rxrpc: Trace protocol errors in received packets

Add a tracepoint (rxrpc_rx_proto) to record protocol errors in received
packets.  The following changes are made:

 (1) Add a function, __rxrpc_abort_eproto(), to note a protocol error on a
     call and mark the call aborted.  This is wrapped by
     rxrpc_abort_eproto() that makes the why string usable in trace.

 (2) Add trace_rxrpc_rx_proto() or rxrpc_abort_eproto() to protocol error
     generation points, replacing rxrpc_abort_call() with the latter.

 (3) Only send an abort packet in rxkad_verify_packet*() if we actually
     managed to abort the call.

Note that a trace event is also emitted if a kernel user (e.g. afs) tries
to send data through a call when it's not in the transmission phase, though
it's not technically a receive event.

Signed-off-by: David Howells <dhowells@redhat.com>

net/rxrpc/insecure.c

@@ -46,7 +46,10 @@ static int none_respond_to_challenge(struct rxrpc_connection *conn,
 				     struct sk_buff *skb,
 				     u32 *_abort_code)
 {
-	*_abort_code = RX_PROTOCOL_ERROR;
+	struct rxrpc_skb_priv *sp = rxrpc_skb(skb);
+
+	trace_rxrpc_rx_eproto(NULL, sp->hdr.serial,
+			      tracepoint_string("chall_none"));
 	return -EPROTO;
 }
 
@@ -54,7 +57,10 @@ static int none_verify_response(struct rxrpc_connection *conn,
 				struct sk_buff *skb,
 				u32 *_abort_code)
 {
-	*_abort_code = RX_PROTOCOL_ERROR;
+	struct rxrpc_skb_priv *sp = rxrpc_skb(skb);
+
+	trace_rxrpc_rx_eproto(NULL, sp->hdr.serial,
+			      tracepoint_string("resp_none"));
 	return -EPROTO;
 }