[PATCH] net/tcp-ao: fix use-after-free of key in del_async path

[HanQuan <eilaimemedsnaimel@gmail.com>]

In tcp_ao_delete_key(), the del_async path skips the current_key
and rnext_key validity checks present in the synchronous path,
assuming these pointers are always NULL on LISTEN sockets.  However,
if a key was added with set_current=1/set_rnext=1 while the socket
was in CLOSE state, current_key and rnext_key will be non-NULL
after listen() transitions the socket to LISTEN.

When such a key is deleted with del_async=1, hlist_del_rcu() and
call_rcu() free the key without clearing the dangling pointers.
After the RCU grace period, getsockopt(TCP_AO_INFO) dereferences
current_key->sndid and rnext_key->rcvid from freed slab memory.

Clear current_key and rnext_key in the del_async path when they
reference the key being deleted.

Fixes: d6732b95b6fb ("net/tcp: Allow asynchronous delete for TCP-AO keys (MKTs)")
Signed-off-by: HanQuan <eilaimemedsnaimel@gmail.com>
---
 net/ipv4/tcp_ao.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/net/ipv4/tcp_ao.c b/net/ipv4/tcp_ao.c
index 2f69bcecae78..a56bb79e15e0 100644
--- a/net/ipv4/tcp_ao.c
+++ b/net/ipv4/tcp_ao.c
@@ -1747,6 +1747,10 @@ static int tcp_ao_delete_key(struct sock *sk, struct tcp_ao_info *ao_info,
 	 * them and we can just free all resources in RCU fashion.
 	 */
 	if (del_async) {
+		if (ao_info->current_key == key)
+			WRITE_ONCE(ao_info->current_key, NULL);
+		if (ao_info->rnext_key == key)
+			WRITE_ONCE(ao_info->rnext_key, NULL);
 		atomic_sub(tcp_ao_sizeof_key(key), &sk->sk_omem_alloc);
 		call_rcu(&key->rcu, tcp_ao_key_free_rcu);
 		return 0;
-- 
2.43.0