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tcp: fix wrong checksum calculation on MTU probing

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With TCP MTU probing enabled and offload TX checksumming disabled,
tcp_mtu_probe() calculated the wrong checksum when a fragment being copied
into the probe's SKB had an odd length. This was caused by the direct use
of skb_copy_and_csum_bits() to calculate the checksum, as it pads the
fragment being copied, if needed. When this fragment was not the last, a
subsequent call used the previous checksum without considering this
padding.

The effect was a stale connection in one way, as even retransmissions
wouldn't solve the problem, because the checksum was never recalculated for
the full SKB length.

Signed-off-by: Douglas Caetano dos Santos <douglascs@taghos.com.br>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Douglas Caetano dos Santos 2016-09-22 15:52:04 -03:00 committed by David S. Miller
parent f44ace4d06
commit 2fe664f1fc
1 changed files with 7 additions and 5 deletions
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12
net/ipv4/tcp_output.c
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@ -1966,12 +1966,14 @@ static int tcp_mtu_probe(struct sock *sk)
len = 0;
tcp_for_write_queue_from_safe(skb, next, sk) {
copy = min_t(int, skb->len, probe_size - len);
if (nskb->ip_summed)
if (nskb->ip_summed) {
skb_copy_bits(skb, 0, skb_put(nskb, copy), copy);
else
nskb->csum = skb_copy_and_csum_bits(skb, 0,
skb_put(nskb, copy),
copy, nskb->csum);
} else {
__wsum csum = skb_copy_and_csum_bits(skb, 0,
skb_put(nskb, copy),
copy, 0);
nskb->csum = csum_block_add(nskb->csum, csum, len);
}
if (skb->len <= copy) {
/* We've eaten all the data from this skb.