Re: [PATCH v2 1/3] bpf: Allow NULL buffers in bpf_dynptr_slice(_rw)

[Alexei Starovoitov <alexei.starovoitov@xxxxxxxxx>]

On Tue, Jul 18, 2023 at 8:26 AM Jakub Kicinski <kuba@xxxxxxxxxx> wrote:
>
> On Mon,  1 May 2023 17:52:16 -0700 Daniel Rosenberg wrote:
> > --- a/include/linux/skbuff.h
> > +++ b/include/linux/skbuff.h
> > @@ -4033,7 +4033,7 @@ __skb_header_pointer(const struct sk_buff *skb, int offset, int len,
> >       if (likely(hlen - offset >= len))
> >               return (void *)data + offset;
> >
> > -     if (!skb || unlikely(skb_copy_bits(skb, offset, buffer, len) < 0))
> > +     if (!skb || !buffer || unlikely(skb_copy_bits(skb, offset, buffer, len) < 0))
> >               return NULL;
>
> First off - please make sure you CC netdev on changes to networking!
>
> Please do not add stupid error checks to core code for BPF safety.
> Wrap the call if you can't guarantee that value is sane, this is
> a very bad precedent.

This is NOT for safety. You misread the code.