policy.c

  1// SPDX-License-Identifier: GPL-2.0
  2/*
  3 * Encryption policy functions for per-file encryption support.
  4 *
  5 * Copyright (C) 2015, Google, Inc.
  6 * Copyright (C) 2015, Motorola Mobility.
  7 *
  8 * Originally written by Michael Halcrow, 2015.
  9 * Modified by Jaegeuk Kim, 2015.
 10 * Modified by Eric Biggers, 2019 for v2 policy support.
 11 */
 12
 13#include <linux/export.h>
 14#include <linux/fs_context.h>
 15#include <linux/mount.h>
 16#include <linux/random.h>
 17#include <linux/seq_file.h>
 18#include <linux/string.h>
 19
 20#include "fscrypt_private.h"
 21
 22/**
 23 * fscrypt_policies_equal() - check whether two encryption policies are the same
 24 * @policy1: the first policy
 25 * @policy2: the second policy
 26 *
 27 * Return: %true if equal, else %false
 28 */
 29bool fscrypt_policies_equal(const union fscrypt_policy *policy1,
 30			    const union fscrypt_policy *policy2)
 31{
 32	if (policy1->version != policy2->version)
 33		return false;
 34
 35	return !memcmp(policy1, policy2, fscrypt_policy_size(policy1));
 36}
 37
 38int fscrypt_policy_to_key_spec(const union fscrypt_policy *policy,
 39			       struct fscrypt_key_specifier *key_spec)
 40{
 41	switch (policy->version) {
 42	case FSCRYPT_POLICY_V1:
 43		key_spec->type = FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR;
 44		memcpy(key_spec->u.descriptor, policy->v1.master_key_descriptor,
 45		       FSCRYPT_KEY_DESCRIPTOR_SIZE);
 46		return 0;
 47	case FSCRYPT_POLICY_V2:
 48		key_spec->type = FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER;
 49		memcpy(key_spec->u.identifier, policy->v2.master_key_identifier,
 50		       FSCRYPT_KEY_IDENTIFIER_SIZE);
 51		return 0;
 52	default:
 53		WARN_ON_ONCE(1);
 54		return -EINVAL;
 55	}
 56}
 57
 58const union fscrypt_policy *fscrypt_get_dummy_policy(struct super_block *sb)
 59{
 60	if (!sb->s_cop->get_dummy_policy)
 61		return NULL;
 62	return sb->s_cop->get_dummy_policy(sb);
 63}
 64
 65/*
 66 * Return %true if the given combination of encryption modes is supported for v1
 67 * (and later) encryption policies.
 68 *
 69 * Do *not* add anything new here, since v1 encryption policies are deprecated.
 70 * New combinations of modes should go in fscrypt_valid_enc_modes_v2() only.
 71 */
 72static bool fscrypt_valid_enc_modes_v1(u32 contents_mode, u32 filenames_mode)
 73{
 74	if (contents_mode == FSCRYPT_MODE_AES_256_XTS &&
 75	    filenames_mode == FSCRYPT_MODE_AES_256_CTS)
 76		return true;
 77
 78	if (contents_mode == FSCRYPT_MODE_AES_128_CBC &&
 79	    filenames_mode == FSCRYPT_MODE_AES_128_CTS)
 80		return true;
 81
 82	if (contents_mode == FSCRYPT_MODE_ADIANTUM &&
 83	    filenames_mode == FSCRYPT_MODE_ADIANTUM)
 84		return true;
 85
 86	return false;
 87}
 88
 89static bool fscrypt_valid_enc_modes_v2(u32 contents_mode, u32 filenames_mode)
 90{
 91	if (contents_mode == FSCRYPT_MODE_AES_256_XTS &&
 92	    filenames_mode == FSCRYPT_MODE_AES_256_HCTR2)
 93		return true;
 94
 95	if (contents_mode == FSCRYPT_MODE_SM4_XTS &&
 96	    filenames_mode == FSCRYPT_MODE_SM4_CTS)
 97		return true;
 98
 99	return fscrypt_valid_enc_modes_v1(contents_mode, filenames_mode);
100}
101
102static bool supported_direct_key_modes(const struct inode *inode,
103				       u32 contents_mode, u32 filenames_mode)
104{
105	const struct fscrypt_mode *mode;
106
107	if (contents_mode != filenames_mode) {
108		fscrypt_warn(inode,
109			     "Direct key flag not allowed with different contents and filenames modes");
110		return false;
111	}
112	mode = &fscrypt_modes[contents_mode];
113
114	if (mode->ivsize < offsetofend(union fscrypt_iv, nonce)) {
115		fscrypt_warn(inode, "Direct key flag not allowed with %s",
116			     mode->friendly_name);
117		return false;
118	}
119	return true;
120}
121
122static bool supported_iv_ino_lblk_policy(const struct fscrypt_policy_v2 *policy,
123					 const struct inode *inode)
124{
125	const char *type = (policy->flags & FSCRYPT_POLICY_FLAG_IV_INO_LBLK_64)
126				? "IV_INO_LBLK_64" : "IV_INO_LBLK_32";
127	struct super_block *sb = inode->i_sb;
128
129	/*
130	 * IV_INO_LBLK_* exist only because of hardware limitations, and
131	 * currently the only known use case for them involves AES-256-XTS.
