rx: Avoid new server calls for big-seq DATA pkts

We currently never open our receive window to more than 32 packets. If
we received a DATA packet for an unrecognized call with a seq of 33 or
more, the packet is almost certainly from a previously-running call
that we were restarted during.

As described in commit 7b204946 (rx: Avoid lastReceiveTime update for
invalid ACKs) and commit "rx: Avoid new server calls for non-DATA
packets", clients can get confused when we respond to calls in these
situations, so drop the packets instead.

Change-Id: I5b3a699bf245375e92ac97a24ad3638cbb3b8f3c
Reviewed-on: https://gerrit.openafs.org/13876
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>

src/rx/rx.c

@@ -3310,6 +3310,20 @@ rxi_ReceiveServerCall(osi_socket socket, struct rx_packet *np,
 	    return NULL;
 	}
 
+	if (np->header.seq > rx_maxReceiveWindow) {
+	    /*
+	     * This is a DATA packet for further along in the call than is
+	     * possible for a new call. This is probably from an existing call
+	     * that was in the middle of running when we were restarted; ignore
+	     * it to avoid confusing clients. (See above comment about non-DATA
+	     * packets.)
+	     */
+	    MUTEX_EXIT(&conn->conn_call_lock);
+	    if (rx_stats_active)
+		rx_atomic_inc(&rx_stats.spuriousPacketsRead);
+	    return NULL;
+	}
+
 	if (rxi_AbortIfServerBusy(socket, conn, np)) {
 	    MUTEX_EXIT(&conn->conn_call_lock);
 	    return NULL;