1 // SPDX-License-Identifier: GPL-2.0
2 /*
3  * Inline encryption support for fscrypt
4  *
5  * Copyright 2019 Google LLC
6  */
7 
8 /*
9  * With "inline encryption", the block layer handles the decryption/encryption
10  * as part of the bio, instead of the filesystem doing the crypto itself via
11  * crypto API.  See Documentation/block/inline-encryption.rst.  fscrypt still
12  * provides the key and IV to use.
13  */
14 
15 #include <linux/blk-crypto.h>
16 #include <linux/blkdev.h>
17 #include <linux/buffer_head.h>
18 #include <linux/sched/mm.h>
19 #include <linux/slab.h>
20 
21 #include "fscrypt_private.h"
22 
23 struct fscrypt_blk_crypto_key {
24 	struct blk_crypto_key base;
25 	int num_devs;
26 	struct request_queue *devs[];
27 };
28 
fscrypt_get_num_devices(struct super_block * sb)29 static int fscrypt_get_num_devices(struct super_block *sb)
30 {
31 	if (sb->s_cop->get_num_devices)
32 		return sb->s_cop->get_num_devices(sb);
33 	return 1;
34 }
35 
fscrypt_get_devices(struct super_block * sb,int num_devs,struct request_queue ** devs)36 static void fscrypt_get_devices(struct super_block *sb, int num_devs,
37 				struct request_queue **devs)
38 {
39 	if (num_devs == 1)
40 		devs[0] = bdev_get_queue(sb->s_bdev);
41 	else
42 		sb->s_cop->get_devices(sb, devs);
43 }
44 
fscrypt_get_dun_bytes(const struct fscrypt_info * ci)45 static unsigned int fscrypt_get_dun_bytes(const struct fscrypt_info *ci)
46 {
47 	struct super_block *sb = ci->ci_inode->i_sb;
48 	unsigned int flags = fscrypt_policy_flags(&ci->ci_policy);
49 	int ino_bits = 64, lblk_bits = 64;
50 
51 	if (flags & FSCRYPT_POLICY_FLAG_DIRECT_KEY)
52 		return offsetofend(union fscrypt_iv, nonce);
53 
54 	if (flags & FSCRYPT_POLICY_FLAG_IV_INO_LBLK_64)
55 		return sizeof(__le64);
56 
57 	if (flags & FSCRYPT_POLICY_FLAG_IV_INO_LBLK_32)
58 		return sizeof(__le32);
59 
60 	/* Default case: IVs are just the file logical block number */
61 	if (sb->s_cop->get_ino_and_lblk_bits)
62 		sb->s_cop->get_ino_and_lblk_bits(sb, &ino_bits, &lblk_bits);
63 	return DIV_ROUND_UP(lblk_bits, 8);
64 }
65 
66 /* Enable inline encryption for this file if supported. */
fscrypt_select_encryption_impl(struct fscrypt_info * ci)67 int fscrypt_select_encryption_impl(struct fscrypt_info *ci)
68 {
69 	const struct inode *inode = ci->ci_inode;
70 	struct super_block *sb = inode->i_sb;
71 	struct blk_crypto_config crypto_cfg;
72 	int num_devs;
73 	struct request_queue **devs;
74 	int i;
75 
76 	/* The file must need contents encryption, not filenames encryption */
77 	if (!S_ISREG(inode->i_mode))
78 		return 0;
79 
80 	/* The crypto mode must have a blk-crypto counterpart */
81 	if (ci->ci_mode->blk_crypto_mode == BLK_ENCRYPTION_MODE_INVALID)
82 		return 0;
83 
84 	/* The filesystem must be mounted with -o inlinecrypt */
85 	if (!(sb->s_flags & SB_INLINECRYPT))
86 		return 0;
87 
88 	/*
89 	 * When a page contains multiple logically contiguous filesystem blocks,
90 	 * some filesystem code only calls fscrypt_mergeable_bio() for the first
91 	 * block in the page. This is fine for most of fscrypt's IV generation
92 	 * strategies, where contiguous blocks imply contiguous IVs. But it
93 	 * doesn't work with IV_INO_LBLK_32. For now, simply exclude
94 	 * IV_INO_LBLK_32 with blocksize != PAGE_SIZE from inline encryption.
