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

Simon Horman
2023-12-18T19:06:46Z

On Mon, Dec 18, 2023 at 12:18:20PM +0800, D. Wythe wrote:
> From: "D. Wythe" <alibuda@linux.alibaba.com>
>
> 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 <alibuda@linux.alibaba.com>

...

> @@ -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,

...