Re: [PATCH net,v3] tcp: fix a signed-integer-overflow bug in tcp_add_backlog()

[Kuniyuki Iwashima <kuniyu@amazon.com>]

From:   Lu Wei <luwei32@huawei.com>
Date:   Fri, 21 Oct 2022 12:06:22 +0800
> The type of sk_rcvbuf and sk_sndbuf in struct sock is int, and
> in tcp_add_backlog(), the variable limit is caculated by adding
> sk_rcvbuf, sk_sndbuf and 64 * 1024, it may exceed the max value
> of int and overflow. This patch reduces the limit budget by
> halving the sndbuf to solve this issue since ACK packets are much
> smaller than the payload.
> 
> Fixes: c9c3321257e1 ("tcp: add tcp_add_backlog()")
> Signed-off-by: Lu Wei <luwei32@huawei.com>

Acked-by: Kuniyuki Iwashima <kuniyu@amazon.com>


> ---
>  net/ipv4/tcp_ipv4.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
> index 7a250ef9d1b7..87d440f47a70 100644
> --- a/net/ipv4/tcp_ipv4.c
> +++ b/net/ipv4/tcp_ipv4.c
> @@ -1874,11 +1874,13 @@ bool tcp_add_backlog(struct sock *sk, struct sk_buff *skb,
>  	__skb_push(skb, hdrlen);
>  
>  no_coalesce:
> +	limit = (u32)READ_ONCE(sk->sk_rcvbuf) + (u32)(READ_ONCE(sk->sk_sndbuf) >> 1);
> +
>  	/* Only socket owner can try to collapse/prune rx queues
>  	 * to reduce memory overhead, so add a little headroom here.
>  	 * Few sockets backlog are possibly concurrently non empty.
>  	 */
> -	limit = READ_ONCE(sk->sk_rcvbuf) + READ_ONCE(sk->sk_sndbuf) + 64*1024;
> +	limit += 64 * 1024;
>  
>  	if (unlikely(sk_add_backlog(sk, skb, limit))) {
>  		bh_unlock_sock(sk);
> -- 
> 2.31.1