xref: /openbmc/linux/fs/crypto/crypto.c (revision a36954f5)
1 /*
2  * This contains encryption functions for per-file encryption.
3  *
4  * Copyright (C) 2015, Google, Inc.
5  * Copyright (C) 2015, Motorola Mobility
6  *
7  * Written by Michael Halcrow, 2014.
8  *
9  * Filename encryption additions
10  *	Uday Savagaonkar, 2014
11  * Encryption policy handling additions
12  *	Ildar Muslukhov, 2014
13  * Add fscrypt_pullback_bio_page()
14  *	Jaegeuk Kim, 2015.
15  *
16  * This has not yet undergone a rigorous security audit.
17  *
18  * The usage of AES-XTS should conform to recommendations in NIST
19  * Special Publication 800-38E and IEEE P1619/D16.
20  */
21 
22 #include <linux/pagemap.h>
23 #include <linux/mempool.h>
24 #include <linux/module.h>
25 #include <linux/scatterlist.h>
26 #include <linux/ratelimit.h>
27 #include <linux/dcache.h>
28 #include <linux/namei.h>
29 #include "fscrypt_private.h"
30 
31 static unsigned int num_prealloc_crypto_pages = 32;
32 static unsigned int num_prealloc_crypto_ctxs = 128;
33 
34 module_param(num_prealloc_crypto_pages, uint, 0444);
35 MODULE_PARM_DESC(num_prealloc_crypto_pages,
36 		"Number of crypto pages to preallocate");
37 module_param(num_prealloc_crypto_ctxs, uint, 0444);
38 MODULE_PARM_DESC(num_prealloc_crypto_ctxs,
39 		"Number of crypto contexts to preallocate");
40 
41 static mempool_t *fscrypt_bounce_page_pool = NULL;
42 
43 static LIST_HEAD(fscrypt_free_ctxs);
44 static DEFINE_SPINLOCK(fscrypt_ctx_lock);
45 
46 struct workqueue_struct *fscrypt_read_workqueue;
47 static DEFINE_MUTEX(fscrypt_init_mutex);
48 
49 static struct kmem_cache *fscrypt_ctx_cachep;
50 struct kmem_cache *fscrypt_info_cachep;
51 
52 /**
53  * fscrypt_release_ctx() - Releases an encryption context
54  * @ctx: The encryption context to release.
55  *
56  * If the encryption context was allocated from the pre-allocated pool, returns
57  * it to that pool. Else, frees it.
58  *
59  * If there's a bounce page in the context, this frees that.
60  */
61 void fscrypt_release_ctx(struct fscrypt_ctx *ctx)
62 {
63 	unsigned long flags;
64 
65 	if (ctx->flags & FS_CTX_HAS_BOUNCE_BUFFER_FL && ctx->w.bounce_page) {
66 		mempool_free(ctx->w.bounce_page, fscrypt_bounce_page_pool);
67 		ctx->w.bounce_page = NULL;
68 	}
69 	ctx->w.control_page = NULL;
70 	if (ctx->flags & FS_CTX_REQUIRES_FREE_ENCRYPT_FL) {
71 		kmem_cache_free(fscrypt_ctx_cachep, ctx);
72 	} else {
73 		spin_lock_irqsave(&fscrypt_ctx_lock, flags);
74 		list_add(&ctx->free_list, &fscrypt_free_ctxs);
75 		spin_unlock_irqrestore(&fscrypt_ctx_lock, flags);
76 	}
77 }
78 EXPORT_SYMBOL(fscrypt_release_ctx);
79 
80 /**
81  * fscrypt_get_ctx() - Gets an encryption context
82  * @inode:       The inode for which we are doing the crypto
83  * @gfp_flags:   The gfp flag for memory allocation
84  *
85  * Allocates and initializes an encryption context.
86  *
87  * Return: An allocated and initialized encryption context on success; error
88  * value or NULL otherwise.
