linux-hardening - Re: [PATCH] media: omap3isp: Use struct

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Date:   Mon, 13 Dec 2021 17:24:16 -0600
From:   "Gustavo A. R. Silva" <gustavoars@...nel.org>
To:     Kees Cook <keescook@...omium.org>
Cc:     Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Arnd Bergmann <arnd@...db.de>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        linux-kernel@...r.kernel.org, linux-media@...r.kernel.org,
        linux-hardening@...r.kernel.org,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>
Subject: Re: [PATCH] media: omap3isp: Use struct_group() for memcpy() region

On Thu, Nov 18, 2021 at 10:43:52AM -0800, 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 struct_group(). 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             | 21 +++++++++++++--------
>  2 files changed, 16 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/media/platform/omap3isp/ispstat.c b/drivers/media/platform/omap3isp/ispstat.c
> index 5b9b57f4d9bf..68cf68dbcace 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;

Shouldn't this be

	data->buf = (uintptr_t)(void *)data64.buf;

instead?

--
Gustavo

> +	memcpy(&data->frame, &data64.frame, sizeof(data->frame));
>  
>  	return 0;
>  }
> diff --git a/include/uapi/linux/omap3isp.h b/include/uapi/linux/omap3isp.h
> index 87b55755f4ff..9a6b3ed11455 100644
> --- a/include/uapi/linux/omap3isp.h
> +++ b/include/uapi/linux/omap3isp.h
> @@ -162,6 +162,7 @@ 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.
> + * @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.
> @@ -176,10 +177,12 @@ struct omap3isp_stat_data {
>  	struct timeval ts;
>  #endif
>  	void __user *buf;
> -	__u32 buf_size;
> -	__u16 frame_number;
> -	__u16 cur_frame;
> -	__u16 config_counter;
> +	__struct_group(/* no type */, frame, /* no attrs */,
> +		__u32 buf_size;
> +		__u16 frame_number;
> +		__u16 cur_frame;
> +		__u16 config_counter;
> +	);
>  };
>  
>  #ifdef __KERNEL__
> @@ -189,10 +192,12 @@ struct omap3isp_stat_data_time32 {
>  		__s32	tv_usec;
>  	} ts;
>  	__u32 buf;
> -	__u32 buf_size;
> -	__u16 frame_number;
> -	__u16 cur_frame;
> -	__u16 config_counter;
> +	__struct_group(/* no type */, frame, /* no attrs */,
> +		__u32 buf_size;
> +		__u16 frame_number;
> +		__u16 cur_frame;
> +		__u16 config_counter;
> +	);
>  };
>  #endif
>  
> -- 
> 2.30.2
> 
> 
> 
>