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Subject[PATCH][RFC] crypto: skcipher: Remove VLA usage
RFC follow-up to https://lkml.kernel.org/r/CAGXu5j+bpLK=EQ9LHkO8V=sdaQwt==6fbGhgn2Vi1E9_WxSGRQ@mail.gmail.com

The core API changes:

struct crypto_sync_skcipher
crypto_alloc_sync_skcipher()
crypto_free_sync_skcipher()
crypto_sync_skcipher_setkey()
skcipher_request_set_sync_tfm()
SKCIPHER_REQUEST_ON_STACK type check

and a single user's refactoring as an example:

drivers/crypto/ccp/ccp-crypto.h
drivers/crypto/ccp/ccp-crypto-aes-xts.c

Does this look correct? If so, I can continue and do the other 60
instances of SKCIPHER_REQUEST_ON_STACK().

Signed-off-by: Kees Cook <keescook@chromium.org>
---
crypto/skcipher.c | 24 +++++++++++++++++
drivers/crypto/ccp/ccp-crypto-aes-xts.c | 10 ++++----
drivers/crypto/ccp/ccp-crypto.h | 2 +-
include/crypto/skcipher.h | 34 ++++++++++++++++++++++++-
4 files changed, 63 insertions(+), 7 deletions(-)

diff --git a/crypto/skcipher.c b/crypto/skcipher.c
index 0bd8c6caa498..4caab81d2d02 100644
--- a/crypto/skcipher.c
+++ b/crypto/skcipher.c
@@ -949,6 +949,30 @@ struct crypto_skcipher *crypto_alloc_skcipher(const char *alg_name,
}
EXPORT_SYMBOL_GPL(crypto_alloc_skcipher);

+struct crypto_sync_skcipher *crypto_alloc_sync_skcipher(
+ const char *alg_name, u32 type, u32 mask)
+{
+ struct crypto_skcipher *tfm;
+
+ /* Only sync algorithms allowed. */
+ mask |= CRYPTO_ALG_ASYNC;
+
+ tfm = crypto_alloc_tfm(alg_name, &crypto_skcipher_type2, type, mask);
+
+ /*
+ * Make sure we do not allocate something that might get used with
+ * an on-stack request: check the request size.
+ */
+ if (!IS_ERR(tfm) && WARN_ON(crypto_skcipher_reqsize(tfm) >
+ MAX_SYNC_SKCIPHER_REQSIZE)) {
+ crypto_free_skcipher(tfm);
+ return ERR_PTR(-EINVAL);
+ }
+
+ return (struct crypto_sync_skcipher *)tfm;
+}
+EXPORT_SYMBOL_GPL(crypto_alloc_sync_skcipher);
+
int crypto_has_skcipher2(const char *alg_name, u32 type, u32 mask)
{
return crypto_type_has_alg(alg_name, &crypto_skcipher_type2,
diff --git a/drivers/crypto/ccp/ccp-crypto-aes-xts.c b/drivers/crypto/ccp/ccp-crypto-aes-xts.c
index 94b5bcf5b628..983c921736b4 100644
--- a/drivers/crypto/ccp/ccp-crypto-aes-xts.c
+++ b/drivers/crypto/ccp/ccp-crypto-aes-xts.c
@@ -102,7 +102,7 @@ static int ccp_aes_xts_setkey(struct crypto_ablkcipher *tfm, const u8 *key,
ctx->u.aes.key_len = key_len / 2;
sg_init_one(&ctx->u.aes.key_sg, ctx->u.aes.key, key_len);

- return crypto_skcipher_setkey(ctx->u.aes.tfm_skcipher, key, key_len);
+ return crypto_sync_skcipher_setkey(ctx->u.aes.tfm_skcipher, key, key_len);
}

static int ccp_aes_xts_crypt(struct ablkcipher_request *req,
@@ -156,7 +156,7 @@ static int ccp_aes_xts_crypt(struct ablkcipher_request *req,
/* Use the fallback to process the request for any
* unsupported unit sizes or key sizes
*/
- skcipher_request_set_tfm(subreq, ctx->u.aes.tfm_skcipher);
+ skcipher_request_set_sync_tfm(subreq, ctx->u.aes.tfm_skcipher);
skcipher_request_set_callback(subreq, req->base.flags,
NULL, NULL);
skcipher_request_set_crypt(subreq, req->src, req->dst,
@@ -203,12 +203,12 @@ static int ccp_aes_xts_decrypt(struct ablkcipher_request *req)
static int ccp_aes_xts_cra_init(struct crypto_tfm *tfm)
{
struct ccp_ctx *ctx = crypto_tfm_ctx(tfm);
- struct crypto_skcipher *fallback_tfm;
+ struct crypto_sync_skcipher *fallback_tfm;

ctx->complete = ccp_aes_xts_complete;
ctx->u.aes.key_len = 0;