89  */
90 struct fscrypt_ctx *fscrypt_get_ctx(const struct inode *inode, gfp_t gfp_flags)
91 {
92 	struct fscrypt_ctx *ctx = NULL;
93 	struct fscrypt_info *ci = inode->i_crypt_info;
94 	unsigned long flags;
95 
96 	if (ci == NULL)
97 		return ERR_PTR(-ENOKEY);
98 
99 	/*
100 	 * We first try getting the ctx from a free list because in
101 	 * the common case the ctx will have an allocated and
102 	 * initialized crypto tfm, so it's probably a worthwhile
103 	 * optimization. For the bounce page, we first try getting it
104 	 * from the kernel allocator because that's just about as fast
105 	 * as getting it from a list and because a cache of free pages
106 	 * should generally be a "last resort" option for a filesystem
107 	 * to be able to do its job.
108 	 */
109 	spin_lock_irqsave(&fscrypt_ctx_lock, flags);
110 	ctx = list_first_entry_or_null(&fscrypt_free_ctxs,
111 					struct fscrypt_ctx, free_list);
112 	if (ctx)
113 		list_del(&ctx->free_list);
114 	spin_unlock_irqrestore(&fscrypt_ctx_lock, flags);
115 	if (!ctx) {
116 		ctx = kmem_cache_zalloc(fscrypt_ctx_cachep, gfp_flags);
117 		if (!ctx)
118 			return ERR_PTR(-ENOMEM);
119 		ctx->flags |= FS_CTX_REQUIRES_FREE_ENCRYPT_FL;
120 	} else {
121 		ctx->flags &= ~FS_CTX_REQUIRES_FREE_ENCRYPT_FL;
122 	}
123 	ctx->flags &= ~FS_CTX_HAS_BOUNCE_BUFFER_FL;
124 	return ctx;
125 }
126 EXPORT_SYMBOL(fscrypt_get_ctx);
127 
128 /**
129  * page_crypt_complete() - completion callback for page crypto
130  * @req: The asynchronous cipher request context
131  * @res: The result of the cipher operation
132  */
133 static void page_crypt_complete(struct crypto_async_request *req, int res)
134 {
135 	struct fscrypt_completion_result *ecr = req->data;
136 
137 	if (res == -EINPROGRESS)
138 		return;
139 	ecr->res = res;
140 	complete(&ecr->completion);
141 }
142 
143 int fscrypt_do_page_crypto(const struct inode *inode, fscrypt_direction_t rw,
144 			   u64 lblk_num, struct page *src_page,
145 			   struct page *dest_page, unsigned int len,
146 			   unsigned int offs, gfp_t gfp_flags)
147 {
148 	struct {
149 		__le64 index;
150 		u8 padding[FS_XTS_TWEAK_SIZE - sizeof(__le64)];
151 	} xts_tweak;
152 	struct skcipher_request *req = NULL;
153 	DECLARE_FS_COMPLETION_RESULT(ecr);
154 	struct scatterlist dst, src;
155 	struct fscrypt_info *ci = inode->i_crypt_info;
156 	struct crypto_skcipher *tfm = ci->ci_ctfm;
157 	int res = 0;
158 
159 	BUG_ON(len == 0);
160 
161 	req = skcipher_request_alloc(tfm, gfp_flags);
162 	if (!req) {
163 		printk_ratelimited(KERN_ERR
164 				"%s: crypto_request_alloc() failed\n",
165 				__func__);
166 		return -ENOMEM;
167 	}
168 
169 	skcipher_request_set_callback(
170 		req, CRYPTO_TFM_REQ_MAY_BACKLOG | CRYPTO_TFM_REQ_MAY_SLEEP,
171 		page_crypt_complete, &ecr);
172 
173 	BUILD_BUG_ON(sizeof(xts_tweak) != FS_XTS_TWEAK_SIZE);
174 	xts_tweak.index = cpu_to_le64(lblk_num);
175 	memset(xts_tweak.padding, 0, sizeof(xts_tweak.padding));
176 
177 	sg_init_table(&dst, 1);
178 	sg_set_page(&dst, dest_page, len, offs);
179 	sg_init_table(&src, 1);
180 	sg_set_page(&src, src_page, len, offs);
181 	skcipher_request_set_crypt(req, &src, &dst, len, &xts_tweak);
182 	if (rw == FS_DECRYPT)
183 		res = crypto_skcipher_decrypt(req);
184 	else
185 		res = crypto_skcipher_encrypt(req);
186 	if (res == -EINPROGRESS || res == -EBUSY) {
187 		BUG_ON(req->base.data != &ecr);
188 		wait_for_completion(&ecr.completion);
189 		res = ecr.res;
190 	}
191 	skcipher_request_free(req);
192 	if (res) {
193 		printk_ratelimited(KERN_ERR
194 			"%s: crypto_skcipher_encrypt() returned %d\n",
