linux-kernel - Re: [PATCH v2 05/20] randstruct: Whitelist struct security_hook

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Message-Id: <201705280704.DHF73450.SJtVOFOOQHFLMF@I-love.SAKURA.ne.jp>
Date:   Sun, 28 May 2017 07:04:25 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:     keescook@...omium.org, hch@...radead.org
Cc:     kernel-hardening@...ts.openwall.com, james.l.morris@...cle.com,
        labbott@...hat.com, x86@...nel.org, linux-kernel@...r.kernel.org,
        linux-security-module@...r.kernel.org
Subject: Re: [PATCH v2 05/20] randstruct: Whitelist struct security_hook_heads cast

Kees Cook wrote:
> On Sat, May 27, 2017 at 1:41 AM, Christoph Hellwig <hch@...radead.org> wrote:
> > On Fri, May 26, 2017 at 01:17:09PM -0700, Kees Cook wrote:
> >> The LSM initialization routines walk security_hook_heads as an array
> >> of struct list_head instead of via names to avoid a ton of needless
> >> source. Whitelist this to avoid the false positive warning from the
> >> plugin:
> >
> > I think this crap just needs to be fixed properly.  If not it almost
> > defeats the protections as the "security" ops are just about everywhere.
> 
> There's nothing unsafe about 3dfc9b02864b19f4dab376f14479ee4ad1de6c9e,
> it just avoids tons of needless code. Tetsuo has some other ideas for
> cleaning it up further, but I don't like it because it removes
> compile-time verification of function types.

Excuse me, but why you think that compile-time verification of function
types is removed?

-	{ .head = &security_hook_heads.HEAD, .hook = { .HEAD = HOOK } }
+	{ .idx = LSM_##HEAD, .hook = { .HEAD = HOOK } }

This change removes dependency on absolute address of security_hook_heads
being known at compile-time. If function types of .hook.HEAD and HOOK
mismatches, the compiler can still warn it.