On Tue, Aug 8, 2017 at 1:41 AM, Eric Dumazet <eric.duma...@gmail.com> wrote:
> From: Eric Dumazet <eduma...@google.com>
>
> 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 <dvyu...@google.com>
> Signed-off-by: Eric Dumazet <eduma...@google.com>
> Cc: Wei Wang <wei...@google.com>
> Cc: Yuchung Cheng <ych...@google.com>
> ---
Acked-by: Yuchung Cheng <ych...@google.com>

Thanks for the fix!

>  net/ipv4/tcp_output.c |    4 ++++
>  1 file changed, 4 insertions(+)
>
> diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
> index 276406a83a37..b7661a68d498 100644
> --- a/net/ipv4/tcp_output.c
> +++ b/net/ipv4/tcp_output.c
> @@ -3436,6 +3436,10 @@ int tcp_connect(struct sock *sk)
>         int err;
>
>         tcp_call_bpf(sk, BPF_SOCK_OPS_TCP_CONNECT_CB);
> +
> +       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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