[PATCH v5 10/11] crypto: ahash: Remove VLA usage for AHASH_REQUEST_ON_STACK
From: Kees Cook <hidden>
Date: 2018-07-17 04:22:07
Also in:
dm-devel, lkml
Subsystem:
crypto api, the rest · Maintainers:
Herbert Xu, "David S. Miller", Linus Torvalds
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 initialization. AHASH_REQUEST_ON_STACK is special, though: it is only ever used for shash-wrapped ahash, so its size is bounded only by non-async hashes. A manual inspection of this shows the largest to be: sizeof(struct shash_desc) + SHASH_MAX_DESCSIZE [1] https://lkml.kernel.org/r/CA+55aFzCG-zNmZwX4A2FQpadafLfEzK6CC=qPXydAacU1RqZWA@mail.gmail.com Signed-off-by: Kees Cook <redacted> --- crypto/shash.c | 9 ++++++++- include/crypto/hash.h | 10 +++++++++- 2 files changed, 17 insertions(+), 2 deletions(-)
diff --git a/crypto/shash.c b/crypto/shash.c
index 8d4746b14dd5..e344560458cb 100644
--- a/crypto/shash.c
+++ b/crypto/shash.c@@ -355,6 +355,7 @@ int crypto_init_shash_ops_async(struct crypto_tfm *tfm) struct crypto_ahash *crt = __crypto_ahash_cast(tfm); struct crypto_shash **ctx = crypto_tfm_ctx(tfm); struct crypto_shash *shash; + size_t reqsize; if (!crypto_mod_get(calg)) return -EAGAIN;
@@ -365,6 +366,12 @@ int crypto_init_shash_ops_async(struct crypto_tfm *tfm) return PTR_ERR(shash); } + reqsize = sizeof(struct shash_desc) + crypto_shash_descsize(shash); + if (WARN_ON(reqsize > AHASH_MAX_REQSIZE)) { + crypto_mod_put(calg); + return -EINVAL; + } + *ctx = shash; tfm->exit = crypto_exit_shash_ops_async;
@@ -383,7 +390,7 @@ int crypto_init_shash_ops_async(struct crypto_tfm *tfm) if (alg->import) crt->import = shash_async_import; - crt->reqsize = sizeof(struct shash_desc) + crypto_shash_descsize(shash); + crt->reqsize = reqsize; return 0; }
diff --git a/include/crypto/hash.h b/include/crypto/hash.h
index 4fcd0e2368cd..2181fb38eab9 100644
--- a/include/crypto/hash.h
+++ b/include/crypto/hash.h@@ -67,9 +67,17 @@ struct ahash_request { #define AHASH_MAX_DIGESTSIZE 512 #define AHASH_MAX_STATESIZE 512 +/* + * HASH_REQUEST_ON_STACK must only be used when wrapping shash (i.e. + * allocated with a CRYPTO_ALG_ASYNC mask), and is generally discouraged + * (just use shash directly). This is really only ever needed when using + * scatter/gather input sources. + */ +#define AHASH_MAX_REQSIZE (sizeof(struct shash_desc) + \ + SHASH_MAX_DESCSIZE) #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 /**
--
2.17.1