diff options
Diffstat (limited to 'security/integrity/evm/evm_crypto.c')
| -rw-r--r-- | security/integrity/evm/evm_crypto.c | 428 |
1 files changed, 428 insertions, 0 deletions
diff --git a/security/integrity/evm/evm_crypto.c b/security/integrity/evm/evm_crypto.c new file mode 100644 index 000000000..b9395f8ef --- /dev/null +++ b/security/integrity/evm/evm_crypto.c @@ -0,0 +1,428 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * Copyright (C) 2005-2010 IBM Corporation + * + * Authors: + * Mimi Zohar <zohar@us.ibm.com> + * Kylene Hall <kjhall@us.ibm.com> + * + * File: evm_crypto.c + * Using root's kernel master key (kmk), calculate the HMAC + */ + +#define pr_fmt(fmt) "EVM: "fmt + +#include <linux/export.h> +#include <linux/crypto.h> +#include <linux/xattr.h> +#include <linux/evm.h> +#include <keys/encrypted-type.h> +#include <crypto/hash.h> +#include <crypto/hash_info.h> +#include "evm.h" + +#define EVMKEY "evm-key" +#define MAX_KEY_SIZE 128 +static unsigned char evmkey[MAX_KEY_SIZE]; +static const int evmkey_len = MAX_KEY_SIZE; + +static struct crypto_shash *hmac_tfm; +static struct crypto_shash *evm_tfm[HASH_ALGO__LAST]; + +static DEFINE_MUTEX(mutex); + +#define EVM_SET_KEY_BUSY 0 + +static unsigned long evm_set_key_flags; + +static const char evm_hmac[] = "hmac(sha1)"; + +/** + * evm_set_key() - set EVM HMAC key from the kernel + * @key: pointer to a buffer with the key data + * @keylen: length of the key data + * + * This function allows setting the EVM HMAC key from the kernel + * without using the "encrypted" key subsystem keys. It can be used + * by the crypto HW kernel module which has its own way of managing + * keys. + * + * key length should be between 32 and 128 bytes long + */ +int evm_set_key(void *key, size_t keylen) +{ + int rc; + + rc = -EBUSY; + if (test_and_set_bit(EVM_SET_KEY_BUSY, &evm_set_key_flags)) + goto busy; + rc = -EINVAL; + if (keylen > MAX_KEY_SIZE) + goto inval; + memcpy(evmkey, key, keylen); + evm_initialized |= EVM_INIT_HMAC; + pr_info("key initialized\n"); + return 0; +inval: + clear_bit(EVM_SET_KEY_BUSY, &evm_set_key_flags); +busy: + pr_err("key initialization failed\n"); + return rc; +} +EXPORT_SYMBOL_GPL(evm_set_key); + +static struct shash_desc *init_desc(char type, uint8_t hash_algo) +{ + long rc; + const char *algo; + struct crypto_shash **tfm, *tmp_tfm; + struct shash_desc *desc; + + if (type == EVM_XATTR_HMAC) { + if (!(evm_initialized & EVM_INIT_HMAC)) { + pr_err_once("HMAC key is not set\n"); + return ERR_PTR(-ENOKEY); + } + tfm = &hmac_tfm; + algo = evm_hmac; + } else { + if (hash_algo >= HASH_ALGO__LAST) + return ERR_PTR(-EINVAL); + + tfm = &evm_tfm[hash_algo]; + algo = hash_algo_name[hash_algo]; + } + + if (*tfm) + goto alloc; + mutex_lock(&mutex); + if (*tfm) + goto unlock; + + tmp_tfm = crypto_alloc_shash(algo, 0, CRYPTO_NOLOAD); + if (IS_ERR(tmp_tfm)) { + pr_err("Can not allocate %s (reason: %ld)\n", algo, + PTR_ERR(tmp_tfm)); + mutex_unlock(&mutex); + return ERR_CAST(tmp_tfm); + } + if (type == EVM_XATTR_HMAC) { + rc = crypto_shash_setkey(tmp_tfm, evmkey, evmkey_len); + if (rc) { + crypto_free_shash(tmp_tfm); + mutex_unlock(&mutex); + return ERR_PTR(rc); + } + } + *tfm = tmp_tfm; +unlock: + mutex_unlock(&mutex); +alloc: + desc = kmalloc(sizeof(*desc) + crypto_shash_descsize(*tfm), + GFP_KERNEL); + if (!desc) + return ERR_PTR(-ENOMEM); + + desc->tfm = *tfm; + + rc = crypto_shash_init(desc); + if (rc) { + kfree(desc); + return ERR_PTR(rc); + } + return desc; +} + +/* Protect against 'cutting & pasting' security.evm xattr, include inode + * specific info. + * + * (Additional directory/file metadata needs to be added for more complete + * protection.) + */ +static void hmac_add_misc(struct shash_desc *desc, struct inode *inode, + char type, char *digest) +{ + struct h_misc { + unsigned long ino; + __u32 generation; + uid_t