xref: /openbmc/linux/fs/crypto/policy.c (revision 44ecda71)
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/fs_context.h>
14  #include <linux/random.h>
15  #include <linux/seq_file.h>
16  #include <linux/string.h>
17  #include <linux/mount.h>
18  #include "fscrypt_private.h"
19  
20  /**
21   * fscrypt_policies_equal() - check whether two encryption policies are the same
22   * @policy1: the first policy
23   * @policy2: the second policy
24   *
25   * Return: %true if equal, else %false
26   */
27  bool fscrypt_policies_equal(const union fscrypt_policy *policy1,
28  			    const union fscrypt_policy *policy2)
29  {
30  	if (policy1->version != policy2->version)
31  		return false;
32  
33  	return !memcmp(policy1, policy2, fscrypt_policy_size(policy1));
34  }
35  
36  int fscrypt_policy_to_key_spec(const union fscrypt_policy *policy,
37  			       struct fscrypt_key_specifier *key_spec)
38  {
39  	switch (policy->version) {
40  	case FSCRYPT_POLICY_V1:
41  		key_spec->type = FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR;
42  		memcpy(key_spec->u.descriptor, policy->v1.master_key_descriptor,
43  		       FSCRYPT_KEY_DESCRIPTOR_SIZE);
44  		return 0;
45  	case FSCRYPT_POLICY_V2:
46  		key_spec->type = FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER;
47  		memcpy(key_spec->u.identifier, policy->v2.master_key_identifier,
48  		       FSCRYPT_KEY_IDENTIFIER_SIZE);
49  		return 0;
50  	default:
51  		WARN_ON(1);
52  		return -EINVAL;
53  	}
54  }
55  
56  static const union fscrypt_policy *
57  fscrypt_get_dummy_policy(struct super_block *sb)
58  {
59  	if (!sb->s_cop->get_dummy_policy)
60  		return NULL;
61  	return sb->s_cop->get_dummy_policy(sb);
62  }
63  
64  static bool fscrypt_valid_enc_modes_v1(u32 contents_mode, u32 filenames_mode)
65  {
66  	if (contents_mode == FSCRYPT_MODE_AES_256_XTS &&
67  	    filenames_mode == FSCRYPT_MODE_AES_256_CTS)
68  		return true;
69  
70  	if (contents_mode == FSCRYPT_MODE_AES_128_CBC &&
71  	    filenames_mode == FSCRYPT_MODE_AES_128_CTS)
72  		return true;
73  
74  	if (contents_mode == FSCRYPT_MODE_ADIANTUM &&
75  	    filenames_mode == FSCRYPT_MODE_ADIANTUM)
76  		return true;
77  
78  	return false;
79  }
80  
81  static bool fscrypt_valid_enc_modes_v2(u32 contents_mode, u32 filenames_mode)
82  {
83  	if (contents_mode == FSCRYPT_MODE_AES_256_XTS &&
84  	    filenames_mode == FSCRYPT_MODE_AES_256_HCTR2)
85  		return true;
86  	return fscrypt_valid_enc_modes_v1(contents_mode, filenames_mode);
87  }
88  
89  static bool supported_direct_key_modes(const struct inode *inode,
90  				       u32 contents_mode, u32 filenames_mode)
91  {
92  	const struct fscrypt_mode *mode;
93  
94  	if (contents_mode != filenames_mode) {
95  		fscrypt_warn(inode,
96  			     "Direct key flag not allowed with different contents and filenames modes");
97  		return false;
98  	}
99  	mode = &fscrypt_modes[contents_mode];
100  
101  	if (mode->ivsize < offsetofend(union fscrypt_iv, nonce)) {
102  		fscrypt_warn(inode, "Direct key flag not allowed with %s",
103  			     mode->friendly_name);
104  		return false;
105  	}
106  	return true;
107  }
108  
109  static bool supported_iv_ino_lblk_policy(const struct fscrypt_policy_v2 *policy,
110  					 const struct inode *inode,
111  					 const char *type,
112  					 int max_ino_bits, int max_lblk_bits)
113  {
114  	struct super_block *sb = inode->i_sb;
115  	int ino_bits = 64, lblk_bits = 64;
116  
117  	/*
118  	 * IV_INO_LBLK_* exist only because of hardware limitations, and
119  	 * currently the only known use case for them involves AES-256-XTS.
