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tree-wide: introduce new safe_fork() helper and port everything over

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This adds a new safe_fork() wrapper around fork() and makes use of it
everywhere. The new wrapper does a couple of things we previously did
manually and separately in a safer, more correct and automatic way:

1. Optionally resets signal handlers/mask in the child

2. Sets a name on all processes we fork off right after forking off (and
   the patch assigns useful names for all processes we fork off now,
   following a systematic naming scheme: always enclosed in () – in order
   to indicate that these are not proper, exec()ed processes, but only
   forked off children, and if the process is long-running with only our
   own code, without execve()'ing something else, it gets am "sd-" prefix.)

3. Optionally closes all file descriptors in the child

4. Optionally sets a PR_SET_DEATHSIG to SIGTERM in the child, in a safe
   way so that the parent dying before this happens being handled
   safely.

5. Optionally reopens the logs

6. Optionally connects stdin/stdout/stderr to /dev/null

7. Debug logs about the forked off processes.
This commit is contained in:
Lennart Poettering
2017-12-25 11:48:21 +01:00
parent d8caff6db6
commit 4c253ed1ca
42 changed files with 448 additions and 507 deletions
Download Patch File Download Diff File Expand all files Collapse all files
src/basic/util.c
+7 -39
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@@ -186,11 +186,11 @@ int prot_from_flags(int flags) {
int fork_agent(pid_t *pid, const int except[], unsigned n_except, const char *path, ...) {
bool stdout_is_tty, stderr_is_tty;
pid_t parent_pid, agent_pid;
sigset_t ss, saved_ss;
pid_t agent_pid;
unsigned n, i;
va_list ap;
char **l;
int r;
assert(pid);
assert(path);
@@ -198,45 +198,13 @@ int fork_agent(pid_t *pid, const int except[], unsigned n_except, const char *pa
/* Spawns a temporary TTY agent, making sure it goes away when
* we go away */
parent_pid = getpid_cached();
/* 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();
if (agent_pid < 0) {
assert_se(sigprocmask(SIG_SETMASK, &saved_ss, NULL) >= 0);
return -errno;
}
if (agent_pid != 0) {
assert_se(sigprocmask(SIG_SETMASK, &saved_ss, NULL) >= 0);
*pid = agent_pid;
r = safe_fork_full("(sd-agent)", except, n_except, FORK_RESET_SIGNALS|FORK_DEATHSIG|FORK_CLOSE_ALL_FDS, &agent_pid);
if (r < 0)
return r;
if (r > 0)
return 0;
}
/* In the child:
*
* Make sure the agent goes away when the parent dies */
if (prctl(PR_SET_PDEATHSIG, SIGTERM) < 0)
_exit(EXIT_FAILURE);
/* Make sure we actually can kill the agent, if we need to, in
* case somebody invoked us from a shell script that trapped
* SIGTERM or so... */
(void) reset_all_signal_handlers();
(void) 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);
/* In the child: */
stdout_is_tty = isatty(STDOUT_FILENO);
stderr_is_tty = isatty(STDERR_FILENO);