netdev - Re: [PATCH v4 10/20] lsm: Refactor return value of LSM hook audit_rule

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Message-ID: <36836e7b94465fd11d3425166ade3f54@paul-moore.com>
Date: Thu, 18 Jul 2024 22:08:08 -0400
From: Paul Moore <paul@...l-moore.com>
To: Xu Kuohai <xukuohai@...weicloud.com>, bpf@...r.kernel.org, netdev@...r.kernel.org, linux-security-module@...r.kernel.org, linux-kselftest@...r.kernel.org, linux-integrity@...r.kernel.org, apparmor@...ts.ubuntu.com, selinux@...r.kernel.org
Cc: Alexei Starovoitov <ast@...nel.org>, Andrii Nakryiko <andrii@...nel.org>, 
	Daniel Borkmann <daniel@...earbox.net>, 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@...gle.com>, Hao Luo <haoluo@...gle.com>, 
	Jiri Olsa <jolsa@...nel.org>, Matt Bobrowski <mattbobrowski@...gle.com>, 
	Brendan Jackman <jackmanb@...omium.org>, James Morris <jmorris@...ei.org>, 
	"Serge E . Hallyn" <serge@...lyn.com>, Khadija Kamran <kamrankhadijadj@...il.com>, 
	Casey Schaufler <casey@...aufler-ca.com>, Ondrej Mosnacek <omosnace@...hat.com>, 
	Kees Cook <keescook@...omium.org>, John Johansen <john.johansen@...onical.com>, 
	Lukas Bulwahn <lukas.bulwahn@...il.com>, Roberto Sassu <roberto.sassu@...wei.com>, 
	Shung-Hsi Yu <shung-hsi.yu@...e.com>, Edward Cree <ecree.xilinx@...il.com>, 
	Alexander Viro <viro@...iv.linux.org.uk>, Christian Brauner <brauner@...nel.org>, 
	Trond Myklebust <trond.myklebust@...merspace.com>, Anna Schumaker <anna@...nel.org>, 
	Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
	Stephen Smalley <stephen.smalley.work@...il.com>
Subject: Re: [PATCH v4 10/20] lsm: Refactor return value of LSM hook  audit_rule_match

On Jul 11, 2024 Xu Kuohai <xukuohai@...weicloud.com> wrote:
> 
> To be consistent with most LSM hooks, convert the return value of
> hook audit_rule_match to 0 or a negative error code.
> 
> Before:
> - Hook audit_rule_match returns 1 if the rule matches, 0 if it not,
>   and negative error code otherwise.
> 
> After:
> - Hook audit_rule_match returns 0 on success or a negative error
>   code on failure. An output parameter @match is introduced to hold
>   the match result on success.
> 
> Signed-off-by: Xu Kuohai <xukuohai@...wei.com>
> ---
>  include/linux/lsm_hook_defs.h     |  3 +-
>  security/apparmor/audit.c         | 22 ++++++-------
>  security/apparmor/include/audit.h |  2 +-
>  security/security.c               | 15 ++++++++-
>  security/selinux/include/audit.h  |  8 +++--
>  security/selinux/ss/services.c    | 54 +++++++++++++++++--------------
>  security/smack/smack_lsm.c        | 19 +++++++----
>  7 files changed, 75 insertions(+), 48 deletions(-)

This is another odd hook, and similar to some of the others in this
patchset, I'm not sure how applicable this would be to a BPF-based
LSM.  I suspect you could safely block this from a BPF LSM and no one
would notice or be upset.

However, if we did want to keep this hook for a BPF LSM, I think it
might be better to encode the "match" results in the return value, just
sticking with a more conventional 0/errno approach.  What do you think
about 0:found/ok, -ENOENT:missing/ok, -ERRNO:other/error?  Yes, some
of the existing LSM audit_match code uses -ENOENT but looking quickly
at those error conditions it seems that we could consider them
equivalent to a "missing" or "failed match" result and use -ENOENT for
both.  If you're really not happy with that overloading, we could use
something like -ENOMSG:missing/ok instead.

Thoughts?

--
paul-moore.com