mdev: do not follow symlinks in /sys (as was intended prior to rev 18811).

If this breaks things, please document why!
mdev,init: use shared code for fd sanitization

function                                             old     new   delta
bb_daemonize_or_rexec                                155     172     +17
mdev_main                                            500     505      +5
init_main                                            907     856     -51
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 2/1 up/down: 22/-51)            Total: -29 bytes

1 files changed, 12 insertions, 5 deletions

diff --git a/util-linux/mdev.c b/util-linux/mdev.c
index c7109373d..9c4938a70 100644
--- a/util-linux/mdev.c
+++ b/util-linux/mdev.c
@@ -19,7 +19,8 @@ struct globals {
 #define root_major (G.root_major)
 #define root_minor (G.root_minor)
 
-#define MAX_SYSFS_DEPTH 3 /* prevent infinite loops in /sys symlinks */
+/* Prevent infinite loops in /sys symlinks */
+#define MAX_SYSFS_DEPTH 3
 
 /* We use additional 64+ bytes in make_device() */
 #define SCRATCH_SIZE 80
@@ -392,11 +393,17 @@ int mdev_main(int argc, char **argv)
         char *env_path;
         RESERVE_CONFIG_BUFFER(temp, PATH_MAX + SCRATCH_SIZE);
 
-#ifdef YOU_WANT_TO_DEBUG_HOTPLUG_EVENTS
+        /* We can be called as hotplug helper */
         /* Kernel cannot provide suitable stdio fds for us, do it ourself */
+#if 1
+        bb_sanitize_stdio();
+#else
+        /* Debug code */
         /* Replace LOGFILE by other file or device name if you need */
 #define LOGFILE "/dev/console"
-        xmove_fd(xopen("/dev/null", O_RDONLY), STDIN_FILENO);
+        /* Just making sure fd 0 is not closed,
+         * we don't really intend to read from it */
+        xmove_fd(xopen("/", O_RDONLY), STDIN_FILENO);
         xmove_fd(xopen(LOGFILE, O_WRONLY|O_APPEND), STDOUT_FILENO);
         xmove_fd(xopen(LOGFILE, O_WRONLY|O_APPEND), STDERR_FILENO);
 #endif
@@ -414,11 +421,11 @@ int mdev_main(int argc, char **argv)
                 root_minor = minor(st.st_dev);
 
                 recursive_action("/sys/block",
-                        ACTION_RECURSE | ACTION_FOLLOWLINKS,
+                        ACTION_RECURSE /* no ACTION_FOLLOWLINKS! */,
                         fileAction, dirAction, temp, 0);
 
                 recursive_action("/sys/class",
-                        ACTION_RECURSE | ACTION_FOLLOWLINKS,
+                        ACTION_RECURSE /* no ACTION_FOLLOWLINKS! */,
                         fileAction, dirAction, temp, 0);
 
         } else {