Commit 9bd780f5 authored Jun 23, 2017 by Paolo Abeni Committed by David S. Miller Jun 23, 2017

udp: fix poll()



Michael reported an UDP breakage caused by the commit b65ac446
("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: b65ac446 ("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>

parent 4b943fae

net/ipv4/udp.c

+17 −10

Original line number	Diff line number	Diff line
		@@ -1446,8 +1446,8 @@ 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)) {
		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,
		@@ -1456,6 +1456,13 @@ static struct sk_buff __first_packet_length(struct sock sk,
		__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;
		}

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