195 			__func__, res);
196 		return res;
197 	}
198 	return 0;
199 }
200 
201 struct page *fscrypt_alloc_bounce_page(struct fscrypt_ctx *ctx,
202 				       gfp_t gfp_flags)
203 {
204 	ctx->w.bounce_page = mempool_alloc(fscrypt_bounce_page_pool, gfp_flags);
205 	if (ctx->w.bounce_page == NULL)
206 		return ERR_PTR(-ENOMEM);
207 	ctx->flags |= FS_CTX_HAS_BOUNCE_BUFFER_FL;
208 	return ctx->w.bounce_page;
209 }
210 
211 /**
212  * fscypt_encrypt_page() - Encrypts a page
213  * @inode:     The inode for which the encryption should take place
214  * @page:      The page to encrypt. Must be locked for bounce-page
215  *             encryption.
216  * @len:       Length of data to encrypt in @page and encrypted
217  *             data in returned page.
218  * @offs:      Offset of data within @page and returned
219  *             page holding encrypted data.
220  * @lblk_num:  Logical block number. This must be unique for multiple
221  *             calls with same inode, except when overwriting
222  *             previously written data.
223  * @gfp_flags: The gfp flag for memory allocation
224  *
225  * Encrypts @page using the ctx encryption context. Performs encryption
226  * either in-place or into a newly allocated bounce page.
227  * Called on the page write path.
228  *
229  * Bounce page allocation is the default.
230  * In this case, the contents of @page are encrypted and stored in an
231  * allocated bounce page. @page has to be locked and the caller must call
232  * fscrypt_restore_control_page() on the returned ciphertext page to
233  * release the bounce buffer and the encryption context.
234  *
235  * In-place encryption is used by setting the FS_CFLG_OWN_PAGES flag in
236  * fscrypt_operations. Here, the input-page is returned with its content
237  * encrypted.
238  *
239  * Return: A page with the encrypted content on success. Else, an
240  * error value or NULL.
241  */
242 struct page *fscrypt_encrypt_page(const struct inode *inode,
243 				struct page *page,
244 				unsigned int len,
245 				unsigned int offs,
246 				u64 lblk_num, gfp_t gfp_flags)
247 
248 {
249 	struct fscrypt_ctx *ctx;
250 	struct page *ciphertext_page = page;
251 	int err;
252 
253 	BUG_ON(len % FS_CRYPTO_BLOCK_SIZE != 0);
254 
255 	if (inode->i_sb->s_cop->flags & FS_CFLG_OWN_PAGES) {
256 		/* with inplace-encryption we just encrypt the page */
257 		err = fscrypt_do_page_crypto(inode, FS_ENCRYPT, lblk_num, page,
258 					     ciphertext_page, len, offs,
259 					     gfp_flags);
260 		if (err)
261 			return ERR_PTR(err);
262 
263 		return ciphertext_page;
264 	}
265 
266 	BUG_ON(!PageLocked(page));
267 
268 	ctx = fscrypt_get_ctx(inode, gfp_flags);
269 	if (IS_ERR(ctx))
270 		return (struct page *)ctx;
271 
272 	/* The encryption operation will require a bounce page. */
273 	ciphertext_page = fscrypt_alloc_bounce_page(ctx, gfp_flags);
274 	if (IS_ERR(ciphertext_page))
275 		goto errout;
276 
277 	ctx->w.control_page = page;
278 	err = fscrypt_do_page_crypto(inode, FS_ENCRYPT, lblk_num,
279 				     page, ciphertext_page, len, offs,
280 				     gfp_flags);
281 	if (err) {
282 		ciphertext_page = ERR_PTR(err);
283 		goto errout;
284 	}
285 	SetPagePrivate(ciphertext_page);
286 	set_page_private(ciphertext_page, (unsigned long)ctx);
287 	lock_page(ciphertext_page);
288 	return ciphertext_page;
289 
290 errout:
291 	fscrypt_release_ctx(ctx);
292 	return ciphertext_page;
293 }
294 EXPORT_SYMBOL(fscrypt_encrypt_page);
295 
296 /**
297  * fscrypt_decrypt_page() - Decrypts a page in-place
298  * @inode:     The corresponding inode for the page to decrypt.
