Commit 0ddf3fb2 authored Jul 18, 2017 by Paolo Abeni Committed by David S. Miller Jul 18, 2017

udp: preserve skb->dst if required for IP options processing



Eric noticed that in udp_recvmsg() we still need to access
skb->dst while processing the IP options.
Since commit 0a463c78 ("udp: avoid a cache miss on dequeue")
skb->dst is no more available at recvmsg() time and bad things
will happen if we enter the relevant code path.

This commit address the issue, avoid clearing skb->dst if
any IP options are present into the relevant skb.
Since the IP CB is contained in the first skb cacheline, we can
test it to decide to leverage the consume_stateless_skb()
optimization, without measurable additional cost in the faster
path.

v1 -> v2: updated commit message tags

Fixes: 0a463c78 ("udp: avoid a cache miss on dequeue")
Reported-by: Andrey Konovalov <andreyknvl@google.com>
Reported-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent 799f9172

net/ipv4/udp.c

+11 −2

Original line number	Diff line number	Diff line
		@@ -1388,6 +1388,11 @@ void skb_consume_udp(struct sock sk, struct sk_buff skb, int len)
		unlock_sock_fast(sk, slow);
		}

		/* we cleared the head states previously only if the skb lacks any IP
		* options, see __udp_queue_rcv_skb().
		*/
		if (unlikely(IPCB(skb)->opt.optlen > 0))
		skb_release_head_state(skb);
		consume_stateless_skb(skb);
		}
		EXPORT_SYMBOL_GPL(skb_consume_udp);
		@@ -1779,7 +1784,11 @@ static int __udp_queue_rcv_skb(struct sock sk, struct sk_buff skb)
		sk_mark_napi_id_once(sk, skb);
		}

		/* clear all pending head states while they are hot in the cache */
		/* At recvmsg() time we need skb->dst to process IP options-related
		* cmsg, elsewhere can we clear all pending head states while they are
		* hot in the cache
		*/
		if (likely(IPCB(skb)->opt.optlen == 0))
		skb_release_head_state(skb);

		rc = __udp_enqueue_schedule_skb(sk, skb);

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