Re: [PATCH bpf-next v1 3/3] selftests/bpf: Cover generic __uninit kfunc output buffers

[Eduard Zingerman <eddyz87@gmail.com>]

On Tue, 2026-09-15 at 16:10 +0200, Kumar Kartikeya Dwivedi wrote:
> Exercise scalar, scalar-only struct and sized output buffers, both with
> uninitialized stack storage and with a checkpoint that poisons prior stores.
> Run the accepted programs and check the values written by the kfuncs.
> 
> Use the annotation-driven loader to repeat cases with CAP_BPF and
> CAP_NET_ADMIN, but without CAP_PERFMON or CAP_SYS_ADMIN. Prepare module BTF
> before dropping capabilities with __prepare_priv so the cases reach the
> verifier. Cover stack-passed output pointers and outputs following by-value
> arguments in both capability modes.
> 
> Cover multiple outputs, an independent output next to a variable-size
> buffer, variable offsets, and write-only maps. Check that read-only maps,
> out-of-bounds outputs, uninitialized aliased inputs, and reads beyond the
> initialized range retain their expected rejection.
> 
> Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
> ---

I think this is a bit over-enthusiastic on adding more tests.
For the actual fix only the following tests are necessary:
- struct_poisoned_at_checkpoint
- sized_buffer_poisoned_at_checkpoint
- uninitialized_input_alias

Also __prepare_priv is kind of a hack.
It works now, but I don't think libbpf was designed with an idea of
dropping capabilities mid-flight in mind.

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