Re: [PATCH RFC v2 bpf-next 3/3] bpf: minimal support for programs hooked into netfilter framework

["Toke Høiland-Jørgensen" <toke@kernel.org>]

Florian Westphal <fw@strlen.de> writes:

> This adds minimal support for BPF_PROG_TYPE_NETFILTER bpf programs
> that will be invoked via the NF_HOOK() points in the ip stack.
>
> Invocation incurs an indirect call.  This is not a necessity: Its
> possible to add 'DEFINE_BPF_DISPATCHER(nf_progs)' and handle the
> program invocation with the same method already done for xdp progs.
>
> This isn't done here to keep the size of this chunk down.
>
> Verifier restricts verdicts to either DROP or ACCEPT.
>
> Signed-off-by: Florian Westphal <fw@strlen.de>
> ---
>  include/linux/bpf_types.h           |  4 ++
>  include/net/netfilter/nf_hook_bpf.h |  6 +++
>  kernel/bpf/btf.c                    |  5 ++
>  kernel/bpf/verifier.c               |  3 ++
>  net/netfilter/nf_bpf_link.c         | 78 ++++++++++++++++++++++++++++-
>  5 files changed, 95 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/bpf_types.h b/include/linux/bpf_types.h
> index d4ee3ccd3753..39a999abb0ce 100644
> --- a/include/linux/bpf_types.h
> +++ b/include/linux/bpf_types.h
> @@ -79,6 +79,10 @@ BPF_PROG_TYPE(BPF_PROG_TYPE_LSM, lsm,
>  #endif
>  BPF_PROG_TYPE(BPF_PROG_TYPE_SYSCALL, bpf_syscall,
>  	      void *, void *)
> +#ifdef CONFIG_NETFILTER
> +BPF_PROG_TYPE(BPF_PROG_TYPE_NETFILTER, netfilter,
> +	      struct bpf_nf_ctx, struct bpf_nf_ctx)
> +#endif
>  
>  BPF_MAP_TYPE(BPF_MAP_TYPE_ARRAY, array_map_ops)
>  BPF_MAP_TYPE(BPF_MAP_TYPE_PERCPU_ARRAY, percpu_array_map_ops)
> diff --git a/include/net/netfilter/nf_hook_bpf.h b/include/net/netfilter/nf_hook_bpf.h
> index 9d1b338e89d7..863cbbcc66f9 100644
> --- a/include/net/netfilter/nf_hook_bpf.h
> +++ b/include/net/netfilter/nf_hook_bpf.h
> @@ -1,2 +1,8 @@
>  /* SPDX-License-Identifier: GPL-2.0 */
> +
> +struct bpf_nf_ctx {
> +	const struct nf_hook_state *state;
> +	struct sk_buff *skb;
> +};
> +
>  int bpf_nf_link_attach(const union bpf_attr *attr, struct bpf_prog *prog);
> diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
> index ef2d8969ed1f..ec6eb78b9aec 100644
> --- a/kernel/bpf/btf.c
> +++ b/kernel/bpf/btf.c
> @@ -25,6 +25,9 @@
>  #include <linux/bsearch.h>
>  #include <linux/kobject.h>
>  #include <linux/sysfs.h>
> +
> +#include <net/netfilter/nf_hook_bpf.h>
> +
>  #include <net/sock.h>
>  #include "../tools/lib/bpf/relo_core.h"
>  
> @@ -7726,6 +7729,8 @@ static int bpf_prog_type_to_kfunc_hook(enum bpf_prog_type prog_type)
>  	case BPF_PROG_TYPE_LWT_XMIT:
>  	case BPF_PROG_TYPE_LWT_SEG6LOCAL:
>  		return BTF_KFUNC_HOOK_LWT;
> +	case BPF_PROG_TYPE_NETFILTER:
> +		return BTF_KFUNC_HOOK_SOCKET_FILTER;

The dynptr patch reuses the actual set between the different IDs, so
this should probably define a new BTF_KFUNC_HOOK_NETFILTER, with an
associated register_btf_kfunc_id_set() call?

-Toke