fs/crypto/keysetup_v1.c - third_party/kernel - Git at Google

 // SPDX-License-Identifier: GPL-2.0
 /*
  * Key setup for v1 encryption policies
  *
  * Copyright 2015, 2019 Google LLC
  */

 /*
  * This file implements compatibility functions for the original encryption
  * policy version ("v1"), including:
  *
  * - Deriving per-file encryption keys using the AES-128-ECB based KDF
  *   (rather than the new method of using HKDF-SHA512)
  *
  * - Retrieving fscrypt master keys from process-subscribed keyrings
  *   (rather than the new method of using a filesystem-level keyring)
  *
  * - Handling policies with the DIRECT_KEY flag set using a master key table
  *   (rather than the new method of implementing DIRECT_KEY with per-mode keys
  *    managed alongside the master keys in the filesystem-level keyring)
  */

 #include <crypto/algapi.h>
 #include <crypto/skcipher.h>
 #include <keys/user-type.h>
 #include <linux/hashtable.h>
 #include <linux/scatterlist.h>

 #include "fscrypt_private.h"

 /* Table of keys referenced by DIRECT_KEY policies */
 static DEFINE_HASHTABLE(fscrypt_direct_keys, 6); /* 6 bits = 64 buckets */
 static DEFINE_SPINLOCK(fscrypt_direct_keys_lock);

 /*
  * v1 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 with sufficient entropy for each inode.  However, it's
  * nonstandard, non-extensible, doesn't evenly distribute the entropy from the
  * master key, and is trivially reversible: an attacker who compromises a
  * derived key can "decrypt" it to get back to the master key, then derive any
  * other key.  For all new code, use HKDF instead.
  *
  * The master key must be at least as long as the derived key.  If the master
  * key is longer, then only the first 'derived_keysize' bytes are used.
  */
 static int derive_key_aes(const u8 *master_key,
 			  const u8 nonce[FSCRYPT_FILE_NONCE_SIZE],
 			  u8 *derived_key, unsigned int derived_keysize)
 {
 	int res = 0;
 	struct skcipher_request *req = NULL;
 	DECLARE_CRYPTO_WAIT(wait);
 	struct scatterlist src_sg, dst_sg;
 	struct crypto_skcipher *tfm = crypto_alloc_skcipher("ecb(aes)", 0, 0);

 	if (IS_ERR(tfm)) {
 		res = PTR_ERR(tfm);
 		tfm = NULL;
 		goto out;
 	}
 	crypto_skcipher_set_flags(tfm, CRYPTO_TFM_REQ_FORBID_WEAK_KEYS);
 	req = skcipher_request_alloc(tfm, GFP_KERNEL);
 	if (!req) {
 		res = -ENOMEM;
 		goto out;
 	}
 	skcipher_request_set_callback(req,
 			CRYPTO_TFM_REQ_MAY_BACKLOG | CRYPTO_TFM_REQ_MAY_SLEEP,
 			crypto_req_done, &wait);
 	res = crypto_skcipher_setkey(tfm, nonce, FSCRYPT_FILE_NONCE_SIZE);
 	if (res < 0)
 		goto out;

 	sg_init_one(&src_sg, master_key, 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_wait_req(crypto_skcipher_encrypt(req), &wait);
 out:
 	skcipher_request_free(req);
 	crypto_free_skcipher(tfm);
 	return res;
 }

 /*
  * Search the current task's subscribed keyrings for a "logon" key with
  * description prefix:descriptor, and if found acquire a read lock on it and
  * return a pointer to its validated payload in *payload_ret.
  */
 static struct key *
 find_and_lock_process_key(const char *prefix,
 			  const u8 descriptor[FSCRYPT_KEY_DESCRIPTOR_SIZE],
 			  unsigned int min_keysize,
 			  const struct fscrypt_key **payload_ret)
 {
 	char *description;
 	struct key *key;
 	const struct user_key_payload *ukp;
 	const struct fscrypt_key *payload;

 	description = kasprintf(GFP_KERNEL, "%s%*phN", prefix,
 				FSCRYPT_KEY_DESCRIPTOR_SIZE, descriptor);
 	if (!description)
 		return ERR_PTR(-ENOMEM);

