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Date:   Wed, 16 Jun 2021 21:22:23 -0700
From:   Kees Cook <keescook@chromium.org>
To:     Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc:     Mauro Carvalho Chehab <mchehab+huawei@kernel.org>,
        Arnd Bergmann <arnd@arndb.de>,
        "Gustavo A. R. Silva" <gustavoars@kernel.org>,
        Sakari Ailus <sakari.ailus@linux.intel.com>,
        linux-kernel@vger.kernel.org, linux-media@vger.kernel.org
Subject: Re: [PATCH] media: omap3isp: Extract struct group for memcpy() region
Message-ID: <202106162119.859E9A80B@keescook>
References: <20210616185938.1225218-1-keescook@chromium.org>
 <YMpUR34kFSbiyi+q@pendragon.ideasonboard.com>
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On Wed, Jun 16, 2021 at 10:43:03PM +0300, Laurent Pinchart wrote:
> Hi Kees,
> 
> Thank you for the patch.
> 
> 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.

However, I don't think anything actually uses any of this code
regardless. ;)

-Kees

> 
> > 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@chromium.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

-- 
Kees Cook