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, 7 insertions, 9 deletions

diff --git a/src/libelogind/sd-bus/bus-container.c b/src/libelogind/sd-bus/bus-container.c
index 8f6d34838..a1242c567 100644
--- a/src/libelogind/sd-bus/bus-container.c
+++ b/src/libelogind/sd-bus/bus-container.c
@@ -62,11 +62,10 @@ int bus_container_connect_socket(sd_bus *b) {
         if (socketpair(AF_UNIX, SOCK_SEQPACKET, 0, pair) < 0)
                 return -errno;
 
-        child = fork();
-        if (child < 0)
-                return -errno;
-
-        if (child == 0) {
+        r = safe_fork("(sd-buscntr)", FORK_RESET_SIGNALS|FORK_DEATHSIG, &child);
+        if (r < 0)
+                return r;
+        if (r == 0) {
                 pid_t grandchild;
 
                 pair[0] = safe_close(pair[0]);
@@ -82,11 +81,10 @@ int bus_container_connect_socket(sd_bus *b) {
                  * comes from a process from within the container, and
                  * not outside of it */
 
-                grandchild = fork();
-                if (grandchild < 0)
+                r = safe_fork("(sd-buscntr2)", FORK_RESET_SIGNALS|FORK_DEATHSIG, &grandchild);
+                if (r < 0)
                         _exit(EXIT_FAILURE);
-
-                if (grandchild == 0) {
+                if (r == 0) {
 
                         r = connect(b->input_fd, &b->sockaddr.sa, b->sockaddr_size);
                         if (r < 0) {