text: // 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
   */
  
  #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;
  
  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;
  	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 == NULL) {
  		mutex_lock(&mutex);
  		if (*tfm)
  			goto out;
  		*tfm = crypto_alloc_shash(algo, 0, CRYPTO_NOLOAD);
  		if (IS_ERR(*tfm)) {
  			rc = PTR_ERR(*tfm);
  			pr_err("Can not allocate %s (reason: %ld)\n", algo, rc);
  			*tfm = NULL;
  			mutex_unlock(&mutex);
  			return ERR_PTR(rc);
  		}
  		if (type == EVM_XATTR_HMAC) {
  			rc = crypto_shash_setkey(*tfm, evmkey, evmkey_len);
  			if (rc) {
  				crypto_free_shash(*tfm);
  				*tfm = NULL;
  				mutex_unlock(&mutex);
  				return ERR_PTR(rc);
  			}
  		}
  out:
  		mutex_unlock(&mutex);
  	}
  
  	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);
  }
  
  /*
   * 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;
  	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_rcu(xattr, &evm_config_xattrnames, list) {
  		bool is_ima = false;
  
  		if (strcmp(xattr->name, XATTR_NAME_IMA) == 0)
  			is_ima = true;
  
  		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;
  			continue;
  		}
  		size = vfs_getxattr_alloc(dentry, xattr->name,
  					  &xattr_value, xattr_size, GFP_NOFS);
  		if (size == -ENOMEM) {
  			error = -ENOMEM;
  			goto out;
  		}
  		if (size < 0)
  			continue;
  
  		error = 0;
  		xattr_size = size;
  		crypto_shash_update(desc, (const u8 *)xattr_value, xattr_size);
  		if (is_ima)
  			ima_present = true;
  	}
  	hmac_add_misc(desc, inode, type, data->digest);
  
  	/* Portable EVM signatures must include an IMA hash */
  	if (type == EVM_XATTR_PORTABLE_DIGSIG && !ima_present)
  		return -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(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(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(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;
  }
  