• Eric Dumazet's avatar
    tcp: provide SYN headers for passive connections · cd8ae852
    Eric Dumazet authored
    This patch allows a server application to get the TCP SYN headers for
    its passive connections.  This is useful if the server is doing
    fingerprinting of clients based on SYN packet contents.
    
    Two socket options are added: TCP_SAVE_SYN and TCP_SAVED_SYN.
    
    The first is used on a socket to enable saving the SYN headers
    for child connections. This can be set before or after the listen()
    call.
    
    The latter is used to retrieve the SYN headers for passive connections,
    if the parent listener has enabled TCP_SAVE_SYN.
    
    TCP_SAVED_SYN is read once, it frees the saved SYN headers.
    
    The data returned in TCP_SAVED_SYN are network (IPv4/IPv6) and TCP
    headers.
    
    Original patch was written by Tom Herbert, I changed it to not hold
    a full skb (and associated dst and conntracking reference).
    
    We have used such patch for about 3 years at Google.
    Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
    Acked-by: default avatarNeal Cardwell <ncardwell@google.com>
    Tested-by: default avatarNeal Cardwell <ncardwell@google.com>
    Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
    cd8ae852
tcp.c 81.2 KB