1/*
2 * linux/fs/ext4/crypto.c
3 *
4 * Copyright (C) 2015, Google, Inc.
5 *
6 * This contains encryption functions for ext4
7 *
8 * Written by Michael Halcrow, 2014.
9 *
10 * Filename encryption additions
11 *	Uday Savagaonkar, 2014
12 * Encryption policy handling additions
13 *	Ildar Muslukhov, 2014
14 *
15 * This has not yet undergone a rigorous security audit.
16 *
17 * The usage of AES-XTS should conform to recommendations in NIST
18 * Special Publication 800-38E and IEEE P1619/D16.
19 */
20
21#include <crypto/hash.h>
22#include <crypto/sha.h>
23#include <keys/user-type.h>
24#include <keys/encrypted-type.h>
25#include <linux/crypto.h>
26#include <linux/ecryptfs.h>
27#include <linux/gfp.h>
28#include <linux/kernel.h>
29#include <linux/key.h>
30#include <linux/list.h>
31#include <linux/mempool.h>
32#include <linux/module.h>
33#include <linux/mutex.h>
34#include <linux/random.h>
35#include <linux/scatterlist.h>
36#include <linux/spinlock_types.h>
37
38#include "ext4_extents.h"
39#include "xattr.h"
40
41/* Encryption added and removed here! (L: */
42
43static unsigned int num_prealloc_crypto_pages = 32;
44static unsigned int num_prealloc_crypto_ctxs = 128;
45
46module_param(num_prealloc_crypto_pages, uint, 0444);
47MODULE_PARM_DESC(num_prealloc_crypto_pages,
48		 "Number of crypto pages to preallocate");
49module_param(num_prealloc_crypto_ctxs, uint, 0444);
50MODULE_PARM_DESC(num_prealloc_crypto_ctxs,
51		 "Number of crypto contexts to preallocate");
52
53static mempool_t *ext4_bounce_page_pool;
54
55static LIST_HEAD(ext4_free_crypto_ctxs);
56static DEFINE_SPINLOCK(ext4_crypto_ctx_lock);
57
58/**
59 * ext4_release_crypto_ctx() - Releases an encryption context
60 * @ctx: The encryption context to release.
61 *
62 * If the encryption context was allocated from the pre-allocated pool, returns
63 * it to that pool. Else, frees it.
64 *
65 * If there's a bounce page in the context, this frees that.
66 */
67void ext4_release_crypto_ctx(struct ext4_crypto_ctx *ctx)
68{
69	unsigned long flags;
70
71	if (ctx->bounce_page) {
72		if (ctx->flags & EXT4_BOUNCE_PAGE_REQUIRES_FREE_ENCRYPT_FL)
73			__free_page(ctx->bounce_page);
74		else
75			mempool_free(ctx->bounce_page, ext4_bounce_page_pool);
76		ctx->bounce_page = NULL;
77	}
78	ctx->control_page = NULL;
79	if (ctx->flags & EXT4_CTX_REQUIRES_FREE_ENCRYPT_FL) {
80		if (ctx->tfm)
81			crypto_free_tfm(ctx->tfm);
82		kfree(ctx);
83	} else {
84		spin_lock_irqsave(&ext4_crypto_ctx_lock, flags);
85		list_add(&ctx->free_list, &ext4_free_crypto_ctxs);
86		spin_unlock_irqrestore(&ext4_crypto_ctx_lock, flags);
87	}
88}
89
90/**
91 * ext4_alloc_and_init_crypto_ctx() - Allocates and inits an encryption context
92 * @mask: The allocation mask.
93 *
94 * Return: An allocated and initialized encryption context on success. An error
95 * value or NULL otherwise.
96 */
97static struct ext4_crypto_ctx *ext4_alloc_and_init_crypto_ctx(gfp_t mask)
98{
99	struct ext4_crypto_ctx *ctx = kzalloc(sizeof(struct ext4_crypto_ctx),
100					      mask);
101
102	if (!ctx)
103		return ERR_PTR(-ENOMEM);
104	return ctx;
105}
106
107/**
108 * ext4_get_crypto_ctx() - Gets an encryption context
109 * @inode:       The inode for which we are doing the crypto
110 *
111 * Allocates and initializes an encryption context.
112 *
113 * Return: An allocated and initialized encryption context on success; error
114 * value or NULL otherwise.