120  	 * That's also all we test currently.  For these reasons, for now only
121  	 * allow AES-256-XTS here.  This can be relaxed later if a use case for
122  	 * IV_INO_LBLK_* with other encryption modes arises.
123  	 */
124  	if (policy->contents_encryption_mode != FSCRYPT_MODE_AES_256_XTS) {
125  		fscrypt_warn(inode,
126  			     "Can't use %s policy with contents mode other than AES-256-XTS",
127  			     type);
128  		return false;
129  	}
130  
131  	/*
132  	 * It's unsafe to include inode numbers in the IVs if the filesystem can
133  	 * potentially renumber inodes, e.g. via filesystem shrinking.
134  	 */
135  	if (!sb->s_cop->has_stable_inodes ||
136  	    !sb->s_cop->has_stable_inodes(sb)) {
137  		fscrypt_warn(inode,
138  			     "Can't use %s policy on filesystem '%s' because it doesn't have stable inode numbers",
139  			     type, sb->s_id);
140  		return false;
141  	}
142  	if (sb->s_cop->get_ino_and_lblk_bits)
143  		sb->s_cop->get_ino_and_lblk_bits(sb, &ino_bits, &lblk_bits);
144  	if (ino_bits > max_ino_bits) {
145  		fscrypt_warn(inode,
146  			     "Can't use %s policy on filesystem '%s' because its inode numbers are too long",
147  			     type, sb->s_id);
148  		return false;
149  	}
150  	if (lblk_bits > max_lblk_bits) {
151  		fscrypt_warn(inode,
152  			     "Can't use %s policy on filesystem '%s' because its block numbers are too long",
153  			     type, sb->s_id);
154  		return false;
155  	}
156  	return true;
157  }
158  
159  static bool fscrypt_supported_v1_policy(const struct fscrypt_policy_v1 *policy,
160  					const struct inode *inode)
161  {
162  	if (!fscrypt_valid_enc_modes_v1(policy->contents_encryption_mode,
163  				     policy->filenames_encryption_mode)) {
164  		fscrypt_warn(inode,
165  			     "Unsupported encryption modes (contents %d, filenames %d)",
166  			     policy->contents_encryption_mode,
167  			     policy->filenames_encryption_mode);
168  		return false;
169  	}
170  
171  	if (policy->flags & ~(FSCRYPT_POLICY_FLAGS_PAD_MASK |
172  			      FSCRYPT_POLICY_FLAG_DIRECT_KEY)) {
173  		fscrypt_warn(inode, "Unsupported encryption flags (0x%02x)",
174  			     policy->flags);
175  		return false;
176  	}
177  
178  	if ((policy->flags & FSCRYPT_POLICY_FLAG_DIRECT_KEY) &&
179  	    !supported_direct_key_modes(inode, policy->contents_encryption_mode,
180  					policy->filenames_encryption_mode))
181  		return false;
182  
183  	if (IS_CASEFOLDED(inode)) {
184  		/* With v1, there's no way to derive dirhash keys. */
185  		fscrypt_warn(inode,
186  			     "v1 policies can't be used on casefolded directories");
187  		return false;
188  	}
189  
190  	return true;
191  }
192  
193  static bool fscrypt_supported_v2_policy(const struct fscrypt_policy_v2 *policy,
194  					const struct inode *inode)
195  {
196  	int count = 0;
197  
198  	if (!fscrypt_valid_enc_modes_v2(policy->contents_encryption_mode,
199  				     policy->filenames_encryption_mode)) {
200  		fscrypt_warn(inode,
201  			     "Unsupported encryption modes (contents %d, filenames %d)",
202  			     policy->contents_encryption_mode,
203  			     policy->filenames_encryption_mode);
204  		return false;