95 	 */
96 	if ((fscrypt_policy_flags(&ci->ci_policy) &
97 	     FSCRYPT_POLICY_FLAG_IV_INO_LBLK_32) &&
98 	    sb->s_blocksize != PAGE_SIZE)
99 		return 0;
100 
101 	/*
102 	 * On all the filesystem's devices, blk-crypto must support the crypto
103 	 * configuration that the file would use.
104 	 */
105 	crypto_cfg.crypto_mode = ci->ci_mode->blk_crypto_mode;
106 	crypto_cfg.data_unit_size = sb->s_blocksize;
107 	crypto_cfg.dun_bytes = fscrypt_get_dun_bytes(ci);
108 	num_devs = fscrypt_get_num_devices(sb);
109 	devs = kmalloc_array(num_devs, sizeof(*devs), GFP_KERNEL);
110 	if (!devs)
111 		return -ENOMEM;
112 	fscrypt_get_devices(sb, num_devs, devs);
113 
114 	for (i = 0; i < num_devs; i++) {
115 		if (!blk_crypto_config_supported(devs[i], &crypto_cfg))
116 			goto out_free_devs;
117 	}
118 
119 	ci->ci_inlinecrypt = true;
120 out_free_devs:
121 	kfree(devs);
122 
123 	return 0;
124 }
125 
fscrypt_prepare_inline_crypt_key(struct fscrypt_prepared_key * prep_key,const u8 * raw_key,const struct fscrypt_info * ci)126 int fscrypt_prepare_inline_crypt_key(struct fscrypt_prepared_key *prep_key,
127 				     const u8 *raw_key,
128 				     const struct fscrypt_info *ci)
129 {
130 	const struct inode *inode = ci->ci_inode;
131 	struct super_block *sb = inode->i_sb;
132 	enum blk_crypto_mode_num crypto_mode = ci->ci_mode->blk_crypto_mode;
133 	int num_devs = fscrypt_get_num_devices(sb);
134 	int queue_refs = 0;
135 	struct fscrypt_blk_crypto_key *blk_key;
136 	int err;
137 	int i;
138 
139 	blk_key = kzalloc(struct_size(blk_key, devs, num_devs), GFP_KERNEL);
140 	if (!blk_key)
141 		return -ENOMEM;
142 
143 	blk_key->num_devs = num_devs;
144 	fscrypt_get_devices(sb, num_devs, blk_key->devs);
145 
146 	err = blk_crypto_init_key(&blk_key->base, raw_key, crypto_mode,
147 				  fscrypt_get_dun_bytes(ci), sb->s_blocksize);
148 	if (err) {
149 		fscrypt_err(inode, "error %d initializing blk-crypto key", err);
150 		goto fail;
151 	}
152 
153 	/*
154 	 * We have to start using blk-crypto on all the filesystem's devices.
155 	 * We also have to save all the request_queue's for later so that the
156 	 * key can be evicted from them.  This is needed because some keys
157 	 * aren't destroyed until after the filesystem was already unmounted
158 	 * (namely, the per-mode keys in struct fscrypt_master_key).
159 	 */
160 	for (i = 0; i < num_devs; i++) {
161 		if (!blk_get_queue(blk_key->devs[i])) {
162 			fscrypt_err(inode, "couldn't get request_queue");
163 			err = -EAGAIN;
164 			goto fail;
165 		}
166 		queue_refs++;
167 
168 		err = blk_crypto_start_using_key(&blk_key->base,
169 						 blk_key->devs[i]);
170 		if (err) {
171 			fscrypt_err(inode,
172 				    "error %d starting to use blk-crypto", err);
173 			goto fail;
174 		}
175 	}
176 	/*
177 	 * Pairs with the smp_load_acquire() in fscrypt_is_key_prepared().
178 	 * I.e., here we publish ->blk_key with a RELEASE barrier so that
179 	 * concurrent tasks can ACQUIRE it.  Note that this concurrency is only
180 	 * possible for per-mode keys, not for per-file keys.