115 */
116struct ext4_crypto_ctx *ext4_get_crypto_ctx(struct inode *inode)
117{
118	struct ext4_crypto_ctx *ctx = NULL;
119	int res = 0;
120	unsigned long flags;
121	struct ext4_encryption_key *key = &EXT4_I(inode)->i_encryption_key;
122
123	if (!ext4_read_workqueue)
124		ext4_init_crypto();
125
126	/*
127	 * We first try getting the ctx from a free list because in
128	 * the common case the ctx will have an allocated and
129	 * initialized crypto tfm, so it's probably a worthwhile
130	 * optimization. For the bounce page, we first try getting it
131	 * from the kernel allocator because that's just about as fast
132	 * as getting it from a list and because a cache of free pages
133	 * should generally be a "last resort" option for a filesystem
134	 * to be able to do its job.
135	 */
136	spin_lock_irqsave(&ext4_crypto_ctx_lock, flags);
137	ctx = list_first_entry_or_null(&ext4_free_crypto_ctxs,
138				       struct ext4_crypto_ctx, free_list);
139	if (ctx)
140		list_del(&ctx->free_list);
141	spin_unlock_irqrestore(&ext4_crypto_ctx_lock, flags);
142	if (!ctx) {
143		ctx = ext4_alloc_and_init_crypto_ctx(GFP_NOFS);
144		if (IS_ERR(ctx)) {
145			res = PTR_ERR(ctx);
146			goto out;
147		}
148		ctx->flags |= EXT4_CTX_REQUIRES_FREE_ENCRYPT_FL;
149	} else {
150		ctx->flags &= ~EXT4_CTX_REQUIRES_FREE_ENCRYPT_FL;
151	}
152
153	/* Allocate a new Crypto API context if we don't already have
154	 * one or if it isn't the right mode. */
155	BUG_ON(key->mode == EXT4_ENCRYPTION_MODE_INVALID);
156	if (ctx->tfm && (ctx->mode != key->mode)) {
157		crypto_free_tfm(ctx->tfm);
158		ctx->tfm = NULL;
159		ctx->mode = EXT4_ENCRYPTION_MODE_INVALID;
160	}
161	if (!ctx->tfm) {
162		switch (key->mode) {
163		case EXT4_ENCRYPTION_MODE_AES_256_XTS:
164			ctx->tfm = crypto_ablkcipher_tfm(
165				crypto_alloc_ablkcipher("xts(aes)", 0, 0));
166			break;
167		case EXT4_ENCRYPTION_MODE_AES_256_GCM:
168			/* TODO(mhalcrow): AEAD w/ gcm(aes);
169			 * crypto_aead_setauthsize() */
170			ctx->tfm = ERR_PTR(-ENOTSUPP);
171			break;
172		default:
173			BUG();
174		}
175		if (IS_ERR_OR_NULL(ctx->tfm)) {
176			res = PTR_ERR(ctx->tfm);
177			ctx->tfm = NULL;
178			goto out;
179		}
180		ctx->mode = key->mode;
181	}
182	BUG_ON(key->size != ext4_encryption_key_size(key->mode));
183
184	/* There shouldn't be a bounce page attached to the crypto
185	 * context at this point. */
186	BUG_ON(ctx->bounce_page);
187
188out:
189	if (res) {
190		if (!IS_ERR_OR_NULL(ctx))
191			ext4_release_crypto_ctx(ctx);
192		ctx = ERR_PTR(res);
193	}
194	return ctx;
195}
196
197struct workqueue_struct *ext4_read_workqueue;
198static DEFINE_MUTEX(crypto_init);
199
200/**
201 * ext4_exit_crypto() - Shutdown the ext4 encryption system
202 */
203void ext4_exit_crypto(void)
204{
205	struct ext4_crypto_ctx *pos, *n;
206
207	list_for_each_entry_safe(pos, n, &ext4_free_crypto_ctxs, free_list) {
208		if (pos->bounce_page) {
209			if (pos->flags &
210			    EXT4_BOUNCE_PAGE_REQUIRES_FREE_ENCRYPT_FL) {
211				__free_page(pos->bounce_page);
212			} else {
213				mempool_free(pos->bounce_page,
214					     ext4_bounce_page_pool);
215			}
216		}
217		if (pos->tfm)
218			crypto_free_tfm(pos->tfm);
219		kfree(pos);
220	}
221	INIT_LIST_HEAD(&ext4_free_crypto_ctxs);
222	if (ext4_bounce_page_pool)
223		mempool_destroy(ext4_bounce_page_pool);
224	ext4_bounce_page_pool = NULL;
225	if (ext4_read_workqueue)
226		destroy_workqueue(ext4_read_workqueue);
227	ext4_read_workqueue = NULL;
228}
229
230/**
231 * ext4_init_crypto() - Set up for ext4 encryption.