205  	}
206  
207  	if (policy->flags & ~(FSCRYPT_POLICY_FLAGS_PAD_MASK |
208  			      FSCRYPT_POLICY_FLAG_DIRECT_KEY |
209  			      FSCRYPT_POLICY_FLAG_IV_INO_LBLK_64 |
210  			      FSCRYPT_POLICY_FLAG_IV_INO_LBLK_32)) {
211  		fscrypt_warn(inode, "Unsupported encryption flags (0x%02x)",
212  			     policy->flags);
213  		return false;
214  	}
215  
216  	count += !!(policy->flags & FSCRYPT_POLICY_FLAG_DIRECT_KEY);
217  	count += !!(policy->flags & FSCRYPT_POLICY_FLAG_IV_INO_LBLK_64);
218  	count += !!(policy->flags & FSCRYPT_POLICY_FLAG_IV_INO_LBLK_32);
219  	if (count > 1) {
220  		fscrypt_warn(inode, "Mutually exclusive encryption flags (0x%02x)",
221  			     policy->flags);
222  		return false;
223  	}
224  
225  	if ((policy->flags & FSCRYPT_POLICY_FLAG_DIRECT_KEY) &&
226  	    !supported_direct_key_modes(inode, policy->contents_encryption_mode,
227  					policy->filenames_encryption_mode))
228  		return false;
229  
230  	if ((policy->flags & FSCRYPT_POLICY_FLAG_IV_INO_LBLK_64) &&
231  	    !supported_iv_ino_lblk_policy(policy, inode, "IV_INO_LBLK_64",
232  					  32, 32))
233  		return false;
234  
235  	/*
236  	 * IV_INO_LBLK_32 hashes the inode number, so in principle it can
237  	 * support any ino_bits.  However, currently the inode number is gotten
238  	 * from inode::i_ino which is 'unsigned long'.  So for now the
239  	 * implementation limit is 32 bits.
240  	 */
241  	if ((policy->flags & FSCRYPT_POLICY_FLAG_IV_INO_LBLK_32) &&
242  	    !supported_iv_ino_lblk_policy(policy, inode, "IV_INO_LBLK_32",
243  					  32, 32))
244  		return false;
245  
246  	if (memchr_inv(policy->__reserved, 0, sizeof(policy->__reserved))) {
247  		fscrypt_warn(inode, "Reserved bits set in encryption policy");
248  		return false;
249  	}
250  
251  	return true;
252  }
253  
254  /**
255   * fscrypt_supported_policy() - check whether an encryption policy is supported
256   * @policy_u: the encryption policy
257   * @inode: the inode on which the policy will be used
258   *
259   * Given an encryption policy, check whether all its encryption modes and other
260   * settings are supported by this kernel on the given inode.  (But we don't
261   * currently don't check for crypto API support here, so attempting to use an
262   * algorithm not configured into the crypto API will still fail later.)
263   *
264   * Return: %true if supported, else %false
265   */
266  bool fscrypt_supported_policy(const union fscrypt_policy *policy_u,
267  			      const struct inode *inode)
268  {
269  	switch (policy_u->version) {
270  	case FSCRYPT_POLICY_V1:
271  		return fscrypt_supported_v1_policy(&policy_u->v1, inode);
272  	case FSCRYPT_POLICY_V2:
273  		return fscrypt_supported_v2_policy(&policy_u->v2, inode);
274  	}
275  	return false;
276  }
277  
278  /**
279   * fscrypt_new_context() - create a new fscrypt_context
280   * @ctx_u: output context
281   * @policy_u: input policy
282   * @nonce: nonce to use
283   *
284   * Create an fscrypt_context for an inode that is being assigned the given
285   * encryption policy.  @nonce must be a new random nonce.
286   *
287   * Return: the size of the new context in bytes.
