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#define _GNU_SOURCE
#include <spawn.h>
#include <sched.h>
#include <unistd.h>
#include <signal.h>
#include <fcntl.h>
#include <sys/wait.h>
#include "syscall.h"
#include "pthread_impl.h"
#include "fdop.h"
#include "libc.h"
static void dummy_0()
{
}
weak_alias(dummy_0, __acquire_ptc);
weak_alias(dummy_0, __release_ptc);
struct args {
int p[2];
sigset_t oldmask;
const char *path;
int (*exec)(const char *, char *const *, char *const *);
const posix_spawn_file_actions_t *fa;
const posix_spawnattr_t *restrict attr;
char *const *argv, *const *envp;
};
static int child(void *args_vp)
{
int i, ret;
struct sigaction sa;
struct args *args = args_vp;
int p = args->p[1];
const posix_spawn_file_actions_t *fa = args->fa;
const posix_spawnattr_t *restrict attr = args->attr;
close(args->p[0]);
/* All signal dispositions must be either SIG_DFL or SIG_IGN
* before signals are unblocked. Otherwise a signal handler
* from the parent might get run in the child while sharing
* memory, with unpredictable and dangerous results. */
for (i=1; i<_NSIG; i++) {
__libc_sigaction(i, 0, &sa);
if (sa.sa_handler!=SIG_DFL && (sa.sa_handler!=SIG_IGN ||
((attr->__flags & POSIX_SPAWN_SETSIGDEF)
&& sigismember(&attr->__def, i) ))) {
sa.sa_handler = SIG_DFL;
__libc_sigaction(i, &sa, 0);
}
}
if (attr->__flags & POSIX_SPAWN_SETPGROUP)
if ((ret=__syscall(SYS_setpgid, 0, attr->__pgrp)))
goto fail;
/* Use syscalls directly because pthread state because the
* library functions attempt to do a multi-threaded synchronized
* id-change, which would trash the parent's state. */
if (attr->__flags & POSIX_SPAWN_RESETIDS)
if ((ret=__syscall(SYS_setgid, __syscall(SYS_getgid))) ||
(ret=__syscall(SYS_setuid, __syscall(SYS_getuid))) )
goto fail;
if (fa && fa->__actions) {
struct fdop *op;
int fd;
for (op = fa->__actions; op->next; op = op->next);
for (; op; op = op->prev) {
/* It's possible that a file operation would clobber
* the pipe fd used for synchronizing with the
* parent. To avoid that, we dup the pipe onto
* an unoccupied fd. */
if (op->fd == p) {
ret = __syscall(SYS_dup, p);
if (ret < 0) goto fail;
__syscall(SYS_close, p);
p = ret;
}
switch(op->cmd) {
case FDOP_CLOSE:
if ((ret=__syscall(SYS_close, op->fd)))
goto fail;
break;
case FDOP_DUP2:
if ((ret=__syscall(SYS_dup2, op->srcfd, op->fd))<0)
goto fail;
break;
case FDOP_OPEN:
fd = __syscall(SYS_open, op->path,
op->oflag | O_LARGEFILE, op->mode);
if ((ret=fd) < 0) goto fail;
if (fd != op->fd) {
if ((ret=__syscall(SYS_dup2, fd, op->fd))<0)
goto fail;
__syscall(SYS_close, fd);
}
break;
}
}
}
/* Close-on-exec flag may have been lost if we moved the pipe
* to a different fd. We don't use F_DUPFD_CLOEXEC above because
* it would fail on older kernels and atomicity is not needed --
* in this process there are no threads or signal handlers. */
__syscall(SYS_fcntl, p, F_SETFD, FD_CLOEXEC);
pthread_sigmask(SIG_SETMASK, (attr->__flags & POSIX_SPAWN_SETSIGMASK)
? &attr->__mask : &args->oldmask, 0);
args->exec(args->path, args->argv, args->envp);
fail:
/* Since sizeof errno < PIPE_BUF, the write is atomic. */
ret = -ret;
if (ret) while (write(p, &ret, sizeof ret) < 0);
_exit(127);
}
int __posix_spawnx(pid_t *restrict res, const char *restrict path,
int (*exec)(const char *, char *const *, char *const *),
const posix_spawn_file_actions_t *fa,
const posix_spawnattr_t *restrict attr,
char *const argv[restrict], char *const envp[restrict])
{
pid_t pid;
char stack[1024];
int ec=0, cs;
struct args args;
if (pipe2(args.p, O_CLOEXEC))
return errno;
pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, &cs);
args.path = path;
args.exec = exec;
args.fa = fa;
args.attr = attr ? attr : &(const posix_spawnattr_t){0};
args.argv = argv;
args.envp = envp;
pthread_sigmask(SIG_BLOCK, SIGALL_SET, &args.oldmask);
/* This lock prevents setuid/setgid operations while the parent
* is sharing memory with the child. Situations where processes
* with different permissions share VM are fundamentally unsafe. */
__acquire_ptc();
pid = __clone(child, stack+sizeof stack, CLONE_VM|SIGCHLD, &args);
close(args.p[1]);
if (pid > 0) {
if (read(args.p[0], &ec, sizeof ec) < sizeof ec) ec = 0;
else waitpid(pid, &(int){0}, 0);
} else {
ec = -pid;
}
/* At this point, the child has either exited or successfully
* performed exec, so the lock may be released. */
__release_ptc();
close(args.p[0]);
if (!ec) *res = pid;
pthread_sigmask(SIG_SETMASK, &args.oldmask, 0);
pthread_setcancelstate(cs, 0);
return ec;
}
int posix_spawn(pid_t *restrict res, const char *restrict path,
const posix_spawn_file_actions_t *fa,
const posix_spawnattr_t *restrict attr,
char *const argv[restrict], char *const envp[restrict])
{
return __posix_spawnx(res, path, execve, fa, attr, argv, envp);
}
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