132	 * That's also all we test currently.  For these reasons, for now only
133	 * allow AES-256-XTS here.  This can be relaxed later if a use case for
134	 * IV_INO_LBLK_* with other encryption modes arises.
135	 */
136	if (policy->contents_encryption_mode != FSCRYPT_MODE_AES_256_XTS) {
137		fscrypt_warn(inode,
138			     "Can't use %s policy with contents mode other than AES-256-XTS",
139			     type);
140		return false;
141	}
142
143	/*
144	 * It's unsafe to include inode numbers in the IVs if the filesystem can
145	 * potentially renumber inodes, e.g. via filesystem shrinking.
146	 */
147	if (!sb->s_cop->has_stable_inodes ||
148	    !sb->s_cop->has_stable_inodes(sb)) {
149		fscrypt_warn(inode,
150			     "Can't use %s policy on filesystem '%s' because it doesn't have stable inode numbers",
151			     type, sb->s_id);
152		return false;
153	}
154
155	/*
156	 * IV_INO_LBLK_64 and IV_INO_LBLK_32 both require that inode numbers fit
157	 * in 32 bits.  In principle, IV_INO_LBLK_32 could support longer inode
158	 * numbers because it hashes the inode number; however, currently the
159	 * inode number is gotten from inode::i_ino which is 'unsigned long'.
160	 * So for now the implementation limit is 32 bits.
161	 */
162	if (!sb->s_cop->has_32bit_inodes) {
163		fscrypt_warn(inode,
164			     "Can't use %s policy on filesystem '%s' because its inode numbers are too long",
165			     type, sb->s_id);
166		return false;
167	}
168
169	/*
170	 * IV_INO_LBLK_64 and IV_INO_LBLK_32 both require that file data unit
171	 * indices fit in 32 bits.
172	 */
173	if (fscrypt_max_file_dun_bits(sb,
174			fscrypt_policy_v2_du_bits(policy, inode)) > 32) {
175		fscrypt_warn(inode,
176			     "Can't use %s policy on filesystem '%s' because its maximum file size is too large",
177			     type, sb->s_id);
178		return false;
179	}
180	return true;
181}
182
183static bool fscrypt_supported_v1_policy(const struct fscrypt_policy_v1 *policy,
184					const struct inode *inode)
185{
186	if (!fscrypt_valid_enc_modes_v1(policy->contents_encryption_mode,
187				     policy->filenames_encryption_mode)) {
188		fscrypt_warn(inode,
189			     "Unsupported encryption modes (contents %d, filenames %d)",
190			     policy->contents_encryption_mode,
191			     policy->filenames_encryption_mode);
192		return false;
193	}
194
195	if (policy->flags & ~(FSCRYPT_POLICY_FLAGS_PAD_MASK |
196			      FSCRYPT_POLICY_FLAG_DIRECT_KEY)) {
197		fscrypt_warn(inode, "Unsupported encryption flags (0x%02x)",
198			     policy->flags);
199		return false;
200	}
201
202	if ((policy->flags & FSCRYPT_POLICY_FLAG_DIRECT_KEY) &&
203	    !supported_direct_key_modes(inode, policy->contents_encryption_mode,
204					policy->filenames_encryption_mode))
205		return false;
206
207	if (IS_CASEFOLDED(inode)) {
208		/* With v1, there's no way to derive dirhash keys. */
209		fscrypt_warn(inode,
210			     "v1 policies can't be used on casefolded directories");
211		return false;
212	}
213
214	return true;
215}
216
217static bool fscrypt_supported_v2_policy(const struct fscrypt_policy_v2 *policy,
218					const struct inode *inode)
219{
220	int count = 0;
221
222	if (!fscrypt_valid_enc_modes_v2(policy->contents_encryption_mode,
223				     policy->filenames_encryption_mode)) {
224		fscrypt_warn(inode,
225			     "Unsupported encryption modes (contents %d, filenames %d)",
226			     policy->contents_encryption_mode,
227			     policy->filenames_encryption_mode);
228		return false;
229	}
230