288   */
289  static int fscrypt_new_context(union fscrypt_context *ctx_u,
290  			       const union fscrypt_policy *policy_u,
291  			       const u8 nonce[FSCRYPT_FILE_NONCE_SIZE])
292  {
293  	memset(ctx_u, 0, sizeof(*ctx_u));
294  
295  	switch (policy_u->version) {
296  	case FSCRYPT_POLICY_V1: {
297  		const struct fscrypt_policy_v1 *policy = &policy_u->v1;
298  		struct fscrypt_context_v1 *ctx = &ctx_u->v1;
299  
300  		ctx->version = FSCRYPT_CONTEXT_V1;
301  		ctx->contents_encryption_mode =
302  			policy->contents_encryption_mode;
303  		ctx->filenames_encryption_mode =
304  			policy->filenames_encryption_mode;
305  		ctx->flags = policy->flags;
306  		memcpy(ctx->master_key_descriptor,
307  		       policy->master_key_descriptor,
308  		       sizeof(ctx->master_key_descriptor));
309  		memcpy(ctx->nonce, nonce, FSCRYPT_FILE_NONCE_SIZE);
310  		return sizeof(*ctx);
311  	}
312  	case FSCRYPT_POLICY_V2: {
313  		const struct fscrypt_policy_v2 *policy = &policy_u->v2;
314  		struct fscrypt_context_v2 *ctx = &ctx_u->v2;
315  
316  		ctx->version = FSCRYPT_CONTEXT_V2;
317  		ctx->contents_encryption_mode =
318  			policy->contents_encryption_mode;
319  		ctx->filenames_encryption_mode =
320  			policy->filenames_encryption_mode;
321  		ctx->flags = policy->flags;
322  		memcpy(ctx->master_key_identifier,
323  		       policy->master_key_identifier,
324  		       sizeof(ctx->master_key_identifier));
325  		memcpy(ctx->nonce, nonce, FSCRYPT_FILE_NONCE_SIZE);
326  		return sizeof(*ctx);
327  	}
328  	}
329  	BUG();
330  }
331  
332  /**
333   * fscrypt_policy_from_context() - convert an fscrypt_context to
334   *				   an fscrypt_policy
335   * @policy_u: output policy
336   * @ctx_u: input context
337   * @ctx_size: size of input context in bytes
338   *
339   * Given an fscrypt_context, build the corresponding fscrypt_policy.
340   *
341   * Return: 0 on success, or -EINVAL if the fscrypt_context has an unrecognized
342   * version number or size.
343   *
344   * This does *not* validate the settings within the policy itself, e.g. the
345   * modes, flags, and reserved bits.  Use fscrypt_supported_policy() for that.
346   */
347  int fscrypt_policy_from_context(union fscrypt_policy *policy_u,
348  				const union fscrypt_context *ctx_u,
349  				int ctx_size)
350  {
351  	memset(policy_u, 0, sizeof(*policy_u));
352  
353  	if (!fscrypt_context_is_valid(ctx_u, ctx_size))
354  		return -EINVAL;
355  
356  	switch (ctx_u->version) {
357  	case FSCRYPT_CONTEXT_V1: {
358  		const struct fscrypt_context_v1 *ctx = &ctx_u->v1;
359  		struct fscrypt_policy_v1 *policy = &policy_u->v1;
360  
361  		policy->version = FSCRYPT_POLICY_V1;
362  		policy->contents_encryption_mode =
363  			ctx->contents_encryption_mode;
364  		policy->filenames_encryption_mode =
365  			ctx->filenames_encryption_mode;
366  		policy->flags = ctx->flags;
367  		memcpy(policy->master_key_descriptor,
368  		       ctx->master_key_descriptor,
369  		       sizeof(policy->master_key_descriptor));
370  		return 0;
371  	}
372  	case FSCRYPT_CONTEXT_V2: {
373  		const struct fscrypt_context_v2 *ctx = &ctx_u->v2;
374  		struct fscrypt_policy_v2 *policy = &policy_u->v2;
375  
376  		policy->version = FSCRYPT_POLICY_V2;
377  		policy->contents_encryption_mode =
378  			ctx->contents_encryption_mode;
379  		policy->filenames_encryption_mode =
380  			ctx->filenames_encryption_mode;
381  		policy->flags = ctx->flags;
382  		memcpy(policy->__reserved, ctx->__reserved,
383  		       sizeof(policy->__reserved));
384  		memcpy(policy->master_key_identifier,
385  		       ctx->master_key_identifier,
