildes was already an open file descriptor,
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it shall be closed before the new file is opened. This avoid
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pontential issues when posix_spawn plus addopen action is called
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with the process already at maximum number of file descriptor
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opened and also for multiple actions on single-open special
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paths (like /dev/watchdog). */
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__close_nocancel (action->action.open_action.fd);
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int ret = __open_nocancel (action->action.open_action.path,
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action->action.
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open_action.oflag | O_LARGEFILE,
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action->action.open_action.mode);
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if (ret == -1)
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goto fail;
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int new_fd = ret;
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/* Make sure the desired file descriptor is used. */
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if (ret != action->action.open_action.fd)
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{
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if (__dup2 (new_fd, action->action.open_action.fd)
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!= action->action.open_action.fd)
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goto fail;
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if (__close_nocancel (new_fd) != 0)
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goto fail;
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}
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}
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break;
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case spawn_do_dup2:
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/* Austin Group issue #411 requires adddup2 action with source
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and destination being equal to remove close-on-exec flag. */
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if (action->action.dup2_action.fd
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== action->action.dup2_action.newfd)
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{
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int fd = action->action.dup2_action.newfd;
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int flags = __fcntl (fd, F_GETFD, 0);
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if (flags == -1)
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goto fail;
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if (__fcntl (fd, F_SETFD, flags & ~FD_CLOEXEC) == -1)
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goto fail;
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}
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else if (__dup2 (action->action.dup2_action.fd,
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action->action.dup2_action.newfd)
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!= action->action.dup2_action.newfd)
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goto fail;
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break;
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case spawn_do_chdir:
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if (__chdir (action->action.chdir_action.path) != 0)
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goto fail;
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break;
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case spawn_do_fchdir:
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if (__fchdir (action->action.fchdir_action.fd) != 0)
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goto fail;
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break;
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case spawn_do_closefrom:
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{
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int lowfd = action->action.closefrom_action.from;
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int r = INLINE_SYSCALL_CALL (close_range, lowfd, ~0U, 0);
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if (r != 0 && !__closefrom_fallback (lowfd, false))
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goto fail;
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} break;
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case spawn_do_tcsetpgrp:
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{
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/* Check if it is possible to avoid an extra syscall. */
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pid_t pgrp = (attr->__flags & POSIX_SPAWN_SETPGROUP) != 0
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&& attr->__pgrp != 0
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? attr->__pgrp : __getpgid (0);
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if (__tcsetpgrp (action->action.setpgrp_action.fd, pgrp) != 0)
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goto fail;
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}
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}
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}
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}
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/* Set the initial signal mask of the child if POSIX_SPAWN_SETSIGMASK
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is set, otherwise restore the previous one. */
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__sigprocmask (SIG_SETMASK, (attr->__flags & POSIX_SPAWN_SETSIGMASK)
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? &attr->__ss : &args->oldmask, 0);
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args->exec (args->file, args->argv, args->envp);
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/* This is compatibility function required to enable posix_spawn run
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script without shebang definition for older posix_spawn versions
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(2.15). */
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maybe_script_execute (args);
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fail:
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/* errno should have an appropriate non-zero value; otherwise,
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there's a bug in glibc or the kernel. For lack of an error code
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(EINTERNALBUG) describing that, use ECHILD. Another option would
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be to set args->err to some negative sentinel and have the parent
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abort(), but that seems needlessly harsh. */
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args->err = errno ? : ECHILD;
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_exit (SPAWN_ERROR);
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}
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/* Spawn a new process executing PATH with the attributes describes in *ATTRP.
