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>

diff --git a/udev.c b/udev.c
index beaa191..926c4b5 100644 (file)
--- a/udev.c
+++ b/udev.c
@@ -72,6 +72,7 @@ int main(int argc, char *argv[], char *envp[])
        const char *devpath;
        const char *subsystem;
        struct sigaction act;
+       int devnull;
        int retval = -EINVAL;
 
        if (argc == 2 && strcmp(argv[1], "-V") == 0) {
@@ -79,7 +80,22 @@ int main(int argc, char *argv[], char *envp[])
                exit(0);
        }
 
+       /* 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("udev");
+       if (devnull < 0)
+               err("fatal, could not open /dev/null");
        udev_init_config();
        dbg("version %s", UDEV_VERSION);
 

diff --git a/udevd.c b/udevd.c
index 79d3e82..ffd2b1f 100644 (file)
--- 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) {