Re: [PATCH net v2] net/x25: Fix overflow when accumulating packets

Jakub Kicinski
2026-04-02T02:48:59Z

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---
net/x25: Fix overflow when accumulating packets

This commit adds a check to prevent x25_sock.fraglen from overflowing
during packet accumulation. It also resets the fragment length when
purging the fragment queue.

> diff --git a/net/x25/x25_in.c b/net/x25/x25_in.c
> index b981a4828d08..cb84c683d249 100644
> --- a/net/x25/x25_in.c
> +++ b/net/x25/x25_in.c
> @@ -34,6 +34,12 @@ static int x25_queue_rx_frame(struct sock *sk, struct sk_buff *skb, int more)
> struct sk_buff *skbo, *skbn = skb;
> struct x25_sock *x25 = x25_sk(sk);
>
> + /* make sure we don't overflow */
> + if (x25->fraglen + skb->len > USHRT_MAX) {
> + kfree_skb(skb);
> + return 1;
> + }

Does this cause the skb to be freed twice?

When x25_queue_rx_frame() frees the skb and returns 1, the caller
x25_state3_machine() leaves its local queued variable as 0 and returns 0.

This 0 value propagates up through x25_process_rx_frame() to callers
like x25_backlog_rcv() or x25_lapb_receive_frame(). Since the return
value indicates the packet was not consumed by the protocol stack, these
upper-level functions will call kfree_skb(skb) again on the already
freed skb.

Would it be safer to return 1 without calling kfree_skb(skb) here so
the callers can handle freeing the unconsumed packet?
--
pw-bot: cr