1/*
  2 * linux/fs/ext4/crypto_key.c
  3 *
  4 * Copyright (C) 2015, Google, Inc.
  5 *
  6 * This contains encryption key functions for ext4
  7 *
  8 * Written by Michael Halcrow, Ildar Muslukhov, and Uday Savagaonkar, 2015.
  9 */
 10
 11#include <crypto/skcipher.h>
 12#include <keys/encrypted-type.h>
 13#include <keys/user-type.h>
 14#include <linux/random.h>
 15#include <linux/scatterlist.h>
 16#include <uapi/linux/keyctl.h>
 17
 18#include "ext4.h"
 19#include "xattr.h"
 20
 21static void derive_crypt_complete(struct crypto_async_request *req, int rc)
 22{
 23	struct ext4_completion_result *ecr = req->data;
 24
 25	if (rc == -EINPROGRESS)
 26		return;
 27
 28	ecr->res = rc;
 29	complete(&ecr->completion);
 30}
 31
 32/**
 33 * ext4_derive_key_aes() - Derive a key using AES-128-ECB
 34 * @deriving_key: Encryption key used for derivation.
 35 * @source_key:   Source key to which to apply derivation.
 36 * @derived_key:  Derived key.
 37 *
 38 * Return: Zero on success; non-zero otherwise.
 39 */
 40static int ext4_derive_key_aes(char deriving_key[EXT4_AES_128_ECB_KEY_SIZE],
 41			       char source_key[EXT4_AES_256_XTS_KEY_SIZE],
 42			       char derived_key[EXT4_AES_256_XTS_KEY_SIZE])
 43{
 44	int res = 0;
 45	struct skcipher_request *req = NULL;
 46	DECLARE_EXT4_COMPLETION_RESULT(ecr);
 47	struct scatterlist src_sg, dst_sg;
 48	struct crypto_skcipher *tfm = crypto_alloc_skcipher("ecb(aes)", 0, 0);
 49
 50	if (IS_ERR(tfm)) {
 51		res = PTR_ERR(tfm);
 52		tfm = NULL;
 53		goto out;
 54	}
 55	crypto_skcipher_set_flags(tfm, CRYPTO_TFM_REQ_WEAK_KEY);
 56	req = skcipher_request_alloc(tfm, GFP_NOFS);
 57	if (!req) {
 58		res = -ENOMEM;
 59		goto out;
 60	}
 61	skcipher_request_set_callback(req,
 62			CRYPTO_TFM_REQ_MAY_BACKLOG | CRYPTO_TFM_REQ_MAY_SLEEP,
 63			derive_crypt_complete, &ecr);
 64	res = crypto_skcipher_setkey(tfm, deriving_key,
 65				     EXT4_AES_128_ECB_KEY_SIZE);
 66	if (res < 0)
 67		goto out;
 68	sg_init_one(&src_sg, source_key, EXT4_AES_256_XTS_KEY_SIZE);
 69	sg_init_one(&dst_sg, derived_key, EXT4_AES_256_XTS_KEY_SIZE);
 70	skcipher_request_set_crypt(req, &src_sg, &dst_sg,
 71				   EXT4_AES_256_XTS_KEY_SIZE, NULL);
 72	res = crypto_skcipher_encrypt(req);
 73	if (res == -EINPROGRESS || res == -EBUSY) {
 74		wait_for_completion(&ecr.completion);
 75		res = ecr.res;
 76	}
 77
 78out:
 79	skcipher_request_free(req);
 80	crypto_free_skcipher(tfm);
 81	return res;
 82}
 83
 84void ext4_free_crypt_info(struct ext4_crypt_info *ci)
 85{
 86	if (!ci)
 87		return;
 88
 89	if (ci->ci_keyring_key)
 90		key_put(ci->ci_keyring_key);
 91	crypto_free_skcipher(ci->ci_ctfm);
 92	kmem_cache_free(ext4_crypt_info_cachep, ci);
 93}
 94
 95void ext4_free_encryption_info(struct inode *inode,
