cifs: cope with negative dentries in cifs_get_root

The loop around lookup_one_len doesn't handle the case where it might
return a negative dentry, which can cause an oops on the next pass
through the loop. Check for that and break out of the loop with an
error of -ENOENT if there is one.

Fixes the panic reported here:

    https://bugzilla.redhat.com/show_bug.cgi?id=727927

Reported-by: TR Bentley <home@trarbentley.net>
Reported-by: Iain Arnell <iarnell@gmail.com>
Cc: Al Viro <viro@ZenIV.linux.org.uk>
Cc: stable@kernel.org
Signed-off-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Steve French <sfrench@us.ibm.com>

1 files changed, 4 insertions, 0 deletions

diff --git a/fs/cifs/cifsfs.c b/fs/cifs/cifsfs.c
index 212e5629cc1d..f93eb948d071 100644
--- a/fs/cifs/cifsfs.c
+++ b/fs/cifs/cifsfs.c
@@ -563,6 +563,10 @@ cifs_get_root(struct smb_vol *vol, struct super_block *sb)
                 mutex_unlock(&dir->i_mutex);
                 dput(dentry);
                 dentry = child;
+                if (!dentry->d_inode) {
+                        dput(dentry);
+                        dentry = ERR_PTR(-ENOENT);
+                }
         } while (!IS_ERR(dentry));
         _FreeXid(xid);
         kfree(full_path);