299  * @page:      The page to decrypt. Must be locked in case
300  *             it is a writeback page (FS_CFLG_OWN_PAGES unset).
301  * @len:       Number of bytes in @page to be decrypted.
302  * @offs:      Start of data in @page.
303  * @lblk_num:  Logical block number.
304  *
305  * Decrypts page in-place using the ctx encryption context.
306  *
307  * Called from the read completion callback.
308  *
309  * Return: Zero on success, non-zero otherwise.
310  */
311 int fscrypt_decrypt_page(const struct inode *inode, struct page *page,
312 			unsigned int len, unsigned int offs, u64 lblk_num)
313 {
314 	if (!(inode->i_sb->s_cop->flags & FS_CFLG_OWN_PAGES))
315 		BUG_ON(!PageLocked(page));
316 
317 	return fscrypt_do_page_crypto(inode, FS_DECRYPT, lblk_num, page, page,
318 				      len, offs, GFP_NOFS);
319 }
320 EXPORT_SYMBOL(fscrypt_decrypt_page);
321 
322 /*
323  * Validate dentries for encrypted directories to make sure we aren't
324  * potentially caching stale data after a key has been added or
325  * removed.
326  */
327 static int fscrypt_d_revalidate(struct dentry *dentry, unsigned int flags)
328 {
329 	struct dentry *dir;
330 	int dir_has_key, cached_with_key;
331 
332 	if (flags & LOOKUP_RCU)
333 		return -ECHILD;
334 
335 	dir = dget_parent(dentry);
336 	if (!d_inode(dir)->i_sb->s_cop->is_encrypted(d_inode(dir))) {
337 		dput(dir);
338 		return 0;
339 	}
340 
341 	/* this should eventually be an flag in d_flags */
342 	spin_lock(&dentry->d_lock);
343 	cached_with_key = dentry->d_flags & DCACHE_ENCRYPTED_WITH_KEY;
344 	spin_unlock(&dentry->d_lock);
345 	dir_has_key = (d_inode(dir)->i_crypt_info != NULL);
346 	dput(dir);
347 
348 	/*
349 	 * If the dentry was cached without the key, and it is a
350 	 * negative dentry, it might be a valid name.  We can't check
351 	 * if the key has since been made available due to locking
352 	 * reasons, so we fail the validation so ext4_lookup() can do
353 	 * this check.
354 	 *
355 	 * We also fail the validation if the dentry was created with
356 	 * the key present, but we no longer have the key, or vice versa.
357 	 */
358 	if ((!cached_with_key && d_is_negative(dentry)) ||
359 			(!cached_with_key && dir_has_key) ||
360 			(cached_with_key && !dir_has_key))
361 		return 0;
362 	return 1;
363 }
364 
365 const struct dentry_operations fscrypt_d_ops = {
366 	.d_revalidate = fscrypt_d_revalidate,
367 };
368 EXPORT_SYMBOL(fscrypt_d_ops);
369 
370 void fscrypt_restore_control_page(struct page *page)
371 {
372 	struct fscrypt_ctx *ctx;
373 
374 	ctx = (struct fscrypt_ctx *)page_private(page);
375 	set_page_private(page, (unsigned long)NULL);
376 	ClearPagePrivate(page);
377 	unlock_page(page);
378 	fscrypt_release_ctx(ctx);
379 }
380 EXPORT_SYMBOL(fscrypt_restore_control_page);
381 
382 static void fscrypt_destroy(void)
383 {
384 	struct fscrypt_ctx *pos, *n;
385 
386 	list_for_each_entry_safe(pos, n, &fscrypt_free_ctxs, free_list)
387 		kmem_cache_free(fscrypt_ctx_cachep, pos);
388 	INIT_LIST_HEAD(&fscrypt_free_ctxs);
389 	mempool_destroy(fscrypt_bounce_page_pool);
390 	fscrypt_bounce_page_pool = NULL;
391 }
392 
393 /**
394  * fscrypt_initialize() - allocate major buffers for fs encryption.