 96			       struct ext4_crypt_info *ci)
 97{
 98	struct ext4_inode_info *ei = EXT4_I(inode);
 99	struct ext4_crypt_info *prev;
100
101	if (ci == NULL)
102		ci = ACCESS_ONCE(ei->i_crypt_info);
103	if (ci == NULL)
104		return;
105	prev = cmpxchg(&ei->i_crypt_info, ci, NULL);
106	if (prev != ci)
107		return;
108
109	ext4_free_crypt_info(ci);
110}
111
112int _ext4_get_encryption_info(struct inode *inode)
113{
114	struct ext4_inode_info *ei = EXT4_I(inode);
115	struct ext4_crypt_info *crypt_info;
116	char full_key_descriptor[EXT4_KEY_DESC_PREFIX_SIZE +
117				 (EXT4_KEY_DESCRIPTOR_SIZE * 2) + 1];
118	struct key *keyring_key = NULL;
119	struct ext4_encryption_key *master_key;
120	struct ext4_encryption_context ctx;
121	const struct user_key_payload *ukp;
122	struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
123	struct crypto_skcipher *ctfm;
124	const char *cipher_str;
125	char raw_key[EXT4_MAX_KEY_SIZE];
126	char mode;
127	int res;
128
129	if (!ext4_read_workqueue) {
130		res = ext4_init_crypto();
131		if (res)
132			return res;
133	}
134
135retry:
136	crypt_info = ACCESS_ONCE(ei->i_crypt_info);
137	if (crypt_info) {
138		if (!crypt_info->ci_keyring_key ||
139		    key_validate(crypt_info->ci_keyring_key) == 0)
140			return 0;
141		ext4_free_encryption_info(inode, crypt_info);
142		goto retry;
143	}
144
145	res = ext4_xattr_get(inode, EXT4_XATTR_INDEX_ENCRYPTION,
146				 EXT4_XATTR_NAME_ENCRYPTION_CONTEXT,
147				 &ctx, sizeof(ctx));
148	if (res < 0) {
149		if (!DUMMY_ENCRYPTION_ENABLED(sbi))
150			return res;
151		ctx.contents_encryption_mode = EXT4_ENCRYPTION_MODE_AES_256_XTS;
152		ctx.filenames_encryption_mode =
153			EXT4_ENCRYPTION_MODE_AES_256_CTS;
154		ctx.flags = 0;
155	} else if (res != sizeof(ctx))
156		return -EINVAL;
157	res = 0;
158
159	crypt_info = kmem_cache_alloc(ext4_crypt_info_cachep, GFP_KERNEL);
160	if (!crypt_info)
161		return -ENOMEM;
162
163	crypt_info->ci_flags = ctx.flags;
164	crypt_info->ci_data_mode = ctx.contents_encryption_mode;
165	crypt_info->ci_filename_mode = ctx.filenames_encryption_mode;
166	crypt_info->ci_ctfm = NULL;
167	crypt_info->ci_keyring_key = NULL;
168	memcpy(crypt_info->ci_master_key, ctx.master_key_descriptor,
169	       sizeof(crypt_info->ci_master_key));
170	if (S_ISREG(inode->i_mode))
171		mode = crypt_info->ci_data_mode;
172	else if (S_ISDIR(inode->i_mode) || S_ISLNK(inode->i_mode))
173		mode = crypt_info->ci_filename_mode;
174	else
175		BUG();
176	switch (mode) {
177	case EXT4_ENCRYPTION_MODE_AES_256_XTS:
178		cipher_str = "xts(aes)";
179		break;
180	case EXT4_ENCRYPTION_MODE_AES_256_CTS:
181		cipher_str = "cts(cbc(aes))";
182		break;
183	default:
184		printk_once(KERN_WARNING
185			    "ext4: unsupported key mode %d (ino %u)\n",
