Avoid propagating shutdown signal to all subprocesses

This was a sort-of-regression with 7233f68

While this behavior might seem desirable in some cases, multi-user
installs like public servers would rather not kill children while
upgrading.

Turns out that pipes are inherited by forks, and writing in one side
means there might be more than one listener that calls
bitlbee_shutdown(). If the parent gets it, the children will get it
too. If a child gets it, the parent and the other children get it too.

This adds a sighandler_shutdown_setup() function that closes any
previously existing pipes and disconnects the events from them, to
create a new one. This is called again after forking each child process.

While I'm sure this fixes the issue, I still don't understand why it
*didn't* kill the forked processes in some cases. Worrying.

1 files changed, 26 insertions, 9 deletions

diff --git a/unix.c b/unix.c
index 30451241..298c8427 100644
--- a/unix.c
+++ b/unix.c
@@ -47,7 +47,11 @@
 
 global_t global;        /* Against global namespace pollution */
 
-static int signal_shutdown_pipe[2] = { -1, -1 };
+static struct {
+	int fd[2];
+	int tag;
+} shutdown_pipe = {{-1 , -1}, 0};
+
 static void sighandler_shutdown(int signal);
 static void sighandler_crash(int signal);
 
@@ -155,13 +159,11 @@ int main(int argc, char *argv[])
 	sig.sa_handler = sighandler_crash;
 	sigaction(SIGSEGV, &sig, &old);
 
-	/* Use a pipe for SIGTERM/SIGINT so the actual signal handler doesn't do anything unsafe */
-	if (pipe(signal_shutdown_pipe) == 0) {
-		b_input_add(signal_shutdown_pipe[0], B_EV_IO_READ, bitlbee_shutdown, NULL);
-		sig.sa_handler = sighandler_shutdown;
-		sigaction(SIGINT, &sig, &old);
-		sigaction(SIGTERM, &sig, &old);
-	}
+	sighandler_shutdown_setup();
+
+	sig.sa_handler = sighandler_shutdown;
+	sigaction(SIGINT, &sig, &old);
+	sigaction(SIGTERM, &sig, &old);
 
 	if (!getuid() || !geteuid()) {
 		log_message(LOGLVL_WARNING, "BitlBee is running with root privileges. Why?");
@@ -255,12 +257,27 @@ static int crypt_main(int argc, char *argv[])
 	return 0;
 }
 
+/* Set up a pipe for SIGTERM/SIGINT so the actual signal handler doesn't do anything unsafe */
+void sighandler_shutdown_setup()
+{
+	if (shutdown_pipe.fd[0] != -1) {
+		/* called again from a forked process, clean up to avoid propagating the signal */
+		b_event_remove(shutdown_pipe.tag);
+		close(shutdown_pipe.fd[0]);
+		close(shutdown_pipe.fd[1]);
+	}
+
+	if (pipe(shutdown_pipe.fd) == 0) {
+		shutdown_pipe.tag = b_input_add(shutdown_pipe.fd[0], B_EV_IO_READ, bitlbee_shutdown, NULL);
+	}
+}
+
 /* Signal handler for SIGTERM and SIGINT */
 static void sighandler_shutdown(int signal)
 {
 	/* Write a single null byte to the pipe, just to send a message to the main loop.
 	 * This gets handled by bitlbee_shutdown (the b_input_add callback for this pipe) */
-	write(signal_shutdown_pipe[1], "", 1);
+	write(shutdown_pipe.fd[1], "", 1);
 }
 
 /* Signal handler for SIGSEGV