bring std(in|out|err) fd's in a sane state

If the kernel forks us as an usermodhelper, we don't have any of
the standard fd's and the first open() will start with fd=0.
This is inherited to all forked childs and confuses later forked
helpers where we want to read from a pipe connected to the helpers
stdout/stderr.

  # ls -l /proc/$(pidof udevd)/fd
  total 6
  dr-x------  2 root root  0 2005-08-18 12:44 .
  dr-xr-xr-x  4 root root  0 2005-08-18 12:44 ..
  lrwx------  1 root root 64 2005-08-18 12:44 0 -> /dev/null
  lrwx------  1 root root 64 2005-08-18 12:44 1 -> socket:[1274617]
  lr-x------  1 root root 64 2005-08-18 12:44 2 -> pipe:[1274618]
  l-wx------  1 root root 64 2005-08-18 12:44 3 -> pipe:[1274618]
  lrwx------  1 root root 64 2005-08-18 12:44 4 -> socket:[1274619]
  lrwx------  1 root root 64 2005-08-18 12:44 5 -> socket:[1274620]

Ouch! This will obviously not redirect sterr, it will kill the pipe
we established between the parent and the child:

  devnull = open("/dev/null", O_RDWR);
  dup2(devnull, STDERR_FILENO);

Signed-off-by: Kay Sievers <kay.sievers@suse.de>

1 files changed, 16 insertions, 10 deletions

diff --git a/udevd.c b/udevd.c
index 79d3e82550..ffd2b1ff3b 100644
--- a/udevd.c
+++ b/udevd.c
@@ -777,7 +777,23 @@ int main(int argc, char *argv[], char *envp[])
 	int daemonize = 0;
 	int i;
 
+	/* set std fd's to /dev/null, if the kernel forks us, we don't have them at all */
+	devnull = open("/dev/null", O_RDWR);
+	if (devnull >= 0)  {
+		if (devnull != STDIN_FILENO)
+			dup2(devnull, STDIN_FILENO);
+		if (devnull != STDOUT_FILENO)
+			dup2(devnull, STDOUT_FILENO);
+		if (devnull != STDERR_FILENO)
+			dup2(devnull, STDERR_FILENO);
+		if (devnull > STDERR_FILENO)
+			close(devnull);
+	}
+
 	logging_init("udevd");
+	if (devnull < 0)
+		err("fatal, could not open /dev/null");
+
 	udev_init_config();
 	dbg("version %s", UDEV_VERSION);
 
@@ -825,16 +841,6 @@ int main(int argc, char *argv[], char *envp[])
 	/* set a reasonable scheduling priority for the daemon */
 	setpriority(PRIO_PROCESS, 0, UDEVD_PRIORITY);
 
-	/* Set fds to dev/null */
-	devnull = open( "/dev/null", O_RDWR );
-	if (devnull > 0)  {
-		dup2(devnull, STDIN_FILENO);
-		dup2(devnull, STDOUT_FILENO);
-		dup2(devnull, STDERR_FILENO);
-		close(devnull);
-	} else
-		err("error opening /dev/null %s", strerror(errno));
-
 	/* setup signal handler pipe */
 	retval = pipe(pipefds);
 	if (retval < 0) {