From: Kees Cook Subject: [PATCH v2 10/11] crypto: ahash: Remove VLA usage for AHASH_REQUEST_ON_STACK Date: Mon, 25 Jun 2018 14:10:25 -0700 Message-ID: <20180625211026.15819-11-keescook@chromium.org> References: <20180625211026.15819-1-keescook@chromium.org> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: Giovanni Cabiddu , Kees Cook , Arnd Bergmann , Eric Biggers , Mike Snitzer , "Gustavo A. R. Silva" , qat-linux@intel.com, linux-kernel@vger.kernel.org, dm-devel@redhat.com, linux-crypto@vger.kernel.org, Lars Persson , Tim Chen , "David S. Miller" , Alasdair Kergon , Rabin Vincent To: Herbert Xu Return-path: In-Reply-To: <20180625211026.15819-1-keescook@chromium.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: dm-devel-bounces@redhat.com Errors-To: dm-devel-bounces@redhat.com List-Id: linux-crypto.vger.kernel.org In the quest to remove all stack VLA usage from the kernel[1], this caps the ahash request size similar to the other limits and adds a sanity check at registration. Unfortunately, these reqsizes can be huge. Looking at all callers of crypto_ahash_set_reqsize(), the largest appears to be 664 bytes, based on a combination of manual inspection and pahole output: 4 dcp_sha_req_ctx 40 crypto4xx_ctx 52 hash_req_ctx 80 ahash_request 88 rk_ahash_rctx 104 sun4i_req_ctx 200 mcryptd_hash_request_ctx 216 safexcel_ahash_req 228 sha1_hash_ctx 228 sha256_hash_ctx 248 img_hash_request_ctx 252 mtk_sha_reqctx 276 sahara_sha_reqctx 304 mv_cesa_ahash_req 316 iproc_reqctx_s 320 caam_hash_state 320 qce_sha_reqctx 356 sha512_hash_ctx 384 ahash_req_ctx 400 chcr_ahash_req_ctx 416 stm32_hash_request_ctx 432 talitos_ahash_req_ctx 462 atmel_sha_reqctx 496 ccp_aes_cmac_req_ctx 616 ccp_sha_req_ctx 664 artpec6_hash_request_context So, this chooses 720 as a larger "round" number for the max. [1] https://lkml.kernel.org/r/CA+55aFzCG-zNmZwX4A2FQpadafLfEzK6CC=qPXydAacU1RqZWA@mail.gmail.com Cc: Herbert Xu Cc: "David S. Miller" Cc: Eric Biggers Cc: Tim Chen Cc: Rabin Vincent Cc: Lars Persson Cc: linux-crypto@vger.kernel.org Signed-off-by: Kees Cook --- include/crypto/hash.h | 3 ++- include/crypto/internal/hash.h | 1 + 2 files changed, 3 insertions(+), 1 deletion(-) diff --git a/include/crypto/hash.h b/include/crypto/hash.h index 5d79e2f0936e..b550077c4767 100644 --- a/include/crypto/hash.h +++ b/include/crypto/hash.h @@ -66,10 +66,11 @@ struct ahash_request { #define AHASH_MAX_DIGESTSIZE 512 #define AHASH_MAX_STATESIZE 512 +#define AHASH_MAX_REQSIZE 720 #define AHASH_REQUEST_ON_STACK(name, ahash) \ char __##name##_desc[sizeof(struct ahash_request) + \ - crypto_ahash_reqsize(ahash)] CRYPTO_MINALIGN_ATTR; \ + AHASH_MAX_REQSIZE] CRYPTO_MINALIGN_ATTR; \ struct ahash_request *name = (void *)__##name##_desc /** diff --git a/include/crypto/internal/hash.h b/include/crypto/internal/hash.h index a0b0ad9d585e..d96ae5f52125 100644 --- a/include/crypto/internal/hash.h +++ b/include/crypto/internal/hash.h @@ -142,6 +142,7 @@ static inline struct ahash_alg *__crypto_ahash_alg(struct crypto_alg *alg) static inline void crypto_ahash_set_reqsize(struct crypto_ahash *tfm, unsigned int reqsize) { + BUG_ON(reqsize > AHASH_MAX_REQSIZE); tfm->reqsize = reqsize; } -- 2.17.1