Re: [PATCH bpf-next v3 01/10] bpf: Add dynptr type for skb metadata

[Eduard Zingerman <eddyz87@gmail.com>]

On Tue, 2025-07-22 at 11:46 -0700, Eduard Zingerman wrote:

[...]

> > @@ -2274,7 +2278,8 @@ static bool reg_is_pkt_pointer_any(const struct bpf_reg_state *reg)
> >  static bool reg_is_dynptr_slice_pkt(const struct bpf_reg_state *reg)
> >  {
> >  	return base_type(reg->type) == PTR_TO_MEM &&
> > -		(reg->type & DYNPTR_TYPE_SKB || reg->type & DYNPTR_TYPE_XDP);
> > +	       (reg->type &
> > +		(DYNPTR_TYPE_SKB | DYNPTR_TYPE_XDP | DYNPTR_TYPE_SKB_META));
> >  }
> 
> Note: This function is used to identify pointers to packet data that
>       might be stale after call to one of the functions in list [1].
>       Once such pointers are identified, verifier would disallow
>       access through these pointers.
>       dynptr_from_skb_meta() is implemented as:
> 
>         bpf_dynptr_init(ptr, skb, BPF_DYNPTR_TYPE_SKB_META, 0, skb_metadata_len(skb));
> 
>       here any read or write goes through skb object, not a pointer derived from it.
>       Given above, is it still necessary to list DYNPTR_FROM_SKB_META here?
>       Or some functions from [1] can change skb_metadata_len(skb)?
> 
> [1] https://elixir.bootlin.com/linux/v6.15.7/source/net/core/filter.c#L7989

Nevermind, it is necessary, otherwise your tests skb_meta_invalid_data_slice*
would be accepted. Sorry for the noise.