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Before running the process perform the actions described in FILE-ACTIONS. */
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static int
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__spawnix (pid_t * pid, const char *file,
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const posix_spawn_file_actions_t * file_actions,
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const posix_spawnattr_t * attrp, char *const argv[],
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char *const envp[], int xflags,
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int (*exec) (const char *, char *const *, char *const *))
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{
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pid_t new_pid;
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struct posix_spawn_args args;
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int ec;
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/* To avoid imposing hard limits on posix_spawn{p} the total number of
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arguments is first calculated to allocate a mmap to hold all possible
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values. */
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ptrdiff_t argc = 0;
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/* Linux allows at most max (0x7FFFFFFF, 1/4 stack size) arguments
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to be used in a execve call. We limit to INT_MAX minus one due the
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compatiblity code that may execute a shell script (maybe_script_execute)
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where it will construct another argument list with an additional
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argument. */
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ptrdiff_t limit = INT_MAX - 1;
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while (argv[argc++] != NULL)
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if (argc == limit)
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{
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errno = E2BIG;
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return errno;
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}
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int prot = (PROT_READ | PROT_WRITE
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| ((GL (dl_stack_flags) & PF_X) ? PROT_EXEC : 0));
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/* Add a slack area for child's stack. */
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size_t argv_size = (argc * sizeof (void *)) + 512;
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/* We need at least a few pages in case the compiler's stack checking is
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enabled. In some configs, it is known to use at least 24KiB. We use
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32KiB to be "safe" from anything the compiler might do. Besides, the
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extra pages won't actually be allocated unless they get used.
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It also acts the slack for spawn_closefrom (including MIPS64 getdents64
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where it might use about 1k extra stack space). */
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argv_size += (32 * 1024);
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size_t stack_size = ALIGN_UP (argv_size, GLRO(dl_pagesize));
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void *stack = __mmap (NULL, stack_size, prot,
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MAP_PRIVATE | MAP_ANONYMOUS | MAP_STACK, -1, 0);
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if (__glibc_unlikely (stack == MAP_FAILED))
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return errno;
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/* Disable asynchronous cancellation. */
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int state;
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__pthread_setcancelstate (PTHREAD_CANCEL_DISABLE, &state);
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/* Child must set args.err to something non-negative - we rely on
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the parent and child sharing VM. */
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args.err = 0;
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args.file = file;
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args.exec = exec;
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args.fa = file_actions;
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args.attr = attrp ? attrp : &(const posix_spawnattr_t) { 0 };
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args.argv = argv;
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args.argc = argc;
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args.envp = envp;
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args.xflags = xflags;
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__libc_signal_block_all (&args.oldmask);
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/* The clone flags used will create a new child that will run in the same
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memory space (CLONE_VM) and the execution of calling thread will be
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suspend until the child calls execve or _exit.
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Also since the calling thread execution will be suspend, there is not
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need for CLONE_SETTLS. Although parent and child share the same TLS
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namespace, there will be no concurrent access for TLS variables (errno
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for instance). */
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struct clone_args clone_args =
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{
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.flags = CLONE_VM | CLONE_VFORK,
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.exit_signal = SIGCHLD,
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.stack = (uintptr_t) stack,
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.stack_size = stack_size,
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};
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new_pid = __clone_internal (&clone_args, __spawni_child, &args);
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/* It needs to collect the case where the auxiliary process was created
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but failed to execute the file (due either any preparation step or
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for execve itself). */
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if (new_pid > 0)
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{
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/* Also, it handles the unlikely case where the auxiliary process was
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terminated before calling execve as if it was successfully. The
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args.err is set to 0 as default and changed to a positive value
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only in case of failure, so in case of premature termination
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due a signal args.err will remain zeroed and it will be up to
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caller to actually collect it. */
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ec = args.err;
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if (ec > 0)
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/* There still an unlikely case where the child is cancelled after
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setting args.err, due to a positive error value. Also there is
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possible pid reuse race (where the kernel allocated the same pid
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to an unrelated process). Unfortunately due synchronization
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issues where the kernel might not have the process collected
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the waitpid below can not use WNOHANG. */
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__waitpid (new_pid, NULL, 0);
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}
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else
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ec = errno;
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__munmap (stack, stack_size);
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if ((ec == 0) && (pid != NULL))
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*pid = new_pid;
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__libc_signal_restore_set (&args.oldmask);
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__pthread_setcancelstate (state, NULL);
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return ec;
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}
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/* Spawn a new process executing PATH with the attributes describes in *ATTRP.
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Before running the process perform the actions described in FILE-ACTIONS. */
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int
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__spawni (pid_t * pid, const char *file,
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const posix_spawn_file_actions_t * acts,
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const posix_spawnattr_t * attrp, char *const argv[],
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char *const envp[], int xflags)
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{
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/* It uses __execvpex to avoid run ENOEXEC in non compatibility mode (it
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will be handled by maybe_script_execute). */
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return __spawnix (pid, file, acts, attrp, argv, envp, xflags,
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xflags & SPAWN_XFLAGS_USE_PATH ? __execvpex :__execve);
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}
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