232 *
233 * We only call this when we start accessing encrypted files, since it
234 * results in memory getting allocated that wouldn't otherwise be used.
235 *
236 * Return: Zero on success, non-zero otherwise.
237 */
238int ext4_init_crypto(void)
239{
240	int i, res;
241
242	mutex_lock(&crypto_init);
243	if (ext4_read_workqueue)
244		goto already_initialized;
245	ext4_read_workqueue = alloc_workqueue("ext4_crypto", WQ_HIGHPRI, 0);
246	if (!ext4_read_workqueue) {
247		res = -ENOMEM;
248		goto fail;
249	}
250
251	for (i = 0; i < num_prealloc_crypto_ctxs; i++) {
252		struct ext4_crypto_ctx *ctx;
253
254		ctx = ext4_alloc_and_init_crypto_ctx(GFP_KERNEL);
255		if (IS_ERR(ctx)) {
256			res = PTR_ERR(ctx);
257			goto fail;
258		}
259		list_add(&ctx->free_list, &ext4_free_crypto_ctxs);
260	}
261
262	ext4_bounce_page_pool =
263		mempool_create_page_pool(num_prealloc_crypto_pages, 0);
264	if (!ext4_bounce_page_pool) {
265		res = -ENOMEM;
266		goto fail;
267	}
268already_initialized:
269	mutex_unlock(&crypto_init);
270	return 0;
271fail:
272	ext4_exit_crypto();
273	mutex_unlock(&crypto_init);
274	return res;
275}
276
277void ext4_restore_control_page(struct page *data_page)
278{
279	struct ext4_crypto_ctx *ctx =
280		(struct ext4_crypto_ctx *)page_private(data_page);
281
282	set_page_private(data_page, (unsigned long)NULL);
283	ClearPagePrivate(data_page);
284	unlock_page(data_page);
285	ext4_release_crypto_ctx(ctx);
286}
287
288/**
289 * ext4_crypt_complete() - The completion callback for page encryption
290 * @req: The asynchronous encryption request context
291 * @res: The result of the encryption operation
292 */
293static void ext4_crypt_complete(struct crypto_async_request *req, int res)
294{
295	struct ext4_completion_result *ecr = req->data;
296
297	if (res == -EINPROGRESS)
298		return;
299	ecr->res = res;
300	complete(&ecr->completion);
301}
302
303typedef enum {
304	EXT4_DECRYPT = 0,
305	EXT4_ENCRYPT,
306} ext4_direction_t;
307
308static int ext4_page_crypto(struct ext4_crypto_ctx *ctx,
309			    struct inode *inode,
310			    ext4_direction_t rw,
311			    pgoff_t index,
312			    struct page *src_page,
313			    struct page *dest_page)
314
315{
316	u8 xts_tweak[EXT4_XTS_TWEAK_SIZE];
317	struct ablkcipher_request *req = NULL;
318	DECLARE_EXT4_COMPLETION_RESULT(ecr);
319	struct scatterlist dst, src;
320	struct ext4_inode_info *ei = EXT4_I(inode);
321	struct crypto_ablkcipher *atfm = __crypto_ablkcipher_cast(ctx->tfm);
322	int res = 0;
323
324	BUG_ON(!ctx->tfm);
325	BUG_ON(ctx->mode != ei->i_encryption_key.mode);
326
327	if (ctx->mode != EXT4_ENCRYPTION_MODE_AES_256_XTS) {
328		printk_ratelimited(KERN_ERR
329				   "%s: unsupported crypto algorithm: %d\n",
330				   __func__, ctx->mode);
331		return -ENOTSUPP;
332	}
333
334	crypto_ablkcipher_clear_flags(atfm, ~0);
335	crypto_tfm_set_flags(ctx->tfm, CRYPTO_TFM_REQ_WEAK_KEY);
336
337	res = crypto_ablkcipher_setkey(atfm, ei->i_encryption_key.raw,
338				       ei->i_encryption_key.size);
339	if (res) {
340		printk_ratelimited(KERN_ERR
341				   "%s: crypto_ablkcipher_setkey() failed\n",
342				   __func__);
343		return res;
344	}
345	req = ablkcipher_request_alloc(atfm, GFP_NOFS);
346	if (!req) {
347		printk_ratelimited(KERN_ERR
