tcp: repair: fix TCP_QUEUE_SEQ implementation

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 <[e-mail]>
Reported-by: syzbot <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

net/ipv4/tcp.c

···
 			err = -EPERM;
 		else if (tp->repair_queue == TCP_SEND_QUEUE)
 			WRITE_ONCE(tp->write_seq, val);
-		else if (tp->repair_queue == TCP_RECV_QUEUE)
+		else if (tp->repair_queue == TCP_RECV_QUEUE) {
 			WRITE_ONCE(tp->rcv_nxt, val);
+			WRITE_ONCE(tp->copied_seq, val);
+		}
 		else
 			err = -EINVAL;
 		break;