Re: [PATCH 5/5] fs: use HKDF implementation from kernel crypto API
On Thu, Jan 07, 2021 at 08:49:52AM +0100, Stephan Mueller wrote: > > > -int fscrypt_init_hkdf(struct fscrypt_hkdf *hkdf, const u8 *master_key, > > > +int fscrypt_init_hkdf(struct fscrypt_hkdf *hkdf, u8 *master_key, > > > unsigned int master_key_size); > > > > It shouldn't be necessary to remove const here. > > Unfortunately it is when adding the pointer to struct kvec > > > > > > > > /* > > > @@ -323,7 +323,7 @@ int fscrypt_init_hkdf(struct fscrypt_hkdf *hkdf, const > > > u8 *master_key, > > > #define HKDF_CONTEXT_INODE_HASH_KEY7 /* info= */ > > > > > > int fscrypt_hkdf_expand(const struct fscrypt_hkdf *hkdf, u8 context, > > > - const u8 *info, unsigned int infolen, > > > + u8 *info, unsigned int infolen, > > > u8 *okm, unsigned int okmlen); > > > > Likewise. In fact some callers rely on 'info' not being modified. > > Same here. If the HKDF API will have a quirk like this, it's better not to "leak" it into the prototypes of these fscrypt functions. Just add the needed casts in fscrypt_init_hkdf() and fscrypt_hkdf_expand(). > > > - err = crypto_shash_setkey(hmac_tfm, prk, sizeof(prk)); > > > + err = crypto_hkdf_setkey(hmac_tfm, seed, ARRAY_SIZE(seed)); > > > if (err) > > > goto err_free_tfm; > > > > It's weird that the salt and key have to be passed in a kvec. > > Why not just have normal function parameters like: > > > > int crypto_hkdf_setkey(struct crypto_shash *hmac_tfm, > > const u8 *key, size_t keysize, > > const u8 *salt, size_t saltsize); > > I wanted to have an identical interface for all types of KDFs to allow turning > them into a template eventually. For example, SP800-108 KDFs only have one > parameter. Hence the use of a kvec. But the API being provided is a library function specifically for HKDF. So there's no need to make it conform to some other API. - Eric
Re: [PATCH 5/5] fs: use HKDF implementation from kernel crypto API
Am Mittwoch, dem 06.01.2021 um 23:19 -0800 schrieb Eric Biggers:
> On Mon, Jan 04, 2021 at 10:50:49PM +0100, Stephan Müller wrote:
> > As the kernel crypto API implements HKDF, replace the
> > file-system-specific HKDF implementation with the generic HKDF
> > implementation.
> >
> > Signed-off-by: Stephan Mueller
> > ---
> > fs/crypto/Kconfig | 2 +-
> > fs/crypto/fscrypt_private.h | 4 +-
> > fs/crypto/hkdf.c | 108 +---
> > 3 files changed, 30 insertions(+), 84 deletions(-)
> >
> > diff --git a/fs/crypto/Kconfig b/fs/crypto/Kconfig
> > index a5f5c30368a2..9450e958f1d1 100644
> > --- a/fs/crypto/Kconfig
> > +++ b/fs/crypto/Kconfig
> > @@ -2,7 +2,7 @@
> > config FS_ENCRYPTION
> > bool "FS Encryption (Per-file encryption)"
> > select CRYPTO
> > - select CRYPTO_HASH
> > + select CRYPTO_HKDF
> > select CRYPTO_SKCIPHER
> > select CRYPTO_LIB_SHA256
> > select KEYS
> > diff --git a/fs/crypto/fscrypt_private.h b/fs/crypto/fscrypt_private.h
> > index 3fa965eb3336..0d6871838099 100644
> > --- a/fs/crypto/fscrypt_private.h
> > +++ b/fs/crypto/fscrypt_private.h
> > @@ -304,7 +304,7 @@ struct fscrypt_hkdf {
> > struct crypto_shash *hmac_tfm;
> > };
> >
> > -int fscrypt_init_hkdf(struct fscrypt_hkdf *hkdf, const u8 *master_key,
> > +int fscrypt_init_hkdf(struct fscrypt_hkdf *hkdf, u8 *master_key,
> > unsigned int master_key_size);
>
> It shouldn't be necessary to remove const here.
