linux-kernel - Re: [PATCH v4 1/3] security: Refactor LSM hooks into an array and enum

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Date:   Wed, 7 Mar 2018 12:23:47 -0800
From:   Casey Schaufler <casey@...aufler-ca.com>
To:     Sargun Dhillon <sargun@...gun.me>
Cc:     LSM <linux-security-module@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
        Kees Cook <keescook@...omium.org>,
        Igor Stoppa <igor.stoppa@...wei.com>
Subject: Re: [PATCH v4 1/3] security: Refactor LSM hooks into an array and
 enum

On 3/7/2018 11:18 AM, Sargun Dhillon wrote:
> On Wed, Mar 7, 2018 at 9:45 AM, Casey Schaufler <casey@...aufler-ca.com> wrote:
>> On 3/6/2018 11:23 PM, Sargun Dhillon wrote:
>>> This commit should have no functional change. It changes the security hook
>>> list heads struct into an array. Additionally, it exposes all of the hooks
>>> via an enum. This loses memory layout randomization as the enum is not
>>> randomized.
>> Please explain why you want to do this. I still dislike it.
>>
> Do you dislike it because of the loss of randomization, or some other reason?

I dislike a huge array of untyped function pointers.
I dislike the loss of type checking in security.c

> The reason for not just having a second list_heads is that it's
> somewhat ugly having to replicate that structure twice -- once for
> dynamic hooks, and once for 'static' hooks.

There was discussion about this some time ago. In the case
where you don't allow dynamic hooks, you mark the lists ro_after_init
whereas in the case with them you don't, but use the locking.


> Instead, we have one enum that LSMs can use and two arrays of heads
> rather than an entire unrolled set of list_heads.

But how is this better? What is the advantage?

>
> If we had a way to randomize this, would it make you comfortable?
>