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 <[email protected]>
Signed-off-by: Hannes Frederic Sowa <[email protected]>
Signed-off-by: Paolo Abeni <[email protected]>
Signed-off-by: David S. Miller <[email protected]>

0 files changed, 0 insertions, 0 deletions