Unfortunately it is when adding the pointer to struct kvec
>
> >
> > /*
> > @@ -323,7 +323,7 @@ int fscrypt_init_hkdf(struct fscrypt_hkdf *hkdf, const
> > u8 *master_key,
> > #define HKDF_CONTEXT_INODE_HASH_KEY7 /* info= */
> >
> > int fscrypt_hkdf_expand(const struct fscrypt_hkdf *hkdf, u8 context,
> > - const u8 *info, unsigned int infolen,
> > + u8 *info, unsigned int infolen,
> > u8 *okm, unsigned int okmlen);
>
> Likewise. In fact some callers rely on 'info' not being modified.
Same here.
>
> > -/*
> > + *
> > * Compute HKDF-Extract using the given master key as the input keying
> > material,
> > * and prepare an HMAC transform object keyed by the resulting
> > pseudorandom key.
> > *
> > * Afterwards, the keyed HMAC transform object can be used for HKDF-
> > Expand many
> > * times without having to recompute HKDF-Extract each time.
> > */
> > -int fscrypt_init_hkdf(struct fscrypt_hkdf *hkdf, const u8 *master_key,
> > +int fscrypt_init_hkdf(struct fscrypt_hkdf *hkdf, u8 *master_key,
> > unsigned int master_key_size)
> > {
> > + /* HKDF-Extract (RFC 5869 section 2.2), unsalted */
> > + const struct kvec seed[] = { {
> > + .iov_base = NULL,
> > + .iov_len = 0
> > + }, {
> > + .iov_base = master_key,
> > + .iov_len = master_key_size
> > + } };
> > struct crypto_shash *hmac_tfm;
> > - u8 prk[HKDF_HASHLEN];
> > int err;
> >
> > hmac_tfm = crypto_alloc_shash(HKDF_HMAC_ALG, 0, 0);
> > @@ -74,16 +65,12 @@ int fscrypt_init_hkdf(struct fscrypt_hkdf *hkdf, const
> > u8 *master_key,
> > return PTR_ERR(hmac_tfm);
> > }
> >
> > - if (WARN_ON(crypto_shash_digestsize(hmac_tfm) != sizeof(prk))) {
> > + if (WARN_ON(crypto_shash_digestsize(hmac_tfm) != HKDF_HASHLEN)) {
> > err = -EINVAL;
> > goto err_free_tfm;
> > }
> >
> > - err = hkdf_extract(hmac_tfm, master_key, master_key_size, prk);
> > - if (err)
> > - goto err_free_tfm;
> > -
> > - err = crypto_shash_setkey(hmac_tfm, prk, sizeof(prk));
> > + err = crypto_hkdf_setkey(hmac_tfm, seed, ARRAY_SIZE(seed));
> > if (err)
> > goto err_free_tfm;
>
> It's weird that the salt and key have to be passed in a kvec.
> Why not just have normal function parameters like:
>
> int crypto_hkdf_setkey(struct crypto_shash *hmac_tfm,
> const u8 *key, size_t keysize,
> const u8 *salt, size_t saltsize);
I wanted to have an identical interface for all types of KDFs to allow turning
them into a template eventually. For example, SP800-108 KDFs only have one
parameter. Hence the use of a kvec.
>
> > int fscrypt_hkdf_expand(const struct fscrypt_hkdf *hkdf, u8 context,
> > - const u8 *info, unsigned int infolen,
> > + u8 *info, unsigned int infolen,
> > u8 *okm, unsigned int okmlen)
> > {
> > - SHASH_DESC_ON_STACK(desc, hkdf->hmac_tfm);
> > - u8 prefix[9];
> > - unsigned int i;
> > - int err;
> > - const u8 *prev = NULL;
> > - u8 counter = 1;
> > - u8 tmp[HKDF_HASHLEN];
> > -
> > - if (WARN_ON(okmlen > 255 *
Re: [PATCH 5/5] fs: use HKDF implementation from kernel crypto API
On Mon, Jan 04, 2021 at 10:50:49PM +0100, Stephan Müller wrote:
> As the kernel crypto API implements HKDF, replace the
> file-system-specific HKDF implementation with the generic HKDF
> implementation.
