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util: fix minimal race where we might miss SIGTERMs when forking off an agent

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Before forking, block all signals, and unblock them afterwards. This way
the child will have them blocked, and we won't lose them.
This commit is contained in:
Lennart Poettering 2014-08-27 21:42:20 +02:00
parent c609cb9898
commit 8a7c93d858
1 changed files with 24 additions and 13 deletions
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37
src/shared/util.c
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@ -5102,9 +5102,9 @@ int fd_inc_rcvbuf(int fd, size_t n) {
} }
int fork_agent(pid_t *pid, const int except[], unsigned n_except, const char *path, ...) { int fork_agent(pid_t *pid, const int except[], unsigned n_except, const char *path, ...) {
pid_t parent_pid, agent_pid;
int fd;
bool stdout_is_tty, stderr_is_tty; bool stdout_is_tty, stderr_is_tty;
pid_t parent_pid, agent_pid;
sigset_t ss, saved_ss;
unsigned n, i; unsigned n, i;
va_list ap; va_list ap;
char **l; char **l;
@ -5112,16 +5112,25 @@ int fork_agent(pid_t *pid, const int except[], unsigned n_except, const char *pa
assert(pid); assert(pid);
assert(path); assert(path);
parent_pid = getpid();
/* Spawns a temporary TTY agent, making sure it goes away when /* Spawns a temporary TTY agent, making sure it goes away when
* we go away */ * we go away */
parent_pid = getpid();
/* First we temporarily block all signals, so that the new
* child has them blocked initially. This way, we can be sure
* that SIGTERMs are not lost we might send to the agent. */
assert_se(sigfillset(&ss) >= 0);
assert_se(sigprocmask(SIG_SETMASK, &ss, &saved_ss) >= 0);
agent_pid = fork(); agent_pid = fork();
if (agent_pid < 0) if (agent_pid < 0) {
assert_se(sigprocmask(SIG_SETMASK, &saved_ss, NULL) >= 0);
return -errno; return -errno;
}
if (agent_pid != 0) { if (agent_pid != 0) {
assert_se(sigprocmask(SIG_SETMASK, &saved_ss, NULL) >= 0);
*pid = agent_pid; *pid = agent_pid;
return 0; return 0;
} }
@ -5132,24 +5141,26 @@ int fork_agent(pid_t *pid, const int except[], unsigned n_except, const char *pa
if (prctl(PR_SET_PDEATHSIG, SIGTERM) < 0) if (prctl(PR_SET_PDEATHSIG, SIGTERM) < 0)
_exit(EXIT_FAILURE); _exit(EXIT_FAILURE);
/* Check whether our parent died before we were able
* to set the death signal */
if (getppid() != parent_pid)
_exit(EXIT_SUCCESS);
/* Don't leak fds to the agent */
close_all_fds(except, n_except);
/* Make sure we actually can kill the agent, if we need to, in /* Make sure we actually can kill the agent, if we need to, in
* case somebody invoked us from a shell script that trapped * case somebody invoked us from a shell script that trapped
* SIGTERM or so... */ * SIGTERM or so... */
reset_all_signal_handlers(); reset_all_signal_handlers();
reset_signal_mask(); reset_signal_mask();
/* Check whether our parent died before we were able
* to set the death signal and unblock the signals */
if (getppid() != parent_pid)
_exit(EXIT_SUCCESS);
/* Don't leak fds to the agent */
close_all_fds(except, n_except);
stdout_is_tty = isatty(STDOUT_FILENO); stdout_is_tty = isatty(STDOUT_FILENO);
stderr_is_tty = isatty(STDERR_FILENO); stderr_is_tty = isatty(STDERR_FILENO);
if (!stdout_is_tty || !stderr_is_tty) { if (!stdout_is_tty || !stderr_is_tty) {
int fd;
/* Detach from stdout/stderr. and reopen /* Detach from stdout/stderr. and reopen
* /dev/tty for them. This is important to * /dev/tty for them. This is important to
* ensure that when systemctl is started via * ensure that when systemctl is started via