linux-kernel - Re: [PATCH v1] LSM: Enable multiple calls to security_add

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Message-ID: <ca662813-e078-c579-d5a8-46ea03542f4b@digikod.net>
Date:   Mon, 8 May 2017 21:24:38 +0200
From:   Mickaël Salaün <mic@...ikod.net>
To:     James Morris <jmorris@...ei.org>,
        Casey Schaufler <casey@...aufler-ca.com>,
        Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Cc:     linux-kernel@...r.kernel.org,
        James Morris <james.l.morris@...cle.com>,
        Kees Cook <keescook@...omium.org>,
        "Serge E . Hallyn" <serge@...lyn.com>,
        linux-security-module@...r.kernel.org
Subject: Re: [PATCH v1] LSM: Enable multiple calls to security_add_hooks() for
 the same LSM

On 01/05/2017 01:28, James Morris wrote:
> On Sat, 29 Apr 2017, Mickaël Salaün wrote:
> 
>> Check if the registering LSM already registered hooks just before. This
>> enable to split hook declarations into multiple files without
>> registering multiple time the same LSM name, starting from commit
>> d69dece5f5b6 ("LSM: Add /sys/kernel/security/lsm").
> 
> Please include a detailed rationale for these patches.  The above tells us 
> very little about why they are needed.

Right, what do you think about that?

The commit d69dece5f5b6 ("LSM: Add /sys/kernel/security/lsm") extend
security_add_hooks() with a new parameter to register the LSM name,
which may be useful to make the list of currently loaded LSM available
to userspace. However, there is no clean way for an LSM no split its
hook declarations into multiple files, which may reduce the mess with
all the included files (needed for LSM hook argument types) and make the
source code easier to review and maintain.

This change allows an LSM to register multiple times its hook while
keeping a consistent list of LSM names as described in
Documentation/security/LSM.txt . The list reflects the order in which
checks are made. This patch only check for the last registered LSM,
which should be the only case. If an LSM register multiple times its
hooks, interleaved with other LSM registrations, which should not
happen, its name will still appear in the same order that the hooks are
called, hence multiple times.

Casey, Tetsuo, are you OK with this approach or do you want me to handle
the case with interleaved hook registration, i.e. no duplicate name nor
following the current Documentation/security/LSM.txt?
What about the API with the NULL name (which is much simpler)?

Regards,
 Mickaël

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