>
> Signed-off-by: Stephan Mueller
> ---
> fs/crypto/Kconfig | 2 +-
> fs/crypto/fscrypt_private.h | 4 +-
> fs/crypto/hkdf.c| 108 +---
> 3 files changed, 30 insertions(+), 84 deletions(-)
>
> diff --git a/fs/crypto/Kconfig b/fs/crypto/Kconfig
> index a5f5c30368a2..9450e958f1d1 100644
> --- a/fs/crypto/Kconfig
> +++ b/fs/crypto/Kconfig
> @@ -2,7 +2,7 @@
> config FS_ENCRYPTION
> bool "FS Encryption (Per-file encryption)"
> select CRYPTO
> - select CRYPTO_HASH
> + select CRYPTO_HKDF
> select CRYPTO_SKCIPHER
> select CRYPTO_LIB_SHA256
> select KEYS
> diff --git a/fs/crypto/fscrypt_private.h b/fs/crypto/fscrypt_private.h
> index 3fa965eb3336..0d6871838099 100644
> --- a/fs/crypto/fscrypt_private.h
> +++ b/fs/crypto/fscrypt_private.h
> @@ -304,7 +304,7 @@ struct fscrypt_hkdf {
> struct crypto_shash *hmac_tfm;
> };
>
> -int fscrypt_init_hkdf(struct fscrypt_hkdf *hkdf, const u8 *master_key,
> +int fscrypt_init_hkdf(struct fscrypt_hkdf *hkdf, u8 *master_key,
> unsigned int master_key_size);
It shouldn't be necessary to remove const here.
>
> /*
> @@ -323,7 +323,7 @@ int fscrypt_init_hkdf(struct fscrypt_hkdf *hkdf, const u8
> *master_key,
> #define HKDF_CONTEXT_INODE_HASH_KEY 7 /* info= */
>
> int fscrypt_hkdf_expand(const struct fscrypt_hkdf *hkdf, u8 context,
> - const u8 *info, unsigned int infolen,
> + u8 *info, unsigned int infolen,
> u8 *okm, unsigned int okmlen);
Likewise. In fact some callers rely on 'info' not being modified.
> -/*
> + *
> * Compute HKDF-Extract using the given master key as the input keying
> material,
> * and prepare an HMAC transform object keyed by the resulting pseudorandom
> key.
> *
> * Afterwards, the keyed HMAC transform object can be used for HKDF-Expand
> many
> * times without having to recompute HKDF-Extract each time.
> */
> -int fscrypt_init_hkdf(struct fscrypt_hkdf *hkdf, const u8 *master_key,
> +int fscrypt_init_hkdf(struct fscrypt_hkdf *hkdf, u8 *master_key,
> unsigned int master_key_size)
> {
> + /* HKDF-Extract (RFC 5869 section 2.2), unsalted */
> + const struct kvec seed[] = { {
> + .iov_base = NULL,
> + .iov_len = 0
> + }, {
> + .iov_base = master_key,
> + .iov_len = master_key_size
> + } };
> struct crypto_shash *hmac_tfm;
> - u8 prk[HKDF_HASHLEN];
> int err;
>
> hmac_tfm = crypto_alloc_shash(HKDF_HMAC_ALG, 0, 0);
> @@ -74,16 +65,12 @@ int fscrypt_init_hkdf(struct fscrypt_hkdf *hkdf, const u8
> *master_key,
> return PTR_ERR(hmac_tfm);
> }
>
> - if (WARN_ON(crypto_shash_digestsize(hmac_tfm) != sizeof(prk))) {
> + if (WARN_ON(crypto_shash_digestsize(hmac_tfm) != HKDF_HASHLEN)) {
> err = -EINVAL;
> goto err_free_tfm;
> }
>
> - err = hkdf_extract(hmac_tfm, master_key, master_key_size, prk);
> - if (err)
> - goto err_free_tfm;
> -
> - err = crypto_shash_setkey(hmac_tfm, prk, sizeof(prk));
> + err = crypto_hkdf_setkey(hmac_tfm, seed, ARRAY_SIZE(seed));
> if (err)
> goto err_free_tfm;
It's weird that the salt and key have to be passed in a kvec.
