diff options
Diffstat (limited to 'fs/ext4/crypto_key.c')
| -rw-r--r-- | fs/ext4/crypto_key.c | 387 |
1 files changed, 387 insertions, 0 deletions
diff --git a/fs/ext4/crypto_key.c b/fs/ext4/crypto_key.c new file mode 100644 index 000000000000..d3d6b28ce9b9 --- /dev/null +++ b/fs/ext4/crypto_key.c @@ -0,0 +1,387 @@ +/* + * linux/fs/ext4/crypto_key.c + * + * Copyright (C) 2015, Google, Inc. + * + * This contains encryption key functions for ext4 + * + * Written by Michael Halcrow, Ildar Muslukhov, and Uday Savagaonkar, 2015. + */ + +#include <keys/encrypted-type.h> +#include <keys/user-type.h> +#include <linux/random.h> +#include <linux/scatterlist.h> +#include <uapi/linux/keyctl.h> + +#include "ext4.h" +#include "ext4_ice.h" +#include "xattr.h" + +static void derive_crypt_complete(struct crypto_async_request *req, int rc) +{ + struct ext4_completion_result *ecr = req->data; + + if (rc == -EINPROGRESS) + return; + + ecr->res = rc; + complete(&ecr->completion); +} + +/** + * ext4_derive_key_v1() - Derive a key using AES-128-ECB + * @deriving_key: Encryption key used for derivation. + * @source_key: Source key to which to apply derivation. + * @derived_key: Derived key. + * + * Return: 0 on success, -errno on failure + */ +static int ext4_derive_key_v1(const char deriving_key[EXT4_AES_128_ECB_KEY_SIZE], + const char source_key[EXT4_AES_256_XTS_KEY_SIZE], + char derived_key[EXT4_AES_256_XTS_KEY_SIZE]) +{ + int res = 0; + struct ablkcipher_request *req = NULL; + DECLARE_EXT4_COMPLETION_RESULT(ecr); + struct scatterlist src_sg, dst_sg; + struct crypto_ablkcipher *tfm = crypto_alloc_ablkcipher("ecb(aes)", 0, + 0); + + if (IS_ERR(tfm)) { + res = PTR_ERR(tfm); + tfm = NULL; + goto out; + } + crypto_ablkcipher_set_flags(tfm, CRYPTO_TFM_REQ_WEAK_KEY); + req = ablkcipher_request_alloc(tfm, GFP_NOFS); + if (!req) { + res = -ENOMEM; + goto out; + } + ablkcipher_request_set_callback(req, + CRYPTO_TFM_REQ_MAY_BACKLOG | CRYPTO_TFM_REQ_MAY_SLEEP, + derive_crypt_complete, &ecr); + res = crypto_ablkcipher_setkey(tfm, deriving_key, + EXT4_AES_128_ECB_KEY_SIZE); + if (res < 0) + goto out; + sg_init_one(&src_sg, source_key, EXT4_AES_256_XTS_KEY_SIZE); + sg_init_one(&dst_sg, derived_key, EXT4_AES_256_XTS_KEY_SIZE); + ablkcipher_request_set_crypt(req, &src_sg, &dst_sg, + EXT4_AES_256_XTS_KEY_SIZE, NULL); + res = crypto_ablkcipher_encrypt(req); + if (res == -EINPROGRESS || res == -EBUSY) { + wait_for_completion(&ecr.completion); + res = ecr.res; + } + +out: + if (req) + ablkcipher_request_free(req); + if (tfm) + crypto_free_ablkcipher(tfm); + return res; +} + +/** + * ext4_derive_key_v2() - Derive a key non-reversibly + * @nonce: the nonce associated with the file + * @master_key: the master key referenced by the file + * @derived_key: (output) the resulting derived key + * + * This function computes the following: + * derived_key[0:127] = AES-256-ENCRYPT(master_key[0:255], nonce) + * derived_key[128:255] = AES-256-ENCRYPT(master_key[0:255], nonce ^ 0x01) + * derived_key[256:383] = AES-256-ENCRYPT(master_key[256:511], nonce) + * derived_key[384:511] = AES-256-ENCRYPT(master_key[256:511], nonce ^ 0x01) + * + * 'nonce ^ 0x01' denotes flipping the low order bit of the last byte. + * + * Unlike the v1 algorithm, the v2 algorithm is "non-reversible", meaning that + * compromising a derived key does not also compromise the master key. + * + * Return: 0 on success, -errno on failure + */ +static int ext4_derive_key_v2(const char nonce[EXT4_KEY_DERIVATION_NONCE_SIZE], + const char master_key[EXT4_MAX_KEY_SIZE], + char derived_key[EXT4_MAX_KEY_SIZE]) +{ + const int noncelen = EXT4_KEY_DERIVATION_NONCE_SIZE; + struct crypto_cipher *tfm; + int err; + int i; + + /* + * Since we only use each transform for a small number of encryptions, + * requesting just "aes" turns out to be significantly faster than + * "ecb(aes)", by about a factor of two. + */ + tfm = crypto_alloc_cipher("aes", 0, 0); + if (IS_ERR(tfm)) + return PTR_ERR(tfm); + + BUILD_BUG_ON(4 * EXT4_KEY_DERIVATION_NONCE_SIZE != EXT4_MAX_KEY_SIZE); + BUILD_BUG_ON(2 * EXT4_AES_256_ECB_KEY_SIZE != EXT4_MAX_KEY_SIZE); + for (i = 0; i < 2; i++) { + memcpy(derived_key, nonce, noncelen); + memcpy(derived_key + noncelen, nonce, noncelen); + derived_key[2 * noncelen - 1] ^= 0x01; + err = crypto_cipher_setkey(tfm, master_key, + EXT4_AES_256_ECB_KEY_SIZE); + if (err) + break; + crypto_cipher_encrypt_one(tfm, derived_key, derived_key); + crypto_cipher_encrypt_one(tfm, derived_key + noncelen, + derived_key + noncelen); + master_key += EXT4_AES_256_ECB_KEY_SIZE; + derived_key += 2 * noncelen; + } + crypto_free_cipher(tfm); + return err; +} + +/** + * ext4_derive_key() - Derive a per-file key from a nonce and master key + * @ctx: the encryption context associated with the file + * @master_key: the master key referenced by the file + * @derived_key: (output) the resulting derived key + * + * Return: 0 on success, -errno on failure + */ +static int ext4_derive_key(const struct ext4_encryption_context *ctx, + const char master_key[EXT4_MAX_KEY_SIZE], + char derived_key[EXT4_MAX_KEY_SIZE]) +{ + BUILD_BUG_ON(EXT4_AES_128_ECB_KEY_SIZE != EXT4_KEY_DERIVATION_NONCE_SIZE); + BUILD_BUG_ON(EXT4_AES_256_XTS_KEY_SIZE != EXT4_MAX_KEY_SIZE); + + /* + * Although the key derivation algorithm is logically independent of the + * choice of encryption modes, in this kernel it is bundled with HEH + * encryption of filenames, which is another crypto improvement that + * requires an on-disk format change and requires userspace to specify + * different encryption policies. + */ + if (ctx->filenames_encryption_mode == EXT4_ENCRYPTION_MODE_AES_256_HEH) + return ext4_derive_key_v2(ctx->nonce, master_key, derived_key); + else + return ext4_derive_key_v1(ctx->nonce, master_key, derived_key); +} + +void ext4_free_crypt_info(struct ext4_crypt_info *ci) +{ + if (!ci) + return; + + if (ci->ci_keyring_key) + key_put(ci->ci_keyring_key); + crypto_free_ablkcipher(ci->ci_ctfm); + kmem_cache_free(ext4_crypt_info_cachep, ci); +} + +void ext4_free_encryption_info(struct inode *inode, + struct ext4_crypt_info *ci) +{ + struct ext4_inode_info *ei = EXT4_I(inode); + struct ext4_crypt_info *prev; + + if (ci == NULL) + ci = ACCESS_ONCE(ei->i_crypt_info); + if (ci == NULL) + return; + prev = cmpxchg(&ei->i_crypt_info, ci, NULL); + if (prev != ci) + return; + + ext4_free_crypt_info(ci); +} + +static int ext4_default_data_encryption_mode(void) +{ + return ext4_is_ice_enabled() ? EXT4_ENCRYPTION_MODE_PRIVATE : + EXT4_ENCRYPTION_MODE_AES_256_XTS; +} + +int _ext4_get_encryption_info(struct inode *inode) +{ + struct ext4_inode_info *ei = EXT4_I(inode); + struct ext4_crypt_info *crypt_info; + char full_key_descriptor[EXT4_KEY_DESC_PREFIX_SIZE + + (EXT4_KEY_DESCRIPTOR_SIZE * 2) + 1]; + struct key *keyring_key = NULL; + struct ext4_encryption_key *master_key; + struct ext4_encryption_context ctx; + const struct user_key_payload *ukp; + struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb); + struct crypto_ablkcipher *ctfm; + const char *cipher_str; + int for_fname = 0; + int mode; + int res; + + res = ext4_init_crypto(); + if (res) + return res; + +retry: + crypt_info = ACCESS_ONCE(ei->i_crypt_info); + if (crypt_info) { + if (!crypt_info->ci_keyring_key || + key_validate(crypt_info->ci_keyring_key) == 0) + return 0; + ext4_free_encryption_info(inode, crypt_info); + goto retry; + } + + res = ext4_xattr_get(inode, EXT4_XATTR_INDEX_ENCRYPTION, + EXT4_XATTR_NAME_ENCRYPTION_CONTEXT, + &ctx, sizeof(ctx)); + if (res < 0) { + if (!DUMMY_ENCRYPTION_ENABLED(sbi)) + return res; + ctx.contents_encryption_mode = + ext4_default_data_encryption_mode(); + ctx.filenames_encryption_mode = + EXT4_ENCRYPTION_MODE_AES_256_CTS; + ctx.flags = 0; + } else if (res != sizeof(ctx)) + return -EINVAL; + res = 0; + + crypt_info = kmem_cache_alloc(ext4_crypt_info_cachep, GFP_KERNEL); + if (!crypt_info) + return -ENOMEM; + + crypt_info->ci_flags = ctx.flags; + crypt_info->ci_data_mode = ctx.contents_encryption_mode; + crypt_info->ci_filename_mode = ctx.filenames_encryption_mode; + crypt_info->ci_ctfm = NULL; + crypt_info->ci_keyring_key = NULL; + memcpy(crypt_info->ci_master_key, ctx.master_key_descriptor, + sizeof(crypt_info->ci_master_key)); + if (S_ISDIR(inode->i_mode) || S_ISLNK(inode->i_mode)) + for_fname = 1; + else if (!S_ISREG(inode->i_mode)) + BUG(); + mode = for_fname ? crypt_info->ci_filename_mode : + crypt_info->ci_data_mode; + switch (mode) { + case EXT4_ENCRYPTION_MODE_AES_256_XTS: + cipher_str = "xts(aes)"; + break; + case EXT4_ENCRYPTION_MODE_AES_256_CTS: + cipher_str = "cts(cbc(aes))"; + break; + case EXT4_ENCRYPTION_MODE_PRIVATE: + cipher_str = "bugon"; + case EXT4_ENCRYPTION_MODE_AES_256_HEH: + cipher_str = "heh(aes)"; + break; + default: + printk_once(KERN_WARNING + "ext4: unsupported