386  		       sizeof(policy->master_key_identifier));
387  		return 0;
388  	}
389  	}
390  	/* unreachable */
391  	return -EINVAL;
392  }
393  
394  /* Retrieve an inode's encryption policy */
395  static int fscrypt_get_policy(struct inode *inode, union fscrypt_policy *policy)
396  {
397  	const struct fscrypt_info *ci;
398  	union fscrypt_context ctx;
399  	int ret;
400  
401  	ci = fscrypt_get_info(inode);
402  	if (ci) {
403  		/* key available, use the cached policy */
404  		*policy = ci->ci_policy;
405  		return 0;
406  	}
407  
408  	if (!IS_ENCRYPTED(inode))
409  		return -ENODATA;
410  
411  	ret = inode->i_sb->s_cop->get_context(inode, &ctx, sizeof(ctx));
412  	if (ret < 0)
413  		return (ret == -ERANGE) ? -EINVAL : ret;
414  
415  	return fscrypt_policy_from_context(policy, &ctx, ret);
416  }
417  
418  static int set_encryption_policy(struct inode *inode,
419  				 const union fscrypt_policy *policy)
420  {
421  	u8 nonce[FSCRYPT_FILE_NONCE_SIZE];
422  	union fscrypt_context ctx;
423  	int ctxsize;
424  	int err;
425  
426  	if (!fscrypt_supported_policy(policy, inode))
427  		return -EINVAL;
428  
429  	switch (policy->version) {
430  	case FSCRYPT_POLICY_V1:
431  		/*
432  		 * The original encryption policy version provided no way of
433  		 * verifying that the correct master key was supplied, which was
434  		 * insecure in scenarios where multiple users have access to the
435  		 * same encrypted files (even just read-only access).  The new
436  		 * encryption policy version fixes this and also implies use of
437  		 * an improved key derivation function and allows non-root users
438  		 * to securely remove keys.  So as long as compatibility with
439  		 * old kernels isn't required, it is recommended to use the new
440  		 * policy version for all new encrypted directories.
441  		 */
442  		pr_warn_once("%s (pid %d) is setting deprecated v1 encryption policy; recommend upgrading to v2.\n",
443  			     current->comm, current->pid);
444  		break;
445  	case FSCRYPT_POLICY_V2:
446  		err = fscrypt_verify_key_added(inode->i_sb,
447  					       policy->v2.master_key_identifier);
448  		if (err)
449  			return err;
450  		if (policy->v2.flags & FSCRYPT_POLICY_FLAG_IV_INO_LBLK_32)
451  			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",
452  				     current->comm, current->pid);
453  		break;
454  	default:
455  		WARN_ON(1);
456  		return -EINVAL;
457  	}
458  
459  	get_random_bytes(nonce, FSCRYPT_FILE_NONCE_SIZE);
460  	ctxsize = fscrypt_new_context(&ctx, policy, nonce);
461  
462  	return inode->i_sb->s_cop->set_context(inode, &ctx, ctxsize, NULL);
463  }
464  
465  int fscrypt_ioctl_set_policy(struct file *filp, const void __user *arg)
466  {
467  	union fscrypt_policy policy;
468  	union fscrypt_policy existing_policy;
469  	struct inode *inode = file_inode(filp);
470  	u8 version;
471  	int size;
472  	int ret;
473  
474  	if (get_user(policy.version, (const u8 __user *)arg))
475  		return -EFAULT;
476  
477  	size = fscrypt_policy_size(&policy);
478  	if (size <= 0)
479  		return -EINVAL;
480  
481  	/*
482  	 * We should just copy the remaining 'size - 1' bytes here, but a
483  	 * bizarre bug in gcc 7 and earlier (fixed by gcc r255731) causes gcc to
484  	 * think that size can be 0 here (despite the check above!) *and* that
485  	 * it's a compile-time constant.  Thus it would think copy_from_user()
486  	 * is passed compile-time constant ULONG_MAX, causing the compile-time
487  	 * buffer overflow check to fail, breaking the build. This only occurred
488  	 * when building an i386 kernel with -Os and branch profiling enabled.
