From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Miller Subject: Re: [PATCH] net: bridge: check the length of skb after nf_bridge_maybe_copy_header() Date: Mon, 03 Jan 2011 09:22:14 -0800 (PST) Message-ID: <20110103.092214.193706896.davem@davemloft.net> References: <1293284490-17114-1-git-send-email-xiaosuo@gmail.com> <20101231.111003.48499853.davem@davemloft.net> Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit Cc: shemminger@linux-foundation.org, bridge@lists.linux-foundation.org, netdev@vger.kernel.org To: xiaosuo@gmail.com Return-path: Received: from 74-93-104-97-Washington.hfc.comcastbusiness.net ([74.93.104.97]:33343 "EHLO sunset.davemloft.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932162Ab1ACRVn (ORCPT ); Mon, 3 Jan 2011 12:21:43 -0500 In-Reply-To: Sender: netdev-owner@vger.kernel.org List-ID: From: Changli Gao Date: Mon, 3 Jan 2011 18:44:59 +0800 > On Sat, Jan 1, 2011 at 3:10 AM, David Miller wrote: >> From: Changli Gao >> Date: Sat, 25 Dec 2010 21:41:30 +0800 >> >>> Since nf_bridge_maybe_copy_header() may change the length of skb, >>> we should check the length of skb after it to handle the ppoe skbs. >>> >>> Signed-off-by: Changli Gao >> >> This is really strange. >> >> packet_length() subtracts VLAN_HLEN from the value it returns, so the >> correct fix seems to be to make this function handle the PPPOE case >> too. >> > > It is correct. The actual MTU of 802.1q frame is 4 bytes larger. For > example, the MTU of ethernet is normally 1500, however the actual MTU > of the 802.1Q is 1504. Yes, I understand this, but I don't see why packet_length() cannot simply account for PPPOE's encapsulation overhead just as it does for VLAN's special MTU considerations.