4.4-stable review patch. If anyone has any objections, please let me know. ------------------ From: Eric Dumazet <edumazet@xxxxxxxxxx> [ 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@xxxxxxxxxx> Signed-off-by: Eric Dumazet <edumazet@xxxxxxxxxx> Cc: Wei Wang <weiwan@xxxxxxxxxx> Cc: Yuchung Cheng <ycheng@xxxxxxxxxx> Acked-by: Wei Wang <weiwan@xxxxxxxxxx> Acked-by: Yuchung Cheng <ycheng@xxxxxxxxxx> Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- net/ipv4/tcp_output.c | 3 +++ 1 file changed, 3 insertions(+) --- a/net/ipv4/tcp_output.c +++ b/net/ipv4/tcp_output.c @@ -3256,6 +3256,9 @@ 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)) {