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    Subject[PATCH 4.9 08/16] tcp: fastopen: tcp_connect() must refresh the route
    Date
    4.9-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Eric Dumazet <edumazet@google.com>


    [ Upstream commit 8ba60924710cde564a3905588b6219741d6356d0 ]

    With new TCP_FASTOPEN_CONNECT socket option, there is a possibility
    to call tcp_connect() while socket sk_dst_cache is either NULL
    or invalid.

    +0 socket(..., SOCK_STREAM, IPPROTO_TCP) = 4
    +0 fcntl(4, F_SETFL, O_RDWR|O_NONBLOCK) = 0
    +0 setsockopt(4, SOL_TCP, TCP_FASTOPEN_CONNECT, [1], 4) = 0
    +0 connect(4, ..., ...) = 0

    << sk->sk_dst_cache becomes obsolete, or even set to NULL >>

    +1 sendto(4, ..., 1000, MSG_FASTOPEN, ..., ...) = 1000

    We need to refresh the route otherwise bad things can happen,
    especially when syzkaller is running on the host :/

    Fixes: 19f6d3f3c8422 ("net/tcp-fastopen: Add new API support")
    Reported-by: Dmitry Vyukov <dvyukov@google.com>
    Signed-off-by: Eric Dumazet <edumazet@google.com>
    Cc: Wei Wang <weiwan@google.com>
    Cc: Yuchung Cheng <ycheng@google.com>
    Acked-by: Wei Wang <weiwan@google.com>
    Acked-by: Yuchung Cheng <ycheng@google.com>
    Signed-off-by: David S. Miller <davem@davemloft.net>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    net/ipv4/tcp_output.c | 3 +++
    1 file changed, 3 insertions(+)

    --- a/net/ipv4/tcp_output.c
    +++ b/net/ipv4/tcp_output.c
    @@ -3344,6 +3344,9 @@ int tcp_connect(struct sock *sk)
    struct sk_buff *buff;
    int err;

    + if (inet_csk(sk)->icsk_af_ops->rebuild_header(sk))
    + return -EHOSTUNREACH; /* Routing failure or similar. */
    +
    tcp_connect_init(sk);

    if (unlikely(tp->repair)) {

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