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Message-ID: <721a70c347d82931d12e5b75b19d132f82ee5ed2.camel@redhat.com>
Date: Wed, 30 Aug 2023 16:19:32 +0200
From: 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.
>
> > @@ -6,6 +6,8 @@
> > #include <linux/types.h> /* for size_t */
> > #include <linux/stddef.h> /* for NULL */
> > #include <linux/errno.h> /* for E2BIG */
> > +#include <linux/overflow.h> /* for check_mul_overflow() */
> > +#include <linux/err.h> /* for ERR_PTR() */
>
> Can we preserve order (to some extent)?
Sure. I just put it there so the comments build a congruent block.
Which order would you prefer?
>
> > #include <linux/stdarg.h>
> > #include <uapi/linux/string.h>
>
> ...
>
> > +/**
> > + * memdup_array_user - duplicate array from user space
>
> > + *
>
> Do we need this blank line?
I more or less directly copied the docstring format from the original
functions (v)memdup_user() in mm/util.c
I guess this is common style?
>
> > + * @src: source address in user space
> > + * @n: number of array members to copy
> > + * @size: size of one array member
> > + *
> > + * Return: an ERR_PTR() on failure. Result is physically
> > + * contiguous, to be freed by kfree().
> > + */
>
> ...
>
> > +/**
> > + * vmemdup_array_user - duplicate array from user space
>
> > + *
>
> Redundant?
No, there are two functions:
* memdup_array_user()
* vmemdup_array_user()
On the deeper layers they utilize kmalloc() or kvmalloc(),
respectively.
Greetings,
P.
>
> > + * @src: source address in user space
> > + * @n: number of array members to copy
> > + * @size: size of one array member
> > + *
> > + * Return: an ERR_PTR() on failure. Result may be not
> > + * physically contiguous. Use kvfree() to free.
> > + */
>
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