231	if (policy->flags & ~(FSCRYPT_POLICY_FLAGS_PAD_MASK |
232			      FSCRYPT_POLICY_FLAG_DIRECT_KEY |
233			      FSCRYPT_POLICY_FLAG_IV_INO_LBLK_64 |
234			      FSCRYPT_POLICY_FLAG_IV_INO_LBLK_32)) {
235		fscrypt_warn(inode, "Unsupported encryption flags (0x%02x)",
236			     policy->flags);
237		return false;
238	}
239
240	count += !!(policy->flags & FSCRYPT_POLICY_FLAG_DIRECT_KEY);
241	count += !!(policy->flags & FSCRYPT_POLICY_FLAG_IV_INO_LBLK_64);
242	count += !!(policy->flags & FSCRYPT_POLICY_FLAG_IV_INO_LBLK_32);
243	if (count > 1) {
244		fscrypt_warn(inode, "Mutually exclusive encryption flags (0x%02x)",
245			     policy->flags);
246		return false;
247	}
248
249	if (policy->log2_data_unit_size) {
250		if (!inode->i_sb->s_cop->supports_subblock_data_units) {
251			fscrypt_warn(inode,
252				     "Filesystem does not support configuring crypto data unit size");
253			return false;
254		}
255		if (policy->log2_data_unit_size > inode->i_blkbits ||
256		    policy->log2_data_unit_size < SECTOR_SHIFT /* 9 */) {
257			fscrypt_warn(inode,
258				     "Unsupported log2_data_unit_size in encryption policy: %d",
259				     policy->log2_data_unit_size);
260			return false;
261		}
262		if (policy->log2_data_unit_size != inode->i_blkbits &&
263		    (policy->flags & FSCRYPT_POLICY_FLAG_IV_INO_LBLK_32)) {
264			/*
265			 * Not safe to enable yet, as we need to ensure that DUN
266			 * wraparound can only occur on a FS block boundary.
267			 */
268			fscrypt_warn(inode,
269				     "Sub-block data units not yet supported with IV_INO_LBLK_32");
270			return false;
271		}
272	}
273
274	if ((policy->flags & FSCRYPT_POLICY_FLAG_DIRECT_KEY) &&
275	    !supported_direct_key_modes(inode, policy->contents_encryption_mode,
276					policy->filenames_encryption_mode))
277		return false;
278
279	if ((policy->flags & (FSCRYPT_POLICY_FLAG_IV_INO_LBLK_64 |
280			      FSCRYPT_POLICY_FLAG_IV_INO_LBLK_32)) &&
281	    !supported_iv_ino_lblk_policy(policy, inode))
282		return false;
283
284	if (memchr_inv(policy->__reserved, 0, sizeof(policy->__reserved))) {
285		fscrypt_warn(inode, "Reserved bits set in encryption policy");
286		return false;
287	}
288
289	return true;
290}
291
292/**
293 * fscrypt_supported_policy() - check whether an encryption policy is supported
294 * @policy_u: the encryption policy
295 * @inode: the inode on which the policy will be used
296 *
297 * Given an encryption policy, check whether all its encryption modes and other
298 * settings are supported by this kernel on the given inode.  (But we don't
299 * currently don't check for crypto API support here, so attempting to use an
300 * algorithm not configured into the crypto API will still fail later.)
301 *
302 * Return: %true if supported, else %false
303 */
304bool fscrypt_supported_policy(const union fscrypt_policy *policy_u,
305			      const struct inode *inode)
306{
307	switch (policy_u->version) {
308	case FSCRYPT_POLICY_V1:
309		return fscrypt_supported_v1_policy(&policy_u->v1, inode);
310	case FSCRYPT_POLICY_V2:
311		return fscrypt_supported_v2_policy(&policy_u->v2, inode);
312	}
313	return false;
314}
315
316/**
317 * fscrypt_new_context() - create a new fscrypt_context
318 * @ctx_u: output context
319 * @policy_u: input policy
320 * @nonce: nonce to use
321 *
322 * Create an fscrypt_context for an inode that is being assigned the given
323 * encryption policy.  @nonce must be a new random nonce.
324 *
325 * Return: the size of the new context in bytes.
