linux-hardening - Re: [PATCH 1/5] string.h: add array-wrappers for (v)memdup

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Date:   Thu, 31 Aug 2023 14:22:08 +0200
From:   Philipp Stanner <pstanner@...hat.com>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     Kees Cook <keescook@...omium.org>,
        Andy Shevchenko <andy@...nel.org>,
        Eric Biederman <ebiederm@...ssion.com>,
        Christian Brauner <brauner@...nel.org>,
        David Disseldorp <ddiss@...e.de>,
        Luis Chamberlain <mcgrof@...nel.org>,
        Siddh Raman Pant <code@...dh.me>,
        Nick Alcock <nick.alcock@...cle.com>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>, Zack Rusin <zackr@...are.com>,
        VMware Graphics Reviewers 
        <linux-graphics-maintainer@...are.com>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        kexec@...ts.infradead.org, linux-hardening@...r.kernel.org,
        David Airlie <airlied@...hat.com>
Subject: Re: [PATCH 1/5] string.h: add array-wrappers for (v)memdup_user()

On Wed, 2023-08-30 at 17:11 +0300, Andy Shevchenko wrote:
> On Wed, Aug 30, 2023 at 4:46 PM Philipp Stanner <pstanner@...hat.com>
> wrote:
> > 
> > Currently, user array duplications are sometimes done without an
> > overflow check. Sometimes the checks are done manually; sometimes
> > the
> > array size is calculated with array_size() and sometimes by
> > calculating
> > n * size directly in code.
> > 
> > Introduce wrappers for arrays for memdup_user() and vmemdup_user()
> > to
> > provide a standardized and safe way for duplicating user arrays.
> > 
> > This is both for new code as well as replacing usage of
> > (v)memdup_user()
> > in existing code that uses, e.g., n * size to calculate array
> > sizes.
> 
> ...
> 
> > --- a/include/linux/string.h
> > +++ b/include/linux/string.h
> 
> I'm wondering if this has no side-effects as string.h/string.c IIRC
> is
> used also for early stages where some of the APIs are not available.
> 

I forgot to address this point in my previous reply.

Who's going to decide whether this is a problem or not?


My personal guess is that this is unlikely to be a problem because

   A. either (v)memdup_user() is available, in which case
      (v)memdup_array_user() will always work – 
   B. or (v)memdup_user() is not available, which would cause the code
      that currently uses (v)memdup_user() for copying arrays to fail
      anyways.


P.