[PATCH net] tcp: repair: fix TCP_QUEUE_SEQ implementation

[PATCH net] tcp: repair: fix TCP_QUEUE_SEQ implementation

[Eric Dumazet]

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>
---
 net/ipv4/tcp.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index eb2d80519f8e5ad165ca3b8acef2b10bdf8b7345..dc77c303e6f7f69b24170010b6a295d179342676 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -2948,8 +2948,10 @@ static int do_tcp_setsockopt(struct sock *sk, int level,
 			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;
-- 
2.25.1.481.gfbce0eb801-goog

Re: [PATCH net] tcp: repair: fix TCP_QUEUE_SEQ implementation

[David Miller]

From: Eric Dumazet <edumazet@google.com>
Date: Wed, 18 Mar 2020 19:21:02 -0700

> 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>

Applied and queued up for -stable, thanks Eric.