Re: [PATCH 1/3] bpf: verifier: Accept dynptr mem as mem in helpers

[Daniel Rosenberg <drosen@google.com>]

On Thu, Apr 6, 2023 at 1:55 PM Andrii Nakryiko
<andrii.nakryiko@gmail.com> wrote:
>
> Something feels off here. Can you paste a bit of verifier log for the
> failure you were getting. And let's have a selftest for this situation
> as well.
>
> ARG_PTR_TO_MEM shouldn't be qualified with the DYNPTR_TYPE flag, it's
> just memory, there is no need to know what type of dynptr it was
> derived from. So if that happens, the problem is somewhere else. Let's
> root cause and fix that. Having a selftest that demonstrates the
> problem will help with that.
>
>
This label is added by dynptr_slice(_rdwr)

if (meta.func_id == special_kfunc_list[KF_bpf_dynptr_slice] ||
   meta.func_id == special_kfunc_list[KF_bpf_dynptr_slice_rdwr]) {
enum bpf_type_flag type_flag =
get_dynptr_type_flag(meta.initialized_dynptr.type);
...
regs[BPF_REG_0].type = PTR_TO_MEM | type_flag;

That extra flag was causing the type to be unexpected later on.
I'll add a selftest for this as well.