From: Simon Baatz <gmbnomis@gmail.com>

Since commit 9ca48d616ed7 ("tcp: do not accept packets beyond
window"), the path leading to SKB_DROP_REASON_TCP_OVERWINDOW in
tcp_data_queue() is probably dead. However, it can be reached now when
tcp_max_receive_window() is larger than tcp_receive_window(). In that
case, increment LINUX_MIB_BEYOND_WINDOW as done in tcp_sequence().

Signed-off-by: Simon Baatz <gmbnomis@gmail.com>
---
 net/ipv4/tcp_input.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 2e1b237608150c2e9c9baf73cf047ed0823ca555..e6b2f4be7723db14acf2ae528df17b6d106b9da9 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -5678,6 +5678,7 @@ static void tcp_data_queue(struct sock *sk, struct sk_buff *skb)
 	if (!before(TCP_SKB_CB(skb)->seq,
 		    tp->rcv_nxt + tcp_receive_window(tp))) {
 		reason = SKB_DROP_REASON_TCP_OVERWINDOW;
+		NET_INC_STATS(sock_net(sk), LINUX_MIB_BEYOND_WINDOW);
 		goto out_of_window;
 	}
 

-- 
2.53.0

On Mon, Mar 9, 2026 at 9:03 AM Simon Baatz via B4 Relay
<devnull+gmbnomis.gmail.com@kernel.org> wrote:
>
> From: Simon Baatz <gmbnomis@gmail.com>
>
> Since commit 9ca48d616ed7 ("tcp: do not accept packets beyond
> window"), the path leading to SKB_DROP_REASON_TCP_OVERWINDOW in
> tcp_data_queue() is probably dead. However, it can be reached now when
> tcp_max_receive_window() is larger than tcp_receive_window(). In that
> case, increment LINUX_MIB_BEYOND_WINDOW as done in tcp_sequence().
>
> Signed-off-by: Simon Baatz <gmbnomis@gmail.com>
> ---
>  net/ipv4/tcp_input.c | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
> index 2e1b237608150c2e9c9baf73cf047ed0823ca555..e6b2f4be7723db14acf2ae528df17b6d106b9da9 100644
> --- a/net/ipv4/tcp_input.c
> +++ b/net/ipv4/tcp_input.c
> @@ -5678,6 +5678,7 @@ static void tcp_data_queue(struct sock *sk, struct sk_buff *skb)
>         if (!before(TCP_SKB_CB(skb)->seq,
>                     tp->rcv_nxt + tcp_receive_window(tp))) {
>                 reason = SKB_DROP_REASON_TCP_OVERWINDOW;
> +               NET_INC_STATS(sock_net(sk), LINUX_MIB_BEYOND_WINDOW);
>                 goto out_of_window;
>         }

Reviewed-by: Eric Dumazet <edumazet@google.com>