On Wed, Jul 12, 2017 at 02:00:32PM -0700, Eric Biggers wrote: > From: Eric Biggers <ebiggers@xxxxxxxxxx> > > By design, the keys which userspace provides in the keyring are not used > to encrypt data directly. Instead, a KDF (Key Derivation Function) is > used to derive a unique encryption key for each inode, given a "master" > key and a nonce. The current KDF encrypts the master key with > AES-128-ECB using the nonce as the AES key. This KDF is ad-hoc and is > not specified in any standard. While it does generate unique derived > keys with sufficient entropy, it has several disadvantages: > > - It's reversible: an attacker who compromises a derived key, e.g. using > a side channel attack, can "decrypt" it to get back to the master key. > > - It's not very extensible because it cannot easily be used to derive > other key material that may be needed and it ties the length of the > derived key closely to the length of the master key. > > - It doesn't evenly distribute the entropy from the master key. For > example, the first 16 bytes of each derived key depend only on the > first 16 bytes of the master key. > > - It uses a public value as an AES key, which is unusual. Ciphers are > rarely evaluated under a threat model where the keys are public and > the messages are secret. > > Solve all these problems for v2 encryption policies by changing the KDF > to HKDF with SHA-512 as the underlying hash function. To derive each > inode's encryption key, HKDF is executed with the master key as the > input key material, a fixed salt, and the per-inode nonce prefixed with > a context byte as the application-specific information string. Unlike > the current KDF, HKDF has been formally published and standardized > [1][2], is nonreversible, can be used to derive any number and length of > secret and/or non-secret keys, and evenly distributes the entropy from > the master key (excepting limits inherent to not using a random salt). > > Note that this introduces a dependency on the security and > implementation of SHA-512, whereas before we were using only AES for > both key derivation and encryption. However, by using HMAC rather than > the hash function directly, HKDF is designed to remain secure even if > various classes of attacks, e.g. collision attacks, are found against > the underlying unkeyed hash function. Even HMAC-MD5 is still considered > secure in practice, despite MD5 itself having been heavily compromised. > > We *could* avoid introducing a hash function by instantiating > HKDF-Expand with CMAC-AES256 as the pseudorandom function rather than > HMAC-SHA512. This would work; however, the HKDF specification doesn't > explicitly allow a non-HMAC pseudorandom function, so it would be less > standard. It would also require skipping HKDF-Extract and changing the > API to accept only 32-byte master keys (since otherwise HKDF-Extract > using CMAC-AES would produce a pseudorandom key only 16 bytes long which > is only enough for AES-128, not AES-256). > > HKDF-SHA512 can require more "crypto work" per key derivation when > compared to the current KDF. However, later in this series, we'll start > caching the HMAC transform for each master key, which will actually make > the real-world performance about the same or even significantly better > than the AES-based KDF as currently implemented. Also, each KDF can > actually be executed on the order of 1 million times per second, so KDF > performance probably isn't actually the bottleneck in practice anyway. > > References: > [1] Krawczyk (2010). "Cryptographic Extraction