| Message ID | 7857050.T7Z3S40VBb@positron.chronox.de (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | Add KDF implementations to crypto API | expand |
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 <smueller@chronox.de> > --- > 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=<empty> */ > > 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 = &context, > + .iov_len = 1, > + }, { > + .iov_base = info, > + .iov_len = infolen, > + } }; > + int err = crypto_hkdf_generate(hkdf->hmac_tfm, > + info_iov, ARRAY_SIZE(info_iov), > + okm, okmlen); > > - err = crypto_shash_init(desc); > - if (err) > - goto out; > - > - if (prev) { > - err = crypto_shash_update(desc, prev, HKDF_HASHLEN); > - if (err) > - goto out; > - } > - > - err = crypto_shash_update(desc, prefix, sizeof(prefix)); > - if (err) > - goto out; > - > - err = crypto_shash_update(desc, info, infolen); > - if (err) > - goto out; > - > - BUILD_BUG_ON(sizeof(counter) != 1); > - if (okmlen - i < HKDF_HASHLEN) { > - err = crypto_shash_finup(desc, &counter, 1, tmp); > - if (err) > - goto out; > - memcpy(&okm[i], tmp, okmlen - i); > - memzero_explicit(tmp, sizeof(tmp)); > - } else { > - err = crypto_shash_finup(desc, &counter, 1, &okm[i]); > - if (err) > - goto out; > - } > - counter++; > - prev = &okm[i]; > - } > - err = 0; > -out: > if (unlikely(err)) > memzero_explicit(okm, okmlen); /* so caller doesn't need to */ > - shash_desc_zero(desc); Shouldn't crypto_hkdf_generate() handle the above memzero_explicit() of the output buffer on error, so that all callers don't need to do it? - Eric
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 <smueller@chronox.de> > > --- > > 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_KEY 7 /* info=<empty> */ > > > > 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 * 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 = &context, > > + .iov_len = 1, > > + }, { > > + .iov_base = info, > > + .iov_len = infolen, > > + } }; > > + int err = crypto_hkdf_generate(hkdf->hmac_tfm, > > + info_iov, ARRAY_SIZE(info_iov), > > + okm, okmlen); > > > > - err = crypto_shash_init(desc); > > - if (err) > > - goto out; > > - > > - if (prev) { > > - err = crypto_shash_update(desc, prev, > > HKDF_HASHLEN); > > - if (err) > > - goto out; > > - } > > - > > - err = crypto_shash_update(desc, prefix, sizeof(prefix)); > > - if (err) > > - goto out; > > - > > - err = crypto_shash_update(desc, info, infolen); > > - if (err) > > - goto out; > > - > > - BUILD_BUG_ON(sizeof(counter) != 1); > > - if (okmlen - i < HKDF_HASHLEN) { > > - err = crypto_shash_finup(desc, &counter, 1, tmp); > > - if (err) > > - goto out; > > - memcpy(&okm[i], tmp, okmlen - i); > > - memzero_explicit(tmp, sizeof(tmp)); > > - } else { > > - err = crypto_shash_finup(desc, &counter, 1, > > &okm[i]); > > - if (err) > > - goto out; > > - } > > - counter++; > > - prev = &okm[i]; > > - } > > - err = 0; > > -out: > > if (unlikely(err)) > > memzero_explicit(okm, okmlen); /* so caller doesn't need > > to */ > > - shash_desc_zero(desc); > > Shouldn't crypto_hkdf_generate() handle the above memzero_explicit() of the > output buffer on error, so that all callers don't need to do it? Yes, I will move it to HKDF (and the SP800-108 KDF as well). Thanks for the review Stephan > > - Eric
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_KEY 7 /* info=<empty> */ > > > > > > 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
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_KEY 7 /* info=<empty> */ 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 <crypto/hash.h> +#include <crypto/hkdf.h> #include <crypto/sha2.h> #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]; - 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 = &context, + .iov_len = 1, + }, { + .iov_base = info, + .iov_len = infolen, + } }; + int err = crypto_hkdf_generate(hkdf->hmac_tfm, + info_iov, ARRAY_SIZE(info_iov), + okm, okmlen); - err = crypto_shash_init(desc); - if (err) - goto out; - - if (prev) { - err = crypto_shash_update(desc, prev, HKDF_HASHLEN); - if (err) - goto out; - } - - err = crypto_shash_update(desc, prefix, sizeof(prefix)); - if (err) - goto out; - - err = crypto_shash_update(desc, info, infolen); - if (err) - goto out; - - BUILD_BUG_ON(sizeof(counter) != 1); - if (okmlen - i < HKDF_HASHLEN) { - err = crypto_shash_finup(desc, &counter, 1, tmp); - if (err) - goto out; - memcpy(&okm[i], tmp, okmlen - i); - memzero_explicit(tmp, sizeof(tmp)); - } else { - err = crypto_shash_finup(desc, &counter, 1, &okm[i]); - if (err) - goto out; - } - counter++; - prev = &okm[i]; - } - err = 0; -out: if (unlikely(err)) memzero_explicit(okm, okmlen); /* so caller doesn't need to */ - shash_desc_zero(desc); return err; }
As the kernel crypto API implements HKDF, replace the file-system-specific HKDF implementation with the generic HKDF implementation. Signed-off-by: Stephan Mueller <smueller@chronox.de> --- fs/crypto/Kconfig | 2 +- fs/crypto/fscrypt_private.h | 4 +- fs/crypto/hkdf.c | 108 +++++++++--------------------------- 3 files changed, 30 insertions(+), 84 deletions(-)