From 2fe664f1fcf7c4da6891f95708a7a56d3c024354 Mon Sep 17 00:00:00 2001 From: Douglas Caetano dos Santos Date: Thu, 22 Sep 2016 15:52:04 -0300 Subject: [PATCH] tcp: fix wrong checksum calculation on MTU probing 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 Signed-off-by: David S. Miller --- net/ipv4/tcp_output.c | 12 +++++++----- 1 file changed, 7 insertions(+), 5 deletions(-) diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c index 5288cec4a2b2..d48d5571e62a 100644 --- a/net/ipv4/tcp_output.c +++ b/net/ipv4/tcp_output.c @@ -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.