and Key Derivation: The > HKDF Scheme". https://eprint.iacr.org/2010/264.pdf > > [2] RFC 5869. "HMAC-based Extract-and-Expand Key Derivation Function > (HKDF)". https://tools.ietf.org/html/rfc5869 > > Signed-off-by: Eric Biggers <ebiggers@xxxxxxxxxx> > --- > fs/crypto/Kconfig | 2 + > fs/crypto/fscrypt_private.h | 14 ++ > fs/crypto/keyinfo.c | 485 +++++++++++++++++++++++++++++++++++--------- > 3 files changed, 405 insertions(+), 96 deletions(-) > > diff --git a/fs/crypto/Kconfig b/fs/crypto/Kconfig > index 02b7d91c9231..bbd4e38b293c 100644 > --- a/fs/crypto/Kconfig > +++ b/fs/crypto/Kconfig > @@ -8,6 +8,8 @@ config FS_ENCRYPTION > select CRYPTO_CTS > select CRYPTO_CTR > select CRYPTO_SHA256 > + select CRYPTO_SHA512 > + select CRYPTO_HMAC > select KEYS > help > Enable encryption of files and directories. This > diff --git a/fs/crypto/fscrypt_private.h b/fs/crypto/fscrypt_private.h > index 5470aac82cab..095e7c16483a 100644 > --- a/fs/crypto/fscrypt_private.h > +++ b/fs/crypto/fscrypt_private.h > @@ -86,6 +86,14 @@ fscrypt_valid_context_format(const struct fscrypt_context *ctx, int size) > return size >= 1 && size == fscrypt_context_size(ctx); > } > > +/* > + * fscrypt_master_key - an in-use master key > + */ > +struct fscrypt_master_key { > + struct crypto_shash *mk_hmac; > + unsigned int mk_size; > +}; > + > /* > * fscrypt_info - the "encryption key" for an inode > * > @@ -99,6 +107,12 @@ struct fscrypt_info { > struct crypto_skcipher *ci_ctfm; > struct crypto_cipher *ci_essiv_tfm; > > + /* > + * The master key with which this inode was "unlocked" > + * (only set for inodes that use a v2+ encryption policy) > + */ > + struct fscrypt_master_key *ci_master_key; > + > /* > * Cached fields from the fscrypt_context needed for encryption policy > * inheritance and enforcement > diff --git a/fs/crypto/keyinfo.c b/fs/crypto/keyinfo.c > index 5591fd24e4b2..7ed1a7fb1308 100644 > --- a/fs/crypto/keyinfo.c > +++ b/fs/crypto/keyinfo.c > @@ -6,17 +6,312 @@ > * This contains encryption key functions. > * > * Written by Michael Halcrow, Ildar Muslukhov, and Uday Savagaonkar, 2015. > + * HKDF support added by Eric Biggers, 2017. > + * > + * The implementation and usage of HKDF should conform to RFC-5869 ("HMAC-based > + * Extract-and-Expand Key Derivation Function"). > */ > > #include <keys/user-type.h> > #include <linux/scatterlist.h> > #include <linux/ratelimit.h> > #include <crypto/aes.h> > +#include <crypto/hash.h> > #include <crypto/sha.h> > #include "fscrypt_private.h" > > static struct crypto_shash *essiv_hash_tfm; > > +/* > + * Any unkeyed cryptographic hash algorithm can be used with HKDF, but we use > + * SHA-512 because it is reasonably secure and efficient; and since it produces > + * a 64-byte digest, deriving an AES-256-XTS key preserves all 64 bytes of > + * entropy from the master key and requires only one iteration of HKDF-Expand. > + */ > +#define HKDF_HMAC_ALG "hmac(sha512)" > +#define HKDF_HASHLEN SHA512_DIGEST_SIZE > + > +/* > + * The list of contexts in which we use HKDF to derive additional keys from a > + * master key. The values in this list are used as the first byte of the > + * application-specific info string to guarantee that info strings are never > + * repeated between contexts. > + * > + * Keys derived with different info strings are cryptographically isolated from > + * each other --- knowledge of one derived key doesn't reveal any others. > + */ > +#define HKDF_CONTEXT_PER_FILE_KEY 1 > + > +/* > + * HKDF consists of two steps: > + * > + * 1. HKDF-Extract: extract a fixed-length