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

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Date:   Wed, 7 Sep 2022 15:25:40 -0700
From:   Kees Cook <keescook@...omium.org>
To:     "Gustavo A. R. Silva" <gustavoars@...nel.org>
Cc:     Hans Verkuil <hverkuil@...all.nl>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-hardening@...r.kernel.org
Subject: Re: [PATCH][next] media: usb: pwc-uncompress: Use flex array
 destination for memcpy()

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@...nel.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@...omium.org>

-- 
Kees Cook