2018-07-16 04:00:36

by Kees Cook

Subject: [PATCH] dm crypt: Convert essiv from ahash to shash

In preparing to remove all stack VLA usage from the kernel[1], this
removes the discouraged use of AHASH_REQUEST_ON_STACK in favor of
the smaller SHASH_DESC_ON_STACK by converting from ahash-wrapped-shash
to direct shash. The stack allocation will be made a fixed size in a
later patch to the crypto subsystem.

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

Signed-off-by: Kees Cook <[email protected]>
---
drivers/md/dm-crypt.c | 31 ++++++++++++++-----------------
1 file changed, 14 insertions(+), 17 deletions(-)

diff --git a/drivers/md/dm-crypt.c b/drivers/md/dm-crypt.c
index b61b069c33af..c4c922990090 100644
--- a/drivers/md/dm-crypt.c
+++ b/drivers/md/dm-crypt.c
@@ -99,7 +99,7 @@ struct crypt_iv_operations {
};

struct iv_essiv_private {
- struct crypto_ahash *hash_tfm;
+ struct crypto_shash *hash_tfm;
u8 *salt;
};

@@ -327,25 +327,22 @@ static int crypt_iv_plain64be_gen(struct crypt_config *cc, u8 *iv,
static int crypt_iv_essiv_init(struct crypt_config *cc)
{
struct iv_essiv_private *essiv = &cc->iv_gen_private.essiv;
- AHASH_REQUEST_ON_STACK(req, essiv->hash_tfm);
- struct scatterlist sg;
+ SHASH_DESC_ON_STACK(desc, essiv->hash_tfm);
struct crypto_cipher *essiv_tfm;
int err;

- sg_init_one(&sg, cc->key, cc->key_size);
- ahash_request_set_tfm(req, essiv->hash_tfm);
- ahash_request_set_callback(req, CRYPTO_TFM_REQ_MAY_SLEEP, NULL, NULL);
- ahash_request_set_crypt(req, &sg, essiv->salt, cc->key_size);
+ desc->tfm = essiv->hash_tfm;
+ desc->flags = CRYPTO_TFM_REQ_MAY_SLEEP;

- err = crypto_ahash_digest(req);
- ahash_request_zero(req);
+ err = crypto_shash_digest(desc, cc->key, cc->key_size, essiv->salt);
+ shash_desc_zero(desc);
if (err)
return err;

essiv_tfm = cc->iv_private;

err = crypto_cipher_setkey(essiv_tfm, essiv->salt,
- crypto_ahash_digestsize(essiv->hash_tfm));
+ crypto_shash_digestsize(essiv->hash_tfm));
if (err)
return err;

@@ -356,7 +353,7 @@ static int crypt_iv_essiv_init(struct crypt_config *cc)
static int crypt_iv_essiv_wipe(struct crypt_config *cc)
{
struct iv_essiv_private *essiv = &cc->iv_gen_private.essiv;
- unsigned salt_size = crypto_ahash_digestsize(essiv->hash_tfm);
+ unsigned salt_size = crypto_shash_digestsize(essiv->hash_tfm);
struct crypto_cipher *essiv_tfm;
int r, err = 0;

@@ -408,7 +405,7 @@ static void crypt_iv_essiv_dtr(struct crypt_config *cc)
struct crypto_cipher *essiv_tfm;
struct iv_essiv_private *essiv = &cc->iv_gen_private.essiv;

- crypto_free_ahash(essiv->hash_tfm);
+ crypto_free_shash(essiv->hash_tfm);
essiv->hash_tfm = NULL;

kzfree(essiv->salt);
@@ -426,7 +423,7 @@ static int crypt_iv_essiv_ctr(struct crypt_config *cc, struct dm_target *ti,
const char *opts)
{
struct crypto_cipher *essiv_tfm = NULL;
- struct crypto_ahash *hash_tfm = NULL;
+ struct crypto_shash *hash_tfm = NULL;
u8 *salt = NULL;
int err;

@@ -436,14 +433,14 @@ static int crypt_iv_essiv_ctr(struct crypt_config *cc, struct dm_target *ti,
}

/* Allocate hash algorithm */
- hash_tfm = crypto_alloc_ahash(opts, 0, CRYPTO_ALG_ASYNC);
+ hash_tfm = crypto_alloc_shash(opts, 0, 0);
if (IS_ERR(hash_tfm)) {
ti->error = "Error initializing ESSIV hash";
err = PTR_ERR(hash_tfm);
goto bad;
}