348				   "%s: crypto_request_alloc() failed\n",
349				   __func__);
350		return -ENOMEM;
351	}
352	ablkcipher_request_set_callback(
353		req, CRYPTO_TFM_REQ_MAY_BACKLOG | CRYPTO_TFM_REQ_MAY_SLEEP,
354		ext4_crypt_complete, &ecr);
355
356	BUILD_BUG_ON(EXT4_XTS_TWEAK_SIZE < sizeof(index));
357	memcpy(xts_tweak, &index, sizeof(index));
358	memset(&xts_tweak[sizeof(index)], 0,
359	       EXT4_XTS_TWEAK_SIZE - sizeof(index));
360
361	sg_init_table(&dst, 1);
362	sg_set_page(&dst, dest_page, PAGE_CACHE_SIZE, 0);
363	sg_init_table(&src, 1);
364	sg_set_page(&src, src_page, PAGE_CACHE_SIZE, 0);
365	ablkcipher_request_set_crypt(req, &src, &dst, PAGE_CACHE_SIZE,
366				     xts_tweak);
367	if (rw == EXT4_DECRYPT)
368		res = crypto_ablkcipher_decrypt(req);
369	else
370		res = crypto_ablkcipher_encrypt(req);
371	if (res == -EINPROGRESS || res == -EBUSY) {
372		BUG_ON(req->base.data != &ecr);
373		wait_for_completion(&ecr.completion);
374		res = ecr.res;
375	}
376	ablkcipher_request_free(req);
377	if (res) {
378		printk_ratelimited(
379			KERN_ERR
380			"%s: crypto_ablkcipher_encrypt() returned %d\n",
381			__func__, res);
382		return res;
383	}
384	return 0;
385}
386
387/**
388 * ext4_encrypt() - Encrypts a page
389 * @inode:          The inode for which the encryption should take place
390 * @plaintext_page: The page to encrypt. Must be locked.
391 *
392 * Allocates a ciphertext page and encrypts plaintext_page into it using the ctx
393 * encryption context.
394 *
395 * Called on the page write path.  The caller must call
396 * ext4_restore_control_page() on the returned ciphertext page to
397 * release the bounce buffer and the encryption context.
398 *
399 * Return: An allocated page with the encrypted content on success. Else, an
400 * error value or NULL.
401 */
402struct page *ext4_encrypt(struct inode *inode,
403			  struct page *plaintext_page)
404{
405	struct ext4_crypto_ctx *ctx;
406	struct page *ciphertext_page = NULL;
407	int err;
408
409	BUG_ON(!PageLocked(plaintext_page));
410
411	ctx = ext4_get_crypto_ctx(inode);
412	if (IS_ERR(ctx))
413		return (struct page *) ctx;
414
415	/* The encryption operation will require a bounce page. */
416	ciphertext_page = alloc_page(GFP_NOFS);
417	if (!ciphertext_page) {
418		/* This is a potential bottleneck, but at least we'll have
419		 * forward progress. */
420		ciphertext_page = mempool_alloc(ext4_bounce_page_pool,
421						 GFP_NOFS);
422		if (WARN_ON_ONCE(!ciphertext_page)) {
423			ciphertext_page = mempool_alloc(ext4_bounce_page_pool,
424							 GFP_NOFS | __GFP_WAIT);
425		}
426		ctx->flags &= ~EXT4_BOUNCE_PAGE_REQUIRES_FREE_ENCRYPT_FL;
427	} else {
428		ctx->flags |= EXT4_BOUNCE_PAGE_REQUIRES_FREE_ENCRYPT_FL;
429	}
430	ctx->bounce_page = ciphertext_page;
431	ctx->control_page = plaintext_page;
432	err = ext4_page_crypto(ctx, inode, EXT4_ENCRYPT, plaintext_page->index,
433			       plaintext_page, ciphertext_page);
434	if (err) {
435		ext4_release_crypto_ctx(ctx);
436		return ERR_PTR(err);
437	}
438	SetPagePrivate(ciphertext_page);
439	set_page_private(ciphertext_page, (unsigned long)ctx);
440	lock_page(ciphertext_page);
441	return ciphertext_page;
442}
443
444/**
445 * ext4_decrypt() - Decrypts a page in-place
446 * @ctx:  The encryption context.
