Re: [PATCH] media: mceusb: Fix potential out-of-bounds shift

[Sean Young <sean@mess.org>]

On Tue, Dec 22, 2020 at 12:07:04PM +0000, James Reynolds wrote:
> When processing a MCE_RSP_GETPORTSTATUS command, the bit index to set in
> ir->txports_cabled comes from response data, and isn't validated.
> 
> As ir->txports_cabled is a u8, nothing should be done if the bit index
> is greater than 7.
> 
> Cc: stable@vger.kernel.org
> Reported-by: syzbot+ec3b3128c576e109171d@syzkaller.appspotmail.com
> Signed-off-by: James Reynolds <jr@memlen.com>
> ---
>  drivers/media/rc/mceusb.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/media/rc/mceusb.c b/drivers/media/rc/mceusb.c
> index f1dbd059ed08..c8d63673e131 100644
> --- a/drivers/media/rc/mceusb.c
> +++ b/drivers/media/rc/mceusb.c
> @@ -1169,7 +1169,7 @@ static void mceusb_handle_command(struct mceusb_dev *ir, u8 *buf_in)
>  		switch (subcmd) {
>  		/* the one and only 5-byte return value command */
>  		case MCE_RSP_GETPORTSTATUS:
> -			if (buf_in[5] == 0)
> +			if (buf_in[5] == 0 && *hi < 8)
>  				ir->txports_cabled |= 1 << *hi;

So *hi is a port number. I don't know of any devices that have more than
2 ports, so this is fine.

Reviewed-by: Sean Young <sean@mess.org>


Thanks

Sean