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/* Copyright (C) 1991-2025 Free Software Foundation, Inc.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library; if not, see
<https://www.gnu.org/licenses/>. */
#include <errno.h>
#include <signal.h>
#include <stdlib.h>
#include <unistd.h>
#include <sigsetops.h>
#include <spawn.h>
#include <pthread.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <stdio.h>
#include <libc-lock.h>
#include <not-errno.h>
#include <not-cancel.h>
#include <internal-signals.h>
#define SHELL_PATH "/bin/sh" /* Path of the shell. */
#define SHELL_NAME "sh" /* Name to give it. */
/* This system implementation aims to be thread-safe, which requires to
restore the signal dispositions for SIGINT and SIGQUIT correctly and to
deal with cancellation by terminating the child process.
The signal disposition restoration on the single-thread case is
straighfoward. For multithreaded case, a reference-counter with a lock
is used, so the first thread will set the SIGINT/SIGQUIT dispositions and
last thread will restore them.
Cancellation handling is done with thread cancellation clean-up handlers
on waitpid call. */
#ifdef _LIBC_REENTRANT
static struct sigaction intr, quit;
static int sa_refcntr;
__libc_lock_define_initialized (static, lock);
# define DO_LOCK() __libc_lock_lock (lock)
# define DO_UNLOCK() __libc_lock_unlock (lock)
# define INIT_LOCK() ({ __libc_lock_init (lock); sa_refcntr = 0; })
# define ADD_REF() sa_refcntr++
# define SUB_REF() --sa_refcntr
#else
# define DO_LOCK()
# define DO_UNLOCK()
# define INIT_LOCK()
# define ADD_REF() 0
# define SUB_REF() 0
#endif
#if defined(_LIBC_REENTRANT) && defined(SIGCANCEL)
struct cancel_handler_args
{
struct sigaction *quit;
struct sigaction *intr;
pid_t pid;
};
static void
cancel_handler (void *arg)
{
struct cancel_handler_args *args = (struct cancel_handler_args *) (arg);
__kill_noerrno (args->pid, SIGKILL);
int state;
__pthread_setcancelstate (PTHREAD_CANCEL_DISABLE, &state);
TEMP_FAILURE_RETRY (__waitpid (args->pid, NULL, 0));
__pthread_setcancelstate (state, NULL);
DO_LOCK ();
if (SUB_REF () == 0)
{
__sigaction (SIGQUIT, args->quit, NULL);
__sigaction (SIGINT, args->intr, NULL);
}
DO_UNLOCK ();
}
#endif
/* Execute LINE as a shell command, returning its status. */
static int
do_system (const char *line)
{
int status = -1;
int ret;
pid_t pid;
struct sigaction sa;
#ifndef _LIBC_REENTRANT
struct sigaction intr, quit;
#endif
sigset_t omask;
sigset_t reset;
sa.sa_handler = SIG_IGN;
sa.sa_flags = 0;
__sigemptyset (&sa.sa_mask);
DO_LOCK ();
if (ADD_REF () == 0)
{
/* sigaction can not fail with SIGINT/SIGQUIT used with SIG_IGN. */
__sigaction (SIGINT, &sa, &intr);
__sigaction (SIGQUIT, &sa, &quit);
}
DO_UNLOCK ();
__sigaddset (&sa.sa_mask, SIGCHLD);
/* sigprocmask can not fail with SIG_BLOCK used with valid input
arguments. */
__sigprocmask (SIG_BLOCK, &sa.sa_mask, &omask);
__sigemptyset (&reset);
if (intr.sa_handler != SIG_IGN)
__sigaddset(&reset, SIGINT);
if (quit.sa_handler != SIG_IGN)
__sigaddset(&reset, SIGQUIT);
posix_spawnattr_t spawn_attr;
/* None of the posix_spawnattr_* function returns an error, including
posix_spawnattr_setflags for the follow specific usage (using valid
flags). */
__posix_spawnattr_init (&spawn_attr);
__posix_spawnattr_setsigmask (&spawn_attr, &omask);
__posix_spawnattr_setsigdefault (&spawn_attr, &reset);
__posix_spawnattr_setflags (&spawn_attr,
POSIX_SPAWN_SETSIGDEF | POSIX_SPAWN_SETSIGMASK);
ret = __posix_spawn (&pid, SHELL_PATH, NULL, &spawn_attr,
(char *const[]){ (char *) SHELL_NAME,
(char *) "-c",
(char *) "--",
(char *) line, NULL },
__environ);
__posix_spawnattr_destroy (&spawn_attr);
if (ret == 0)
{
/* Cancellation results in cleanup handlers running as exceptions in
the block where they were installed, so it is safe to reference
stack variable allocate in the broader scope. */
#if defined(_LIBC_REENTRANT) && defined(SIGCANCEL)
struct cancel_handler_args cancel_args =
{
.quit = &quit,
.intr = &intr,
.pid = pid
};
__libc_cleanup_region_start (1, cancel_handler, &cancel_args);
#endif
/* Note the system() is a cancellation point. But since we call
waitpid() which itself is a cancellation point we do not
have to do anything here. */
if (TEMP_FAILURE_RETRY (__waitpid (pid, &status, 0)) != pid)
status = -1;
#if defined(_LIBC_REENTRANT) && defined(SIGCANCEL)
__libc_cleanup_region_end (0);
#endif
}
else if (ret == EAGAIN || ret == ENOMEM)
/* POSIX states that failure to create a child process should
return -1. */
status = -1;
else
/* POSIX states that failure to execute the shell should return
as if the shell had terminated using _exit(127). */
status = W_EXITCODE (127, 0);
/* sigaction can not fail with SIGINT/SIGQUIT used with old
disposition. Same applies for sigprocmask. */
DO_LOCK ();
if (SUB_REF () == 0)
{
__sigaction (SIGINT, &intr, NULL);
__sigaction (SIGQUIT, &quit, NULL);
}
DO_UNLOCK ();
__sigprocmask (SIG_SETMASK, &omask, NULL);
if (ret != 0)
__set_errno (ret);
return status;
}
int
__libc_system (const char *line)
{
if (line == NULL)
/* Check that we have a command processor available. It might
not be available after a chroot(), for example. */
return do_system ("exit 0") == 0;
return do_system (line);
}
weak_alias (__libc_system, system)
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