[PATCH net 3/6] net: openvswitch: conntrack: fix helper UAF due to extensions realloc

[Ilya Maximets]

While calling the helpers, a raw pointer to the extensions area is
wired into expectations list:

  -> nf_ct_helper()
   -> helper->help()
    -> nf_ct_expect_related_report()
     -> nf_ct_expect_insert()
      -> hlist_add_head_rcu(&exp->lnode, &master_help->expectations)

In case the connection is not confirmed yet, more extensions can be
added afterwards with *_ext_add() calls reallocating the extension
space and leaving the now invalid pointer in the expectations list
that is later accessed while removing the expectation.

Make sure that helpers are called at the end after all the other
extensions are already added.

Note that the helper rejection now leaves the mark and labels set,
but that's not different from how the NAT was handled before or how
the mark and the labels were handled on confirmation failure.  And
there are no atomicity guarantees provided by the API anyway.

Fixes: cae3a2627520 ("openvswitch: Allow attaching helpers to ct action")
Cc: stable@xxxxxxxxxxxxxxx
Reported-by: Axel Mierczuk <axel.mierczuk@xxxxxxxxxxxxx>
Signed-off-by: Ilya Maximets <i.maximets@xxxxxxx>
---
 net/openvswitch/conntrack.c | 19 +++++++++++++++----
 1 file changed, 15 insertions(+), 4 deletions(-)

diff --git a/net/openvswitch/conntrack.c b/net/openvswitch/conntrack.c
index c20f096eef40e..d3326edcabf76 100644
--- a/net/openvswitch/conntrack.c
+++ b/net/openvswitch/conntrack.c
@@ -817,11 +817,14 @@ static int __ovs_ct_lookup(struct net *net, struct sw_flow_key *key,
 			}
 		}
 
-		/* Call the helper only if:
-		 * - nf_conntrack_in() was executed above ("!cached"), or
-		 * - When committing an unconfirmed connection.
+		/* Call the helper only if nf_conntrack_in() was executed
+		 * above ("!cached").
+		 *
+		 * For unconfirmed connections it will be called later during
+		 * commit as we need to have all the other extensions allocated
+		 * before the call.
 		 */
-		if ((nf_ct_is_confirmed(ct) ? !cached : info->commit)) {
+		if (nf_ct_is_confirmed(ct) && !cached) {
 			int err = nf_ct_helper(skb, ct, ctinfo, info->family);
 
 			err = verdict_to_errno(err);
@@ -1025,6 +1028,14 @@ static int ovs_ct_commit(struct net *net, struct sw_flow_key *key,
 			return err;
 
 		nf_conn_act_ct_ext_add(skb, ct, ctinfo);
+
+		/* Call the helpers now.  We couldn't do this before as
+		 * all the extensions must be allocated before the call.
+		 */
+		err = nf_ct_helper(skb, ct, ctinfo, info->family);
+		err = verdict_to_errno(err);
+		if (err)
+			return err;
 	} else if (IS_ENABLED(CONFIG_NF_CONNTRACK_LABELS) &&
 		   labels_nonzero(&info->labels.mask)) {
 		err = ovs_ct_set_labels(ct, key, &info->labels.value,
-- 
2.55.0