ila: block BH in ila_output()

As explained in commit 1378817486d6 ("tipc: block BH
before using dst_cache"), net/core/dst_cache.c
helpers need to be called with BH disabled.

ila_output() is called from lwtunnel_output()
possibly from process context, and under rcu_read_lock().

We might be interrupted by a softirq, re-enter ila_output()
and corrupt dst_cache data structures.

Fix the race by using local_bh_disable().

Signed-off-by: Eric Dumazet <[e-mail]>
Acked-by: Paolo Abeni <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Jakub Kicinski <[e-mail]>

net/ipv6/ila/ila_lwt.c

···
 		return orig_dst->lwtstate->orig_output(net, sk, skb);
 	}
 
+	local_bh_disable();
 	dst = dst_cache_get(&ilwt->dst_cache);
+	local_bh_enable();
 	if (unlikely(!dst)) {
 		struct ipv6hdr *ip6h = ipv6_hdr(skb);
 		struct flowi6 fl6;
···
 			goto drop;
 		}
 
-		if (ilwt->connected)
+		if (ilwt->connected) {
+			local_bh_disable();
 			dst_cache_set_ip6(&ilwt->dst_cache, dst, &fl6.saddr);
+			local_bh_enable();
+		}
 	}
 
 	skb_dst_set(skb, dst);