Re: [PATCH] LSM: Make security_hook_heads a local variable.

From: Casey Schaufler <casey@schaufler-ca.com>
To: Igor Stoppa <igor.stoppa@huawei.com>,
	Christoph Hellwig <hch@infradead.org>,
	Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: linux-security-module@vger.kernel.org, linux-mm@kvack.org,
	kernel-hardening@lists.openwall.com,
	linux-kernel@vger.kernel.org,
	Greg KH <gregkh@linuxfoundation.org>,
	James Morris <james.l.morris@oracle.com>,
	Kees Cook <keescook@chromium.org>,
	Paul Moore <paul@paul-moore.com>,
	Stephen Smalley <sds@tycho.nsa.gov>
Subject: Re: [PATCH] LSM: Make security_hook_heads a local variable.
Date: Mon, 22 May 2017 13:32:59 -0700	[thread overview]
Message-ID: <af26581e-6f5a-3fc2-dc58-8376328a0ad9@schaufler-ca.com> (raw)
In-Reply-To: <d25e2fd3-da11-4ec0-8edc-f1327c04fa6e@huawei.com>

On 5/22/2017 12:50 PM, Igor Stoppa wrote:
> On 22/05/17 18:09, Casey Schaufler wrote:
>> On 5/22/2017 7:03 AM, Christoph Hellwig wrote:
> [...]
>
>>> But even with those we can still chain
>>> them together with a list with external linkage.
>> I gave up that approach in 2012. Too many unnecessary calls to
>> null functions, and massive function vectors with a tiny number
>> of non-null entries. From a data structure standpoint, it was
>> just wrong. The list scheme is exactly right for the task at
>> hand.
> I understand this as a green light, for me to continue with the plan of
> using LSM Hooks as example for making dynamically allocated data become
> read-only, using also Tetsuo's patch (thanks, btw).

I still don't like the assumption that a structure of
N elements can be assumed to be the same as an array
of N elements. Putting on my hardening hat, however, I
like the smalloc() solution to keeping the hook lists
safe, so I am willing to swallow the objection to using
offsets to address the existing exposure.

>
> Is that correct?
>
> ---
> thanks, igor
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