OpenSolaris_b135/lib/libc/port/stdio/system.c
/*
* CDDL HEADER START
*
* The contents of this file are subject to the terms of the
* Common Development and Distribution License (the "License").
* You may not use this file except in compliance with the License.
*
* You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
* or http://www.opensolaris.org/os/licensing.
* See the License for the specific language governing permissions
* and limitations under the License.
*
* When distributing Covered Code, include this CDDL HEADER in each
* file and include the License file at usr/src/OPENSOLARIS.LICENSE.
* If applicable, add the following below this CDDL HEADER, with the
* fields enclosed by brackets "[]" replaced with your own identifying
* information: Portions Copyright [yyyy] [name of copyright owner]
*
* CDDL HEADER END
*/
/*
* Copyright 2008 Sun Microsystems, Inc. All rights reserved.
* Use is subject to license terms.
*/
/* Copyright (c) 1988 AT&T */
/* All Rights Reserved */
#include "lint.h"
#include "mtlib.h"
#include <sys/types.h>
#include <sys/wait.h>
#include <signal.h>
#include <stdlib.h>
#include <wait.h>
#include <sys/stat.h>
#include <unistd.h>
#include <memory.h>
#include <thread.h>
#include <pthread.h>
#include <errno.h>
#include <synch.h>
#include <spawn.h>
#include "libc.h"
extern const char **_environ;
extern int __xpg4; /* defined in _xpg4.c; 0 if not xpg4-compiled program */
extern const sigset_t maskset; /* all maskable signals */
static mutex_t sys_lock = DEFAULTMUTEX; /* protects the following */
static uint_t sys_count = 0; /* number of threads in system() */
static struct sigaction sys_ibuf; /* saved SIGINT sigaction */
static struct sigaction sys_qbuf; /* saved SIGQUIT sigaction */
static struct sigaction ignore = {0, {SIG_IGN}, {0}};
/*
* Things needed by the cancellation cleanup handler.
*/
typedef struct {
sigset_t savemask; /* saved signal mask */
pid_t pid; /* if nonzero, the child's pid */
} cleanup_t;
/*
* Daemon thread whose sole function is to reap an abandoned child.
* Also invoked from pclose() (see port/stdio/popen.c).
*/
void *
reapchild(void *arg)
{
pid_t pid = (pid_t)(uintptr_t)arg;
int cancel_state;
(void) pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, &cancel_state);
while (waitpid(pid, NULL, 0) == -1) {
if (errno != EINTR)
break;
}
(void) pthread_setcancelstate(cancel_state, NULL);
return (NULL);
}
/*
* Cancellation cleanup handler.
* If we were cancelled in waitpid(), create a daemon thread to
* reap our abandoned child. No other thread can do this for us.
* It would be better if there were a system call to disinherit
* a child process (give it to init, just as though we exited).
*/
static void
cleanup(void *arg)
{
cleanup_t *cup = arg;
if (cup->pid != 0) { /* we were cancelled; abandoning our pid */
(void) thr_sigsetmask(SIG_SETMASK, &maskset, NULL);
(void) thr_create(NULL, 0,
reapchild, (void *)(uintptr_t)cup->pid,
THR_DAEMON, NULL);
}
lmutex_lock(&sys_lock);
if (--sys_count == 0) { /* leaving system() */
/*
* There are no remaining threads in system(), so
* restore the SIGINT and SIGQUIT signal actions.
*/
(void) sigaction(SIGINT, &sys_ibuf, NULL);
(void) sigaction(SIGQUIT, &sys_qbuf, NULL);
}
lmutex_unlock(&sys_lock);
(void) thr_sigsetmask(SIG_SETMASK, &cup->savemask, NULL);
}
int
system(const char *cmd)
{
cleanup_t cu;
pid_t w;
int status;
int error;
sigset_t mask;
struct stat64 buf;
const char *shpath;
char *argv[4];
posix_spawnattr_t attr;
static const char *sun_path = "/bin/sh";
static const char *xpg4_path = "/usr/xpg4/bin/sh";
static const char *shell = "sh";
shpath = __xpg4? xpg4_path : sun_path;
if (cmd == NULL) {
if (stat64(shpath, &buf) != 0) {
return (0);
} else if (getuid() == buf.st_uid) {
/* exec for user */
if ((buf.st_mode & 0100) == 0)
return (0);
} else if (getgid() == buf.st_gid) {
/* exec for group */
if ((buf.st_mode & 0010) == 0)
return (0);
} else if ((buf.st_mode & 0001) == 0) { /* exec for others */
return (0);
}
return (1);
}
/*
* Initialize the posix_spawn() attributes structure.