uid; + gid_t gid; + umode_t mode; + } hmac_misc; + + memset(&hmac_misc, 0, sizeof(hmac_misc)); + /* Don't include the inode or generation number in portable + * signatures + */ + if (type != EVM_XATTR_PORTABLE_DIGSIG) { + hmac_misc.ino = inode->i_ino; + hmac_misc.generation = inode->i_generation; + } + /* The hmac uid and gid must be encoded in the initial user + * namespace (not the filesystems user namespace) as encoding + * them in the filesystems user namespace allows an attack + * where first they are written in an unprivileged fuse mount + * of a filesystem and then the system is tricked to mount the + * filesystem for real on next boot and trust it because + * everything is signed. + */ + hmac_misc.uid = from_kuid(&init_user_ns, inode->i_uid); + hmac_misc.gid = from_kgid(&init_user_ns, inode->i_gid); + hmac_misc.mode = inode->i_mode; + crypto_shash_update(desc, (const u8 *)&hmac_misc, sizeof(hmac_misc)); + if ((evm_hmac_attrs & EVM_ATTR_FSUUID) && + type != EVM_XATTR_PORTABLE_DIGSIG) + crypto_shash_update(desc, (u8 *)&inode->i_sb->s_uuid, UUID_SIZE); + crypto_shash_final(desc, digest); + + pr_debug("hmac_misc: (%zu) [%*phN]\n", sizeof(struct h_misc), + (int)sizeof(struct h_misc), &hmac_misc); +} + +/* + * Dump large security xattr values as a continuous ascii hexademical string. + * (pr_debug is limited to 64 bytes.) + */ +static void dump_security_xattr(const char *prefix, const void *src, + size_t count) +{ +#if defined(DEBUG) || defined(CONFIG_DYNAMIC_DEBUG) + char *asciihex, *p; + + p = asciihex = kmalloc(count * 2 + 1, GFP_KERNEL); + if (!asciihex) + return; + + p = bin2hex(p, src, count); + *p = 0; + pr_debug("%s: (%zu) %.*s\n", prefix, count, (int)count * 2, asciihex); + kfree(asciihex); +#endif +} + +/* + * Calculate the HMAC value across the set of protected security xattrs. + * + * Instead of retrieving the requested xattr, for performance, calculate + * the hmac using the requested xattr value. Don't alloc/free memory for + * each xattr, but attempt to re-use the previously allocated memory. + */ +static int evm_calc_hmac_or_hash(struct dentry *dentry, + const char *req_xattr_name, + const char *req_xattr_value, + size_t req_xattr_value_len, + uint8_t type, struct evm_digest *data) +{ + struct inode *inode = d_backing_inode(dentry); + struct xattr_list *xattr; + struct shash_desc *desc; + size_t xattr_size = 0; + char *xattr_value = NULL; + int error; + int size, user_space_size; + bool ima_present = false; + + if (!(inode->i_opflags & IOP_XATTR) || + inode->i_sb->s_user_ns != &init_user_ns) + return -EOPNOTSUPP; + + desc = init_desc(type, data->hdr.algo); + if (IS_ERR(desc)) + return PTR_ERR(desc); + + data->hdr.length = crypto_shash_digestsize(desc->tfm); + + error = -ENODATA; + list_for_each_entry_lockless(xattr, &evm_config_xattrnames, list) { + bool is_ima = false; + + if (strcmp(xattr->name, XATTR_NAME_IMA) == 0) + is_ima = true; + + /* + * Skip non-enabled xattrs for locally calculated + * signatures/HMACs. + */ + if (type != EVM_XATTR_PORTABLE_DIGSIG && !xattr->enabled) + continue; + + if ((req_xattr_name && req_xattr_value) + && !strcmp(xattr->name, req_xattr_name)) { + error = 0; + crypto_shash_update(desc, (const u8 *)req_xattr_value, + req_xattr_value_len); + if (is_ima) + ima_present = true; + + if (req_xattr_value_len < 64) + pr_debug("%s: (%zu) [%*phN]\n", req_xattr_name, + req_xattr_value_len, + (int)req_xattr_value_len, + req_xattr_value); + else + dump_security_xattr(req_xattr_name, + req_xattr_value, + req_xattr_value_len); + continue; + } + size = vfs_getxattr_alloc(&init_user_ns, dentry, xattr->name, + &xattr_value, xattr_size, GFP_NOFS); + if (size == -ENOMEM) { + error = -ENOMEM; + goto out; + } + if (size < 0) + continue; + + user_space_size = vfs_getxattr(&init_user_ns, dentry, + xattr->name, NULL, 0); + if (user_space_size != size) + pr_debug("file %s: xattr %s size mismatch (kernel: %d, user: %d)\n", + dentry->d_name.name, xattr->name, size, + user_space_size); + error = 0; + xattr_size = size; + crypto_shash_update(desc, (const u8 *)xattr_value, xattr_size); + if (is_ima) + ima_present = true; + + if (xattr_size < 64) + pr_debug("%s: (%zu) [%*phN]", xattr->name, xattr_size, + (int)xattr_size, xattr_value); + else + dump_security_xattr(xattr->name, xattr_value, + xattr_size); + } + hmac_add_misc(desc, inode, type, data->digest); + + /* Portable EVM signatures must include an IMA hash */ + if (type == EVM_XATTR_PORTABLE_DIGSIG && !ima_present) + error = -EPERM; +out: + kfree(xattr_value); + kfree(desc); + return error; +} + +int evm_calc_hmac(struct dentry *dentry, const char *req_xattr_name, + const char *req_xattr_value, size_t req_xattr_value_len, + struct evm_digest *data) +{ + return evm_calc_hmac_or_hash(dentry, req_xattr_name, req_xattr_value, + req_xattr_value_len, EVM_XATTR_HMAC, data); +} + +int evm_calc_hash(struct dentry *dentry, const char *req_xattr_name, + const char *req_xattr_value, size_t req_xattr_value_len, + char type, struct evm_digest *data) +{ + return evm_calc_hmac_or_hash(dentry, req_xattr_name, req_xattr_value, + req_xattr_value_len, type, data); +} + +static int evm_is_immutable(struct dentry *dentry, struct inode *inode) +{ + const struct evm_ima_xattr_data *xattr_data = NULL; + struct integrity_iint_cache *iint; + int rc = 0; + + iint = integrity_iint_find(inode); + if (iint && (iint->flags & EVM_IMMUTABLE_DIGSIG)) + return 1; + + /* Do this the hard way */ + rc = vfs_getxattr_alloc(&init_user_ns, dentry, XATTR_NAME_EVM, + (char **)&xattr_data, 0, GFP_NOFS); + if (rc <= 0) { + if (rc == -ENODATA) + return 0; + return rc; + } + if (xattr_data->type == EVM_XATTR_PORTABLE_DIGSIG) + rc = 1; + else + rc = 0; + + kfree(xattr_data); + return rc; +} + + +/* + * Calculate the hmac and update security.evm xattr + * + * Expects to be called with i_mutex locked. + */ +int evm_update_evmxattr(struct dentry *dentry, const char *xattr_name, + const char *xattr_value, size_t xattr_value_len) +{ + struct inode *inode = d_backing_inode(dentry); + struct evm_digest data; + int rc = 0; + + /* + * Don't permit any transformation of the EVM xattr if the signature + * is of an immutable type + */ + rc = evm_is_immutable(dentry, inode); + if (rc < 0) + return rc; + if (rc) + return -EPERM; + + data.hdr.algo = HASH_ALGO_SHA1; + rc = evm_calc_hmac(dentry, xattr_name, xattr_value, + xattr_value_len, &data); + if (rc == 0) { + data.hdr.xattr.sha1.type = EVM_XATTR_HMAC; + rc = __vfs_setxattr_noperm(&init_user_ns, dentry, + XATTR_NAME_EVM, + &data.hdr.xattr.data[1], + SHA1_DIGEST_SIZE + 1, 0); + } else if (rc == -ENODATA && (inode->i_opflags & IOP_XATTR)) { + rc = __vfs_removexattr(&init_user_ns, dentry, XATTR_NAME_EVM); + } + return rc; +} + +int evm_init_hmac(struct inode *inode, const struct xattr *lsm_xattr, + char *hmac_val) +{ + struct shash_desc *desc; + + desc = init_desc(EVM_XATTR_HMAC, HASH_ALGO_SHA1); + if (IS_ERR(desc)) { + pr_info("init_desc failed\n"); + return PTR_ERR(desc); + } + + crypto_shash_update(desc, lsm_xattr->value, lsm_xattr->value_len); + hmac_add_misc(desc, inode, EVM_XATTR_HMAC, hmac_val); + kfree(desc); + return 0; +} + +/* + * Get the key from the TPM for the SHA1-HMAC + */ +int evm_init_key(void) +{ + struct key *evm_key; + struct encrypted_key_payload *ekp; + int rc; + + evm_key = request_key(&key_type_encrypted, EVMKEY, NULL); + if (IS_ERR(evm_key)) + return -ENOENT; + + down_read(&evm_key->sem); + ekp = evm_key->payload.data[0]; + + rc = evm_set_key(ekp->decrypted_data, ekp->decrypted_datalen); + + /* burn the original key contents */ + memset(ekp->decrypted_data, 0, ekp->decrypted_datalen); + up_read(&evm_key->sem); + key_put(evm_key); + return rc; +} |