326 */
327static int fscrypt_new_context(union fscrypt_context *ctx_u,
328			       const union fscrypt_policy *policy_u,
329			       const u8 nonce[FSCRYPT_FILE_NONCE_SIZE])
330{
331	memset(ctx_u, 0, sizeof(*ctx_u));
332
333	switch (policy_u->version) {
334	case FSCRYPT_POLICY_V1: {
335		const struct fscrypt_policy_v1 *policy = &policy_u->v1;
336		struct fscrypt_context_v1 *ctx = &ctx_u->v1;
337
338		ctx->version = FSCRYPT_CONTEXT_V1;
339		ctx->contents_encryption_mode =
340			policy->contents_encryption_mode;
341		ctx->filenames_encryption_mode =
342			policy->filenames_encryption_mode;
343		ctx->flags = policy->flags;
344		memcpy(ctx->master_key_descriptor,
345		       policy->master_key_descriptor,
346		       sizeof(ctx->master_key_descriptor));
347		memcpy(ctx->nonce, nonce, FSCRYPT_FILE_NONCE_SIZE);
348		return sizeof(*ctx);
349	}
350	case FSCRYPT_POLICY_V2: {
351		const struct fscrypt_policy_v2 *policy = &policy_u->v2;
352		struct fscrypt_context_v2 *ctx = &ctx_u->v2;
353
354		ctx->version = FSCRYPT_CONTEXT_V2;
355		ctx->contents_encryption_mode =
356			policy->contents_encryption_mode;
357		ctx->filenames_encryption_mode =
358			policy->filenames_encryption_mode;
359		ctx->flags = policy->flags;
360		ctx->log2_data_unit_size = policy->log2_data_unit_size;
361		memcpy(ctx->master_key_identifier,
362		       policy->master_key_identifier,
363		       sizeof(ctx->master_key_identifier));
364		memcpy(ctx->nonce, nonce, FSCRYPT_FILE_NONCE_SIZE);
365		return sizeof(*ctx);
366	}
367	}
368	BUG();
369}
370
371/**
372 * fscrypt_policy_from_context() - convert an fscrypt_context to
373 *				   an fscrypt_policy
374 * @policy_u: output policy
375 * @ctx_u: input context
376 * @ctx_size: size of input context in bytes
377 *
378 * Given an fscrypt_context, build the corresponding fscrypt_policy.
379 *
380 * Return: 0 on success, or -EINVAL if the fscrypt_context has an unrecognized
381 * version number or size.
382 *
383 * This does *not* validate the settings within the policy itself, e.g. the
384 * modes, flags, and reserved bits.  Use fscrypt_supported_policy() for that.
385 */
386int fscrypt_policy_from_context(union fscrypt_policy *policy_u,
387				const union fscrypt_context *ctx_u,
388				int ctx_size)
389{
390	memset(policy_u, 0, sizeof(*policy_u));
391
392	if (!fscrypt_context_is_valid(ctx_u, ctx_size))
393		return -EINVAL;
394
395	switch (ctx_u->version) {
396	case FSCRYPT_CONTEXT_V1: {
397		const struct fscrypt_context_v1 *ctx = &ctx_u->v1;
398		struct fscrypt_policy_v1 *policy = &policy_u->v1;
399
400		policy->version = FSCRYPT_POLICY_V1;
401		policy->contents_encryption_mode =
402			ctx->contents_encryption_mode;
403		policy->filenames_encryption_mode =
404			ctx->filenames_encryption_mode;
405		policy->flags = ctx->flags;
406		memcpy(policy->master_key_descriptor,
407		       ctx->master_key_descriptor,
408		       sizeof(policy->master_key_descriptor));
409		return 0;
410	}
411	case FSCRYPT_CONTEXT_V2: {
412		const struct fscrypt_context_v2 *ctx = &ctx_u->v2;
413		struct fscrypt_policy_v2 *policy = &policy_u->v2;
414
415		policy->version = FSCRYPT_POLICY_V2;
416		policy->contents_encryption_mode =
417			ctx->contents_encryption_mode;
418		policy->filenames_encryption_mode =
419			ctx->filenames_encryption_mode;
420		policy->flags = ctx->flags;
421		policy->log2_data_unit_size = ctx->log2_data_unit_size;
422		memcpy(policy->__reserved, ctx->__reserved,
423		       sizeof(policy->__reserved));
424		memcpy(policy->master_key_identifier,
425		       ctx->master_key_identifier,
426		       sizeof(policy->master_key_identifier));