*
* The setting of POSIX_SPAWN_WAITPID_NP ensures that no
* wait-for-multiple wait() operation will reap our child
* and that the child will not be automatically reaped due
* to the disposition of SIGCHLD being set to be ignored.
* Only a specific wait for the specific pid will be able
* to reap the child. Since no other thread knows the pid
* of our child, this should be safe enough.
*
* The POSIX_SPAWN_NOEXECERR_NP flag tells posix_spawn() not
* to fail if the shell cannot be executed, but rather cause
* a child to be created that simply performs _exit(127).
* This is in order to satisfy the Posix requirement on system():
* The system function shall behave as if a child process were
* created using fork(), and the child process invoked the sh
* utility using execl(). If some error prevents the command
* language interpreter from executing after the child process
* is created, the return value from system() shall be as if
* the command language interpreter had terminated using
* exit(127) or _exit(127).
*/
error = posix_spawnattr_init(&attr);
if (error == 0)
error = posix_spawnattr_setflags(&attr,
POSIX_SPAWN_SETSIGMASK | POSIX_SPAWN_SETSIGDEF |
POSIX_SPAWN_NOSIGCHLD_NP | POSIX_SPAWN_WAITPID_NP |
POSIX_SPAWN_NOEXECERR_NP);
/*
* The POSIX spec for system() requires us to block SIGCHLD,
* the rationale being that the process's signal handler for
* SIGCHLD, if any, should not be called when our child exits.
* This doesn't work for a multithreaded process because some
* other thread could receive the SIGCHLD.
*
* The above setting of POSIX_SPAWN_NOSIGCHLD_NP ensures that no
* SIGCHLD signal will be posted for our child when it exits, so
* we don't have to block SIGCHLD to meet the intent of the spec.
* We block SIGCHLD anyway, just because the spec requires it.
*/
(void) sigemptyset(&mask);
(void) sigaddset(&mask, SIGCHLD);
(void) thr_sigsetmask(SIG_BLOCK, &mask, &cu.savemask);
/*
* Tell posix_spawn() to restore the signal mask in the child.
*/
if (error == 0)
error = posix_spawnattr_setsigmask(&attr, &cu.savemask);
/*
* We are required to set the disposition of SIGINT and SIGQUIT
* to be ignored for the duration of the system() operation.
*
* We allow more than one thread to call system() concurrently by
* keeping a count of such threads. The signal actions are set
* to SIG_IGN when the first thread calls system(). They are
* restored in cleanup() when the last thread exits system().
*
* However, system() is still MT-unsafe because sigaction() has
* a process-wide effect and some other thread may also be
* setting the signal actions for SIGINT or SIGQUIT.
*/
lmutex_lock(&sys_lock);
if (sys_count++ == 0) {
(void) sigaction(SIGINT, &ignore, &sys_ibuf);
(void) sigaction(SIGQUIT, &ignore, &sys_qbuf);
}
lmutex_unlock(&sys_lock);
/*
* If SIGINT and SIGQUIT were not already SIG_IGN, tell
* posix_spawn() to make them SIG_DFL in the child,
* else leave them as SIG_IGN in the child.
*/
(void) sigemptyset(&mask);
if (sys_ibuf.sa_handler != SIG_IGN)
(void) sigaddset(&mask, SIGINT);
if (sys_qbuf.sa_handler != SIG_IGN)
(void) sigaddset(&mask, SIGQUIT);
if (error == 0)
error = posix_spawnattr_setsigdefault(&attr, &mask);
argv[0] = (char *)shell;
argv[1] = "-c";
argv[2] = (char *)cmd;
argv[3] = NULL;
if (error == 0)
error = posix_spawn(&cu.pid, shpath, NULL, &attr,
(char *const *)argv, (char *const *)_environ);
(void) posix_spawnattr_destroy(&attr);
if (error) {
errno = error;
status = -1;
} else {
/*
* system() is a cancellation point and so is waitpid().
*/
pthread_cleanup_push(cleanup, &cu);
do {
w = waitpid(cu.pid, &status, 0);
} while (w == -1 && errno == EINTR);
pthread_cleanup_pop(0);
if (w == -1)
status = -1;
}
error = errno;
cu.pid = 0;
cleanup(&cu);
errno = error;
return (status);
}