| // 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 |
| * @size: 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; |
| } |