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udp: fix poll()

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Michael reported an UDP breakage caused by the commit b65ac44674
("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: b65ac44674 ("udp: try to avoid 2 cache miss on dequeue")
Reported-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Paolo Abeni 2017-06-23 14:19:51 +02:00 committed by David S. Miller
parent 4b943faedf
commit 9bd780f5e0
1 changed files with 17 additions and 10 deletions
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27
net/ipv4/udp.c
View file

@ -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;
}