Re: [PATCH] media: dw2102: fix OOB read on firmware size not a multiple of 64

[Vasileios Almpanis <vasilisalmpanis@gmail.com>]

On 8/6/26 7:47 PM, Vasileios Almpanis wrote:
> dw2102_load_firmware() copies the firmware into a buffer of exactly
> fw->size bytes, then walks it in 0x40-byte steps while always passing
> 0x40 as the transfer length. When fw->size is not a multiple of 64 the
> last chunk reads past the end of the allocation producing the following
> splat:
>
>    dvb-usb: downloading firmware from file 'dvb-usb-dw3101.fw'
>    dw2102: start downloading DW210X firmware
>    ==================================================================
>    BUG: KASAN: slab-out-of-bounds in dw210x_op_rw+0xb6/0x180 drivers/media/usb/dvb-usb/dw2102.c:102
>    Read of size 64 at addr ffff88802bcf2ba0 by task kworker/1:2/803
>    Call Trace:
>     <TASK>
>     kasan_report+0x117/0x150 mm/kasan/report.c:595
>     check_region_inline mm/kasan/generic.c:-1 [inline]
>     kasan_check_range+0x264/0x2c0 mm/kasan/generic.c:200
>     __asan_memcpy+0x29/0x70 mm/kasan/shadow.c:105
>     dw210x_op_rw+0xb6/0x180 drivers/media/usb/dvb-usb/dw2102.c:102
>     dw2102_load_firmware+0x2b4/0x970 drivers/media/usb/dvb-usb/dw2102.c:1906
>
> Fix this by clamping the last chunk to the remaining bytes;
I sent this patch to syzbot for testing and it reported success.
https://syzkaller.appspot.com/bug?extid=f408eac9faa61d5a1927

Tested-by: syzbot+f408eac9faa61d5a1927@syzkaller.appspotmail.com
> Cc: stable@vger.kernel.org
> Reported-by: syzbot+f408eac9faa61d5a1927@syzkaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=f408eac9faa61d5a1927
> Fixes: 7fd4828f6cc5 ("V4L/DVB (8421): Adds support for Dvbworld DVB-S 2102 USB card")
> Signed-off-by: Vasileios Almpanis <vasilisalmpanis@gmail.com>
> ---
>   drivers/media/usb/dvb-usb/dw2102.c | 6 ++++--
>   1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/media/usb/dvb-usb/dw2102.c b/drivers/media/usb/dvb-usb/dw2102.c
> index 4fecf2f965e9..4e26e1776977 100644
> --- a/drivers/media/usb/dvb-usb/dw2102.c
> +++ b/drivers/media/usb/dvb-usb/dw2102.c
> @@ -1902,9 +1902,11 @@ static int dw2102_load_firmware(struct usb_device *dev,
>   	if (p) {
>   		memcpy(p, fw->data, fw->size);
>   		for (i = 0; i < fw->size; i += 0x40) {
> +			int len = min_t(size_t, fw->size - i, 0x40);
> +
>   			b = (u8 *)p + i;
> -			if (dw210x_op_rw(dev, 0xa0, i, 0, b, 0x40,
> -					 DW210X_WRITE_MSG) != 0x40) {
> +			if (dw210x_op_rw(dev, 0xa0, i, 0, b, len,
> +					 DW210X_WRITE_MSG) != len) {
>   				err("error while transferring firmware");
>   				ret = -EINVAL;
>   				break;
>
> ---
> base-commit: fcaeecb8b0cd44f77d03b28de0671258d4db18f8
> change-id: 20260806-dvb-307714ff6225
>
> Best regards,
> --
> Vasileios Almpanis <vasilisalmpanis@gmail.com>
>