Re: [PATCH] [v2] drbd: dynamically allocate shash descriptor

[Kees Cook]

On Mon, Jul 22, 2019 at 02:26:34PM +0200, Arnd Bergmann wrote:
> Building with clang and KASAN, we get a warning about an overly large
> stack frame on 32-bit architectures:
> 
> drivers/block/drbd/drbd_receiver.c:921:31: error: stack frame size of 1280 bytes in function 'conn_connect'
>       [-Werror,-Wframe-larger-than=]
> 
> We already allocate other data dynamically in this function, so
> just do the same for the shash descriptor, which makes up most of
> this memory.
> 
> Link: https://lore.kernel.org/lkml/20190617132440.2721536-1-arnd@xxxxxxxx/
> Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>

Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>

-Kees

> ---
> v2:
> - don't try to zero a NULL descriptor pointer,
>   based on review from Roland Kammerer.
> ---
>  drivers/block/drbd/drbd_receiver.c | 14 ++++++++++++--
>  1 file changed, 12 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/block/drbd/drbd_receiver.c b/drivers/block/drbd/drbd_receiver.c
> index 90ebfcae0ce6..2b3103c30857 100644
> --- a/drivers/block/drbd/drbd_receiver.c
> +++ b/drivers/block/drbd/drbd_receiver.c
> @@ -5417,7 +5417,7 @@ static int drbd_do_auth(struct drbd_connection *connection)
>  	unsigned int key_len;
>  	char secret[SHARED_SECRET_MAX]; /* 64 byte */
>  	unsigned int resp_size;
> -	SHASH_DESC_ON_STACK(desc, connection->cram_hmac_tfm);
> +	struct shash_desc *desc;
>  	struct packet_info pi;
>  	struct net_conf *nc;
>  	int err, rv;
> @@ -5430,6 +5430,13 @@ static int drbd_do_auth(struct drbd_connection *connection)
>  	memcpy(secret, nc->shared_secret, key_len);
>  	rcu_read_unlock();
>  
> +	desc = kmalloc(sizeof(struct shash_desc) +
> +		       crypto_shash_descsize(connection->cram_hmac_tfm),
> +		       GFP_KERNEL);
> +	if (!desc) {
> +		rv = -1;
> +		goto fail;
> +	}
>  	desc->tfm = connection->cram_hmac_tfm;
>  
>  	rv = crypto_shash_setkey(connection->cram_hmac_tfm, (u8 *)secret, key_len);
> @@ -5571,7 +5578,10 @@ static int drbd_do_auth(struct drbd_connection *connection)
>  	kfree(peers_ch);
>  	kfree(response);
>  	kfree(right_response);
> -	shash_desc_zero(desc);
> +	if (desc) {
> +		shash_desc_zero(desc);
> +		kfree(desc);
> +	}
>  
>  	return rv;
>  }
> -- 
> 2.20.0
> 

-- 
Kees Cook