Re: [RFC PATCH bpf-next v2 01/11] bpf: Set kfunc dynptr arg type flag based on prototype

[Eduard Zingerman <eddyz87@gmail.com>]

On Fri, 2026-03-06 at 22:44 -0800, Amery Hung wrote:
> The verifier should decide whether a dynptr argument is read-only
> based on if the type is "const struct bpf_dynptr *", not the type of
> the register passed to the kfunc. This currently does not cause issues
> because existing kfuncs that mutate struct bpf_dynptr are constructors
> (e.g., bpf_dynptr_from_xxx and bpf_dynptr_clone). These kfuncs have
> additional check in process_dynptr_func() to make sure the stack slot
> does not contain initialized dynptr. Nonetheless, this should still be
> fixed to avoid future issues when there is a non-constructor dynptr
> kfunc that can mutate dynptr. This is also a small step toward unifying
> kfunc and helper handling in the verifier, where the first step is to
> generate kfunc prototype similar to bpf_func_proto before the main
> verification loop.
> 
> We also need to correctly mark some kfunc arguments as "const struct
> bpf_dynptr *" to align with other kfuncs that take non-mutable dynptr
> argument and to not break their usage. Adding const qualifier does
> not break backward compatibility.
> 
> Signed-off-by: Amery Hung <ameryhung@gmail.com>
> ---

Acked-by: Eduard Zingerman <eddyz87@gmail.com>

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