427		return 0;
428	}
429	}
430	/* unreachable */
431	return -EINVAL;
432}
433
434/* Retrieve an inode's encryption policy */
435static int fscrypt_get_policy(struct inode *inode, union fscrypt_policy *policy)
436{
437	const struct fscrypt_inode_info *ci;
438	union fscrypt_context ctx;
439	int ret;
440
441	ci = fscrypt_get_inode_info(inode);
442	if (ci) {
443		/* key available, use the cached policy */
444		*policy = ci->ci_policy;
445		return 0;
446	}
447
448	if (!IS_ENCRYPTED(inode))
449		return -ENODATA;
450
451	ret = inode->i_sb->s_cop->get_context(inode, &ctx, sizeof(ctx));
452	if (ret < 0)
453		return (ret == -ERANGE) ? -EINVAL : ret;
454
455	return fscrypt_policy_from_context(policy, &ctx, ret);
456}
457
458static int set_encryption_policy(struct inode *inode,
459				 const union fscrypt_policy *policy)
460{
461	u8 nonce[FSCRYPT_FILE_NONCE_SIZE];
462	union fscrypt_context ctx;
463	int ctxsize;
464	int err;
465
466	if (!fscrypt_supported_policy(policy, inode))
467		return -EINVAL;
468
469	switch (policy->version) {
470	case FSCRYPT_POLICY_V1:
471		/*
472		 * The original encryption policy version provided no way of
473		 * verifying that the correct master key was supplied, which was
474		 * insecure in scenarios where multiple users have access to the
475		 * same encrypted files (even just read-only access).  The new
476		 * encryption policy version fixes this and also implies use of
477		 * an improved key derivation function and allows non-root users
478		 * to securely remove keys.  So as long as compatibility with
479		 * old kernels isn't required, it is recommended to use the new
480		 * policy version for all new encrypted directories.
481		 */
482		pr_warn_once("%s (pid %d) is setting deprecated v1 encryption policy; recommend upgrading to v2.\n",
483			     current->comm, current->pid);
484		break;
485	case FSCRYPT_POLICY_V2:
486		err = fscrypt_verify_key_added(inode->i_sb,
487					       policy->v2.master_key_identifier);
488		if (err)
489			return err;
490		if (policy->v2.flags & FSCRYPT_POLICY_FLAG_IV_INO_LBLK_32)
491			pr_warn_once("%s (pid %d) is setting an IV_INO_LBLK_32 encryption policy.  This should only be used if there are certain hardware limitations.\n",
492				     current->comm, current->pid);
493		break;
494	default:
495		WARN_ON_ONCE(1);
496		return -EINVAL;
497	}
498
499	get_random_bytes(nonce, FSCRYPT_FILE_NONCE_SIZE);
500	ctxsize = fscrypt_new_context(&ctx, policy, nonce);
501
502	return inode->i_sb->s_cop->set_context(inode, &ctx, ctxsize, NULL);
503}
504
505int fscrypt_ioctl_set_policy(struct file *filp, const void __user *arg)
506{
507	union fscrypt_policy policy;
508	union fscrypt_policy existing_policy;
509	struct inode *inode = file_inode(filp);
510	u8 version;
511	int size;
512	int ret;
513
514	if (get_user(policy.version, (const u8 __user *)arg))
515		return -EFAULT;
516
517	size = fscrypt_policy_size(&policy);
518	if (size <= 0)
519		return -EINVAL;
520
521	/*
522	 * We should just copy the remaining 'size - 1' bytes here, but a
523	 * bizarre bug in gcc 7 and earlier (fixed by gcc r255731) causes gcc to
524	 * think that size can be 0 here (despite the check above!) *and* that
525	 * it's a compile-time constant.  Thus it would think copy_from_user()
526	 * is passed compile-time constant ULONG_MAX, causing the compile-time
527	 * buffer overflow check to fail, breaking the build. This only occurred
528	 * when building an i386 kernel with -Os and branch profiling enabled.
529	 *
530	 * Work around it by just copying the first byte again...
