Re: [PATCH 11/11] crypto: skcipher: Remove VLA usage for SKCIPHER_REQUEST_ON_STACK

Christophe Leroy
2018-06-20T20:22:44Z

On 06/20/2018 07:04 PM, 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.
>
> [1] https://lkml.kernel.org/r/CA+55aFzCG-zNmZwX4A2FQpadafLfEzK6CC=qPXydAacU1RqZWA@mail.gmail.com
>
> Signed-off-by: Kees Cook <keescook@chromium.org>

crypto/echainiv.c: In function ‘echainiv_encrypt’:
crypto/echainiv.c:88:1: warning: the frame size of 2120 bytes is larger
than 1024 bytes [-Wframe-larger-than=]
crypto/authenc.c: In function ‘crypto_authenc_copy_assoc’:
crypto/authenc.c:197:1: warning: the frame size of 2120 bytes is larger
than 1024 bytes [-Wframe-larger-than=]
crypto/authencesn.c: In function ‘crypto_authenc_esn_copy’:
crypto/authencesn.c:194:1: warning: the frame size of 2120 bytes is
larger than 1024 bytes [-Wframe-larger-than=]
crypto/algif_aead.c: In function ‘crypto_aead_copy_sgl’:
crypto/algif_aead.c:90:1: warning: the frame size of 2120 bytes is
larger than 1024 bytes [-Wframe-larger-than=]

Christophe

> ---
> 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);
> skcipher->reqsize = reqsize;
> }
>
> diff --git a/include/crypto/skcipher.h b/include/crypto/skcipher.h
> index 2f327f090c3e..25294d0089b2 100644
> --- a/include/crypto/skcipher.h
> +++ b/include/crypto/skcipher.h
> @@ -139,9 +139,11 @@ struct skcipher_alg {
> struct crypto_alg base;
> };
>
> +#define SKCIPHER_MAX_REQSIZE (PAGE_SIZE / 8)
> +
> #define SKCIPHER_REQUEST_ON_STACK(name, tfm) \
> char __##name##_desc[sizeof(struct skcipher_request) + \
> - crypto_skcipher_reqsize(tfm)] CRYPTO_MINALIGN_ATTR; \
> + SKCIPHER_MAX_REQSIZE] CRYPTO_MINALIGN_ATTR; \
> struct skcipher_request *name = (void *)__##name##_desc
>
> /**
>