• Su, Xuemin's avatar
    udp reuseport: fix packet of same flow hashed to different socket · d1e37288
    Su, Xuemin authored
    There is a corner case in which udp packets belonging to a same
    flow are hashed to different socket when hslot->count changes from 10
    to 11:
    
    1) When hslot->count <= 10, __udp_lib_lookup() searches udp_table->hash,
    and always passes 'daddr' to udp_ehashfn().
    
    2) When hslot->count > 10, __udp_lib_lookup() searches udp_table->hash2,
    but may pass 'INADDR_ANY' to udp_ehashfn() if the sockets are bound to
    INADDR_ANY instead of some specific addr.
    
    That means when hslot->count changes from 10 to 11, the hash calculated by
    udp_ehashfn() is also changed, and the udp packets belonging to a same
    flow will be hashed to different socket.
    
    This is easily reproduced:
    1) Create 10 udp sockets and bind all of them to 0.0.0.0:40000.
    2) From the same host send udp packets to 127.0.0.1:40000, record the
    socket index which receives the packets.
    3) Create 1 more udp socket and bind it to 0.0.0.0:44096. The number 44096
    is 40000 + UDP_HASH_SIZE(4096), this makes the new socket put into the
    same hslot as the aformentioned 10 sockets, and makes the hslot->count
    change from 10 to 11.
    4) From the same host send udp packets to 127.0.0.1:40000, and the socket
    index which receives the packets will be different from the one received
    in step 2.
    This should not happen as the socket bound to 0.0.0.0:44096 should not
    change the behavior of the sockets bound to 0.0.0.0:40000.
    
    It's the same case for IPv6, and this patch also fixes that.
    Signed-off-by: default avatarSu, Xuemin <suxm@chinanetcenter.com>
    Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
    Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
    d1e37288
udp.c 37.2 KB