[PATCH v6 03/18] crypto: hash: Remove VLA usage

Kees Cook
2018-07-24T16:49:21Z

In the quest to remove all stack VLA usage from the kernel[1], this
removes the VLAs in SHASH_DESC_ON_STACK (via crypto_shash_descsize())
by using the maximum allowable size (which is now more clearly captured
in a macro), along with a few other cases. Similar limits are turned into
macros as well.

A review of existing sizes shows that SHA512_DIGEST_SIZE (64) is the
largest digest size and that sizeof(struct sha3_state) (360) is the
largest descriptor size. The corresponding maximums are reduced.

[1] https://lkml.kernel.org/r/CA+55aFzCG-zNmZwX4A2FQpadafLfEzK6CC=qPXydAacU1RqZWA@mail.gmail.com

Signed-off-by: Kees Cook <keescook@chromium.org>
---
crypto/ahash.c | 4 ++--
crypto/algif_hash.c | 2 +-
crypto/shash.c | 6 +++---
include/crypto/hash.h | 6 +++++-
4 files changed, 11 insertions(+), 7 deletions(-)

diff --git a/crypto/ahash.c b/crypto/ahash.c
index a64c143165b1..78aaf2158c43 100644
--- a/crypto/ahash.c
+++ b/crypto/ahash.c
@@ -550,8 +550,8 @@ static int ahash_prepare_alg(struct ahash_alg *alg)
{
struct crypto_alg *base = &alg->halg.base;

- if (alg->halg.digestsize > PAGE_SIZE / 8 ||
- alg->halg.statesize > PAGE_SIZE / 8 ||
+ if (alg->halg.digestsize > HASH_MAX_DIGESTSIZE ||
+ alg->halg.statesize > HASH_MAX_STATESIZE ||
alg->halg.statesize == 0)
return -EINVAL;

diff --git a/crypto/algif_hash.c b/crypto/algif_hash.c
index bfcf595fd8f9..d0cde541beb6 100644
--- a/crypto/algif_hash.c
+++ b/crypto/algif_hash.c
@@ -239,7 +239,7 @@ static int hash_accept(struct socket *sock, struct socket *newsock, int flags,
struct alg_sock *ask = alg_sk(sk);
struct hash_ctx *ctx = ask->private;
struct ahash_request *req = &ctx->req;
- char state[crypto_ahash_statesize(crypto_ahash_reqtfm(req)) ? : 1];
+ char state[HASH_MAX_STATESIZE];
struct sock *sk2;
struct alg_sock *ask2;
struct hash_ctx *ctx2;
diff --git a/crypto/shash.c b/crypto/shash.c
index 5d732c6bb4b2..86d76b5c626c 100644
--- a/crypto/shash.c
+++ b/crypto/shash.c
@@ -458,9 +458,9 @@ static int shash_prepare_alg(struct shash_alg *alg)
{
struct crypto_alg *base = &alg->base;

- if (alg->digestsize > PAGE_SIZE / 8 ||
- alg->descsize > PAGE_SIZE / 8 ||
- alg->statesize > PAGE_SIZE / 8)
+ if (alg->digestsize > HASH_MAX_DIGESTSIZE ||
+ alg->descsize > HASH_MAX_DESCSIZE ||
+ alg->statesize > HASH_MAX_STATESIZE)
return -EINVAL;

base->cra_type = &crypto_shash_type;
diff --git a/include/crypto/hash.h b/include/crypto/hash.h
index 76e432cab75d..21587011ab0f 100644
--- a/include/crypto/hash.h
+++ b/include/crypto/hash.h
@@ -151,9 +151,13 @@ struct shash_desc {
void *__ctx[] CRYPTO_MINALIGN_ATTR;
};

+#define HASH_MAX_DIGESTSIZE 64
+#define HASH_MAX_DESCSIZE 360
+#define HASH_MAX_STATESIZE 512
+
#define SHASH_DESC_ON_STACK(shash, ctx) \
char __##shash##_desc[sizeof(struct shash_desc) + \
- crypto_shash_descsize(ctx)] CRYPTO_MINALIGN_ATTR; \
+ HASH_MAX_DESCSIZE] CRYPTO_MINALIGN_ATTR; \
struct shash_desc *shash = (struct shash_desc *)__##shash##_desc

/**
--
2.17.1