tcp: diag: Dont report negative values for rx queue

Both netlink and /proc/net/tcp interfaces can report transient
negative values for rx queue.

ss ->
State   Recv-Q Send-Q  Local Address:Port  Peer Address:Port
ESTAB   -6     6       127.0.0.1:45956     127.0.0.1:3333 

netstat ->
tcp   4294967290      6 127.0.0.1:37784  127.0.0.1:3333 ESTABLISHED

This is because we dont lock socket while computing 
tp->rcv_nxt - tp->copied_seq,
and another CPU can update copied_seq before rcv_next in RX path.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 1 insertions, 1 deletions

diff --git a/net/ipv4/tcp_diag.c b/net/ipv4/tcp_diag.c
index fcbcd4ff6c5f..939edb3b8e4d 100644
--- a/net/ipv4/tcp_diag.c
+++ b/net/ipv4/tcp_diag.c
@@ -27,7 +27,7 @@ static void tcp_diag_get_info(struct sock *sk, struct inet_diag_msg *r,
                 r->idiag_rqueue = sk->sk_ack_backlog;
                 r->idiag_wqueue = sk->sk_max_ack_backlog;
         } else {
-                r->idiag_rqueue = tp->rcv_nxt - tp->copied_seq;
+                r->idiag_rqueue = max_t(int, tp->rcv_nxt - tp->copied_seq, 0);
                 r->idiag_wqueue = tp->write_seq - tp->snd_una;
         }
         if (info != NULL)