• Wei Dong's avatar
    [NET]: Fix bugs in "Whether sock accept queue is full" checking · 8488df89
    Wei Dong authored
    	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.
    Signed-off-by: default avatarWei Dong <weid@np.css.fujitsu.com>
    Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
    8488df89
sock.h 40.3 KB