Re: [RESEND PATCH v2 bpf-next] bpf: Cleanup check_refcount_ok

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On Mon, 8 Aug 2022 at 19:16, Dave Marchevsky <davemarchevsky@xxxxxx> wrote:
>
> Discussion around a recently-submitted patch provided historical
> context for check_refcount_ok [0]. Specifically, the function and its
> helpers - may_be_acquire_function and arg_type_may_be_refcounted -
> predate the OBJ_RELEASE type flag and the addition of many more helpers
> with acquire/release semantics.
>
> The purpose of check_refcount_ok is to ensure:
>   1) Helper doesn't have multiple uses of return reg's ref_obj_id
>   2) Helper with release semantics only has one arg needing to be
>   released, since that's tracked using meta->ref_obj_id
>
> With current verifier, it's safe to remove check_refcount_ok and its
> helpers. Since addition of OBJ_RELEASE type flag, case 2) has been
> handled by the arg_type_is_release check in check_func_arg. To ensure
> case 1) won't result in verifier silently prioritizing one use of
> ref_obj_id, this patch adds a helper_multiple_ref_obj_use check which
> fails loudly if a helper passes > 1 test for use of ref_obj_id.
>
>   [0]: lore.kernel.org/bpf/20220713234529.4154673-1-davemarchevsky@xxxxxx
>
> Signed-off-by: Dave Marchevsky <davemarchevsky@xxxxxx>
> Acked-by: Martin KaFai Lau <kafai@xxxxxx>
> Acked-by: Joanne Koong <joannelkoong@xxxxxxxxx>

Acked-by: Kumar Kartikeya Dwivedi <memxor@xxxxxxxxx>



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