key mode %d (ino %u)\n", + mode, (unsigned) inode->i_ino); + res = -ENOKEY; + goto out; + } + if (DUMMY_ENCRYPTION_ENABLED(sbi)) { + memset(crypt_info->ci_raw_key, 0x42, EXT4_AES_256_XTS_KEY_SIZE); + goto got_key; + } + memcpy(full_key_descriptor, EXT4_KEY_DESC_PREFIX, + EXT4_KEY_DESC_PREFIX_SIZE); + sprintf(full_key_descriptor + EXT4_KEY_DESC_PREFIX_SIZE, + "%*phN", EXT4_KEY_DESCRIPTOR_SIZE, + ctx.master_key_descriptor); + full_key_descriptor[EXT4_KEY_DESC_PREFIX_SIZE + + (2 * EXT4_KEY_DESCRIPTOR_SIZE)] = '\0'; + keyring_key = request_key(&key_type_logon, full_key_descriptor, NULL); + if (IS_ERR(keyring_key)) { + res = PTR_ERR(keyring_key); + keyring_key = NULL; + goto out; + } + crypt_info->ci_keyring_key = keyring_key; + if (keyring_key->type != &key_type_logon) { + printk_once(KERN_WARNING + "ext4: key type must be logon\n"); + res = -ENOKEY; + goto out; + } + down_read(&keyring_key->sem); + ukp = user_key_payload(keyring_key); + if (!ukp) { + /* key was revoked before we acquired its semaphore */ + res = -EKEYREVOKED; + up_read(&keyring_key->sem); + goto out; + } + if (ukp->datalen != sizeof(struct ext4_encryption_key)) { + res = -EINVAL; + up_read(&keyring_key->sem); + goto out; + } + master_key = (struct ext4_encryption_key *)ukp->data; + BUILD_BUG_ON(EXT4_AES_128_ECB_KEY_SIZE != + EXT4_KEY_DERIVATION_NONCE_SIZE); + if (master_key->size != EXT4_AES_256_XTS_KEY_SIZE) { + printk_once(KERN_WARNING + "ext4: key size incorrect: %d\n", + master_key->size); + res = -ENOKEY; + up_read(&keyring_key->sem); + goto out; + } + res = ext4_derive_key(&ctx, master_key->raw, + crypt_info->ci_raw_key); + up_read(&keyring_key->sem); + if (res) + goto out; +got_key: + if (for_fname || + (crypt_info->ci_data_mode != EXT4_ENCRYPTION_MODE_PRIVATE)) { + ctfm = crypto_alloc_ablkcipher(cipher_str, 0, 0); + if (!ctfm || IS_ERR(ctfm)) { + res = ctfm ? PTR_ERR(ctfm) : -ENOMEM; + pr_debug("%s: error %d (inode %u) allocating crypto tfm\n", + __func__, res, (unsigned) inode->i_ino); + goto out; + } + crypt_info->ci_ctfm = ctfm; + crypto_ablkcipher_clear_flags(ctfm, ~0); + crypto_tfm_set_flags(crypto_ablkcipher_tfm(ctfm), + CRYPTO_TFM_REQ_WEAK_KEY); + res = crypto_ablkcipher_setkey(ctfm, crypt_info->ci_raw_key, + ext4_encryption_key_size(mode)); + if (res) + goto out; + memzero_explicit(crypt_info->ci_raw_key, + sizeof(crypt_info->ci_raw_key)); + } else if (!ext4_is_ice_enabled()) { + pr_warn("%s: ICE support not available\n", + __func__); + res = -EINVAL; + goto out; + } + if (cmpxchg(&ei->i_crypt_info, NULL, crypt_info) != NULL) { + ext4_free_crypt_info(crypt_info); + goto retry; + } + return 0; + +out: + if (res == -ENOKEY) + res = 0; + memzero_explicit(crypt_info->ci_raw_key, + sizeof(crypt_info->ci_raw_key)); + ext4_free_crypt_info(crypt_info); + return res; +} + +int ext4_has_encryption_key(struct inode *inode) +{ + struct ext4_inode_info *ei = EXT4_I(inode); + + return (ei->i_crypt_info != NULL); +} |