ldpd: detach stdin/stdout/stderr from the child processes

Doing a "ssh user@node 'ldpd -d'" was making the SSH session hang. In
the original OpenBSD's ldpd(8) daemon, the daemon function takes care
of connecting stdin/stdout/stderr to /dev/null. In the FRR port, this
only happens in the frr_run() function, after all children have been
forked. Ideally we could try to rearrange libfrr.c and ldpd.c in a way
that start_child() is called only after the parent connects the standard
I/O streams to /dev/null. But since this issue needs an immediate
fix, let's do this workaround for now. Note: even when running on the
foreground, all log messages from the child processes are sent to the
parent process, which then prints the messages to stdout/stderr and/or
to a log file.

Reported-by: Martin Winter <mwinter@opensourcerouting.org>
Signed-off-by: Renato Westphal <renato@opensourcerouting.org>

1 files changed, 7 insertions, 1 deletions

diff --git a/ldpd/ldpd.c b/ldpd/ldpd.c
index 303baf463b..e3510c210a 100644
--- a/ldpd/ldpd.c
+++ b/ldpd/ldpd.c
@@ -450,7 +450,7 @@ static pid_t
 start_child(enum ldpd_process p, char *argv0, int fd_async, int fd_sync)
 {
 	char	*argv[3];
-	int	 argc = 0;
+	int	 argc = 0, nullfd;
 	pid_t	 pid;
 
 	switch (pid = fork()) {
@@ -464,6 +464,12 @@ start_child(enum ldpd_process p, char *argv0, int fd_async, int fd_sync)
 		return (pid);
 	}
 
+	nullfd = open("/dev/null", O_RDONLY | O_NOCTTY);
+	dup2(nullfd, 0);
+	dup2(nullfd, 1);
+	dup2(nullfd, 2);
+	close(nullfd);
+
 	if (dup2(fd_async, LDPD_FD_ASYNC) == -1)
 		fatal("cannot setup imsg async fd");
 	if (dup2(fd_sync, LDPD_FD_SYNC) == -1)