Re: [PATCH][next] media: usb: pwc-uncompress: Use flex array destination for memcpy()

From: Kees Cook <keescook@chromium.org>
To: "Gustavo A. R. Silva" <gustavoars@kernel.org>
Cc: Hans Verkuil <hverkuil@xs4all.nl>,
	Mauro Carvalho Chehab <mchehab@kernel.org>,
	linux-media@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-hardening@vger.kernel.org
Subject: Re: [PATCH][next] media: usb: pwc-uncompress: Use flex array destination for memcpy()
Date: Wed, 7 Sep 2022 15:25:40 -0700	[thread overview]
Message-ID: <202209071525.AFFA11872@keescook> (raw)
In-Reply-To: <YxjpMMUb3WP5Rbu7@work>

On Wed, Sep 07, 2022 at 07:55:44PM +0100, Gustavo A. R. Silva wrote:
> In preparation for FORTIFY_SOURCE performing run-time destination buffer
> bounds checking for memcpy(), specify the destination output buffer
> explicitly, instead of asking memcpy() to write past the end of what looked
> like a fixed-size object.
> 
> Notice that raw_frame is a pointer to a structure that contains
> flexible-array member rawframe[]:
> 
> drivers/media/usb/pwc/pwc.h:
> 190 struct pwc_raw_frame {
> 191         __le16 type;            /* type of the webcam */
> 192         __le16 vbandlength;     /* Size of 4 lines compressed (used by the
> 193                                    decompressor) */
> 194         __u8   cmd[4];          /* the four byte of the command (in case of
> 195                                    nala, only the first 3 bytes is filled) */
> 196         __u8   rawframe[];      /* frame_size = H / 4 * vbandlength */
> 197 } __packed;
> 
> Link: https://github.com/KSPP/linux/issues/200
> Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>

Thanks! Yeah, this looks very similar to other transformations like
this. And this one even had the flex array already! :)

Reviewed-by: Kees Cook <keescook@chromium.org>

-- 
Kees Cook