pseudorandom key from the > + * input keying material and optional salt. > + * 2. HDKF-Expand: expand the pseudorandom key into output keying material of > + * any length, parameterized by an application-specific info string. > + * > + * HKDF-Extract can be skipped if the input is already a good pseudorandom key > + * that is at least as long as the hash. While the fscrypt master keys should > + * already be good pseudorandom keys, when using encryption algorithms that use > + * short keys (e.g. AES-128-CBC) we'd like to permit the master key to be > + * shorter than HKDF_HASHLEN bytes. Thus, we still must do HKDF-Extract. > + * > + * Ideally, HKDF-Extract would be passed a random salt for each distinct input > + * key. Details about the advantages of a random salt can be found in the HKDF > + * paper (Krawczyk, 2010; "Cryptographic Extraction and Key Derivation: The HKDF > + * Scheme"). However, we do not have the ability to store a salt on a > + * per-master-key basis. Thus, we have to use a fixed salt. This is sufficient > + * as long as the master keys are already pseudorandom and are long enough to > + * make dictionary attacks infeasible. This should be the case if userspace > + * used a cryptographically secure random number generator, e.g. /dev/urandom, Modulo entropy gathered since boot. > + * to generate the master keys. > + * > + * For the fixed salt we use "fscrypt_hkdf_salt" rather than default of all 0's > + * defined by RFC-5869. This is only to be slightly more robust against > + * userspace (unwisely) reusing the master keys for different purposes. > + * Logically, it's more likely that the keys would be passed to unsalted > + * HKDF-SHA512 than specifically to "fscrypt_hkdf_salt"-salted HKDF-SHA512. > + * (Of course, a random salt would be better for this purpose.) > + */ > + > +#define HKDF_SALT "fscrypt_hkdf_salt" > +#define HKDF_SALT_LEN (sizeof(HKDF_SALT) - 1) > + > +/* > + * HKDF-Extract (RFC-5869 section 2.2). This extracts a pseudorandom key 'prk' > + * from the input key material 'ikm' and a salt. (See explanation above for why > + * we use a fixed salt.) > + */ > +static int hkdf_extract(struct crypto_shash *hmac, > + const u8 *ikm, unsigned int ikmlen, > + u8 prk[HKDF_HASHLEN]) > +{ > + SHASH_DESC_ON_STACK(desc, hmac); > + int err; > + > + desc->tfm = hmac; > + desc->flags = 0; > + > + err = crypto_shash_setkey(hmac, HKDF_SALT, HKDF_SALT_LEN); > + if (err) > + goto out; > + > + err = crypto_shash_digest(desc, ikm, ikmlen, prk); > +out: > + shash_desc_zero(desc); > + return err; > +} > + > +/* > + * HKDF-Expand (RFC-5869 section 2.3). This expands the pseudorandom key, which > + * has already been keyed into 'hmac', into 'okmlen' bytes of output keying > + * material, parameterized by the application-specific information string of > + * 'info' prefixed with the 'context' byte. ('context' isn't part of the HKDF > + * specification; it's just a prefix we add to our application-specific info > + * strings to guarantee that we don't accidentally repeat an info string when > + * using HKDF for different purposes.) > + */ > +static int hkdf_expand(struct crypto_shash *hmac, u8 context, > + const u8 *info, unsigned int infolen, > + u8 *okm, unsigned int okmlen) > +{ > + SHASH_DESC_ON_STACK(desc, hmac); > + int err; > + const u8 *prev = NULL; > + unsigned int i; > + u8 counter = 1; > + u8 tmp[HKDF_HASHLEN]; > + > + desc->tfm = hmac; > + desc->flags = 0; > + > + if (unlikely(okmlen > 255 * HKDF_HASHLEN)) > + return -EINVAL; > + > + for (i = 0; i < okmlen; i += HKDF_HASHLEN) { > + > + 