From mboxrd@z Thu Jan 1 00:00:00 1970 From: Michal Schmidt Subject: [PATCH] GRO: fix merging a paged skb after non-paged skbs Date: Mon, 24 Jan 2011 18:47:52 +0100 Message-ID: <20110124184752.1d0947dd@delilah> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Cc: netdev@vger.kernel.org, Herbert Xu , Ben Hutchings To: David Miller Return-path: Received: from mx1.redhat.com ([209.132.183.28]:63117 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751882Ab1AXRsE (ORCPT ); Mon, 24 Jan 2011 12:48:04 -0500 Sender: netdev-owner@vger.kernel.org List-ID: Suppose that several linear skbs of the same flow were received by GRO. They were thus merged into one skb with a frag_list. Then a new skb of the same flow arrives, but it is a paged skb with data starting in its frags[]. Before adding the skb to the frag_list skb_gro_receive() will of course adjust the skb to throw away the headers. It correctly modifies the page_offset and size of the frag, but it leaves incorrect information in the skb: ->data_len is not decreased at all. ->len is decreased only by headlen, as if no change were done to the frag. Later in a receiving process this causes skb_copy_datagram_iovec() to return -EFAULT and this is seen in userspace as the result of the recv() syscall. In practice the bug can be reproduced with the sfc driver. By default the driver uses an adaptive scheme when it switches between using napi_gro_receive() (with skbs) and napi_gro_frags() (with pages). The bug is reproduced when under rx load with enough successful GRO merging the driver decides to switch from the former to the latter. Manual control is also possible, so reproducing this is easy with netcat: - on machine1 (with sfc): nc -l 12345 > /dev/null - on machine2: nc machine1 12345 < /dev/zero - on machine1: echo 1 > /sys/module/sfc/parameters/rx_alloc_method # use skbs echo 2 > /sys/module/sfc/parameters/rx_alloc_method # use pages - See that nc has quit suddenly. Signed-off-by: Michal Schmidt --- net/core/skbuff.c | 2 +- 1 files changed, 1 insertions(+), 1 deletions(-) diff --git a/net/core/skbuff.c b/net/core/skbuff.c index d31bb36..c231f5b 100644 --- a/net/core/skbuff.c +++ b/net/core/skbuff.c @@ -2746,7 +2746,7 @@ merge: if (offset > headlen) { skbinfo->frags[0].page_offset += offset - headlen; skbinfo->frags[0].size -= offset - headlen; - offset = headlen; + skb->data_len -= offset - headlen; } __skb_pull(skb, offset); -- 1.7.1