Subject: Re: [RFC nf-next v2 1/2] netfilter: bpf: support prog update

From: Simon Horman <[email-masked]>
Date: Mon, 18 Dec 2023 19:06:40 +0000

On Mon, Dec 18, 2023 at 12:18:20PM +0800, D. Wythe wrote:
> From: "D. Wythe" <[email-masked]>
> 
> To support the prog update, we need to ensure that the prog seen
> within the hook is always valid. Considering that hooks are always
> protected by rcu_read_lock(), which provide us the ability to
> access the prog under rcu.
> 
> Signed-off-by: D. Wythe <[email-masked]>

...

> @@ -26,8 +17,20 @@ struct bpf_nf_link {
>  	struct net *net;
>  	u32 dead;
>  	const struct nf_defrag_hook *defrag_hook;
> +	struct rcu_head head;
>  };
>  
> +static unsigned int nf_hook_run_bpf(void *bpf_link, struct sk_buff *skb,
> +				    const struct nf_hook_state *s)
> +{
> +	const struct bpf_nf_link *nf_link = bpf_link;
> +	struct bpf_nf_ctx ctx = {
> +		.state = s,
> +		.skb = skb,
> +	};
> +	return bpf_prog_run(rcu_dereference(nf_link->link.prog), &ctx);

Hi,

AFAICT nf_link->link.prog isn't annotated as __rcu,
so perhaps rcu_dereference() is not correct here?

In any case, sparse seems a bit unhappy:

  .../nf_bpf_link.c:31:29: error: incompatible types in comparison expression (different address spaces):
  .../nf_bpf_link.c:31:29:    struct bpf_prog [noderef] __rcu *
  .../nf_bpf_link.c:31:29:    struct bpf_prog *

> +}
> +
>  #if IS_ENABLED(CONFIG_NF_DEFRAG_IPV4) || IS_ENABLED(CONFIG_NF_DEFRAG_IPV6)
>  static const struct nf_defrag_hook *
>  get_proto_defrag_hook(struct bpf_nf_link *link,

...