 	key = request_key(&key_type_logon, description, NULL);
 	kfree(description);
 	if (IS_ERR(key))
 		return key;

 	down_read(&key->sem);
 	ukp = user_key_payload_locked(key);

 	if (!ukp) /* was the key revoked before we acquired its semaphore? */
 		goto invalid;

 	payload = (const struct fscrypt_key *)ukp->data;

 	if (ukp->datalen != sizeof(struct fscrypt_key) ||
 	    payload->size < 1 || payload->size > FSCRYPT_MAX_KEY_SIZE) {
 		fscrypt_warn(NULL,
 			     "key with description '%s' has invalid payload",
 			     key->description);
 		goto invalid;
 	}

 	if (payload->size < min_keysize) {
 		fscrypt_warn(NULL,
 			     "key with description '%s' is too short (got %u bytes, need %u+ bytes)",
 			     key->description, payload->size, min_keysize);
 		goto invalid;
 	}

 	*payload_ret = payload;
 	return key;

 invalid:
 	up_read(&key->sem);
 	key_put(key);
 	return ERR_PTR(-ENOKEY);
 }

 /* Master key referenced by DIRECT_KEY policy */
 struct fscrypt_direct_key {
 	struct super_block		*dk_sb;
 	struct hlist_node		dk_node;
 	refcount_t			dk_refcount;
 	const struct fscrypt_mode	*dk_mode;
 	struct fscrypt_prepared_key	dk_key;
 	u8				dk_descriptor[FSCRYPT_KEY_DESCRIPTOR_SIZE];
 	u8				dk_raw[FSCRYPT_MAX_KEY_SIZE];
 };

 static void free_direct_key(struct fscrypt_direct_key *dk)
 {
 	if (dk) {
 		fscrypt_destroy_prepared_key(dk->dk_sb, &dk->dk_key);
 		kfree_sensitive(dk);
 	}
 }

 void fscrypt_put_direct_key(struct fscrypt_direct_key *dk)
 {
 	if (!refcount_dec_and_lock(&dk->dk_refcount, &fscrypt_direct_keys_lock))
 		return;
 	hash_del(&dk->dk_node);
 	spin_unlock(&fscrypt_direct_keys_lock);

 	free_direct_key(dk);
 }

 /*
  * Find/insert the given key into the fscrypt_direct_keys table.  If found, it
  * is returned with elevated refcount, and 'to_insert' is freed if non-NULL.  If
  * not found, 'to_insert' is inserted and returned if it's non-NULL; otherwise
  * NULL is returned.
  */
 static struct fscrypt_direct_key *
 find_or_insert_direct_key(struct fscrypt_direct_key *to_insert,
 			  const u8 *raw_key, const struct fscrypt_info *ci)
 {
 	unsigned long hash_key;
 	struct fscrypt_direct_key *dk;

 	/*
 	 * Careful: to avoid potentially leaking secret key bytes via timing
 	 * information, we must key the hash table by descriptor rather than by
 	 * raw key, and use crypto_memneq() when comparing raw keys.
 	 */

 	BUILD_BUG_ON(sizeof(hash_key) > FSCRYPT_KEY_DESCRIPTOR_SIZE);
 	memcpy(&hash_key, ci->ci_policy.v1.master_key_descriptor,
 	       sizeof(hash_key));

 	spin_lock(&fscrypt_direct_keys_lock);
 	hash_for_each_possible(fscrypt_direct_keys, dk, dk_node, hash_key) {
 		if (memcmp(ci->ci_policy.v1.master_key_descriptor,
 			   dk->dk_descriptor, FSCRYPT_KEY_DESCRIPTOR_SIZE) != 0)
 			continue;
 		if (ci->ci_mode != dk->dk_mode)
 			continue;
 		if (!fscrypt_is_key_prepared(&dk->dk_key, ci))
 			continue;
 		if (crypto_memneq(raw_key, dk->dk_raw, ci->ci_mode->keysize))
 			continue;
 		/* using existing tfm with same (descriptor, mode, raw_key) */
 		refcount_inc(&dk->dk_refcount);
 		spin_unlock(&fscrypt_direct_keys_lock);
 		free_direct_key(to_insert);
 		return dk;
 	}
 	if (to_insert)
 		hash_add(fscrypt_direct_keys, &to_insert->dk_node, hash_key);
 	spin_unlock(&fscrypt_direct_keys_lock);
 	return to_insert;
 }

