rxrpc: Make service call handling more robust

Make the following changes to improve the robustness of the code that sets
up a new service call:

 (1) Cache the rxrpc_sock struct obtained in rxrpc_data_ready() to do a
     service ID check and pass that along to rxrpc_new_incoming_call().
     This means that I can remove the check from rxrpc_new_incoming_call()
     without the need to worry about the socket attached to the local
     endpoint getting replaced - which would invalidate the check.

 (2) Cache the rxrpc_peer struct, thereby allowing the peer search to be
     done once.  The peer is passed to rxrpc_new_incoming_call(), thereby
     saving the need to repeat the search.

     This also reduces the possibility of rxrpc_publish_service_conn()
     BUG()'ing due to the detection of a duplicate connection, despite the
     initial search done by rxrpc_find_connection_rcu() having turned up
     nothing.

     This BUG() shouldn't ever get hit since rxrpc_data_ready() *should* be
     non-reentrant and the result of the initial search should still hold
     true, but it has proven possible to hit.

     I *think* this may be due to __rxrpc_lookup_peer_rcu() cutting short
     the iteration over the hash table if it finds a matching peer with a
     zero usage count, but I don't know for sure since it's only ever been
     hit once that I know of.

     Another possibility is that a bug in rxrpc_data_ready() that checked
     the wrong byte in the header for the RXRPC_CLIENT_INITIATED flag
     might've let through a packet that caused a spurious and invalid call
     to be set up.  That is addressed in another patch.

 (3) Fix __rxrpc_lookup_peer_rcu() to skip peer records that have a zero
     usage count rather than stopping and returning not found, just in case
     there's another peer record behind it in the bucket.

 (4) Don't search the peer records in rxrpc_alloc_incoming_call(), but
     rather either use the peer cached in (2) or, if one wasn't found,
     preemptively install a new one.

Fixes: 8496af50eb38 ("rxrpc: Use RCU to access a peer's service connection tree")
Signed-off-by: David Howells <dhowells@redhat.com>

1 files changed, 4 insertions, 3 deletions

diff --git a/net/rxrpc/input.c b/net/rxrpc/input.c
index a569e9e010d1..800f5b8a1baa 100644
--- a/net/rxrpc/input.c
+++ b/net/rxrpc/input.c
@@ -1128,7 +1128,8 @@ void rxrpc_data_ready(struct sock *udp_sk)
 	struct rxrpc_call *call = NULL;
 	struct rxrpc_skb_priv *sp;
 	struct rxrpc_local *local = udp_sk->sk_user_data;
-	struct rxrpc_sock *rx;
+	struct rxrpc_peer *peer = NULL;
+	struct rxrpc_sock *rx = NULL;
 	struct sk_buff *skb;
 	unsigned int channel;
 	int ret, skew = 0;
@@ -1250,7 +1251,7 @@ void rxrpc_data_ready(struct sock *udp_sk)
 		}
 	}
 
-	conn = rxrpc_find_connection_rcu(local, skb);
+	conn = rxrpc_find_connection_rcu(local, skb, &peer);
 	if (conn) {
 		if (sp->hdr.securityIndex != conn->security_ix)
 			goto wrong_security;
@@ -1339,7 +1340,7 @@ void rxrpc_data_ready(struct sock *udp_sk)
 			goto bad_message_unlock;
 		if (sp->hdr.seq != 1)
 			goto discard_unlock;
-		call = rxrpc_new_incoming_call(local, conn, skb);
+		call = rxrpc_new_incoming_call(local, rx, peer, conn, skb);
 		if (!call) {
 			rcu_read_unlock();
 			goto reject_packet;