From mboxrd@z Thu Jan 1 00:00:00 1970 From: Vlad Yasevich Subject: Re: Fix bugs in "Whether sock accept queue is full" checking Date: Thu, 22 Feb 2007 13:09:46 -0500 Message-ID: <45DDDC6A.6080205@hp.com> References: <1171470657.7414.15.camel@LINE> <20070222.031310.85405859.davem@davemloft.net> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: weid@np.css.fujitsu.com, netdev@vger.kernel.org To: David Miller Return-path: Received: from atlrel7.hp.com ([156.153.255.213]:56778 "EHLO atlrel7.hp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751281AbXBVSJs (ORCPT ); Thu, 22 Feb 2007 13:09:48 -0500 In-Reply-To: <20070222.031310.85405859.davem@davemloft.net> Sender: netdev-owner@vger.kernel.org List-Id: netdev.vger.kernel.org David Miller wrote: > From: weidong > Date: Wed, 14 Feb 2007 11:30:57 -0500 > >> when I use linux TCP socket, and find there is a bug in function >> sk_acceptq_is_full(). > ... >> Consider an example: >> >> After listen(sockfd, 1) system call, sk->sk_max_ack_backlog is set to >> 1. As we know, sk->sk_ack_backlog is initialized to 0. Assuming accept() >> system call is not invoked now. >> >> 1. 1st connection comes. invoke sk_acceptq_is_full(). sk- >>> sk_ack_backlog=0 sk->sk_max_ack_backlog=1, function return 0 accept >> this connection. Increase the sk->sk_ack_backlog >> 2. 2nd connection comes. invoke sk_acceptq_is_full(). sk- >>> sk_ack_backlog=1 sk->sk_max_ack_backlog=1, function return 0 accept >> this connection. Increase the sk->sk_ack_backlog >> 3. 3rd connection comes. invoke sk_acceptq_is_full(). sk- >>> sk_ack_backlog=2 sk->sk_max_ack_backlog=1, function return 1. Refuse >> this connection. >> >> I think it has bugs. after listen system call. sk->sk_max_ack_backlog=1 >> but now it can accept 2 connections. The following patch can fix this >> problem. >> >> signed-off-by: Wei Dong > > Thank you very much for the detailed analysis and fix. > > Actually, this bug exists all over the tree I believe, not just > in TCP. I would like to audit all uses of sk_ack_backlog and > sk_max_ack_backlog before applying your patch, so please give > me some time to perform a quick audit. > > Thank you. Hi David I can confirm the same problem exists in SCTP because of the use of sk_acceptq_is_full(). -vlad