When I wrote the new NFS/SELinux mount options code I was working under
the assumption that nfs_xdev_get_sb() would always give a new superblock
without the security struct initialized. I now have a report of a user
in which we hit BUG_ON(newsbsec->initialized) indicating to me that NFS
is reusing a superblock. The user says that he only has one mount to
the server in fstab, but doesn't know much about the server setup. Is
it expected that nfs_xdev_get_sb might reuse a superblock? If so maybe
we want this patch below? Instead of me BUGing every time selinux sees
a reused superblock we but only if the reused superblock has different
security options than the old one. I can't reproduce the issue so I
can't really test it....
comments? should NFS be reusing a superblock here? Can the NFS people
let me know how I can trigger it to make sure my patch fixes it?
-Eric
---
security/selinux/hooks.c | 38 ++++++++++++++++++++++++++++++++++----
1 files changed, 34 insertions(+), 4 deletions(-)
diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index 89bb6d3..71b01a4 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -760,13 +760,43 @@ 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);
+ /*
+ * check to make sure something isn't trying to reuse a superblock that
+ * isn't actually the same. if it is, that's the FS fault, not ours
+ */
+ if (unlikely(newsbsec->initialized)) {
+ struct security_mnt_opts new_opts, old_opts;
+ int i;
+
+ if (newsb == oldsb)
+ return;
+
+ if (selinux_get_mnt_opts(newsb, &new_opts))
+ return;
+ if (selinux_get_mnt_opts(oldsb, &old_opts)) {
+ security_free_mnt_opts(&new_opts);
+ return;
+ }
+
+ BUG_ON(new_opts.num_mnt_opts != old_opts.num_mnt_opts);
+
+ /*
+ * this is safe since _get_mnt_opts puts things in the same
+ * order every time.
+ */
+ for (i = 0; i < new_opts.num_mnt_opts; i++) {
+ BUG_ON(new_opts.mnt_opts_flags[i] != old_opts.mnt_opts_flags[i]);
+ BUG_ON(strcmp(new_opts.mnt_opts[i], old_opts.mnt_opts[i]));
+ }
+
+ security_free_mnt_opts(&new_opts);
+ security_free_mnt_opts(&old_opts);
+ return;
+ }
+
mutex_lock(&newsbsec->lock);
newsbsec->flags = oldsbsec->flags;
--
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