Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934527AbcKML0a (ORCPT ); Sun, 13 Nov 2016 06:26:30 -0500 Received: from mail.linuxfoundation.org ([140.211.169.12]:36038 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933577AbcKML01 (ORCPT ); Sun, 13 Nov 2016 06:26:27 -0500 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Douglas Caetano dos Santos , "David S. Miller" Subject: [PATCH 4.4 03/34] tcp: fix wrong checksum calculation on MTU probing Date: Sun, 13 Nov 2016 12:24:35 +0100 Message-Id: <20161113112400.170257776@linuxfoundation.org> X-Mailer: git-send-email 2.10.2 In-Reply-To: <20161113112400.008903838@linuxfoundation.org> References: <20161113112400.008903838@linuxfoundation.org> User-Agent: quilt/0.65 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1817 Lines: 51 4.4-stable review patch. If anyone has any objections, please let me know. ------------------ From: Douglas Caetano dos Santos [ Upstream commit 2fe664f1fcf7c4da6891f95708a7a56d3c024354 ] 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 Signed-off-by: Greg Kroah-Hartman --- net/ipv4/tcp_output.c | 12 +++++++----- 1 file changed, 7 insertions(+), 5 deletions(-) --- a/net/ipv4/tcp_output.c +++ b/net/ipv4/tcp_output.c @@ -1950,12 +1950,14 @@ 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.