[PATCH] Try to provide a bit of security for hardlinks to /dev entries.

diff --git a/udev-remove.c b/udev-remove.c
index 27ff5bc0a2e12d38167ba1db43d85ca78ac3ccf0..4f2cd479c03b1146bc4b9d425869d3524eded04d 100644 (file)
--- a/udev-remove.c
+++ b/udev-remove.c
@@ -65,6 +65,41 @@ static int delete_path(char *path)
        return 0;
 }
 
+/** Remove all permissions on the device node, before
+  * unlinking it. This fixes a security issue.
+  * If the user created a hard-link to the device node,
+  * he can't use it any longer, because he lost permission
+  * to do so.
+  */
+static int secure_unlink(const char *filename)
+{
+       int retval;
+
+       retval = chown(filename, 0, 0);
+       if (retval) {
+               dbg("chown(%s, 0, 0) failed with error '%s'",
+                   filename, strerror(errno));
+               /* We continue nevertheless.
+                * I think it's very unlikely for chown
+                * to fail here, if the file exists.
+                */
+       }
+       retval = chmod(filename, 0000);
+       if (retval) {
+               dbg("chmod(%s, 0000) failed with error '%s'",
+                   filename, strerror(errno));
+               /* We continue nevertheless. */
+       }
+       retval = unlink(filename);
+       if (errno == ENOENT)
+               retval = 0;
+       if (retval) {
+               dbg("unlink(%s) failed with error '%s'",
+                       filename, strerror(errno));
+       }
+       return retval;
+}
+
 static int delete_node(struct udevice *dev)
 {
        char filename[NAME_SIZE];
@@ -79,14 +114,9 @@ static int delete_node(struct udevice *dev)
        strfieldcat(filename, dev->name);
 
        info("removing device node '%s'", filename);
-       retval = unlink(filename);
-       if (errno == ENOENT)
-               retval = 0;
-       if (retval) {
-               dbg("unlink(%s) failed with error '%s'",
-                       filename, strerror(errno));
+       retval = secure_unlink(filename);
+       if (retval)
                return retval;
-       }
 
        /* remove partition nodes */
        if (dev->partitions > 0) {
@@ -94,7 +124,7 @@ static int delete_node(struct udevice *dev)
                for (i = 1; i <= dev->partitions; i++) {
                        strfieldcpy(partitionname, filename);
                        strintcat(partitionname, i);
-                       unlink(partitionname);
+                       secure_unlink(partitionname);
                }
        }