From mboxrd@z Thu Jan 1 00:00:00 1970 From: Michal Schmidt Subject: [PATCH v2] GRO: fix merging a paged skb after non-paged skbs Date: Mon, 24 Jan 2011 23:08:48 +0100 Message-ID: <20110124230848.577187e9@delilah> References: <20110124184752.1d0947dd@delilah> <1295894693.2755.58.camel@edumazet-laptop> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Cc: David Miller , netdev@vger.kernel.org, Herbert Xu , Ben Hutchings To: Eric Dumazet Return-path: Received: from mx1.redhat.com ([209.132.183.28]:2980 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750892Ab1AXWKB (ORCPT ); Mon, 24 Jan 2011 17:10:01 -0500 In-Reply-To: <1295894693.2755.58.camel@edumazet-laptop> 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. [v2: Modified by Eric Dumazet to avoid advancing skb->data past the end and to use a temporary variable.] Signed-off-by: Michal Schmidt --- Eric, I think skb->data is pretty much irrelevant at that point, because the skb's headlen is going to become zero, but admittedly it seems cleaner this way. Thanks. net/core/skbuff.c | 8 ++++++-- 1 files changed, 6 insertions(+), 2 deletions(-) diff --git a/net/core/skbuff.c b/net/core/skbuff.c index d31bb36..7cd1bc8 100644 --- a/net/core/skbuff.c +++ b/net/core/skbuff.c @@ -2744,8 +2744,12 @@ int skb_gro_receive(struct sk_buff **head, struct sk_buff *skb) merge: if (offset > headlen) { - skbinfo->frags[0].page_offset += offset - headlen; - skbinfo->frags[0].size -= offset - headlen; + unsigned int eat = offset - headlen; + + skbinfo->frags[0].page_offset += eat; + skbinfo->frags[0].size -= eat; + skb->data_len -= eat; + skb->len -= eat; offset = headlen; } -- 1.7.3.4