- salt = kzalloc(crypto_ahash_digestsize(hash_tfm), GFP_KERNEL);
+ salt = kzalloc(crypto_shash_digestsize(hash_tfm), GFP_KERNEL);
if (!salt) {
ti->error = "Error kmallocing salt storage in ESSIV";
err = -ENOMEM;
@@ -454,7 +451,7 @@ static int crypt_iv_essiv_ctr(struct crypt_config *cc, struct dm_target *ti,
cc->iv_gen_private.essiv.hash_tfm = hash_tfm;

essiv_tfm = alloc_essiv_cipher(cc, ti, salt,
- crypto_ahash_digestsize(hash_tfm));
+ crypto_shash_digestsize(hash_tfm));
if (IS_ERR(essiv_tfm)) {
crypt_iv_essiv_dtr(cc);
return PTR_ERR(essiv_tfm);
@@ -465,7 +462,7 @@ static int crypt_iv_essiv_ctr(struct crypt_config *cc, struct dm_target *ti,

bad:
if (hash_tfm && !IS_ERR(hash_tfm))
- crypto_free_ahash(hash_tfm);
+ crypto_free_shash(hash_tfm);
kfree(salt);
return err;
}
--
2.17.1


--
Kees Cook
Pixel Security

2018-07-16 10:24:57

by Arnd Bergmann

Subject: Re: [PATCH] dm crypt: Convert essiv from ahash to shash

On Mon, Jul 16, 2018 at 5:59 AM, Kees Cook <[email protected]> wrote:
> In preparing to remove all stack VLA usage from the kernel[1], this
> removes the discouraged use of AHASH_REQUEST_ON_STACK in favor of
> the smaller SHASH_DESC_ON_STACK by converting from ahash-wrapped-shash
> to direct shash. The stack allocation will be made a fixed size in a
> later patch to the crypto subsystem.
>
> [1] https://lkml.kernel.org/r/CA+55aFzCG-zNmZwX4A2FQpadafLfEzK6CC=qPXydAacU1RqZWA@mail.gmail.com
>
> Signed-off-by: Kees Cook <[email protected]>

This looks very nice, it should also make the operation more efficient in the
process by removing one indirection layer.

Arnd

2018-07-16 17:21:42

by Eric Biggers

Subject: Re: [PATCH] dm crypt: Convert essiv from ahash to shash

On Sun, Jul 15, 2018 at 08:59:12PM -0700, Kees Cook wrote:
> In preparing to remove all stack VLA usage from the kernel[1], this
> removes the discouraged use of AHASH_REQUEST_ON_STACK in favor of
> the smaller SHASH_DESC_ON_STACK by converting from ahash-wrapped-shash
> to direct shash. The stack allocation will be made a fixed size in a
> later patch to the crypto subsystem.
>
> [1] https://lkml.kernel.org/r/CA+55aFzCG-zNmZwX4A2FQpadafLfEzK6CC=qPXydAacU1RqZWA@mail.gmail.com
>
> Signed-off-by: Kees Cook <[email protected]>

