From 9bd780f5e0663035d41a95a6b87eced011ba7e2a Mon Sep 17 00:00:00 2001 From: Paolo Abeni Date: Fri, 23 Jun 2017 14:19:51 +0200 Subject: [PATCH] udp: fix poll() Michael reported an UDP breakage caused by the commit b65ac44674dd ("udp: try to avoid 2 cache miss on dequeue"). The function __first_packet_length() can update the checksum bits of the pending skb, making the scratched area out-of-sync, and setting skb->csum, if the skb was previously in need of checksum validation. On later recvmsg() for such skb, checksum validation will be invoked again - due to the wrong udp_skb_csum_unnecessary() value - and will fail, causing the valid skb to be dropped. This change addresses the issue refreshing the scratch area in __first_packet_length() after the possible checksum update. Fixes: b65ac44674dd ("udp: try to avoid 2 cache miss on dequeue") Reported-by: Michael Ellerman Signed-off-by: Hannes Frederic Sowa Signed-off-by: Paolo Abeni Signed-off-by: David S. Miller --- net/ipv4/udp.c | 27 +++++++++++++++++---------- 1 file changed, 17 insertions(+), 10 deletions(-) diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c index 067a607917f9..47c7aa0501af 100644 --- a/net/ipv4/udp.c +++ b/net/ipv4/udp.c @@ -1446,16 +1446,23 @@ static struct sk_buff *__first_packet_length(struct sock *sk, { struct sk_buff *skb; - while ((skb = skb_peek(rcvq)) != NULL && - udp_lib_checksum_complete(skb)) { - __UDP_INC_STATS(sock_net(sk), UDP_MIB_CSUMERRORS, - IS_UDPLITE(sk)); - __UDP_INC_STATS(sock_net(sk), UDP_MIB_INERRORS, - IS_UDPLITE(sk)); - atomic_inc(&sk->sk_drops); - __skb_unlink(skb, rcvq); - *total += skb->truesize; - kfree_skb(skb); + while ((skb = skb_peek(rcvq)) != NULL) { + if (udp_lib_checksum_complete(skb)) { + __UDP_INC_STATS(sock_net(sk), UDP_MIB_CSUMERRORS, + IS_UDPLITE(sk)); + __UDP_INC_STATS(sock_net(sk), UDP_MIB_INERRORS, + IS_UDPLITE(sk)); + atomic_inc(&sk->sk_drops); + __skb_unlink(skb, rcvq); + *total += skb->truesize; + kfree_skb(skb); + } else { + /* the csum related bits could be changed, refresh + * the scratch area + */ + udp_set_dev_scratch(skb); + break; + } } return skb; } -- 2.20.1