util: reset signals when we fork off agents

If we invoke agents, we should make sure we actually can kill them
again. I mean, it's probably not our job to cleanup the signals if our
tools are invoked in weird contexts, but at least we should make sure,
that the subprocesses we invoke and intend to control work as intended.

Also see:

http://lists.freedesktop.org/archives/systemd-devel/2014-August/022460.html

src/shared/util.c

@@ -959,6 +959,18 @@ int reset_all_signal_handlers(void) {
         return r;
 }
 
+int reset_signal_mask(void) {
+        sigset_t ss;
+
+        if (sigemptyset(&ss) < 0)
+                return -errno;
+
+        if (sigprocmask(SIG_SETMASK, &ss, NULL) < 0)
+                return -errno;
+
+        return 0;
+}
+
 char *strstrip(char *s) {
         char *e;
 
@@ -5131,6 +5143,12 @@ int fork_agent(pid_t *pid, const int except[], unsigned n_except, const char *pa
         /* 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
+         * case somebody invoked us from a shell script that trapped
+         * SIGTERM or so... */
+        reset_all_signal_handlers();
+        reset_signal_mask();
+
         stdout_is_tty = isatty(STDOUT_FILENO);
         stderr_is_tty = isatty(STDERR_FILENO);
 

src/shared/util.h

@@ -274,6 +274,7 @@ int readlink_and_make_absolute(const char *p, char **r);
 int readlink_and_canonicalize(const char *p, char **r);
 
 int reset_all_signal_handlers(void);
+int reset_signal_mask(void);
 
 char *strstrip(char *s);
 char *delete_chars(char *s, const char *bad);