linux-kernel - Re: [PATCH] wusbcore: Fix one more crypto-on-the-stack bug

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Date:   Mon, 12 Dec 2016 22:44:47 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org,
        Eric Biggers <ebiggers3@...il.com>,
        linux-crypto@...r.kernel.org,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Stephan Mueller <smueller@...onox.de>
Subject: Re: [PATCH] wusbcore: Fix one more crypto-on-the-stack bug

On Mon, Dec 12, 2016 at 12:52:45PM -0800, Andy Lutomirski wrote:
> The driver put a constant buffer of all zeros on the stack and
> pointed a scatterlist entry at it.  This doesn't work with virtual
> stacks.  Make the buffer static to fix it.
> 
> Cc: stable@...r.kernel.org # 4.9 only
> Reported-by: Eric Biggers <ebiggers3@...il.com>
> Signed-off-by: Andy Lutomirski <luto@...nel.org>
> ---
>  drivers/usb/wusbcore/crypto.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/usb/wusbcore/crypto.c b/drivers/usb/wusbcore/crypto.c
> index 79451f7ef1b7..a7e007a0cd49 100644
> --- a/drivers/usb/wusbcore/crypto.c
> +++ b/drivers/usb/wusbcore/crypto.c
> @@ -216,7 +216,7 @@ static int wusb_ccm_mac(struct crypto_skcipher *tfm_cbc,
>  	struct scatterlist sg[4], sg_dst;
>  	void *dst_buf;
>  	size_t dst_size;
> -	const u8 bzero[16] = { 0 };
> +	static const u8 bzero[16] = { 0 };

Hm, can static memory handle DMA?  That's a requirement of the USB
stack, does this data later end up being sent down to a USB host
controller?

thanks,

greg k-h