447 * @page: The page to decrypt. Must be locked.
448 *
449 * Decrypts page in-place using the ctx encryption context.
450 *
451 * Called from the read completion callback.
452 *
453 * Return: Zero on success, non-zero otherwise.
454 */
455int ext4_decrypt(struct ext4_crypto_ctx *ctx, struct page *page)
456{
457	BUG_ON(!PageLocked(page));
458
459	return ext4_page_crypto(ctx, page->mapping->host,
460				EXT4_DECRYPT, page->index, page, page);
461}
462
463/*
464 * Convenience function which takes care of allocating and
465 * deallocating the encryption context
466 */
467int ext4_decrypt_one(struct inode *inode, struct page *page)
468{
469	int ret;
470
471	struct ext4_crypto_ctx *ctx = ext4_get_crypto_ctx(inode);
472
473	if (!ctx)
474		return -ENOMEM;
475	ret = ext4_decrypt(ctx, page);
476	ext4_release_crypto_ctx(ctx);
477	return ret;
478}
479
480int ext4_encrypted_zeroout(struct inode *inode, struct ext4_extent *ex)
481{
482	struct ext4_crypto_ctx	*ctx;
483	struct page		*ciphertext_page = NULL;
484	struct bio		*bio;
485	ext4_lblk_t		lblk = ex->ee_block;
486	ext4_fsblk_t		pblk = ext4_ext_pblock(ex);
487	unsigned int		len = ext4_ext_get_actual_len(ex);
488	int			err = 0;
489
490	BUG_ON(inode->i_sb->s_blocksize != PAGE_CACHE_SIZE);
491
492	ctx = ext4_get_crypto_ctx(inode);
493	if (IS_ERR(ctx))
494		return PTR_ERR(ctx);
495
496	ciphertext_page = alloc_page(GFP_NOFS);
497	if (!ciphertext_page) {
498		/* This is a potential bottleneck, but at least we'll have
499		 * forward progress. */
500		ciphertext_page = mempool_alloc(ext4_bounce_page_pool,
501						 GFP_NOFS);
502		if (WARN_ON_ONCE(!ciphertext_page)) {
503			ciphertext_page = mempool_alloc(ext4_bounce_page_pool,
504							 GFP_NOFS | __GFP_WAIT);
505		}
506		ctx->flags &= ~EXT4_BOUNCE_PAGE_REQUIRES_FREE_ENCRYPT_FL;
507	} else {
508		ctx->flags |= EXT4_BOUNCE_PAGE_REQUIRES_FREE_ENCRYPT_FL;
509	}
510	ctx->bounce_page = ciphertext_page;
511
512	while (len--) {
513		err = ext4_page_crypto(ctx, inode, EXT4_ENCRYPT, lblk,
514				       ZERO_PAGE(0), ciphertext_page);
515		if (err)
516			goto errout;
517
518		bio = bio_alloc(GFP_KERNEL, 1);
519		if (!bio) {
520			err = -ENOMEM;
521			goto errout;
522		}
523		bio->bi_bdev = inode->i_sb->s_bdev;
524		bio->bi_iter.bi_sector = pblk;
525		err = bio_add_page(bio, ciphertext_page,
526				   inode->i_sb->s_blocksize, 0);
527		if (err) {
528			bio_put(bio);
529			goto errout;
530		}
531		err = submit_bio_wait(WRITE, bio);
532		if (err)
533			goto errout;
534	}
535	err = 0;
536errout:
537	ext4_release_crypto_ctx(ctx);
538	return err;
539}
540
541bool ext4_valid_contents_enc_mode(uint32_t mode)
542{
543	return (mode == EXT4_ENCRYPTION_MODE_AES_256_XTS);
544}
545
546/**
547 * ext4_validate_encryption_key_size() - Validate the encryption key size
548 * @mode: The key mode.
549 * @size: The key size to validate.
550 *
551 * Return: The validated key size for @mode. Zero if invalid.
552 */
553uint32_t ext4_validate_encryption_key_size(uint32_t mode, uint32_t size)
554{
555	if (size == ext4_encryption_key_size(mode))
556		return size;
557	return 0;
558}
559