186			    mode, (unsigned) inode->i_ino);
187		res = -ENOKEY;
188		goto out;
189	}
190	if (DUMMY_ENCRYPTION_ENABLED(sbi)) {
191		memset(raw_key, 0x42, EXT4_AES_256_XTS_KEY_SIZE);
192		goto got_key;
193	}
194	memcpy(full_key_descriptor, EXT4_KEY_DESC_PREFIX,
195	       EXT4_KEY_DESC_PREFIX_SIZE);
196	sprintf(full_key_descriptor + EXT4_KEY_DESC_PREFIX_SIZE,
197		"%*phN", EXT4_KEY_DESCRIPTOR_SIZE,
198		ctx.master_key_descriptor);
199	full_key_descriptor[EXT4_KEY_DESC_PREFIX_SIZE +
200			    (2 * EXT4_KEY_DESCRIPTOR_SIZE)] = '\0';
201	keyring_key = request_key(&key_type_logon, full_key_descriptor, NULL);
202	if (IS_ERR(keyring_key)) {
203		res = PTR_ERR(keyring_key);
204		keyring_key = NULL;
205		goto out;
206	}
207	crypt_info->ci_keyring_key = keyring_key;
208	if (keyring_key->type != &key_type_logon) {
209		printk_once(KERN_WARNING
210			    "ext4: key type must be logon\n");
211		res = -ENOKEY;
212		goto out;
213	}
214	down_read(&keyring_key->sem);
215	ukp = user_key_payload(keyring_key);
216	if (ukp->datalen != sizeof(struct ext4_encryption_key)) {
217		res = -EINVAL;
218		up_read(&keyring_key->sem);
219		goto out;
220	}
221	master_key = (struct ext4_encryption_key *)ukp->data;
222	BUILD_BUG_ON(EXT4_AES_128_ECB_KEY_SIZE !=
223		     EXT4_KEY_DERIVATION_NONCE_SIZE);
224	if (master_key->size != EXT4_AES_256_XTS_KEY_SIZE) {
225		printk_once(KERN_WARNING
226			    "ext4: key size incorrect: %d\n",
227			    master_key->size);
228		res = -ENOKEY;
229		up_read(&keyring_key->sem);
230		goto out;
231	}
232	res = ext4_derive_key_aes(ctx.nonce, master_key->raw,
233				  raw_key);
234	up_read(&keyring_key->sem);
235	if (res)
236		goto out;
237got_key:
238	ctfm = crypto_alloc_skcipher(cipher_str, 0, 0);
239	if (!ctfm || IS_ERR(ctfm)) {
240		res = ctfm ? PTR_ERR(ctfm) : -ENOMEM;
241		printk(KERN_DEBUG
242		       "%s: error %d (inode %u) allocating crypto tfm\n",
243		       __func__, res, (unsigned) inode->i_ino);
244		goto out;
245	}
246	crypt_info->ci_ctfm = ctfm;
247	crypto_skcipher_clear_flags(ctfm, ~0);
248	crypto_tfm_set_flags(crypto_skcipher_tfm(ctfm),
249			     CRYPTO_TFM_REQ_WEAK_KEY);
250	res = crypto_skcipher_setkey(ctfm, raw_key,
251				     ext4_encryption_key_size(mode));
252	if (res)
253		goto out;
254	memzero_explicit(raw_key, sizeof(raw_key));
255	if (cmpxchg(&ei->i_crypt_info, NULL, crypt_info) != NULL) {
256		ext4_free_crypt_info(crypt_info);
257		goto retry;
258	}
259	return 0;
260
261out:
262	if (res == -ENOKEY)
263		res = 0;
264	ext4_free_crypt_info(crypt_info);
265	memzero_explicit(raw_key, sizeof(raw_key));
266	return res;
267}
268
269int ext4_has_encryption_key(struct inode *inode)
270{
271	struct ext4_inode_info *ei = EXT4_I(inode);
272
273	return (ei->i_crypt_info != NULL);
274}