181 	 */
182 	smp_store_release(&prep_key->blk_key, blk_key);
183 	return 0;
184 
185 fail:
186 	for (i = 0; i < queue_refs; i++)
187 		blk_put_queue(blk_key->devs[i]);
188 	kfree_sensitive(blk_key);
189 	return err;
190 }
191 
fscrypt_destroy_inline_crypt_key(struct fscrypt_prepared_key * prep_key)192 void fscrypt_destroy_inline_crypt_key(struct fscrypt_prepared_key *prep_key)
193 {
194 	struct fscrypt_blk_crypto_key *blk_key = prep_key->blk_key;
195 	int i;
196 
197 	if (blk_key) {
198 		for (i = 0; i < blk_key->num_devs; i++) {
199 			blk_crypto_evict_key(blk_key->devs[i], &blk_key->base);
200 			blk_put_queue(blk_key->devs[i]);
201 		}
202 		kfree_sensitive(blk_key);
203 	}
204 }
205 
__fscrypt_inode_uses_inline_crypto(const struct inode * inode)206 bool __fscrypt_inode_uses_inline_crypto(const struct inode *inode)
207 {
208 	return inode->i_crypt_info->ci_inlinecrypt;
209 }
210 EXPORT_SYMBOL_GPL(__fscrypt_inode_uses_inline_crypto);
211 
fscrypt_generate_dun(const struct fscrypt_info * ci,u64 lblk_num,u64 dun[BLK_CRYPTO_DUN_ARRAY_SIZE])212 static void fscrypt_generate_dun(const struct fscrypt_info *ci, u64 lblk_num,
213 				 u64 dun[BLK_CRYPTO_DUN_ARRAY_SIZE])
214 {
215 	union fscrypt_iv iv;
216 	int i;
217 
218 	fscrypt_generate_iv(&iv, lblk_num, ci);
219 
220 	BUILD_BUG_ON(FSCRYPT_MAX_IV_SIZE > BLK_CRYPTO_MAX_IV_SIZE);
221 	memset(dun, 0, BLK_CRYPTO_MAX_IV_SIZE);
222 	for (i = 0; i < ci->ci_mode->ivsize/sizeof(dun[0]); i++)
223 		dun[i] = le64_to_cpu(iv.dun[i]);
224 }
225 
226 /**
227  * fscrypt_set_bio_crypt_ctx() - prepare a file contents bio for inline crypto
228  * @bio: a bio which will eventually be submitted to the file
229  * @inode: the file's inode
230  * @first_lblk: the first file logical block number in the I/O
231  * @gfp_mask: memory allocation flags - these must be a waiting mask so that
232  *					bio_crypt_set_ctx can't fail.
233  *
234  * If the contents of the file should be encrypted (or decrypted) with inline
235  * encryption, then assign the appropriate encryption context to the bio.
236  *
237  * Normally the bio should be newly allocated (i.e. no pages added yet), as
238  * otherwise fscrypt_mergeable_bio() won't work as intended.
239  *
240  * The encryption context will be freed automatically when the bio is freed.
241  */
fscrypt_set_bio_crypt_ctx(struct bio * bio,const struct inode * inode,u64 first_lblk,gfp_t gfp_mask)242 void fscrypt_set_bio_crypt_ctx(struct bio *bio, const struct inode *inode,
243 			       u64 first_lblk, gfp_t gfp_mask)
244 {
245 	const struct fscrypt_info *ci;
246 	u64 dun[BLK_CRYPTO_DUN_ARRAY_SIZE];
247 
248 	if (!fscrypt_inode_uses_inline_crypto(inode))
249 		return;
250 	ci = inode->i_crypt_info;
251 
252 	fscrypt_generate_dun(ci, first_lblk, dun);
253 	bio_crypt_set_ctx(bio, &ci->ci_enc_key.blk_key->base, dun, gfp_mask);
254 }
255 EXPORT_SYMBOL_GPL(fscrypt_set_bio_crypt_ctx);
256 
257 /* Extract the inode and logical block number from a buffer_head. */
bh_get_inode_and_lblk_num(const struct buffer_head * bh,const struct inode ** inode_ret,u64 * lblk_num_ret)258 static bool bh_get_inode_and_lblk_num(const struct buffer_head *bh,
259 				      const struct inode **inode_ret,
260 				      u64 *lblk_num_ret)
261 {
262 	struct page *page = bh->b_page;
263 	const struct address_space *mapping;
264 	const struct inode *inode;
265 
266 	/*
267 	 * The ext4 journal (jbd2) can submit a buffer_head it directly created
268 	 * for a non-pagecache page.  fscrypt doesn't care about these.
