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SubjectRe: [PATCH v8 9/9] crypto: skcipher: Remove VLA usage for SKCIPHER_REQUEST_ON_STACK
On Tue, Aug 07, 2018 at 02:18:43PM -0700, Kees Cook wrote:
> In the quest to remove all stack VLA usage from the kernel[1], this
> caps the skcipher request size similar to other limits and adds a sanity
> check at registration. Looking at instrumented tcrypt output, the largest
> is for lrw:
>
> crypt: testing lrw(aes)
> crypto_skcipher_set_reqsize: 8
> crypto_skcipher_set_reqsize: 88
> crypto_skcipher_set_reqsize: 472
>
> [1] https://lkml.kernel.org/r/CA+55aFzCG-zNmZwX4A2FQpadafLfEzK6CC=qPXydAacU1RqZWA@mail.gmail.com
>
> Signed-off-by: Kees Cook <keescook@chromium.org>
> ---
> include/crypto/internal/skcipher.h | 1 +
> include/crypto/skcipher.h | 4 +++-
> 2 files changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/include/crypto/internal/skcipher.h b/include/crypto/internal/skcipher.h
> index e42f7063f245..5035482cbe68 100644
> --- a/include/crypto/internal/skcipher.h
> +++ b/include/crypto/internal/skcipher.h
> @@ -130,6 +130,7 @@ static inline struct crypto_skcipher *crypto_spawn_skcipher(
> static inline void crypto_skcipher_set_reqsize(
> struct crypto_skcipher *skcipher, unsigned int reqsize)
> {
> + BUG_ON(reqsize > SKCIPHER_MAX_REQSIZE);

Please do not add these BUG_ONs. Instead allow this function to
fail and check for the failure in the caller.

Thanks,
--
Email: Herbert Xu <herbert@gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt

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