531	 */
532	version = policy.version;
533	if (copy_from_user(&policy, arg, size))
534		return -EFAULT;
535	policy.version = version;
536
537	if (!inode_owner_or_capable(&nop_mnt_idmap, inode))
538		return -EACCES;
539
540	ret = mnt_want_write_file(filp);
541	if (ret)
542		return ret;
543
544	inode_lock(inode);
545
546	ret = fscrypt_get_policy(inode, &existing_policy);
547	if (ret == -ENODATA) {
548		if (!S_ISDIR(inode->i_mode))
549			ret = -ENOTDIR;
550		else if (IS_DEADDIR(inode))
551			ret = -ENOENT;
552		else if (!inode->i_sb->s_cop->empty_dir(inode))
553			ret = -ENOTEMPTY;
554		else
555			ret = set_encryption_policy(inode, &policy);
556	} else if (ret == -EINVAL ||
557		   (ret == 0 && !fscrypt_policies_equal(&policy,
558							&existing_policy))) {
559		/* The file already uses a different encryption policy. */
560		ret = -EEXIST;
561	}
562
563	inode_unlock(inode);
564
565	mnt_drop_write_file(filp);
566	return ret;
567}
568EXPORT_SYMBOL(fscrypt_ioctl_set_policy);
569
570/* Original ioctl version; can only get the original policy version */
571int fscrypt_ioctl_get_policy(struct file *filp, void __user *arg)
572{
573	union fscrypt_policy policy;
574	int err;
575
576	err = fscrypt_get_policy(file_inode(filp), &policy);
577	if (err)
578		return err;
579
580	if (policy.version != FSCRYPT_POLICY_V1)
581		return -EINVAL;
582
583	if (copy_to_user(arg, &policy, sizeof(policy.v1)))
584		return -EFAULT;
585	return 0;
586}
587EXPORT_SYMBOL(fscrypt_ioctl_get_policy);
588
589/* Extended ioctl version; can get policies of any version */
590int fscrypt_ioctl_get_policy_ex(struct file *filp, void __user *uarg)
591{
592	struct fscrypt_get_policy_ex_arg arg;
593	union fscrypt_policy *policy = (union fscrypt_policy *)&arg.policy;
594	size_t policy_size;
595	int err;
596
597	/* arg is policy_size, then policy */
598	BUILD_BUG_ON(offsetof(typeof(arg), policy_size) != 0);
599	BUILD_BUG_ON(offsetofend(typeof(arg), policy_size) !=
600		     offsetof(typeof(arg), policy));
601	BUILD_BUG_ON(sizeof(arg.policy) != sizeof(*policy));
602
603	err = fscrypt_get_policy(file_inode(filp), policy);
604	if (err)
605		return err;
606	policy_size = fscrypt_policy_size(policy);
607
608	if (copy_from_user(&arg, uarg, sizeof(arg.policy_size)))
609		return -EFAULT;
610
611	if (policy_size > arg.policy_size)
612		return -EOVERFLOW;
613	arg.policy_size = policy_size;
614
615	if (copy_to_user(uarg, &arg, sizeof(arg.policy_size) + policy_size))
616		return -EFAULT;
617	return 0;
618}
619EXPORT_SYMBOL_GPL(fscrypt_ioctl_get_policy_ex);
620
621/* FS_IOC_GET_ENCRYPTION_NONCE: retrieve file's encryption nonce for testing */
622int fscrypt_ioctl_get_nonce(struct file *filp, void __user *arg)
623{
624	struct inode *inode = file_inode(filp);
625	union fscrypt_context ctx;
626	int ret;
627
628	ret = inode->i_sb->s_cop->get_context(inode, &ctx, sizeof(ctx));
629	if (ret < 0)
630		return ret;
631	if (!fscrypt_context_is_valid(&ctx, ret))
632		return -EINVAL;
633	if (copy_to_user(arg, fscrypt_context_nonce(&ctx),
634			 FSCRYPT_FILE_NONCE_SIZE))
635		return -EFAULT;
636	return 0;
637}
638EXPORT_SYMBOL_GPL(fscrypt_ioctl_get_nonce);
639
640/**
641 * fscrypt_has_permitted_context() - is a file's encryption policy permitted
642 *				     within its directory?
643 *
644 * @parent: inode for parent directory
645 * @child: inode for file being looked up, opened, or linked into @parent
646 *
647 * Filesystems must call this before permitting access to an inode in a
648 * situation where the parent directory is encrypted (either before allowing
649 * ->lookup() to succeed, or for a regular file before allowing it to be opened)
650 * and before any operation that involves linking an inode into an encrypted
651 * directory, including link, rename, and cross rename.  It enforces the
652 * constraint that within a given encrypted directory tree, all files use the
653 * same encryption policy.  The pre-access check is needed to detect potentially
654 * malicious offline violations of this constraint, while the link and rename
655 * checks are needed to prevent online violations of this constraint.
656 *
657 * Return: 1 if permitted, 0 if forbidden.
658 */
659int fscrypt_has_permitted_context(struct inode *parent, struct inode *child)
660{
661	union fscrypt_policy parent_policy, child_policy;
662	int err, err1, err2;
663
664	/* No restrictions on file types which are never encrypted */
665	if (!S_ISREG(child->i_mode) && !S_ISDIR(child->i_mode) &&
666	    !S_ISLNK(child->i_mode))
667		return 1;
668
669	/* No restrictions if the parent directory is unencrypted */
670	if (!IS_ENCRYPTED(parent))
671		return 1;
672
673	/* Encrypted directories must not contain unencrypted files */
674	if (!IS_ENCRYPTED(child))
675		return 0;
676
677	/*
678	 * Both parent and child are encrypted, so verify they use the same
679	 * encryption policy.  Compare the cached policies if the keys are
680	 * available, otherwise retrieve and compare the fscrypt_contexts.
