[dm-devel] [PATCH v2 10/11] crypto: ahash: Remove VLA usage for AHASH_REQUEST_ON_STACK

[Kees Cook]

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