From: Eric Dumazet <edumazet@google.com>
Date: Wed, 18 Mar 2020 19:21:02 -0700
Subject: tcp: repair: fix TCP_QUEUE_SEQ implementation
Git-commit: 6cd6cbf593bfa3ae6fc3ed34ac21da4d35045425
Patch-mainline: 5.6
References: networking-stable-20_03_28

When application uses TCP_QUEUE_SEQ socket option to
change tp->rcv_next, we must also update tp->copied_seq.

Otherwise, stuff relying on tcp_inq() being precise can
eventually be confused.

For example, tcp_zerocopy_receive() might crash because
it does not expect tcp_recv_skb() to return NULL.

We could add tests in various places to fix the issue,
or simply make sure tcp_inq() wont return a random value,
and leave fast path as it is.

Note that this fixes ioctl(fd, SIOCINQ, &val) at the same
time.

Fixes: ee9952831cfd ("tcp: Initial repair mode")
Fixes: 05255b823a61 ("tcp: add TCP_ZEROCOPY_RECEIVE support for zerocopy receive")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: syzbot <syzkaller@googlegroups.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
---
 net/ipv4/tcp.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -2472,8 +2472,10 @@ static int do_tcp_setsockopt(struct sock
 			err = -EPERM;
 		else if (tp->repair_queue == TCP_SEND_QUEUE)
 			tp->write_seq = val;
-		else if (tp->repair_queue == TCP_RECV_QUEUE)
+		else if (tp->repair_queue == TCP_RECV_QUEUE) {
 			tp->rcv_nxt = val;
+			WRITE_ONCE(tp->copied_seq, val);
+		}
 		else
 			err = -EINVAL;
 		break;