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Date: Wed, 14 Feb 2007 11:30:57 -0500 From: weidong <weid@...css.fujitsu.com> To: netdev@...r.kernel.org Cc: davem@...emloft.net Subject: Fix bugs in "Whether sock accept queue is full" checking Hi, All when I use linux TCP socket, and find there is a bug in function sk_acceptq_is_full(). When a new SYN comes, TCP module first checks its validation. If valid, send SYN,ACK to the client and add the sock to the syn hash table. Next time if received the valid ACK for SYN,ACK from the client. server will accept this connection and increase the sk->sk_ack_backlog -- which is done in function tcp_check_req().We check wether acceptq is full in function tcp_v4_syn_recv_sock(). 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 <weid@...css.fujitsu.com> diff -ruN old/include/net/sock.h new/include/net/sock.h --- old/include/net/sock.h 2007-02-03 08:38:21.000000000 -0500 +++ new/include/net/sock.h 2007-02-03 08:38:30.000000000 -0500 @@ -426,7 +426,7 @@ static inline int sk_acceptq_is_full(struct sock *sk) { - return sk->sk_ack_backlog > sk->sk_max_ack_backlog; + return sk->sk_ack_backlog >= sk->sk_max_ack_backlog; } /* - To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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