Why not just have normal function parameters like:
int crypto_hkdf_setkey(struct crypto_shash *hmac_tfm,
const u8 *key, size_t keysize,
const u8 *salt, size_t saltsize);
> int fscrypt_hkdf_expand(const struct fscrypt_hkdf *hkdf, u8 context,
> - const u8 *info, unsigned int infolen,
> + u8 *info, unsigned int infolen,
> u8 *okm, unsigned int okmlen)
> {
> - SHASH_DESC_ON_STACK(desc, hkdf->hmac_tfm);
> - u8 prefix[9];
> - unsigned int i;
> - int err;
> - const u8 *prev = NULL;
> - u8 counter = 1;
> - u8 tmp[HKDF_HASHLEN];
> -
> - if (WARN_ON(okmlen > 255 * HKDF_HASHLEN))
> - return -EINVAL;
> -
> - desc->tfm = hkdf->hmac_tfm;
> -
> - memcpy(prefix, "fscrypt\0", 8);
> - prefix[8] = context;
> -
> - for (i = 0; i < okmlen; i += HKDF_HASHLEN) {
> + const struct kvec info_iov[] = { {
> + .iov_base = "fscrypt\0",
> + .iov_len = 8,
> + }, {
> + .iov_base = ,
> + .iov_len = 1,
> + }, {
> + .iov_base = info,
> + .iov_len = infolen,
> + } };
> + int err = crypto_hkdf_generate(hkdf->hmac_tfm,
> +info_iov, ARRAY_SIZE(info_iov),
> +okm,
[PATCH 5/5] fs: use HKDF implementation from kernel crypto API
As the kernel crypto API implements HKDF, replace the
file-system-specific HKDF implementation with the generic HKDF
implementation.
Signed-off-by: Stephan Mueller
---
fs/crypto/Kconfig | 2 +-
fs/crypto/fscrypt_private.h | 4 +-
fs/crypto/hkdf.c| 108 +---
3 files changed, 30 insertions(+), 84 deletions(-)
diff --git a/fs/crypto/Kconfig b/fs/crypto/Kconfig
index a5f5c30368a2..9450e958f1d1 100644
--- a/fs/crypto/Kconfig
+++ b/fs/crypto/Kconfig
@@ -2,7 +2,7 @@
config FS_ENCRYPTION
bool "FS Encryption (Per-file encryption)"
select CRYPTO
- select CRYPTO_HASH
+ select CRYPTO_HKDF
select CRYPTO_SKCIPHER
select CRYPTO_LIB_SHA256
select KEYS
diff --git a/fs/crypto/fscrypt_private.h b/fs/crypto/fscrypt_private.h
index 3fa965eb3336..0d6871838099 100644
--- a/fs/crypto/fscrypt_private.h
+++ b/fs/crypto/fscrypt_private.h
@@ -304,7 +304,7 @@ struct fscrypt_hkdf {
struct crypto_shash *hmac_tfm;
};
-int fscrypt_init_hkdf(struct fscrypt_hkdf *hkdf, const u8 *master_key,
+int fscrypt_init_hkdf(struct fscrypt_hkdf *hkdf, u8 *master_key,
unsigned int master_key_size);
/*
@@ -323,7 +323,7 @@ int fscrypt_init_hkdf(struct fscrypt_hkdf *hkdf, const u8
*master_key,
#define HKDF_CONTEXT_INODE_HASH_KEY7 /* info= */
int fscrypt_hkdf_expand(const struct fscrypt_hkdf *hkdf, u8 context,
- const u8 *info, unsigned int infolen,
+ u8 *info, unsigned int infolen,
u8 *okm, unsigned int okmlen);
void fscrypt_destroy_hkdf(struct fscrypt_hkdf *hkdf);
diff --git a/fs/crypto/hkdf.c b/fs/crypto/hkdf.c
index e0ec21055505..f837cb8ec0a5 100644
--- a/fs/crypto/hkdf.c
+++ b/fs/crypto/hkdf.c
@@ -9,7 +9,7 @@
* Copyright 2019 Google LLC
*/
-#include
+#include
#include
#include "fscrypt_private.h"
@@ -37,34 +37,25 @@
* unnecessarily long master keys. Thus fscrypt still does HKDF-Extract. No
* salt is used, since fscrypt master keys should already be pseudorandom and
* there's no way to persist a random salt per master key from kernel mode.
