netdev - Re: [PATCH bpf-next v3 02/10] bpf: Enable read access to skb metadata with bpf_dynptr

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Message-ID: <3d765f43d5b2d186f2de09c1dddeb32d8ff6e46a.camel@gmail.com>
Date: Tue, 22 Jul 2025 11:49:14 -0700
From: Eduard Zingerman <eddyz87@...il.com>
To: Jakub Sitnicki <jakub@...udflare.com>, bpf@...r.kernel.org
Cc: Alexei Starovoitov <ast@...nel.org>, Andrii Nakryiko
 <andrii@...nel.org>,  Arthur Fabre <arthur@...hurfabre.com>, Daniel
 Borkmann <daniel@...earbox.net>, Eric Dumazet	 <edumazet@...gle.com>, Jakub
 Kicinski <kuba@...nel.org>, Jesper Dangaard Brouer	 <hawk@...nel.org>,
 Jesse Brandeburg <jbrandeburg@...udflare.com>, Joanne Koong	
 <joannelkoong@...il.com>, Lorenzo Bianconi <lorenzo@...nel.org>, Martin
 KaFai Lau <martin.lau@...ux.dev>, Toke
 Høiland-Jørgensen <thoiland@...hat.com>,  Yan Zhai
 <yan@...udflare.com>, kernel-team@...udflare.com, netdev@...r.kernel.org,
 Stanislav Fomichev	 <sdf@...ichev.me>
Subject: Re: [PATCH bpf-next v3 02/10] bpf: Enable read access to skb
 metadata with bpf_dynptr_read

On Mon, 2025-07-21 at 12:52 +0200, Jakub Sitnicki wrote:

[...]

> diff --git a/net/core/filter.c b/net/core/filter.c
> index c17b628c08f5..4b787c56b220 100644
> --- a/net/core/filter.c
> +++ b/net/core/filter.c
> @@ -11978,6 +11978,18 @@ bpf_sk_base_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
>  	return func;
>  }
>  
> +int bpf_skb_meta_load_bytes(const struct sk_buff *skb, u32 offset,
> +			    void *dst, u32 len)
> +{
> +	u32 meta_len = skb_metadata_len(skb);
> +
> +	if (len > meta_len || offset > meta_len - len)
> +		return -E2BIG; /* out of bounds */
> +
> +	memmove(dst, skb_metadata_end(skb) - meta_len + offset, len);
> +	return 0;
> +}
> +

Nit: is it possible to use bpf_skb_meta_pointer() here to avoid
     duplicating range check in both bpf_skb_meta_load_bytes()
     and bpf_skb_meta_store_bytes()?

>  static int dynptr_from_skb_meta(struct __sk_buff *skb_, u64 flags,
>  				struct bpf_dynptr *ptr_, bool rdonly)
>  {