rxrpc: Fix call crypto state cleanup

Fix the cleanup of the crypto state on a call after the call has been
disconnected.  As the call has been disconnected, its connection ref has
been discarded and so we can't go through that to get to the security ops
table.

Fix this by caching the security ops pointer in the rxrpc_call struct and
using that when freeing the call security state.  Also use this in other
places we're dealing with call-specific security.

The symptoms look like:

    BUG: KASAN: use-after-free in rxrpc_release_call+0xb2d/0xb60
    net/rxrpc/call_object.c:481
    Read of size 8 at addr ffff888062ffeb50 by task syz-executor.5/4764

Fixes: 1db88c5343 ("rxrpc: Fix -Wframe-larger-than= warnings from on-stack crypto")
Reported-by: syzbot+eed305768ece6682bb7f@syzkaller.appspotmail.com
Signed-off-by: David Howells <dhowells@redhat.com>

net/rxrpc/ar-internal.h

@@ -556,6 +556,7 @@ struct rxrpc_call {
 	struct rxrpc_peer	*peer;		/* Peer record for remote address */
 	struct rxrpc_sock __rcu	*socket;	/* socket responsible */
 	struct rxrpc_net	*rxnet;		/* Network namespace to which call belongs */
+	const struct rxrpc_security *security;	/* applied security module */
 	struct mutex		user_mutex;	/* User access mutex */
 	unsigned long		ack_at;		/* When deferred ACK needs to happen */
 	unsigned long		ack_lost_at;	/* When ACK is figured as lost */

net/rxrpc/call_accept.c

@@ -307,6 +307,7 @@ static struct rxrpc_call *rxrpc_alloc_incoming_call(struct rxrpc_sock *rx,
 
 	rxrpc_see_call(call);
 	call->conn = conn;
+	call->security = conn->security;
 	call->peer = rxrpc_get_peer(conn->params.peer);
 	call->cong_cwnd = call->peer->cong_cwnd;
 	return call;

net/rxrpc/call_object.c

@@ -493,10 +493,10 @@ void rxrpc_release_call(struct rxrpc_sock *rx, struct rxrpc_call *call)
 
 	_debug("RELEASE CALL %p (%d CONN %p)", call, call->debug_id, conn);
 
-	if (conn) {
+	if (conn)
 		rxrpc_disconnect_call(call);
-		conn->security->free_call_crypto(call);
-	}
+	if (call->security)
+		call->security->free_call_crypto(call);
 
 	rxrpc_cleanup_ring(call);
 	_leave("");

net/rxrpc/conn_client.c

@@ -353,6 +353,7 @@ static int rxrpc_get_client_conn(struct rxrpc_sock *rx,
 
 	if (cp->exclusive) {
 		call->conn = candidate;
+		call->security = candidate->security;
 		call->security_ix = candidate->security_ix;
 		call->service_id = candidate->service_id;
 		_leave(" = 0 [exclusive %d]", candidate->debug_id);
@@ -404,6 +405,7 @@ static int rxrpc_get_client_conn(struct rxrpc_sock *rx,
 candidate_published:
 	set_bit(RXRPC_CONN_IN_CLIENT_CONNS, &candidate->flags);
 	call->conn = candidate;
+	call->security = candidate->security;
 	call->security_ix = candidate->security_ix;
 	call->service_id = candidate->service_id;
 	spin_unlock(&local->client_conns_lock);
@@ -426,6 +428,7 @@ found_extant_conn:
 
 	spin_lock(&conn->channel_lock);
 	call->conn = conn;
+	call->security = conn->security;
 	call->security_ix = conn->security_ix;
 	call->service_id = conn->service_id;
 	list_add_tail(&call->chan_wait_link, &conn->waiting_calls);

net/rxrpc/recvmsg.c

@@ -251,8 +251,8 @@ static int rxrpc_verify_packet(struct rxrpc_call *call, struct sk_buff *skb,
 		seq += subpacket;
 	}
 
-	return call->conn->security->verify_packet(call, skb, offset, len,
-						   seq, cksum);
+	return call->security->verify_packet(call, skb, offset, len,
+					     seq, cksum);
 }
 
 /*
@@ -291,7 +291,7 @@ static int rxrpc_locate_data(struct rxrpc_call *call, struct sk_buff *skb,
 
 	*_offset = offset;
 	*_len = len;
-	call->conn->security->locate_data(call, skb, _offset, _len);
+	call->security->locate_data(call, skb, _offset, _len);
 	return 0;
 }
 

net/rxrpc/sendmsg.c

@@ -419,7 +419,7 @@ static int rxrpc_send_data(struct rxrpc_sock *rx,
 				 call->tx_winsize)
 				sp->hdr.flags |= RXRPC_MORE_PACKETS;
 
-			ret = conn->security->secure_packet(
+			ret = call->security->secure_packet(
 				call, skb, skb->mark, skb->head);
 			if (ret < 0)
 				goto out;