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, &context, 1); One potential shortcut would be to just increment context on each iteration rather than maintain the counter. > + if (err) > + goto out; > + > + err = crypto_shash_update(desc, info, infolen); > + if (err) > + goto out; > + > + 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: > + shash_desc_zero(desc); > + return err; > +} > + > +static void put_master_key(struct fscrypt_master_key *k) > +{ > + if (!k) > + return; > + > + crypto_free_shash(k->mk_hmac); > + kzfree(k); > +} > + > +/* > + * Allocate a fscrypt_master_key, given the keyring key payload. This includes > + * allocating and keying an HMAC transform so that we can efficiently derive a HMAC? an fscrypt_master_key? > + * the per-inode encryption keys with HKDF-Expand later. > + */ > +static struct fscrypt_master_key * > +alloc_master_key(const struct fscrypt_key *payload) > +{ > + struct fscrypt_master_key *k; > + int err; > + u8 prk[HKDF_HASHLEN]; > + > + k = kzalloc(sizeof(*k), GFP_NOFS); > + if (!k) > + return ERR_PTR(-ENOMEM); > + k->mk_size = payload->size; > + > + k->mk_hmac = crypto_alloc_shash(HKDF_HMAC_ALG, 0, 0); > + if (IS_ERR(k->mk_hmac)) { > + err = PTR_ERR(k->mk_hmac); > + k->mk_hmac = NULL; > + pr_warn("fscrypt: error allocating " HKDF_HMAC_ALG ": %d\n", > + err); > + goto fail; > + } > + > + BUG_ON(crypto_shash_digestsize(k->mk_hmac) != sizeof(prk)); > + > + err = hkdf_extract(k->mk_hmac, payload->raw, payload->size, prk); > + if (err) > + goto fail; > + > + err = crypto_shash_setkey(k->mk_hmac, prk, sizeof(prk)); > + if (err) > + goto fail; Why not memzero prk? > +out: > + memzero_explicit(prk, sizeof(prk)); > + return k; > + > +fail: > + put_master_key(k); > + k = ERR_PTR(err); > + goto out; > +} > + > +static void release_keyring_key(struct key *keyring_key) > +{ > + up_read(&keyring_key->sem); > + key_put(keyring_key); > +} > + > +/* > + * Find, lock, and validate the master key with the keyring description > + * prefix:descriptor. It must be released with release_keyring_key() later. > + */ > +static struct key * > +find_and_lock_keyring_key(const char *prefix, > + const u8 descriptor[FS_KEY_DESCRIPTOR_SIZE], > + unsigned int min_keysize, > + const struct fscrypt_key **payload_ret) > +{ > + char *description; > + struct key *keyring_key; > + const struct user_key_payload *ukp; > + const struct fscrypt_key *payload; > + > + description = kasprintf(GFP_NOFS, "%s%*phN", prefix, > + FS_KEY_DESCRIPTOR_SIZE, descriptor); > + if (!description) > + return ERR_PTR(-ENOMEM); > + > + keyring_key = request_key(&key_type_logon, description, NULL); > + if (IS_ERR(keyring_key)) > + goto out; > + > + down_read(&keyring_key->sem); > + ukp = user_key_payload_locked(keyring_key); > + payload = (const struct fscrypt_key *)ukp->data; > + > + if (ukp->datalen != sizeof(struct fscrypt_key) || > + payload->size == 0 || payload->size > FS_MAX_KEY_SIZE) { > + pr_warn_ratelimited("fscrypt: key '%s' has invalid payload\n", > + description); > + goto invalid; > + } > + > + /* > + * With the legacy AES-based KDF the master key must be at least as long > + * as the derived key. With HKDF we could accept a shorter master key; > + * however, that would mean the derived key wouldn't contain as much > + * entropy as intended. So don't allow it in either case. > + */ > + if (payload->size < min_keysize) { > + pr_warn_ratelimited("fscrypt: key '%s' is too short (got %u bytes, wanted %u+ bytes)\n", > + description, payload->size, min_keysize); > + goto invalid; > + } > + > + *payload_ret = payload; > +out: > + kfree(description); > + return keyring_key; > + > +invalid: > + release_keyring_key(keyring_key); > + keyring_key = ERR_PTR(-ENOKEY); > + goto out; > +} > + > +static struct fscrypt_master_key * > +load_master_key_from_keyring(const struct inode *inode, > + const u8 descriptor[FS_KEY_DESCRIPTOR_SIZE], > + unsigned int min_keysize) > +{ > + struct key *keyring_key; > + const struct fscrypt_key *payload; > + struct fscrypt_master_key *master_key; > + > + keyring_key = find_and_lock_keyring_key(FS_KEY_DESC_PREFIX, descriptor, > + min_keysize, &payload); > + if (keyring_key == ERR_PTR(-ENOKEY) && inode->i_sb->s_cop->key_prefix) { > + keyring_key = find_and_lock_keyring_key( > + inode->i_sb->s_cop->key_prefix, > + descriptor, min_keysize, &payload); > + } > + if (IS_ERR(keyring_key)) > + return ERR_CAST(keyring_key); > + > + master_key = alloc_master_key(payload); > + > + release_keyring_key(keyring_key); > + > + return master_key; > +} > + > static void derive_crypt_complete(struct crypto_async_request *req, int rc) > { > struct fscrypt_completion_result *ecr = req->data; > @@ -28,107 +323,100 @@ static void derive_crypt_complete(struct crypto_async_request *req, int rc) > complete(&ecr->completion); > } > > -/** > - * derive_key_aes() - Derive a key using AES-128-ECB > - * @deriving_key: Encryption key used for derivation. > - * @source_key: Source key to which to apply derivation. > - * @derived_raw_key: Derived raw key. > - * > - * Return: Zero on success; non-zero otherwise. > +/* > + * Legacy key derivation function. This generates the derived key by encrypting > + * the master key with AES-128-ECB using the nonce as the AES key. This > + * provides a unique derived key for each inode, but it's nonstandard, isn't > + * very extensible, and has the weakness that it's trivially reversible: an > + * attacker who compromises a derived key, e.g. with a side channel attack, can > + * "decrypt" it to get back to the master key, then derive any other key. > */ > -static int derive_key_aes(u8 deriving_key[FS_AES_128_ECB_KEY_SIZE], > - const struct fscrypt_key *source_key, > - u8 derived_raw_key[FS_MAX_KEY_SIZE]) > +static int derive_key_aes(const struct fscrypt_key *master_key, > + const struct fscrypt_context *ctx, > + u8 *derived_key, unsigned int derived_keysize) > { > - int res = 0; > + int err; > struct skcipher_request *req = NULL; > DECLARE_FS_COMPLETION_RESULT(ecr); > struct scatterlist src_sg, dst_sg; > - struct crypto_skcipher *tfm = crypto_alloc_skcipher("ecb(aes)", 0, 0); > + struct crypto_skcipher *tfm; > + > + tfm = crypto_alloc_skcipher("ecb(aes)", 0, 0); > + if (IS_ERR(tfm)) > + return PTR_ERR(tfm); > > - if (IS_ERR(tfm)) { > - res = PTR_ERR(tfm); > - tfm = NULL; > - goto out; > - } > crypto_skcipher_set_flags(tfm, CRYPTO_TFM_REQ_WEAK_KEY); > req = skcipher_request_alloc(tfm, GFP_NOFS); > if (!req) { > - res = -ENOMEM; > + err = -ENOMEM; > goto out; > } > skcipher_request_set_callback(req, > CRYPTO_TFM_REQ_MAY_BACKLOG | CRYPTO_TFM_REQ_MAY_SLEEP, > derive_crypt_complete, &ecr); > - res = crypto_skcipher_setkey(tfm, deriving_key, > - FS_AES_128_ECB_KEY_SIZE); > - if (res < 0) > + > + BUILD_BUG_ON(sizeof(ctx->nonce) != FS_AES_128_ECB_KEY_SIZE); > + err = crypto_skcipher_setkey(tfm, ctx->nonce, sizeof(ctx->nonce)); > + if (err) > goto out; > > - sg_init_one(&src_sg, source_key->raw, source_key->size); > - sg_init_one(&dst_sg, derived_raw_key, source_key->size); > - skcipher_request_set_crypt(req, &src_sg, &dst_sg, source_key->size, > + sg_init_one(&src_sg, master_key->raw, derived_keysize); > + sg_init_one(&dst_sg, derived_key, derived_keysize); > + skcipher_request_set_crypt(req, &src_sg, &dst_sg, derived_keysize, > NULL); > - res = crypto_skcipher_encrypt(req); > - if (res == -EINPROGRESS || res == -EBUSY) { > + err = crypto_skcipher_encrypt(req); > + if (err == -EINPROGRESS || err == -EBUSY) { > wait_for_completion(&ecr.completion); > - res = ecr.res; > + err = ecr.res; > } > out: > skcipher_request_free(req); > crypto_free_skcipher(tfm); > - return res; > + return err; > } > > -static int validate_user_key(struct fscrypt_info *crypt_info, > - struct fscrypt_context *ctx, u8 *raw_key, > - const char *prefix, int min_keysize) > +/* > + * HKDF-based key derivation function. This uses HKDF-SHA512 to derive a unique > + * encryption key for each inode, using the inode's nonce prefixed with a > + * context byte as the application-specific information string. This is more > + * flexible than the legacy AES-based KDF and has the advantage that it's > + * non-reversible: an attacker who compromises a derived key cannot calculate > + * the master key or any other derived keys. > + */ > +static int derive_key_hkdf(const struct fscrypt_master_key *master_key, > + const struct fscrypt_context *ctx, > + u8 *derived_key, unsigned int derived_keysize) > { > - char *description; > - struct key *keyring_key; > - struct fscrypt_key *master_key; > - const struct user_key_payload *ukp; > - int res; > + return hkdf_expand(master_key->mk_hmac, HKDF_CONTEXT_PER_FILE_KEY, > + ctx->nonce, sizeof(ctx->nonce), > + derived_key, derived_keysize); > +} > > - description = kasprintf(GFP_NOFS, "%s%*phN", prefix, > - FS_KEY_DESCRIPTOR_SIZE, > - ctx->master_key_descriptor); > - if (!description) > - return -ENOMEM; > +static int find_and_derive_key_v1(const struct inode *inode, > + const struct fscrypt_context *ctx, > + u8 *derived_key, unsigned int derived_keysize) > +{ > + struct key *keyring_key; > + const struct fscrypt_key *payload; > + int err; > > - keyring_key = request_key(&key_type_logon, description, NULL); > - kfree(description); > + keyring_key = find_and_lock_keyring_key(FS_KEY_DESC_PREFIX, > + ctx->master_key_descriptor, > + derived_keysize, &payload); > + if (keyring_key == ERR_PTR(-ENOKEY) && inode->i_sb->s_cop->key_prefix) { > + keyring_key = find_and_lock_keyring_key( > + inode->i_sb->s_cop->key_prefix, > + ctx->master_key_descriptor, > + derived_keysize, &payload); > + } > if (IS_ERR(keyring_key)) > return PTR_ERR(keyring_key); > - down_read(&keyring_key->sem); > > - if (keyring_key->type != &key_type_logon) { > - printk_once(KERN_WARNING > - "%s: key type must be logon\n", __func__); > - res = -ENOKEY; > - goto out; > - } > - ukp = user_key_payload_locked(keyring_key); > - if (ukp->datalen != sizeof(struct fscrypt_key)) { > - res = -EINVAL; > - goto out; > - } > - master_key = (struct fscrypt_key *)ukp->data; > - BUILD_BUG_ON(FS_AES_128_ECB_KEY_SIZE != FS_KEY_DERIVATION_NONCE_SIZE); > - > - if (master_key->size < min_keysize || master_key->size > FS_MAX_KEY_SIZE > - || master_key->size % AES_BLOCK_SIZE != 0) { > - printk_once(KERN_WARNING > - "%s: key size incorrect: %d\n", > - __func__, master_key->size); > - res = -ENOKEY; > - goto out; > - } > - res = derive_key_aes(ctx->nonce, master_key, raw_key); > -out: > - up_read(&keyring_key->sem); > - key_put(keyring_key); > - return res; > + err = derive_key_aes(payload, ctx, derived_key, derived_keysize); > + > + release_keyring_key(keyring_key); > + > + return err; > } > > static const struct { > @@ -179,6 +467,7 @@ static void put_crypt_info(struct fscrypt_info *ci) > > crypto_free_skcipher(ci->ci_ctfm); > crypto_free_cipher(ci->ci_essiv_tfm); > + put_master_key(ci->ci_master_key); > kmem_cache_free(fscrypt_info_cachep, ci); > } > > @@ -254,8 +543,8 @@ int fscrypt_get_encryption_info(struct inode *inode) > struct fscrypt_context ctx; > struct crypto_skcipher *ctfm; > const char *cipher_str; > - int keysize; > - u8 *raw_key = NULL; > + unsigned int derived_keysize; > + u8 *derived_key = NULL; > int res; > > if (inode->i_crypt_info) > @@ -296,33 +585,40 @@ int fscrypt_get_encryption_info(struct inode *inode) > memcpy(crypt_info->ci_master_key_descriptor, ctx.master_key_descriptor, > FS_KEY_DESCRIPTOR_SIZE); > > - res = determine_cipher_type(crypt_info, inode, &cipher_str, &keysize); > + res = determine_cipher_type(crypt_info, inode, &cipher_str, > + &derived_keysize); > if (res) > goto out; > > /* > - * This cannot be a stack buffer because it is passed to the scatterlist > - * crypto API as part of key derivation. > + * This cannot be a stack buffer because it may be passed to the > + * scatterlist crypto API during key derivation. > */ > res = -ENOMEM; > - raw_key = kmalloc(FS_MAX_KEY_SIZE, GFP_NOFS); > - if (!raw_key) > + derived_key = kmalloc(FS_MAX_KEY_SIZE, GFP_NOFS); > + if (!derived_key) > goto out; > > - res = validate_user_key(crypt_info, &ctx, raw_key, FS_KEY_DESC_PREFIX, > - keysize); > - if (res && inode->i_sb->s_cop->key_prefix) { > - int res2 = validate_user_key(crypt_info, &ctx, raw_key, > - inode->i_sb->s_cop->key_prefix, > - keysize); > - if (res2) { > - if (res2 == -ENOKEY) > - res = -ENOKEY; > + if (ctx.version == FSCRYPT_CONTEXT_V1) { > + res = find_and_derive_key_v1(inode, &ctx, derived_key, > + derived_keysize); Why not make this consistent with the else clause, i.e. doing load_master_key_from_keyring() followed by derive_key_v1()? > + } else { > + crypt_info->ci_master_key = > + load_master_key_from_keyring(inode, > + ctx.master_key_descriptor, > + derived_keysize); > + if (IS_ERR(crypt_info->ci_master_key)) { > + res = PTR_ERR(crypt_info->ci_master_key); > + crypt_info->ci_master_key = NULL; > goto out; > } > - } else if (res) { > - goto out; > + > + res = derive_key_hkdf(crypt_info->ci_master_key, &ctx, > + derived_key, derived_keysize); > } > + if (res) > + goto out; > + > ctfm = crypto_alloc_skcipher(cipher_str, 0, 0); > if (!ctfm || IS_ERR(ctfm)) { > res = ctfm ? PTR_ERR(ctfm) : -ENOMEM; > @@ -333,17 +629,14 @@ int fscrypt_get_encryption_info(struct inode *inode) > crypt_info->ci_ctfm = ctfm; > crypto_skcipher_clear_flags(ctfm, ~0); > crypto_skcipher_set_flags(ctfm, CRYPTO_TFM_REQ_WEAK_KEY); > - /* > - * if the provided key is longer than keysize, we use the first > - * keysize bytes of the derived key only > - */ > - res = crypto_skcipher_setkey(ctfm, raw_key, keysize); > + res = crypto_skcipher_setkey(ctfm, derived_key, derived_keysize); > if (res) > goto out; > > if (S_ISREG(inode->i_mode) && > crypt_info->ci_data_mode == FS_ENCRYPTION_MODE_AES_128_CBC) { > - res = init_essiv_generator(crypt_info, raw_key, keysize); > + res = init_essiv_generator(crypt_info, derived_key, > + derived_keysize); > if (res) { > pr_debug("%s: error %d (inode %lu) allocating essiv tfm\n", > __func__, res, inode->i_ino); > @@ -356,7 +649,7 @@ int fscrypt_get_encryption_info(struct inode *inode) > if (res == -ENOKEY) > res = 0; > put_crypt_info(crypt_info); > - kzfree(raw_key); > + kzfree(derived_key); > return res; > } > EXPORT_SYMBOL(fscrypt_get_encryption_info); > -- > 2.13.2.932.g7449e964c-goog >
