CIFS: Fix oops while mounting with prefixpath

commit fec11dd9a0109fe52fd631e5c510778d6cbff6cc caused
a regression when we have already mounted //server/share/a
and want to mount //server/share/a/b.

The problem is that lookup_one_len calls __lookup_hash
with nd pointer as NULL. Then __lookup_hash calls
do_revalidate in the case when dentry exists and we end
up with NULL pointer deference in cifs_d_revalidate:

if (nd->flags & LOOKUP_RCU)
	return -ECHILD;

Fix this by checking nd for NULL.

Signed-off-by: Pavel Shilovsky <piastryyy@gmail.com>
Reviewed-by: Shirish Pargaonkar <shirishp@us.ibm.com>
CC: Stable <stable@kernel.org>
Signed-off-by: Steve French <sfrench@us.ibm.com>

1 files changed, 1 insertions, 1 deletions

diff --git a/fs/cifs/dir.c b/fs/cifs/dir.c
index 8e9d37d44e9d..c1bd0306d6c6 100644
--- a/fs/cifs/dir.c
+++ b/fs/cifs/dir.c
@@ -636,7 +636,7 @@ lookup_out:
 static int
 cifs_d_revalidate(struct dentry *direntry, struct nameidata *nd)
 {
-        if (nd->flags & LOOKUP_RCU)
+        if (nd && (nd->flags & LOOKUP_RCU))
                 return -ECHILD;
 
         if (direntry->d_inode) {