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SubjectRe: [PATCH] USB: wusbcore: crypto: Remove VLA usage
From
Date

I just discovered an issue with this patch. Please, drop it. I'll send
v2 shortly.

Thanks
--
Gustavo

On 03/16/2018 08:01 AM, Gustavo A. R. Silva wrote:
> In preparation to enabling -Wvla, remove VLA and replace it
> with dynamic memory allocation instead.
>
> The use of stack Variable Length Arrays needs to be avoided, as they
> can be a vector for stack exhaustion, which can be both a runtime bug
> or a security flaw. Also, in general, as code evolves it is easy to
> lose track of how big a VLA can get. Thus, we can end up having runtime
> failures that are hard to debug.
>
> Also, fixed as part of the directive to remove all VLAs from
> the kernel: https://lkml.org/lkml/2018/3/7/621
>
> Notice that in this particular case, an alternative to kzalloc is kcalloc,
> in which case the code would look as follows instead:
>
> iv = kcalloc(crypto_skcipher_ivsize(tfm_cbc), sizeof(*iv), GFP_KERNEL);
>
> but if the data type of _iv_ never changes, or the type size is always one
> byte, kzalloc is good enough.
>
> Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
> ---
> drivers/usb/wusbcore/crypto.c | 11 +++++++----
> 1 file changed, 7 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/usb/wusbcore/crypto.c b/drivers/usb/wusbcore/crypto.c
> index 4c00be2d..3511473 100644
> --- a/drivers/usb/wusbcore/crypto.c
> +++ b/drivers/usb/wusbcore/crypto.c
> @@ -202,7 +202,7 @@ static int wusb_ccm_mac(struct crypto_skcipher *tfm_cbc,
> struct scatterlist sg[4], sg_dst;
> void *dst_buf;
> size_t dst_size;
> - u8 iv[crypto_skcipher_ivsize(tfm_cbc)];
> + u8 *iv;
> size_t zero_padding;
>
> /*
> @@ -222,9 +222,11 @@ static int wusb_ccm_mac(struct crypto_skcipher *tfm_cbc,
> zero_padding;
> dst_buf = kzalloc(dst_size, GFP_KERNEL);
> if (!dst_buf)
> - goto error_dst_buf;
> + goto error_alloc;
>
> - memset(iv, 0, sizeof(iv));
> + iv = kzalloc(crypto_skcipher_ivsize(tfm_cbc), GFP_KERNEL);
> + if (!iv)
> + goto error_alloc;
>
> /* Setup B0 */
> scratch->b0.flags = 0x59; /* Format B0 */
> @@ -276,8 +278,9 @@ static int wusb_ccm_mac(struct crypto_skcipher *tfm_cbc,
> bytewise_xor(mic, &scratch->ax, iv, 8);
> result = 8;
> error_cbc_crypt:
> + kfree(iv);
> kfree(dst_buf);
> -error_dst_buf:
> +error_alloc:
> return result;
> }
>
>


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