SELinux: don't BUG if fs reuses a superblock

I (wrongly) assumed that nfs_xdev_get_sb() would not ever share a superblock
and so cloning mount options would always be correct.  Turns out that isn't
the case and we could fall over a BUG_ON() that wasn't a BUG at all.  Since
there is little we can do to reconcile different mount options this patch
just leaves the sb alone and the first set of options wins.

Signed-off-by: Eric Paris <eparis@redhat.com>
Acked-by: Stephen Smalley <sds@tycho.nsa.gov>
Acked-by: Trond Myklebust <trond.myklebust@fys.uio.no>
Signed-off-by: James Morris <jmorris@namei.org>

diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index 89bb6d3..d39b59c 100644 (file)
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -760,13 +760,13 @@ static void selinux_sb_clone_mnt_opts(const struct super_block *oldsb,
         * this early in the boot process. */
        BUG_ON(!ss_initialized);
 
-       /* this might go away sometime down the line if there is a new user
-        * of clone, but for now, nfs better not get here... */
-       BUG_ON(newsbsec->initialized);
-
        /* how can we clone if the old one wasn't set up?? */
        BUG_ON(!oldsbsec->initialized);
 
+       /* if fs is reusing a sb, just let its options stand... */
+       if (newsbsec->initialized)
+               return;
+
        mutex_lock(&newsbsec->lock);
 
        newsbsec->flags = oldsbsec->flags;