395  * @cop_flags:  fscrypt operations flags
396  *
397  * We only call this when we start accessing encrypted files, since it
398  * results in memory getting allocated that wouldn't otherwise be used.
399  *
400  * Return: Zero on success, non-zero otherwise.
401  */
402 int fscrypt_initialize(unsigned int cop_flags)
403 {
404 	int i, res = -ENOMEM;
405 
406 	/*
407 	 * No need to allocate a bounce page pool if there already is one or
408 	 * this FS won't use it.
409 	 */
410 	if (cop_flags & FS_CFLG_OWN_PAGES || fscrypt_bounce_page_pool)
411 		return 0;
412 
413 	mutex_lock(&fscrypt_init_mutex);
414 	if (fscrypt_bounce_page_pool)
415 		goto already_initialized;
416 
417 	for (i = 0; i < num_prealloc_crypto_ctxs; i++) {
418 		struct fscrypt_ctx *ctx;
419 
420 		ctx = kmem_cache_zalloc(fscrypt_ctx_cachep, GFP_NOFS);
421 		if (!ctx)
422 			goto fail;
423 		list_add(&ctx->free_list, &fscrypt_free_ctxs);
424 	}
425 
426 	fscrypt_bounce_page_pool =
427 		mempool_create_page_pool(num_prealloc_crypto_pages, 0);
428 	if (!fscrypt_bounce_page_pool)
429 		goto fail;
430 
431 already_initialized:
432 	mutex_unlock(&fscrypt_init_mutex);
433 	return 0;
434 fail:
435 	fscrypt_destroy();
436 	mutex_unlock(&fscrypt_init_mutex);
437 	return res;
438 }
439 
440 /**
441  * fscrypt_init() - Set up for fs encryption.
442  */
443 static int __init fscrypt_init(void)
444 {
445 	fscrypt_read_workqueue = alloc_workqueue("fscrypt_read_queue",
446 							WQ_HIGHPRI, 0);
447 	if (!fscrypt_read_workqueue)
448 		goto fail;
449 
450 	fscrypt_ctx_cachep = KMEM_CACHE(fscrypt_ctx, SLAB_RECLAIM_ACCOUNT);
451 	if (!fscrypt_ctx_cachep)
452 		goto fail_free_queue;
453 
454 	fscrypt_info_cachep = KMEM_CACHE(fscrypt_info, SLAB_RECLAIM_ACCOUNT);
455 	if (!fscrypt_info_cachep)
456 		goto fail_free_ctx;
457 
458 	return 0;
459 
460 fail_free_ctx:
461 	kmem_cache_destroy(fscrypt_ctx_cachep);
462 fail_free_queue:
463 	destroy_workqueue(fscrypt_read_workqueue);
464 fail:
465 	return -ENOMEM;
466 }
467 module_init(fscrypt_init)
468 
469 /**
470  * fscrypt_exit() - Shutdown the fs encryption system
471  */
472 static void __exit fscrypt_exit(void)
473 {
474 	fscrypt_destroy();
475 
476 	if (fscrypt_read_workqueue)
477 		destroy_workqueue(fscrypt_read_workqueue);
478 	kmem_cache_destroy(fscrypt_ctx_cachep);
479 	kmem_cache_destroy(fscrypt_info_cachep);
480 }
481 module_exit(fscrypt_exit);
482 
483 MODULE_LICENSE("GPL");
484