269 	 */
270 	mapping = page_mapping(page);
271 	if (!mapping)
272 		return false;
273 	inode = mapping->host;
274 
275 	*inode_ret = inode;
276 	*lblk_num_ret = ((u64)page->index << (PAGE_SHIFT - inode->i_blkbits)) +
277 			(bh_offset(bh) >> inode->i_blkbits);
278 	return true;
279 }
280 
281 /**
282  * fscrypt_set_bio_crypt_ctx_bh() - prepare a file contents bio for inline
283  *				    crypto
284  * @bio: a bio which will eventually be submitted to the file
285  * @first_bh: the first buffer_head for which I/O will be submitted
286  * @gfp_mask: memory allocation flags
287  *
288  * Same as fscrypt_set_bio_crypt_ctx(), except this takes a buffer_head instead
289  * of an inode and block number directly.
290  */
fscrypt_set_bio_crypt_ctx_bh(struct bio * bio,const struct buffer_head * first_bh,gfp_t gfp_mask)291 void fscrypt_set_bio_crypt_ctx_bh(struct bio *bio,
292 				  const struct buffer_head *first_bh,
293 				  gfp_t gfp_mask)
294 {
295 	const struct inode *inode;
296 	u64 first_lblk;
297 
298 	if (bh_get_inode_and_lblk_num(first_bh, &inode, &first_lblk))
299 		fscrypt_set_bio_crypt_ctx(bio, inode, first_lblk, gfp_mask);
300 }
301 EXPORT_SYMBOL_GPL(fscrypt_set_bio_crypt_ctx_bh);
302 
303 /**
304  * fscrypt_mergeable_bio() - test whether data can be added to a bio
305  * @bio: the bio being built up
306  * @inode: the inode for the next part of the I/O
307  * @next_lblk: the next file logical block number in the I/O
308  *
309  * When building a bio which may contain data which should undergo inline
310  * encryption (or decryption) via fscrypt, filesystems should call this function
311  * to ensure that the resulting bio contains only contiguous data unit numbers.
312  * This will return false if the next part of the I/O cannot be merged with the
313  * bio because either the encryption key would be different or the encryption
314  * data unit numbers would be discontiguous.
315  *
316  * fscrypt_set_bio_crypt_ctx() must have already been called on the bio.
317  *
318  * Return: true iff the I/O is mergeable
319  */
fscrypt_mergeable_bio(struct bio * bio,const struct inode * inode,u64 next_lblk)320 bool fscrypt_mergeable_bio(struct bio *bio, const struct inode *inode,
321 			   u64 next_lblk)
322 {
323 	const struct bio_crypt_ctx *bc = bio->bi_crypt_context;
324 	u64 next_dun[BLK_CRYPTO_DUN_ARRAY_SIZE];
325 
326 	if (!!bc != fscrypt_inode_uses_inline_crypto(inode))
327 		return false;
328 	if (!bc)
329 		return true;
330 
331 	/*
332 	 * Comparing the key pointers is good enough, as all I/O for each key
333 	 * uses the same pointer.  I.e., there's currently no need to support
334 	 * merging requests where the keys are the same but the pointers differ.
335 	 */
336 	if (bc->bc_key != &inode->i_crypt_info->ci_enc_key.blk_key->base)
337 		return false;
338 
339 	fscrypt_generate_dun(inode->i_crypt_info, next_lblk, next_dun);
340 	return bio_crypt_dun_is_contiguous(bc, bio->bi_iter.bi_size, next_dun);
341 }
342 EXPORT_SYMBOL_GPL(fscrypt_mergeable_bio);
343 
344 /**
345  * fscrypt_mergeable_bio_bh() - test whether data can be added to a bio
346  * @bio: the bio being built up
347  * @next_bh: the next buffer_head for which I/O will be submitted
348  *
349  * Same as fscrypt_mergeable_bio(), except this takes a buffer_head instead of
350  * an inode and block number directly.
351  *
352  * Return: true iff the I/O is mergeable
353  */
fscrypt_mergeable_bio_bh(struct bio * bio,const struct buffer_head * next_bh)354 bool fscrypt_mergeable_bio_bh(struct bio *bio,
355 			      const struct buffer_head *next_bh)
356 {
357 	const struct inode *inode;
358 	u64 next_lblk;
359 
360 	if (!bh_get_inode_and_lblk_num(next_bh, &inode, &next_lblk))
361 		return !bio->bi_crypt_context;
362 
363 	return fscrypt_mergeable_bio(bio, inode, next_lblk);
364 }
365 EXPORT_SYMBOL_GPL(fscrypt_mergeable_bio_bh);
366