Messages in this thread Patch in this message | | | 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 |
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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 <herbert@gondor.apana.org.au> Cc: "David S. Miller" <davem@davemloft.net> Cc: Eric Biggers <ebiggers@google.com> Cc: Tim Chen <tim.c.chen@linux.intel.com> Cc: Rabin Vincent <rabinv@axis.com> Cc: Lars Persson <larper@axis.com> Cc: linux-crypto@vger.kernel.org Signed-off-by: Kees Cook <keescook@chromium.org> --- 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
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