 /* Prepare to encrypt directly using the master key in the given mode */
 static struct fscrypt_direct_key *
 fscrypt_get_direct_key(const struct fscrypt_info *ci, const u8 *raw_key)
 {
 	struct fscrypt_direct_key *dk;
 	int err;

 	/* Is there already a tfm for this key? */
 	dk = find_or_insert_direct_key(NULL, raw_key, ci);
 	if (dk)
 		return dk;

 	/* Nope, allocate one. */
 	dk = kzalloc(sizeof(*dk), GFP_KERNEL);
 	if (!dk)
 		return ERR_PTR(-ENOMEM);
 	dk->dk_sb = ci->ci_inode->i_sb;
 	refcount_set(&dk->dk_refcount, 1);
 	dk->dk_mode = ci->ci_mode;
 	err = fscrypt_prepare_key(&dk->dk_key, raw_key, ci);
 	if (err)
 		goto err_free_dk;
 	memcpy(dk->dk_descriptor, ci->ci_policy.v1.master_key_descriptor,
 	       FSCRYPT_KEY_DESCRIPTOR_SIZE);
 	memcpy(dk->dk_raw, raw_key, ci->ci_mode->keysize);

 	return find_or_insert_direct_key(dk, raw_key, ci);

 err_free_dk:
 	free_direct_key(dk);
 	return ERR_PTR(err);
 }

 /* v1 policy, DIRECT_KEY: use the master key directly */
 static int setup_v1_file_key_direct(struct fscrypt_info *ci,
 				    const u8 *raw_master_key)
 {
 	struct fscrypt_direct_key *dk;

 	dk = fscrypt_get_direct_key(ci, raw_master_key);
 	if (IS_ERR(dk))
 		return PTR_ERR(dk);
 	ci->ci_direct_key = dk;
 	ci->ci_enc_key = dk->dk_key;
 	return 0;
 }

 /* v1 policy, !DIRECT_KEY: derive the file's encryption key */
 static int setup_v1_file_key_derived(struct fscrypt_info *ci,
 				     const u8 *raw_master_key)
 {
 	u8 *derived_key;
 	int err;

 	/*
 	 * This cannot be a stack buffer because it will be passed to the
 	 * scatterlist crypto API during derive_key_aes().
 	 */
 	derived_key = kmalloc(ci->ci_mode->keysize, GFP_KERNEL);
 	if (!derived_key)
 		return -ENOMEM;

 	err = derive_key_aes(raw_master_key, ci->ci_nonce,
 			     derived_key, ci->ci_mode->keysize);
 	if (err)
 		goto out;

 	err = fscrypt_set_per_file_enc_key(ci, derived_key);
 out:
 	kfree_sensitive(derived_key);
 	return err;
 }

 int fscrypt_setup_v1_file_key(struct fscrypt_info *ci, const u8 *raw_master_key)
 {
 	if (ci->ci_policy.v1.flags & FSCRYPT_POLICY_FLAG_DIRECT_KEY)
 		return setup_v1_file_key_direct(ci, raw_master_key);
 	else
 		return setup_v1_file_key_derived(ci, raw_master_key);
 }

 int fscrypt_setup_v1_file_key_via_subscribed_keyrings(struct fscrypt_info *ci)
 {
 	struct key *key;
 	const struct fscrypt_key *payload;
 	int err;

 	key = find_and_lock_process_key(FSCRYPT_KEY_DESC_PREFIX,
 					ci->ci_policy.v1.master_key_descriptor,
 					ci->ci_mode->keysize, &payload);
 	if (key == ERR_PTR(-ENOKEY) && ci->ci_inode->i_sb->s_cop->key_prefix) {
 		key = find_and_lock_process_key(ci->ci_inode->i_sb->s_cop->key_prefix,
 						ci->ci_policy.v1.master_key_descriptor,
 						ci->ci_mode->keysize, &payload);
 	}
 	if (IS_ERR(key))
 		return PTR_ERR(key);

 	err = fscrypt_setup_v1_file_key(ci, payload->raw);
 	up_read(&key->sem);
 	key_put(key);
 	return err;
 }
	// SPDX-License-Identifier: GPL-2.0
	/*
	* Key setup for v1 encryption policies
	*
	* Copyright 2015, 2019 Google LLC
	*/

