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, 11 insertions, 24 deletions

diff --git a/net/rxrpc/peer_object.c b/net/rxrpc/peer_object.c
index 1dc7648e3eff..70083e8fb6e5 100644
--- a/net/rxrpc/peer_object.c
+++ b/net/rxrpc/peer_object.c
@@ -124,11 +124,9 @@ static struct rxrpc_peer *__rxrpc_lookup_peer_rcu(
 	struct rxrpc_net *rxnet = local->rxnet;
 
 	hash_for_each_possible_rcu(rxnet->peer_hash, peer, hash_link, hash_key) {
-		if (rxrpc_peer_cmp_key(peer, local, srx, hash_key) == 0) {
-			if (atomic_read(&peer->usage) == 0)
-				return NULL;
+		if (rxrpc_peer_cmp_key(peer, local, srx, hash_key) == 0 &&
+		    atomic_read(&peer->usage) > 0)
 			return peer;
-		}
 	}
 
 	return NULL;
@@ -299,34 +297,23 @@ static struct rxrpc_peer *rxrpc_create_peer(struct rxrpc_local *local,
 }
 
 /*
- * Set up a new incoming peer.  The address is prestored in the preallocated
- * peer.
+ * Set up a new incoming peer.  There shouldn't be any other matching peers
+ * since we've already done a search in the list from the non-reentrant context
+ * (the data_ready handler) that is the only place we can add new peers.
  */
-struct rxrpc_peer *rxrpc_lookup_incoming_peer(struct rxrpc_local *local,
-					      struct rxrpc_peer *prealloc)
+void rxrpc_new_incoming_peer(struct rxrpc_local *local, struct rxrpc_peer *peer)
 {
-	struct rxrpc_peer *peer;
 	struct rxrpc_net *rxnet = local->rxnet;
 	unsigned long hash_key;
 
-	hash_key = rxrpc_peer_hash_key(local, &prealloc->srx);
-	prealloc->local = local;
-	rxrpc_init_peer(prealloc, hash_key);
+	hash_key = rxrpc_peer_hash_key(local, &peer->srx);
+	peer->local = local;
+	rxrpc_init_peer(peer, hash_key);
 
 	spin_lock(&rxnet->peer_hash_lock);
-
-	/* Need to check that we aren't racing with someone else */
-	peer = __rxrpc_lookup_peer_rcu(local, &prealloc->srx, hash_key);
-	if (peer && !rxrpc_get_peer_maybe(peer))
-		peer = NULL;
-	if (!peer) {
-		peer = prealloc;
-		hash_add_rcu(rxnet->peer_hash, &peer->hash_link, hash_key);
-		list_add_tail(&peer->keepalive_link, &rxnet->peer_keepalive_new);
-	}
-
+	hash_add_rcu(rxnet->peer_hash, &peer->hash_link, hash_key);
+	list_add_tail(&peer->keepalive_link, &rxnet->peer_keepalive_new);
 	spin_unlock(&rxnet->peer_hash_lock);
-	return peer;
 }
 
 /*