linux-kernel - Re: [PATCH v2 2/3] binder: do not initialize locals passed to copy_from

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Message-ID: <202003050010.A1A965BF37@keescook>
Date:   Thu, 5 Mar 2020 00:26:24 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Dan Carpenter <dan.carpenter@...cle.com>
Cc:     "open list:ANDROID DRIVERS" <devel@...verdev.osuosl.org>,
        Jann Horn <jannh@...gle.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Arve Hjønnevåg <arve@...roid.com>,
        Ingo Molnar <mingo@...hat.com>,
        Alexander Potapenko <glider@...gle.com>,
        Joe Perches <joe@...ches.com>,
        Dmitriy Vyukov <dvyukov@...gle.com>,
        Todd Kjos <tkjos@...gle.com>
Subject: Re: [PATCH v2 2/3] binder: do not initialize locals passed to
 copy_from_user()

On Thu, Mar 05, 2020 at 11:07:56AM +0300, Dan Carpenter wrote:
> On Wed, Mar 04, 2020 at 10:13:40AM -0800, Kees Cook wrote:
> > On Tue, Mar 03, 2020 at 12:38:32PM +0300, Dan Carpenter wrote:
> > > The real fix is to initialize everything manually, the automated
> > > initialization is a hardenning feature which many people will disable.
> > 
> > I cannot disagree more with this sentiment. Linus has specifically said he
> > wants this initialization on by default[1],
> 
> Fine, but as long as it's a configurable thing then we need to manually
> initialize as well or it's still a CVE etc.  It will take a while before
> we drop support for old versions of GCC as well.

Yes, I agree; that's totally true. We need to continue to fix all the
uninitialized flaws we encounter unless this is on by default for all
supported compiler versions (which will be a looong time). (But it's
not relevant to this patch because copy_from_user() does already do
the initialization.)

This set of patches was about dealing with the pathological cases of
auto-init colliding with functions that do, in fact, fully init. Though
I must say, I remain concerned about inventing such markings for fear
they'll be used in places where the "trust me, it's fully initialized"
state does not actually hold[1] but the author thinks it does.

-Kees

[1] https://lore.kernel.org/netdev/1509471094.3828.26.camel@edumazet-glaptop3.roam.corp.google.com/

-- 
Kees Cook