cifs: verify that tcon is valid before dereference in cifs_kill_sb

On umount, cifs_sb->tlink_tree might contain entries that do not represent
a valid tcon.
Check the tcon for error before we dereference it.

Signed-off-by: Ronnie Sahlberg <lsahlber@redhat.com>
Cc: stable@vger.kernel.org
Reviewed-by: Shyam Prasad N <sprasad@microsoft.com>
Reported-by: Xiaoli Feng <xifeng@redhat.com>
Signed-off-by: Steve French <stfrench@microsoft.com>

diff --git a/fs/cifs/cifsfs.c b/fs/cifs/cifsfs.c
index aba0783..2b1a1c0 100644 (file)
--- a/fs/cifs/cifsfs.c
+++ b/fs/cifs/cifsfs.c
@@ -266,10 +266,11 @@ static void cifs_kill_sb(struct super_block *sb)
         * before we kill the sb.
         */
        if (cifs_sb->root) {
-               node = rb_first(root);
-               while (node != NULL) {
+               for (node = rb_first(root); node; node = rb_next(node)) {
                        tlink = rb_entry(node, struct tcon_link, tl_rbnode);
                        tcon = tlink_tcon(tlink);
+                       if (IS_ERR(tcon))
+                               continue;
                        cfid = &tcon->crfid;
                        mutex_lock(&cfid->fid_mutex);
                        if (cfid->dentry) {
@@ -277,7 +278,6 @@ static void cifs_kill_sb(struct super_block *sb)
                                cfid->dentry = NULL;
                        }
                        mutex_unlock(&cfid->fid_mutex);
-                       node = rb_next(node);
                }
 
                /* finally release root dentry */