	/*
	* This file implements compatibility functions for the original encryption
	* policy version ("v1"), including:
	*
	* - Deriving per-file encryption keys using the AES-128-ECB based KDF
	* (rather than the new method of using HKDF-SHA512)
	*
	* - Retrieving fscrypt master keys from process-subscribed keyrings
	* (rather than the new method of using a filesystem-level keyring)
	*
	* - Handling policies with the DIRECT_KEY flag set using a master key table
	* (rather than the new method of implementing DIRECT_KEY with per-mode keys
	* managed alongside the master keys in the filesystem-level keyring)
	*/

	#include <crypto/algapi.h>
	#include <crypto/skcipher.h>
	#include <keys/user-type.h>
	#include <linux/hashtable.h>
	#include <linux/scatterlist.h>

	#include "fscrypt_private.h"

	/* Table of keys referenced by DIRECT_KEY policies */
	static DEFINE_HASHTABLE(fscrypt_direct_keys, 6); /* 6 bits = 64 buckets */
	static DEFINE_SPINLOCK(fscrypt_direct_keys_lock);

	/*
	* v1 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 with sufficient entropy for each inode. However, it's
	* nonstandard, non-extensible, doesn't evenly distribute the entropy from the
	* master key, and is trivially reversible: an attacker who compromises a
	* derived key can "decrypt" it to get back to the master key, then derive any
	* other key. For all new code, use HKDF instead.
	*
	* The master key must be at least as long as the derived key. If the master
	* key is longer, then only the first 'derived_keysize' bytes are used.
	*/
	static int derive_key_aes(const u8 *master_key,
	const u8 nonce[FSCRYPT_FILE_NONCE_SIZE],
	u8 *derived_key, unsigned int derived_keysize)
	{
	int res = 0;
	struct skcipher_request *req = NULL;
	DECLARE_CRYPTO_WAIT(wait);
	struct scatterlist src_sg, dst_sg;
	struct crypto_skcipher *tfm = crypto_alloc_skcipher("ecb(aes)", 0, 0);

	if (IS_ERR(tfm)) {
	res = PTR_ERR(tfm);
	tfm = NULL;
	goto out;
	}
	crypto_skcipher_set_flags(tfm, CRYPTO_TFM_REQ_FORBID_WEAK_KEYS);
	req = skcipher_request_alloc(tfm, GFP_KERNEL);
	if (!req) {
	res = -ENOMEM;
	goto out;
	}
	skcipher_request_set_callback(req,
	CRYPTO_TFM_REQ_MAY_BACKLOG \| CRYPTO_TFM_REQ_MAY_SLEEP,
	crypto_req_done, &wait);
	res = crypto_skcipher_setkey(tfm, nonce, FSCRYPT_FILE_NONCE_SIZE);
	if (res < 0)
	goto out;

	sg_init_one(&src_sg, master_key, 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_wait_req(crypto_skcipher_encrypt(req), &wait);
	out:
	skcipher_request_free(req);
	crypto_free_skcipher(tfm);
	return res;
	}

	/*
	* Search the current task's subscribed keyrings for a "logon" key with
	* description prefix:descriptor, and if found acquire a read lock on it and
	* return a pointer to its validated payload in *payload_ret.
	*/
	static struct key *
	find_and_lock_process_key(const char *prefix,
	const u8 descriptor[FSCRYPT_KEY_DESCRIPTOR_SIZE],
	unsigned int min_keysize,
	const struct fscrypt_key **payload_ret)
	{
	char *description;
	struct key *key;
	const struct user_key_payload *ukp;
	const struct fscrypt_key *payload;

