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

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.

1 files changed, 5 insertions, 10 deletions

diff --git a/src/sulogin-shell/sulogin-shell.c b/src/sulogin-shell/sulogin-shell.c
index 70659df417..a6e0e0476f 100644
--- a/src/sulogin-shell/sulogin-shell.c
+++ b/src/sulogin-shell/sulogin-shell.c
@@ -81,18 +81,13 @@ static int start_default_target(sd_bus *bus) {
 
 static int fork_wait(const char* const cmdline[]) {
         pid_t pid;
+        int r;
 
-        pid = fork();
-        if (pid < 0)
-                return log_error_errno(errno, "fork(): %m");
-        if (pid == 0) {
-
+        r = safe_fork("(sulogin)", FORK_RESET_SIGNALS|FORK_DEATHSIG, &pid);
+        if (r < 0)
+                return log_error_errno(r, "fork(): %m");
+        if (r == 0) {
                 /* Child */
-
-                (void) reset_all_signal_handlers();
-                (void) reset_signal_mask();
-                assert_se(prctl(PR_SET_PDEATHSIG, SIGTERM) == 0);
-
                 execv(cmdline[0], (char**) cmdline);
                 log_error_errno(errno, "Failed to execute %s: %m", cmdline[0]);
                 _exit(EXIT_FAILURE); /* Operational error */