From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dimitris Michailidis Subject: [PATCH net] net: fix pskb_trim_rcsum_slow() with odd trim offset Date: Fri, 19 Oct 2018 17:07:13 -0700 Message-ID: <20181020000713.228659-1-dmichail@google.com> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Cc: netdev@vger.kernel.org, Dimitris Michailidis To: edumazet@google.com, davem@davemloft.net Return-path: Received: from mail-io1-f73.google.com ([209.85.166.73]:54535 "EHLO mail-io1-f73.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726459AbeJTIRk (ORCPT ); Sat, 20 Oct 2018 04:17:40 -0400 Received: by mail-io1-f73.google.com with SMTP id l21-v6so18285691ioc.21 for ; Fri, 19 Oct 2018 17:09:19 -0700 (PDT) Sender: netdev-owner@vger.kernel.org List-ID: We've been getting checksum errors involving small UDP packets, usually 59B packets with 1 extra non-zero padding byte. netdev_rx_csum_fault() has been complaining that HW is providing bad checksums. Turns out the problem is in pskb_trim_rcsum_slow(), introduced in commit 88078d98d1bb ("net: pskb_trim_rcsum() and CHECKSUM_COMPLETE are friends"). The source of the problem is that when the bytes we are trimming start at an odd address, as in the case of the 1 padding byte above, skb_checksum() returns a byte-swapped value. We cannot just combine this with skb->csum using csum_sub(). We need to use csum_block_sub() here that takes into account the parity of the start address and handles the swapping. Matches existing code in __skb_postpull_rcsum() and esp_remove_trailer(). Fixes: 88078d98d1bb ("net: pskb_trim_rcsum() and CHECKSUM_COMPLETE are friends") Signed-off-by: Dimitris Michailidis --- net/core/skbuff.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/net/core/skbuff.c b/net/core/skbuff.c index 428094b577fc..f817f336595d 100644 --- a/net/core/skbuff.c +++ b/net/core/skbuff.c @@ -1846,8 +1846,9 @@ int pskb_trim_rcsum_slow(struct sk_buff *skb, unsigned int len) if (skb->ip_summed == CHECKSUM_COMPLETE) { int delta = skb->len - len; - skb->csum = csum_sub(skb->csum, - skb_checksum(skb, len, delta, 0)); + skb->csum = csum_block_sub(skb->csum, + skb_checksum(skb, len, delta, 0), + len); } return __pskb_trim(skb, len); } -- 2.19.1.568.g152ad8e336-goog