	description = kasprintf(GFP_KERNEL, "%s%*phN", prefix,
	FSCRYPT_KEY_DESCRIPTOR_SIZE, descriptor);
	if (!description)
	return ERR_PTR(-ENOMEM);

	key = request_key(&key_type_logon, description, NULL);
	kfree(description);
	if (IS_ERR(key))
	return key;

	down_read(&key->sem);
	ukp = user_key_payload_locked(key);

	if (!ukp) /* was the key revoked before we acquired its semaphore? */
	goto invalid;

	payload = (const struct fscrypt_key *)ukp->data;

	if (ukp->datalen != sizeof(struct fscrypt_key) \|\|
	payload->size < 1 \|\| payload->size > FSCRYPT_MAX_KEY_SIZE) {
	fscrypt_warn(NULL,
	"key with description '%s' has invalid payload",
	key->description);
	goto invalid;
	}

	if (payload->size < min_keysize) {
	fscrypt_warn(NULL,
	"key with description '%s' is too short (got %u bytes, need %u+ bytes)",
	key->description, payload->size, min_keysize);
	goto invalid;
	}

	*payload_ret = payload;
	return key;

	invalid:
	up_read(&key->sem);
	key_put(key);
	return ERR_PTR(-ENOKEY);
	}

	/* Master key referenced by DIRECT_KEY policy */
	struct fscrypt_direct_key {
	struct super_block *dk_sb;
	struct hlist_node dk_node;
	refcount_t dk_refcount;
	const struct fscrypt_mode *dk_mode;
	struct fscrypt_prepared_key dk_key;
	u8 dk_descriptor[FSCRYPT_KEY_DESCRIPTOR_SIZE];
	u8 dk_raw[FSCRYPT_MAX_KEY_SIZE];
	};

	static void free_direct_key(struct fscrypt_direct_key *dk)
	{
	if (dk) {
	fscrypt_destroy_prepared_key(dk->dk_sb, &dk->dk_key);
	kfree_sensitive(dk);
	}
	}

	void fscrypt_put_direct_key(struct fscrypt_direct_key *dk)
	{
	if (!refcount_dec_and_lock(&dk->dk_refcount, &fscrypt_direct_keys_lock))
	return;
	hash_del(&dk->dk_node);
	spin_unlock(&fscrypt_direct_keys_lock);

	free_direct_key(dk);
	}

	/*
	* Find/insert the given key into the fscrypt_direct_keys table. If found, it
	* is returned with elevated refcount, and 'to_insert' is freed if non-NULL. If
	* not found, 'to_insert' is inserted and returned if it's non-NULL; otherwise
	* NULL is returned.
	*/
	static struct fscrypt_direct_key *
	find_or_insert_direct_key(struct fscrypt_direct_key *to_insert,
	const u8 raw_key, const struct fscrypt_info ci)
	{
	unsigned long hash_key;
	struct fscrypt_direct_key *dk;

	/*
	* Careful: to avoid potentially leaking secret key bytes via timing
	* information, we must key the hash table by descriptor rather than by
	* raw key, and use crypto_memneq() when comparing raw keys.
	*/

	BUILD_BUG_ON(sizeof(hash_key) > FSCRYPT_KEY_DESCRIPTOR_SIZE);
	memcpy(&hash_key, ci->ci_policy.v1.master_key_descriptor,
	sizeof(hash_key));

	spin_lock(&fscrypt_direct_keys_lock);
	hash_for_each_possible(fscrypt_direct_keys, dk, dk_node, hash_key) {
	if (memcmp(ci->ci_policy.v1.master_key_descriptor,
	dk->dk_descriptor, FSCRYPT_KEY_DESCRIPTOR_SIZE) != 0)
	continue;
	if (ci->ci_mode != dk->dk_mode)
	continue;
	if (!fscrypt_is_key_prepared(&dk->dk_key, ci))
	continue;
	if (crypto_memneq(raw_key, dk->dk_raw, ci->ci_mode->keysize))
	continue;
	/* using existing tfm with same (descriptor, mode, raw_key) */
	refcount_inc(&dk->dk_refcount);
	spin_unlock(&fscrypt_direct_keys_lock);
	free_direct_key(to_insert);
	return dk;
	}
	if (to_insert)
	hash_add(fscrypt_direct_keys, &to_insert->dk_node, hash_key);
	spin_unlock(&fscrypt_direct_keys_lock);
	return to_insert;
	}

