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

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Date:   Tue, 27 Jul 2021 18:50:33 -0700
From:   Kees Cook <keescook@...omium.org>
To:     "Gustavo A. R. Silva" <gustavoars@...nel.org>
Cc:     linux-hardening@...r.kernel.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
Subject: Re: [PATCH 01/64] media: omap3isp: Extract struct group for memcpy()
 region

On Tue, Jul 27, 2021 at 07:55:46PM -0500, Gustavo A. R. Silva wrote:
> 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 = { };
> >  	int ret;
> >  
> >  	ret = omap3isp_stat_request_statistics(stat, &data64);
> > @@ -521,7 +521,8 @@ int omap3isp_stat_request_statistics_time32(struct ispstat *stat,
> >  
> >  	data->ts.tv_sec = data64.ts.tv_sec;
> >  	data->ts.tv_usec = data64.ts.tv_usec;
> > -	memcpy(&data->buf, &data64.buf, sizeof(*data) - sizeof(data->ts));
> > +	data->buf = (uintptr_t)data64.buf;
> > +	memcpy(&data->frame, &data64.buf, sizeof(data->frame));
> 
> I think this should be:
> 
> 	memcpy(..., &data64.frame, ...);
> 
> instead.

Whoops; thanks! This is what I get for temporarily silencing the
read-overflow warnings. :)

-Kees

-- 
Kees Cook