Re: [PATCH] USB: usbtmc: prevent kernel-infoleak

[Greg KH <gregkh@linuxfoundation.org>]

On Wed, Sep 04, 2024 at 09:55:43PM +0800, Edward Adam Davis wrote:
> The syzbot reported a kernel-usb-infoleak in usbtmc_write,
> we need to clear the structure before filling fields.

Really?


> 
> Fixes: 4ddc645f40e9 ("usb: usbtmc: Add ioctl for vendor specific write")
> Reported-and-tested-by: syzbot+9d34f80f841e948c3fdb@syzkaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=9d34f80f841e948c3fdb
> Signed-off-by: Edward Adam Davis <eadavis@qq.com>
> ---
>  drivers/usb/class/usbtmc.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/usb/class/usbtmc.c b/drivers/usb/class/usbtmc.c
> index 6bd9fe565385..e9ddaa9b580d 100644
> --- a/drivers/usb/class/usbtmc.c
> +++ b/drivers/usb/class/usbtmc.c
> @@ -759,6 +759,7 @@ static struct urb *usbtmc_create_urb(void)
>  		usb_free_urb(urb);
>  		return NULL;
>  	}
> +	memset(dmabuf, 0, bufsize);

To do this simpler, kzmalloc() above this would be nice.

But, this feels odd, where is the data leaking from?  This is used for
both the read and write path, but where is the leak happening?  A short
read?  If so, we need to properly truncate the buffer being sent to
userspace and not send the unread data.  If a short write, that makes no
sense.

So this needs a bit more work, please find the real issue here and don't
paper over the problem with "set it all to 0" like this.

thanks,

greg k-h