linux-kernel - Re: [PATCH bpf-next v4 2/2] bpf: Refactor bpf_tracing_func_proto() and remove bpf_get_probe_write

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Message-ID: <6cb6d9e6-bc7a-4915-ba98-e52f94c7d9c3@iogearbox.net>
Date: Fri, 29 Nov 2024 17:43:50 +0100
From: Daniel Borkmann <daniel@...earbox.net>
To: Marco Elver <elver@...gle.com>, Alexei Starovoitov <ast@...nel.org>,
 Andrii Nakryiko <andrii@...nel.org>
Cc: Martin KaFai Lau <martin.lau@...ux.dev>,
 Eduard Zingerman <eddyz87@...il.com>, Song Liu <song@...nel.org>,
 Yonghong Song <yonghong.song@...ux.dev>,
 John Fastabend <john.fastabend@...il.com>, KP Singh <kpsingh@...nel.org>,
 Stanislav Fomichev <sdf@...ichev.me>, Hao Luo <haoluo@...gle.com>,
 Jiri Olsa <jolsa@...nel.org>, Nikola Grcevski <nikola.grcevski@...fana.com>,
 bpf@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH bpf-next v4 2/2] bpf: Refactor bpf_tracing_func_proto()
 and remove bpf_get_probe_write_proto()

On 11/29/24 9:59 AM, Marco Elver wrote:
> With bpf_get_probe_write_proto() no longer printing a message, we can
> avoid it being a special case with its own permission check.
> 
> Refactor bpf_tracing_func_proto() similar to bpf_base_func_proto() to
> have a section conditional on bpf_token_capable(CAP_SYS_ADMIN), where
> the proto for bpf_probe_write_user() is returned. Finally, remove the
> unnecessary bpf_get_probe_write_proto().
> 
> This simplifies the code, and adding additional CAP_SYS_ADMIN-only
> helpers in future avoids duplicating the same CAP_SYS_ADMIN check.
> 
> Suggested-by: Andrii Nakryiko <andrii@...nel.org>
> Signed-off-by: Marco Elver <elver@...gle.com>
> Acked-by: Jiri Olsa <jolsa@...nel.org>

Given the abuse that has been done with this helper, my preference is
we don't encourage wider use via bpf_token_capable.. but fair enough,
as long as it stays behind security_locked_down.

Acked-by: Daniel Borkmann <daniel@...earbox.net>