Reviewed-by: Eric Biggers <[email protected]>

> ---
> drivers/md/dm-crypt.c | 31 ++++++++++++++-----------------
> 1 file changed, 14 insertions(+), 17 deletions(-)
>
> diff --git a/drivers/md/dm-crypt.c b/drivers/md/dm-crypt.c
> index b61b069c33af..c4c922990090 100644
> --- a/drivers/md/dm-crypt.c
> +++ b/drivers/md/dm-crypt.c
> @@ -99,7 +99,7 @@ struct crypt_iv_operations {
> };
>
> struct iv_essiv_private {
> - struct crypto_ahash *hash_tfm;
> + struct crypto_shash *hash_tfm;
> u8 *salt;
> };
>
> @@ -327,25 +327,22 @@ static int crypt_iv_plain64be_gen(struct crypt_config *cc, u8 *iv,
> static int crypt_iv_essiv_init(struct crypt_config *cc)
> {
> struct iv_essiv_private *essiv = &cc->iv_gen_private.essiv;
> - AHASH_REQUEST_ON_STACK(req, essiv->hash_tfm);
> - struct scatterlist sg;
> + SHASH_DESC_ON_STACK(desc, essiv->hash_tfm);
> struct crypto_cipher *essiv_tfm;
> int err;
>
> - sg_init_one(&sg, cc->key, cc->key_size);
> - ahash_request_set_tfm(req, essiv->hash_tfm);
> - ahash_request_set_callback(req, CRYPTO_TFM_REQ_MAY_SLEEP, NULL, NULL);
> - ahash_request_set_crypt(req, &sg, essiv->salt, cc->key_size);
> + desc->tfm = essiv->hash_tfm;
> + desc->flags = CRYPTO_TFM_REQ_MAY_SLEEP;
>
> - err = crypto_ahash_digest(req);
> - ahash_request_zero(req);
> + err = crypto_shash_digest(desc, cc->key, cc->key_size, essiv->salt);
> + shash_desc_zero(desc);
> if (err)
> return err;
>
> essiv_tfm = cc->iv_private;
>
> err = crypto_cipher_setkey(essiv_tfm, essiv->salt,
> - crypto_ahash_digestsize(essiv->hash_tfm));
> + crypto_shash_digestsize(essiv->hash_tfm));
> if (err)
> return err;
>
> @@ -356,7 +353,7 @@ static int crypt_iv_essiv_init(struct crypt_config *cc)
> static int crypt_iv_essiv_wipe(struct crypt_config *cc)
> {
> struct iv_essiv_private *essiv = &cc->iv_gen_private.essiv;
> - unsigned salt_size = crypto_ahash_digestsize(essiv->hash_tfm);
> + unsigned salt_size = crypto_shash_digestsize(essiv->hash_tfm);
> struct crypto_cipher *essiv_tfm;
> int r, err = 0;
>
> @@ -408,7 +405,7 @@ static void crypt_iv_essiv_dtr(struct crypt_config *cc)
> struct crypto_cipher *essiv_tfm;
> struct iv_essiv_private *essiv = &cc->iv_gen_private.essiv;
>
> - crypto_free_ahash(essiv->hash_tfm);
> + crypto_free_shash(essiv->hash_tfm);
> essiv->hash_tfm = NULL;
>
> kzfree(essiv->salt);
> @@ -426,7 +423,7 @@ static int crypt_iv_essiv_ctr(struct crypt_config *cc, struct dm_target *ti,
> const char *opts)
> {
> struct crypto_cipher *essiv_tfm = NULL;
> - struct crypto_ahash *hash_tfm = NULL;
> + struct crypto_shash *hash_tfm = NULL;
> u8 *salt = NULL;
> int err;
>
> @@ -436,14 +433,14 @@ static int crypt_iv_essiv_ctr(struct crypt_config *cc, struct dm_target *ti,
> }
>
> /* Allocate hash algorithm */
> - hash_tfm = crypto_alloc_ahash(opts, 0, CRYPTO_ALG_ASYNC);
> + hash_tfm = crypto_alloc_shash(opts, 0, 0);
> if (IS_ERR(hash_tfm)) {
> ti->error = "Error initializing ESSIV hash";
> err = PTR_ERR(hash_tfm);
> goto bad;
> }
>
> - salt = kzalloc(crypto_ahash_digestsize(hash_tfm), GFP_KERNEL);
> + salt = kzalloc(crypto_shash_digestsize(hash_tfm), GFP_KERNEL);
> if (!salt) {
> ti->error = "Error kmallocing salt storage in ESSIV";
> err = -ENOMEM;
> @@ -454,7 +451,7 @@ static int crypt_iv_essiv_ctr(struct crypt_config *cc, struct dm_target *ti,
> cc->iv_gen_private.essiv.hash_tfm = hash_tfm;
>
> essiv_tfm = alloc_essiv_cipher(cc, ti, salt,
> - crypto_ahash_digestsize(hash_tfm));
> + crypto_shash_digestsize(hash_tfm));
> if (IS_ERR(essiv_tfm)) {
> crypt_iv_essiv_dtr(cc);
> return PTR_ERR(essiv_tfm);
> @@ -465,7 +462,7 @@ static int crypt_iv_essiv_ctr(struct crypt_config *cc, struct dm_target *ti,
>
> bad:
> if (hash_tfm && !IS_ERR(hash_tfm))
> - crypto_free_ahash(hash_tfm);
> + crypto_free_shash(hash_tfm);
> kfree(salt);
> return err;
> }
> --
> 2.17.1
>
>
> --
> Kees Cook
> Pixel Security