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[PATCH 4.12 10/17] tcp: fastopen: tcp_connect() must refresh the route




4.12-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
@@ -3361,6 +3361,9 @@ 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)) {