681	 *
682	 * Note that the fscrypt_context retrieval will be required frequently
683	 * when accessing an encrypted directory tree without the key.
684	 * Performance-wise this is not a big deal because we already don't
685	 * really optimize for file access without the key (to the extent that
686	 * such access is even possible), given that any attempted access
687	 * already causes a fscrypt_context retrieval and keyring search.
688	 *
689	 * In any case, if an unexpected error occurs, fall back to "forbidden".
690	 */
691
692	err = fscrypt_get_encryption_info(parent, true);
693	if (err)
694		return 0;
695	err = fscrypt_get_encryption_info(child, true);
696	if (err)
697		return 0;
698
699	err1 = fscrypt_get_policy(parent, &parent_policy);
700	err2 = fscrypt_get_policy(child, &child_policy);
701
702	/*
703	 * Allow the case where the parent and child both have an unrecognized
704	 * encryption policy, so that files with an unrecognized encryption
705	 * policy can be deleted.
706	 */
707	if (err1 == -EINVAL && err2 == -EINVAL)
708		return 1;
709
710	if (err1 || err2)
711		return 0;
712
713	return fscrypt_policies_equal(&parent_policy, &child_policy);
714}
715EXPORT_SYMBOL(fscrypt_has_permitted_context);
716
717/*
718 * Return the encryption policy that new files in the directory will inherit, or
719 * NULL if none, or an ERR_PTR() on error.  If the directory is encrypted, also
720 * ensure that its key is set up, so that the new filename can be encrypted.
721 */
722const union fscrypt_policy *fscrypt_policy_to_inherit(struct inode *dir)
723{
724	int err;
725
726	if (IS_ENCRYPTED(dir)) {
727		err = fscrypt_require_key(dir);
728		if (err)
729			return ERR_PTR(err);
730		return &fscrypt_get_inode_info_raw(dir)->ci_policy;
731	}
732
733	return fscrypt_get_dummy_policy(dir->i_sb);
734}
735
736/**
737 * fscrypt_context_for_new_inode() - create an encryption context for a new inode
738 * @ctx: where context should be written
739 * @inode: inode from which to fetch policy and nonce
740 *
741 * Given an in-core "prepared" (via fscrypt_prepare_new_inode) inode,
742 * generate a new context and write it to ctx. ctx _must_ be at least
743 * FSCRYPT_SET_CONTEXT_MAX_SIZE bytes.
744 *
745 * Return: size of the resulting context or a negative error code.
746 */
747int fscrypt_context_for_new_inode(void *ctx, struct inode *inode)
748{
749	struct fscrypt_inode_info *ci = fscrypt_get_inode_info_raw(inode);
750
751	BUILD_BUG_ON(sizeof(union fscrypt_context) !=
752			FSCRYPT_SET_CONTEXT_MAX_SIZE);
753
754	/* fscrypt_prepare_new_inode() should have set up the key already. */
755	if (WARN_ON_ONCE(!ci))
756		return -ENOKEY;
757
758	return fscrypt_new_context(ctx, &ci->ci_policy, ci->ci_nonce);
759}
760EXPORT_SYMBOL_GPL(fscrypt_context_for_new_inode);
761
762/**
763 * fscrypt_set_context() - Set the fscrypt context of a new inode
764 * @inode: a new inode
765 * @fs_data: private data given by FS and passed to ->set_context()
766 *
767 * This should be called after fscrypt_prepare_new_inode(), generally during a
768 * filesystem transaction.  Everything here must be %GFP_NOFS-safe.
769 *
770 * Return: 0 on success, -errno on failure
771 */
772int fscrypt_set_context(struct inode *inode, void *fs_data)
773{
774	struct fscrypt_inode_info *ci;
775	union fscrypt_context ctx;
776	int ctxsize;
777
778	ctxsize = fscrypt_context_for_new_inode(&ctx, inode);
779	if (ctxsize < 0)
780		return ctxsize;
781
782	/*
783	 * This may be the first time the inode number is available, so do any
784	 * delayed key setup that requires the inode number.
