sch_cake: fix srchost/dsthost hashing mode

When adding support for using the skb->hash value as the flow hash in CAKE,
I accidentally introduced a logic error that broke the host-only isolation
modes of CAKE (srchost and dsthost keywords). Specifically, the flow_hash
variable should stay initialised to 0 in cake_hash() in pure host-based
hashing mode. Add a check for this before using the skb->hash value as
flow_hash.

Fixes: b0c19ed ("sch_cake: Take advantage of skb->hash where appropriate")
Reported-by: Pete Heist <[email protected]>
Tested-by: Pete Heist <[email protected]>
Signed-off-by: Toke Høiland-Jørgensen <[email protected]>
Signed-off-by: David S. Miller <[email protected]>

Author: tohojo

net/sched/sch_cake.c

@@ -720,7 +720,7 @@ static u32 cake_hash(struct cake_tin_data *q, const struct sk_buff *skb,
 skip_hash:
 	if (flow_override)
 		flow_hash = flow_override - 1;
-	else if (use_skbhash)
+	else if (use_skbhash && (flow_mode & CAKE_FLOW_FLOWS))
 		flow_hash = skb->hash;
 	if (host_override) {
 		dsthost_hash = host_override - 1;