linux-kernel - Re: [PATCH] media: omap3isp: Extract struct group for memcpy() region

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Message-ID: <YNOxuybjpLxr6sin@pendragon.ideasonboard.com>
Date:   Thu, 24 Jun 2021 01:12:11 +0300
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     Mauro Carvalho Chehab <mchehab+huawei@...nel.org>,
        Arnd Bergmann <arnd@...db.de>,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        linux-kernel@...r.kernel.org, linux-media@...r.kernel.org
Subject: Re: [PATCH] media: omap3isp: Extract struct group for memcpy() region

Hi Kees,

On Wed, Jun 16, 2021 at 09:22:23PM -0700, Kees Cook wrote:
> On Wed, Jun 16, 2021 at 10:43:03PM +0300, Laurent Pinchart wrote:
> > On Wed, Jun 16, 2021 at 11:59:38AM -0700, Kees Cook wrote:
> > > Avoid writing past the end of a structure member by wrapping the target
> > > region in a common named structure. This additionally fixes a
> > > misalignment of the copy (since the size of "buf" changes between 64-bit
> > > and 32-bit).
> > 
> > Could you have been mislead by the data64 name ? The difference between
> > omap3isp_stat_data_time and omap3isp_stat_data_time32 is the size of the
> > ts field, using 32-bit timestamps with legacy userspace, and 64-bit
> > timestamps with more recent userspace. In both cases we're dealing with
> > a 32-bit platform, as the omap3isp is not used in any 64-bit ARM SoC.
> > The size of void __user *buf is thus 4 bytes in all cases, as is __u32
> > buf.
> 
> Ah, yes, that's true. I was hitting this on arm64 builds
> (CONFIG_COMPILE_TEST) where __user *buf is 64-bit. So, the "additionally
> fixes" bit above is misleading in the sense that nothing was ever built
> in the real world like that.
> 
> The patch still fixes the compile-time warnings, though.

I What's the compile-time warning ? I tried compiling the driver for
ARM64 and didn't notice any.

> However, I don't think anything actually uses any of this code
> regardless. ;)
> 
> > > I actually think this code is completely unused in the real world:
> > > I don't think it could have ever worked, as 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));
> > >  
> > >  	return 0;
> > >  }
> > > diff --git a/include/uapi/linux/omap3isp.h b/include/uapi/linux/omap3isp.h
> > > index 87b55755f4ff..0a16af91621f 100644
> > > --- a/include/uapi/linux/omap3isp.h
> > > +++ b/include/uapi/linux/omap3isp.h
> > > @@ -159,13 +159,25 @@ struct omap3isp_h3a_aewb_config {
> > >  };
> > >  
> > >  /**
> > > - * struct omap3isp_stat_data - Statistic data sent to or received from user
> > > - * @ts: Timestamp of returned framestats.
> > > - * @buf: Pointer to pass to user.
> > > + * struct omap3isp_stat_frame - Statistic data without timestamp nor pointer.
> > > + * @buf_size: Size of buffer.
> > >   * @frame_number: Frame number of requested stats.
> > >   * @cur_frame: Current frame number being processed.
> > >   * @config_counter: Number of the configuration associated with the data.
> > >   */
> > > +struct omap3isp_stat_frame {
> > > +	__u32 buf_size;
> > > +	__u16 frame_number;
> > > +	__u16 cur_frame;
> > > +	__u16 config_counter;
> > > +};
> > > +
> > > +/**
> > > + * struct omap3isp_stat_data - Statistic data sent to or received from user
> > > + * @ts: Timestamp of returned framestats.
> > > + * @buf: Pointer to pass to user.
> > > + * @frame: Statistic data for frame.
> > > + */
> > >  struct omap3isp_stat_data {
> > >  #ifdef __KERNEL__
> > >  	struct {
> > > @@ -176,10 +188,15 @@ struct omap3isp_stat_data {
> > >  	struct timeval ts;
> > >  #endif
> > >  	void __user *buf;
> > > -	__u32 buf_size;
> > > -	__u16 frame_number;
> > > -	__u16 cur_frame;
> > > -	__u16 config_counter;
> > > +	union {
> > > +		struct {
> > > +			__u32 buf_size;
> > > +			__u16 frame_number;
> > > +			__u16 cur_frame;
> > > +			__u16 config_counter;
> > > +		};
> > > +		struct omap3isp_stat_frame frame;
> > > +	};
> > >  };
> > >  
> > >  #ifdef __KERNEL__
> > > @@ -189,10 +206,15 @@ struct omap3isp_stat_data_time32 {
> > >  		__s32	tv_usec;
> > >  	} ts;
> > >  	__u32 buf;
> > > -	__u32 buf_size;
> > > -	__u16 frame_number;
> > > -	__u16 cur_frame;
> > > -	__u16 config_counter;
> > > +	union {
> > > +		struct {
> > > +			__u32 buf_size;
> > > +			__u16 frame_number;
> > > +			__u16 cur_frame;
> > > +			__u16 config_counter;
> > > +		};
> > > +		struct omap3isp_stat_frame frame;
> > > +	};
> > >  };
> > >  #endif
> > >  

-- 
Regards,

Laurent Pinchart