	/* Prepare to encrypt directly using the master key in the given mode */
	static struct fscrypt_direct_key *
	fscrypt_get_direct_key(const struct fscrypt_info ci, const u8 raw_key)
	{
	struct fscrypt_direct_key *dk;
	int err;

	/* Is there already a tfm for this key? */
	dk = find_or_insert_direct_key(NULL, raw_key, ci);
	if (dk)
	return dk;

	/* Nope, allocate one. */
	dk = kzalloc(sizeof(*dk), GFP_KERNEL);
	if (!dk)
	return ERR_PTR(-ENOMEM);
	dk->dk_sb = ci->ci_inode->i_sb;
	refcount_set(&dk->dk_refcount, 1);
	dk->dk_mode = ci->ci_mode;
	err = fscrypt_prepare_key(&dk->dk_key, raw_key, ci);
	if (err)
	goto err_free_dk;
	memcpy(dk->dk_descriptor, ci->ci_policy.v1.master_key_descriptor,
	FSCRYPT_KEY_DESCRIPTOR_SIZE);
	memcpy(dk->dk_raw, raw_key, ci->ci_mode->keysize);

	return find_or_insert_direct_key(dk, raw_key, ci);

	err_free_dk:
	free_direct_key(dk);
	return ERR_PTR(err);
	}

	/* v1 policy, DIRECT_KEY: use the master key directly */
	static int setup_v1_file_key_direct(struct fscrypt_info *ci,
	const u8 *raw_master_key)
	{
	struct fscrypt_direct_key *dk;

	dk = fscrypt_get_direct_key(ci, raw_master_key);
	if (IS_ERR(dk))
	return PTR_ERR(dk);
	ci->ci_direct_key = dk;
	ci->ci_enc_key = dk->dk_key;
	return 0;
	}

	/* v1 policy, !DIRECT_KEY: derive the file's encryption key */
	static int setup_v1_file_key_derived(struct fscrypt_info *ci,
	const u8 *raw_master_key)
	{
	u8 *derived_key;
	int err;

	/*
	* This cannot be a stack buffer because it will be passed to the
	* scatterlist crypto API during derive_key_aes().
	*/
	derived_key = kmalloc(ci->ci_mode->keysize, GFP_KERNEL);
	if (!derived_key)
	return -ENOMEM;

	err = derive_key_aes(raw_master_key, ci->ci_nonce,
	derived_key, ci->ci_mode->keysize);
	if (err)
	goto out;

	err = fscrypt_set_per_file_enc_key(ci, derived_key);
	out:
	kfree_sensitive(derived_key);
	return err;
	}

	int fscrypt_setup_v1_file_key(struct fscrypt_info ci, const u8 raw_master_key)
	{
	if (ci->ci_policy.v1.flags & FSCRYPT_POLICY_FLAG_DIRECT_KEY)
	return setup_v1_file_key_direct(ci, raw_master_key);
	else
	return setup_v1_file_key_derived(ci, raw_master_key);
	}

	int fscrypt_setup_v1_file_key_via_subscribed_keyrings(struct fscrypt_info *ci)
	{
	struct key *key;
	const struct fscrypt_key *payload;
	int err;

	key = find_and_lock_process_key(FSCRYPT_KEY_DESC_PREFIX,
	ci->ci_policy.v1.master_key_descriptor,
	ci->ci_mode->keysize, &payload);
	if (key == ERR_PTR(-ENOKEY) && ci->ci_inode->i_sb->s_cop->key_prefix) {
	key = find_and_lock_process_key(ci->ci_inode->i_sb->s_cop->key_prefix,
	ci->ci_policy.v1.master_key_descriptor,
	ci->ci_mode->keysize, &payload);
	}
	if (IS_ERR(key))
	return PTR_ERR(key);

	err = fscrypt_setup_v1_file_key(ci, payload->raw);
	up_read(&key->sem);
	key_put(key);
	return err;
	}