- fallback_tfm = crypto_alloc_skcipher("xts(aes)", 0,
+ fallback_tfm = crypto_alloc_sync_skcipher("xts(aes)", 0,
CRYPTO_ALG_ASYNC |
CRYPTO_ALG_NEED_FALLBACK);
if (IS_ERR(fallback_tfm)) {
@@ -226,7 +226,7 @@ static void ccp_aes_xts_cra_exit(struct crypto_tfm *tfm)
{
struct ccp_ctx *ctx = crypto_tfm_ctx(tfm);

- crypto_free_skcipher(ctx->u.aes.tfm_skcipher);
+ crypto_free_sync_skcipher(ctx->u.aes.tfm_skcipher);
}

static int ccp_register_aes_xts_alg(struct list_head *head,
diff --git a/drivers/crypto/ccp/ccp-crypto.h b/drivers/crypto/ccp/ccp-crypto.h
index b9fd090c46c2..28819e11db96 100644
--- a/drivers/crypto/ccp/ccp-crypto.h
+++ b/drivers/crypto/ccp/ccp-crypto.h
@@ -88,7 +88,7 @@ static inline struct ccp_crypto_ahash_alg *
/***** AES related defines *****/
struct ccp_aes_ctx {
/* Fallback cipher for XTS with unsupported unit sizes */
- struct crypto_skcipher *tfm_skcipher;
+ struct crypto_sync_skcipher *tfm_skcipher;

/* Cipher used to generate CMAC K1/K2 keys */
struct crypto_cipher *tfm_cipher;
diff --git a/include/crypto/skcipher.h b/include/crypto/skcipher.h
index 2f327f090c3e..4435f3a3d621 100644
--- a/include/crypto/skcipher.h
+++ b/include/crypto/skcipher.h
@@ -65,6 +65,10 @@ struct crypto_skcipher {
struct crypto_tfm base;
};

+struct crypto_sync_skcipher {
+ struct crypto_skcipher base;
+};
+
/**
* struct skcipher_alg - symmetric key cipher definition
* @min_keysize: Minimum key size supported by the transformation. This is the
@@ -139,9 +143,17 @@ struct skcipher_alg {
struct crypto_alg base;
};

+#define MAX_SYNC_SKCIPHER_REQSIZE 384
+/*
+ * This performs a type-check against the "tfm" argument to make sure
+ * all users have the correct skcipher tfm for doing on-stack requests.
+ */
#define SKCIPHER_REQUEST_ON_STACK(name, tfm) \
char __##name##_desc[sizeof(struct skcipher_request) + \
- crypto_skcipher_reqsize(tfm)] CRYPTO_MINALIGN_ATTR; \
+ MAX_SYNC_SKCIPHER_REQSIZE + \
+ (!(sizeof((struct crypto_sync_skcipher *)1 == \
+ (typeof(tfm))1))) \
+ ] CRYPTO_MINALIGN_ATTR; \
struct skcipher_request *name = (void *)__##name##_desc

/**
@@ -197,6 +209,9 @@ static inline struct crypto_skcipher *__crypto_skcipher_cast(
struct crypto_skcipher *crypto_alloc_skcipher(const char *alg_name,
u32 type, u32 mask);

+struct crypto_sync_skcipher *crypto_alloc_sync_skcipher(const char *alg_name,
+ u32 type, u32 mask);
+
static inline struct crypto_tfm *crypto_skcipher_tfm(
struct crypto_skcipher *tfm)
{
@@ -212,6 +227,11 @@ static inline void crypto_free_skcipher(struct crypto_skcipher *tfm)
crypto_destroy_tfm(tfm, crypto_skcipher_tfm(tfm));
}

+static inline void crypto_free_sync_skcipher(struct crypto_sync_skcipher *tfm)
+{
+ crypto_free_skcipher(&tfm->base);
+}
+
/**
* crypto_has_skcipher() - Search for the availability of an skcipher.
* @alg_name: is the cra_name / name or cra_driver_name / driver name of the
@@ -401,6 +421,12 @@ static inline int crypto_skcipher_setkey(struct crypto_skcipher *tfm,
return tfm->setkey(tfm, key, keylen);
}

+static inline int crypto_sync_skcipher_setkey(struct crypto_sync_skcipher *tfm,
+ const u8 *key, unsigned int keylen)
+{
+ return crypto_skcipher_setkey(&tfm->base, key, keylen);
+}
+
static inline unsigned int crypto_skcipher_default_keysize(
struct crypto_skcipher *tfm)
{
@@ -500,6 +526,12 @@ static inline void skcipher_request_set_tfm(struct skcipher_request *req,
req->base.tfm = crypto_skcipher_tfm(tfm);
}

+static inline void skcipher_request_set_sync_tfm(struct skcipher_request *req,
+ struct crypto_sync_skcipher *tfm)
+{
+ skcipher_request_set_tfm(req, &tfm->base);
+}
+
static inline struct skcipher_request *skcipher_request_cast(
struct crypto_async_request *req)
{
--
2.17.1

--
Kees Cook
Pixel Security

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