Subject: Re: [Patch bpf] skmsg: check sk_rcvbuf limit before queuing to ingress_skb

From: Jakub Sitnicki <[email-masked]>
Date: Wed, 30 Jun 2021 11:21:25 +0200

On Tue, Jun 29, 2021 at 08:20 AM CEST, Cong Wang wrote:

[...]

> @@ -854,7 +854,8 @@ static int sk_psock_skb_redirect(struct sk_psock *from, struct sk_buff *skb)
>  		return -EIO;
>  	}
>  	spin_lock_bh(&psock_other->ingress_lock);
> -	if (!sk_psock_test_state(psock_other, SK_PSOCK_TX_ENABLED)) {
> +	if (!sk_psock_test_state(psock_other, SK_PSOCK_TX_ENABLED) ||
> +	    atomic_read(&sk_other->sk_rmem_alloc) > sk_other->sk_rcvbuf) {
>  		spin_unlock_bh(&psock_other->ingress_lock);
>  		skb_bpf_redirect_clear(skb);
>  		sock_drop(from->sk, skb);
> @@ -930,7 +931,8 @@ static int sk_psock_verdict_apply(struct sk_psock *psock, struct sk_buff *skb,
>  		}
>  		if (err < 0) {
>  			spin_lock_bh(&psock->ingress_lock);
> -			if (sk_psock_test_state(psock, SK_PSOCK_TX_ENABLED)) {
> +			if (sk_psock_test_state(psock, SK_PSOCK_TX_ENABLED) &&
> +			    atomic_read(&sk_other->sk_rmem_alloc) <= sk_other->sk_rcvbuf) {
>  				skb_queue_tail(&psock->ingress_skb, skb);
>  				schedule_work(&psock->work);
>  				err = 0;

I belive access to sk_rcvbuf should be annotated with READ_ONCE (for
KCSAN's sake) as we don't lock the egress socket. See 8265792bf887 [1]
("net: silence KCSAN warnings around sk_add_backlog() calls") for
guidance.

[1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=8265792bf8871acc2d00fd03883d830e2249d395