netdev - Re: [PATCH 01/64] media: omap3isp: Extract struct group for memcpy() region

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Message-ID: <20210728085921.GV5047@twin.jikos.cz>
Date:   Wed, 28 Jul 2021 10:59:22 +0200
From:   David Sterba <dsterba@...e.cz>
To:     Kees Cook <keescook@...omium.org>
Cc:     linux-hardening@...r.kernel.org,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        Keith Packard <keithpac@...zon.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org, linux-wireless@...r.kernel.org,
        netdev@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        linux-staging@...ts.linux.dev, linux-block@...r.kernel.org,
        linux-kbuild@...r.kernel.org, clang-built-linux@...glegroups.com,
        nborisov@...e.com
Subject: Re: [PATCH 01/64] media: omap3isp: Extract struct group for memcpy()
 region

On Tue, Jul 27, 2021 at 01:57:52PM -0700, Kees Cook wrote:
> In preparation for FORTIFY_SOURCE performing compile-time and run-time
> field bounds checking for memcpy(), memmove(), and memset(), avoid
> intentionally writing across neighboring fields.  Wrap the target region
> in a common named structure. This additionally fixes a theoretical
> misalignment of the copy (since the size of "buf" changes between 64-bit
> and 32-bit, but this is likely never built for 64-bit).
> 
> FWIW, I think this code is totally broken on 64-bit (which appears to
> not be a "real" build configuration): it would either always fail (with
> an uninitialized data->buf_size) or would cause corruption in userspace
> due to the copy_to_user() in the call path against an uninitialized
> data->buf value:
> 
> omap3isp_stat_request_statistics_time32(...)
>     struct omap3isp_stat_data data64;
>     ...
>     omap3isp_stat_request_statistics(stat, &data64);
> 
> int omap3isp_stat_request_statistics(struct ispstat *stat,
>                                      struct omap3isp_stat_data *data)
>     ...
>     buf = isp_stat_buf_get(stat, data);
> 
> static struct ispstat_buffer *isp_stat_buf_get(struct ispstat *stat,
>                                                struct omap3isp_stat_data *data)
> ...
>     if (buf->buf_size > data->buf_size) {
>             ...
>             return ERR_PTR(-EINVAL);
>     }
>     ...
>     rval = copy_to_user(data->buf,
>                         buf->virt_addr,
>                         buf->buf_size);
> 
> Regardless, additionally initialize data64 to be zero-filled to avoid
> undefined behavior.
> 
> Fixes: 378e3f81cb56 ("media: omap3isp: support 64-bit version of omap3isp_stat_data")
> Signed-off-by: Kees Cook <keescook@...omium.org>
> ---
>  drivers/media/platform/omap3isp/ispstat.c |  5 +--
>  include/uapi/linux/omap3isp.h             | 44 +++++++++++++++++------
>  2 files changed, 36 insertions(+), 13 deletions(-)
> 
> diff --git a/drivers/media/platform/omap3isp/ispstat.c b/drivers/media/platform/omap3isp/ispstat.c
> index 5b9b57f4d9bf..ea8222fed38e 100644
> --- a/drivers/media/platform/omap3isp/ispstat.c
> +++ b/drivers/media/platform/omap3isp/ispstat.c
> @@ -512,7 +512,7 @@ int omap3isp_stat_request_statistics(struct ispstat *stat,
>  int omap3isp_stat_request_statistics_time32(struct ispstat *stat,
>  					struct omap3isp_stat_data_time32 *data)
>  {
> -	struct omap3isp_stat_data data64;
> +	struct omap3isp_stat_data data64 = { };

Should this be { 0 } ?

We've seen patches trying to switch from { 0 } to {  } but the answer
was that { 0 } is supposed to be used,
http://www.ex-parrot.com/~chris/random/initialise.html

(from https://lore.kernel.org/lkml/fbddb15a-6e46-3f21-23ba-b18f66e3448a@suse.com/)