- */
-
-/* HKDF-Extract (RFC 5869 section 2.2), unsalted */
-static int hkdf_extract(struct crypto_shash *hmac_tfm, const u8 *ikm,
- unsigned int ikmlen, u8 prk[HKDF_HASHLEN])
-{
- static const u8 default_salt[HKDF_HASHLEN];
- int err;
-
- err = crypto_shash_setkey(hmac_tfm, default_salt, HKDF_HASHLEN);
- if (err)
- return err;
-
- return crypto_shash_tfm_digest(hmac_tfm, ikm, ikmlen, prk);
-}
-
-/*
+ *
* Compute HKDF-Extract using the given master key as the input keying
material,
* and prepare an HMAC transform object keyed by the resulting pseudorandom
key.
*
* Afterwards, the keyed HMAC transform object can be used for HKDF-Expand many
* times without having to recompute HKDF-Extract each time.
*/
-int fscrypt_init_hkdf(struct fscrypt_hkdf *hkdf, const u8 *master_key,
+int fscrypt_init_hkdf(struct fscrypt_hkdf *hkdf, u8 *master_key,
unsigned int master_key_size)
{
+ /* HKDF-Extract (RFC 5869 section 2.2), unsalted */
+ const struct kvec seed[] = { {
+ .iov_base = NULL,
+ .iov_len = 0
+ }, {
+ .iov_base = master_key,
+ .iov_len = master_key_size
+ } };
struct crypto_shash *hmac_tfm;
- u8 prk[HKDF_HASHLEN];
int err;
hmac_tfm = crypto_alloc_shash(HKDF_HMAC_ALG, 0, 0);
@@ -74,16 +65,12 @@ int fscrypt_init_hkdf(struct fscrypt_hkdf *hkdf, const u8
*master_key,
return PTR_ERR(hmac_tfm);
}
- if (WARN_ON(crypto_shash_digestsize(hmac_tfm) != sizeof(prk))) {
+ if (WARN_ON(crypto_shash_digestsize(hmac_tfm) != HKDF_HASHLEN)) {
err = -EINVAL;
goto err_free_tfm;
}
- err = hkdf_extract(hmac_tfm, master_key, master_key_size, prk);
- if (err)
- goto err_free_tfm;
-
- err = crypto_shash_setkey(hmac_tfm, prk, sizeof(prk));
+ err = crypto_hkdf_setkey(hmac_tfm, seed, ARRAY_SIZE(seed));
if (err)
goto err_free_tfm;
@@ -93,7 +80,6 @@ int fscrypt_init_hkdf(struct fscrypt_hkdf *hkdf, const u8
*master_key,
err_free_tfm:
crypto_free_shash(hmac_tfm);
out:
- memzero_explicit(prk, sizeof(prk));
return err;
}
@@ -109,65 +95,25 @@ int fscrypt_init_hkdf(struct fscrypt_hkdf *hkdf, const u8
*master_key,
* accidentally repeat an info string when using HKDF for different purposes.)
*/
int fscrypt_hkdf_expand(const struct fscrypt_hkdf *hkdf, u8 context,
- const u8 *info, unsigned int infolen,
+ u8 *info, unsigned int infolen,
u8 *okm, unsigned int okmlen)
{
- SHASH_DESC_ON_STACK(desc, hkdf->hmac_tfm);
- u8 prefix[9];
-
