Re: [PATCH nf-next] netfilter: add and use nf_hook_slow_list()

[Edward Cree <ecree@solarflare.com>]

On 09/10/2019 15:30, Florian Westphal wrote:
> At this time, NF_HOOK_LIST() macro will iterate the list and then call
> nf_hook() for each skb.
>
> This makes it so the entire list is passed into the netfilter core.
> The advantage is that we only need to fetch the rule blob once per list
> instead of per-skb.  If no rules are present, the list operations
> can be elided entirely.
>
> NF_HOOK_LIST only supports ipv4 and ipv6, but those are the only
> callers.
>
> Cc: Edward Cree <ecree@solarflare.com>
> Signed-off-by: Florian Westphal <fw@strlen.de>
> ---
LGTM (but see below).
Acked-by: Edward Cree <ecree@solarflare.com>
>  include/linux/netfilter.h | 41 +++++++++++++++++++++++++++++----------
>  net/netfilter/core.c      | 20 +++++++++++++++++++
>  2 files changed, 51 insertions(+), 10 deletions(-)
>
> diff --git a/include/linux/netfilter.h b/include/linux/netfilter.h
> index 77ebb61faf48..eb312e7ca36e 100644
> --- a/include/linux/netfilter.h
> +++ b/include/linux/netfilter.h
> @@ -199,6 +199,8 @@ extern struct static_key nf_hooks_needed[NFPROTO_NUMPROTO][NF_MAX_HOOKS];
>  int nf_hook_slow(struct sk_buff *skb, struct nf_hook_state *state,
>                const struct nf_hook_entries *e, unsigned int i);
>
> +void nf_hook_slow_list(struct list_head *head, struct nf_hook_state *state,
> +                    const struct nf_hook_entries *e);
>  /**
>   *   nf_hook - call a netfilter hook
>   *
> @@ -311,17 +313,36 @@ NF_HOOK_LIST(uint8_t pf, unsigned int hook, struct net *net, struct sock *sk,
>            struct list_head *head, struct net_device *in, struct net_device *out,
>            int (*okfn)(struct net *, struct sock *, struct sk_buff *))
>  {
> -     struct sk_buff *skb, *next;
> -     struct list_head sublist;
> -
> -     INIT_LIST_HEAD(&sublist);
> -     list_for_each_entry_safe(skb, next, head, list) {
> -             list_del(&skb->list);
> -             if (nf_hook(pf, hook, net, sk, skb, in, out, okfn) == 1)
> -                     list_add_tail(&skb->list, &sublist);
> +     struct nf_hook_entries *hook_head = NULL;
> +
> +#ifdef CONFIG_JUMP_LABEL
> +     if (__builtin_constant_p(pf) &&
> +         __builtin_constant_p(hook) &&
> +         !static_key_false(&nf_hooks_needed[pf][hook]))
> +             return;
> +#endif
> +
> +     rcu_read_lock();
> +     switch (pf) {
> +     case NFPROTO_IPV4:
> +             hook_head = rcu_dereference(net->nf.hooks_ipv4[hook]);
> +             break;
> +     case NFPROTO_IPV6:
> +             hook_head = rcu_dereference(net->nf.hooks_ipv6[hook]);
> +             break;
> +     default:
> +             WARN_ON_ONCE(1);
> +             break;
>       }
> -     /* Put passed packets back on main list */
> -     list_splice(&sublist, head);
> +
> +     if (hook_head) {
> +             struct nf_hook_state state;
> +
> +             nf_hook_state_init(&state, hook, pf, in, out, sk, net, okfn);
> +
> +             nf_hook_slow_list(head, &state, hook_head);
> +     }
> +     rcu_read_unlock();
>  }
>
>  /* Call setsockopt() */
> diff --git a/net/netfilter/core.c b/net/netfilter/core.c
> index 5d5bdf450091..306587b07a4f 100644
> --- a/net/netfilter/core.c
> +++ b/net/netfilter/core.c
> @@ -536,6 +536,26 @@ int nf_hook_slow(struct sk_buff *skb, struct nf_hook_state *state,
>  }
>  EXPORT_SYMBOL(nf_hook_slow);
>
> +void nf_hook_slow_list(struct list_head *head, struct nf_hook_state *state,
> +                    const struct nf_hook_entries *e)
> +{
> +     struct sk_buff *skb, *next;
> +     struct list_head sublist;
> +     int ret;
> +
> +     INIT_LIST_HEAD(&sublist);
> +
> +     list_for_each_entry_safe(skb, next, head, list) {
> +             list_del(&skb->list);
I know this was just copied from the existing code, but I've been getting
 a lot more paranoid lately about skbs escaping with non-NULL ->next
 pointers, since several bugs of that kind have turned up elsewhere.
So should this maybe be skb_list_del_init()?

-Ed
> +             ret = nf_hook_slow(skb, state, e, 0);
> +             if (ret == 1)
> +                     list_add_tail(&skb->list, &sublist);
> +     }
> +     /* Put passed packets back on main list */
> +     list_splice(&sublist, head);
> +}
> +EXPORT_SYMBOL(nf_hook_slow_list);
> +
>  /* This needs to be compiled in any case to avoid dependencies between the
>   * nfnetlink_queue code and nf_conntrack.
>   */

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