785	 */
786	ci = fscrypt_get_inode_info_raw(inode);
787	if (ci->ci_policy.version == FSCRYPT_POLICY_V2 &&
788	    (ci->ci_policy.v2.flags & FSCRYPT_POLICY_FLAG_IV_INO_LBLK_32))
789		fscrypt_hash_inode_number(ci, ci->ci_master_key);
790
791	return inode->i_sb->s_cop->set_context(inode, &ctx, ctxsize, fs_data);
792}
793EXPORT_SYMBOL_GPL(fscrypt_set_context);
794
795/**
796 * fscrypt_parse_test_dummy_encryption() - parse the test_dummy_encryption mount option
797 * @param: the mount option
798 * @dummy_policy: (input/output) the place to write the dummy policy that will
799 *	result from parsing the option.  Zero-initialize this.  If a policy is
800 *	already set here (due to test_dummy_encryption being given multiple
801 *	times), then this function will verify that the policies are the same.
802 *
803 * Return: 0 on success; -EINVAL if the argument is invalid; -EEXIST if the
804 *	   argument conflicts with one already specified; or -ENOMEM.
805 */
806int fscrypt_parse_test_dummy_encryption(const struct fs_parameter *param,
807				struct fscrypt_dummy_policy *dummy_policy)
808{
809	const char *arg = "v2";
810	union fscrypt_policy *policy;
811	int err;
812
813	if (param->type == fs_value_is_string && *param->string)
814		arg = param->string;
815
816	policy = kzalloc(sizeof(*policy), GFP_KERNEL);
817	if (!policy)
818		return -ENOMEM;
819
820	if (!strcmp(arg, "v1")) {
821		policy->version = FSCRYPT_POLICY_V1;
822		policy->v1.contents_encryption_mode = FSCRYPT_MODE_AES_256_XTS;
823		policy->v1.filenames_encryption_mode = FSCRYPT_MODE_AES_256_CTS;
824		memset(policy->v1.master_key_descriptor, 0x42,
825		       FSCRYPT_KEY_DESCRIPTOR_SIZE);
826	} else if (!strcmp(arg, "v2")) {
827		policy->version = FSCRYPT_POLICY_V2;
828		policy->v2.contents_encryption_mode = FSCRYPT_MODE_AES_256_XTS;
829		policy->v2.filenames_encryption_mode = FSCRYPT_MODE_AES_256_CTS;
830		fscrypt_get_test_dummy_key_identifier(
831				policy->v2.master_key_identifier);
832	} else {
833		err = -EINVAL;
834		goto out;
835	}
836
837	if (dummy_policy->policy) {
838		if (fscrypt_policies_equal(policy, dummy_policy->policy))
839			err = 0;
840		else
841			err = -EEXIST;
842		goto out;
843	}
844	dummy_policy->policy = policy;
845	policy = NULL;
846	err = 0;
847out:
848	kfree(policy);
849	return err;
850}
851EXPORT_SYMBOL_GPL(fscrypt_parse_test_dummy_encryption);
852
853/**
854 * fscrypt_dummy_policies_equal() - check whether two dummy policies are equal
855 * @p1: the first test dummy policy (may be unset)
856 * @p2: the second test dummy policy (may be unset)
857 *
858 * Return: %true if the dummy policies are both set and equal, or both unset.
859 */
860bool fscrypt_dummy_policies_equal(const struct fscrypt_dummy_policy *p1,
861				  const struct fscrypt_dummy_policy *p2)
862{
863	if (!p1->policy && !p2->policy)
864		return true;
865	if (!p1->policy || !p2->policy)
866		return false;
867	return fscrypt_policies_equal(p1->policy, p2->policy);
868}
869EXPORT_SYMBOL_GPL(fscrypt_dummy_policies_equal);
870
871/**
872 * fscrypt_show_test_dummy_encryption() - show '-o test_dummy_encryption'
873 * @seq: the seq_file to print the option to
874 * @sep: the separator character to use
875 * @sb: the filesystem whose options are being shown
876 *
877 * Show the test_dummy_encryption mount option, if it was specified.
878 * This is mainly used for /proc/mounts.
879 */
880void fscrypt_show_test_dummy_encryption(struct seq_file *seq, char sep,
881					struct super_block *sb)
882{
883	const union fscrypt_policy *policy = fscrypt_get_dummy_policy(sb);
884	int vers;
885
886	if (!policy)
887		return;
888
889	vers = policy->version;
890	if (vers == FSCRYPT_POLICY_V1) /* Handle numbering quirk */
891		vers = 1;
892
893	seq_printf(seq, "%ctest_dummy_encryption=v%d", sep, vers);
894}
895EXPORT_SYMBOL_GPL(fscrypt_show_test_dummy_encryption);