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, 4 insertions, 9 deletions

diff --git a/src/libsystemd/sd-bus/bus-socket.c b/src/libsystemd/sd-bus/bus-socket.c
index d72cb616e0..013bdb05a0 100644
--- a/src/libsystemd/sd-bus/bus-socket.c
+++ b/src/libsystemd/sd-bus/bus-socket.c
@@ -715,19 +715,14 @@ int bus_socket_exec(sd_bus *b) {
         if (r < 0)
                 return -errno;
 
-        pid = fork();
-        if (pid < 0) {
+        r = safe_fork_full("(sd-busexec)", s+1, 1, FORK_RESET_SIGNALS|FORK_CLOSE_ALL_FDS, &pid);
+        if (r < 0) {
                 safe_close_pair(s);
-                return -errno;
+                return r;
         }
-        if (pid == 0) {
+        if (r == 0) {
                 /* Child */
 
-                (void) reset_all_signal_handlers();
-                (void) reset_signal_mask();
-
-                close_all_fds(s+1, 1);
-
                 assert_se(dup3(s[1], STDIN_FILENO, 0) == STDIN_FILENO);
                 assert_se(dup3(s[1], STDOUT_FILENO, 0) == STDOUT_FILENO);