rxrpc: Fix insufficient receive notification generation

[ Upstream commit f71dbf2f ]

In rxrpc_input_data(), rxrpc_notify_socket() is called if the base sequence
number of the packet is immediately following the hard-ack point at the end
of the function.  However, this isn't sufficient, since the recvmsg side
may have been advancing the window and then overrun the position in which
we're adding - at which point rx_hard_ack >= seq0 and no notification is
generated.

Fix this by always generating a notification at the end of the input
function.

Without this, a long call may stall, possibly indefinitely.

Fixes: 248f219c ("rxrpc: Rewrite the data and ack handling code")
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

net/rxrpc/input.c

@@ -612,10 +612,8 @@ static void rxrpc_input_data(struct rxrpc_call *call, struct sk_buff *skb,
 				  false, true,
 				  rxrpc_propose_ack_input_data);
 
-	if (sp->hdr.seq == READ_ONCE(call->rx_hard_ack) + 1) {
 	trace_rxrpc_notify_socket(call->debug_id, serial);
 	rxrpc_notify_socket(call);
-	}
 
 unlock:
 	spin_unlock(&call->input_lock);