4.4-stable review patch. If anyone has any objections, please let me know.
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From: Yuchung Cheng ycheng@google.com
[ Upstream commit 16ae6aa1705299789f71fdea59bfb119c1fbd9c0 ]
The TCP repair sequence of operation is to first set the socket in repair mode, then inject the TCP stats into the socket with repair socket options, then call connect() to re-activate the socket. The connect syscall simply returns and set state to ESTABLISHED mode. As a result Fast Open is meaningless for TCP repair.
However allowing sendto() system call with MSG_FASTOPEN flag half-way during the repair operation could unexpectedly cause data to be sent, before the operation finishes changing the internal TCP stats (e.g. MSS). This in turn triggers TCP warnings on inconsistent packet accounting.
The fix is to simply disallow Fast Open operation once the socket is in the repair mode.
Reported-by: syzbot syzkaller@googlegroups.com Signed-off-by: Yuchung Cheng ycheng@google.com Reviewed-by: Neal Cardwell ncardwell@google.com Reviewed-by: Eric Dumazet edumazet@google.com Signed-off-by: David S. Miller davem@davemloft.net Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- net/ipv4/tcp.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
--- a/net/ipv4/tcp.c +++ b/net/ipv4/tcp.c @@ -1108,7 +1108,7 @@ int tcp_sendmsg(struct sock *sk, struct lock_sock(sk);
flags = msg->msg_flags; - if (flags & MSG_FASTOPEN) { + if ((flags & MSG_FASTOPEN) && !tp->repair) { err = tcp_sendmsg_fastopen(sk, msg, &copied_syn, size); if (err == -EINPROGRESS && copied_syn > 0) goto out;