489  	 *
490  	 * Work around it by just copying the first byte again...
491  	 */
492  	version = policy.version;
493  	if (copy_from_user(&policy, arg, size))
494  		return -EFAULT;
495  	policy.version = version;
496  
497  	if (!inode_owner_or_capable(&init_user_ns, inode))
498  		return -EACCES;
499  
500  	ret = mnt_want_write_file(filp);
501  	if (ret)
502  		return ret;
503  
504  	inode_lock(inode);
505  
506  	ret = fscrypt_get_policy(inode, &existing_policy);
507  	if (ret == -ENODATA) {
508  		if (!S_ISDIR(inode->i_mode))
509  			ret = -ENOTDIR;
510  		else if (IS_DEADDIR(inode))
511  			ret = -ENOENT;
512  		else if (!inode->i_sb->s_cop->empty_dir(inode))
513  			ret = -ENOTEMPTY;
514  		else
515  			ret = set_encryption_policy(inode, &policy);
516  	} else if (ret == -EINVAL ||
517  		   (ret == 0 && !fscrypt_policies_equal(&policy,
518  							&existing_policy))) {
519  		/* The file already uses a different encryption policy. */
520  		ret = -EEXIST;
521  	}
522  
523  	inode_unlock(inode);
524  
525  	mnt_drop_write_file(filp);
526  	return ret;
527  }
528  EXPORT_SYMBOL(fscrypt_ioctl_set_policy);
529  
530  /* Original ioctl version; can only get the original policy version */
531  int fscrypt_ioctl_get_policy(struct file *filp, void __user *arg)
532  {
533  	union fscrypt_policy policy;
534  	int err;
535  
536  	err = fscrypt_get_policy(file_inode(filp), &policy);
537  	if (err)
538  		return err;
539  
540  	if (policy.version != FSCRYPT_POLICY_V1)
541  		return -EINVAL;
542  
543  	if (copy_to_user(arg, &policy, sizeof(policy.v1)))
544  		return -EFAULT;
545  	return 0;
546  }
547  EXPORT_SYMBOL(fscrypt_ioctl_get_policy);
548  
549  /* Extended ioctl version; can get policies of any version */
550  int fscrypt_ioctl_get_policy_ex(struct file *filp, void __user *uarg)
551  {
552  	struct fscrypt_get_policy_ex_arg arg;
553  	union fscrypt_policy *policy = (union fscrypt_policy *)&arg.policy;
554  	size_t policy_size;
555  	int err;
556  
557  	/* arg is policy_size, then policy */
558  	BUILD_BUG_ON(offsetof(typeof(arg), policy_size) != 0);
559  	BUILD_BUG_ON(offsetofend(typeof(arg), policy_size) !=
560  		     offsetof(typeof(arg), policy));
561  	BUILD_BUG_ON(sizeof(arg.policy) != sizeof(*policy));
562  
563  	err = fscrypt_get_policy(file_inode(filp), policy);
564  	if (err)
565  		return err;
566  	policy_size = fscrypt_policy_size(policy);
567  
568  	if (copy_from_user(&arg, uarg, sizeof(arg.policy_size)))
569  		return -EFAULT;
570  
571  	if (policy_size > arg.policy_size)
572  		return -EOVERFLOW;
573  	arg.policy_size = policy_size;
574  
575  	if (copy_to_user(uarg, &arg, sizeof(arg.policy_size) + policy_size))
576  		return -EFAULT;
577  	return 0;
578  }
579  EXPORT_SYMBOL_GPL(fscrypt_ioctl_get_policy_ex);
580  
581  /* FS_IOC_GET_ENCRYPTION_NONCE: retrieve file's encryption nonce for testing */
582  int fscrypt_ioctl_get_nonce(struct file *filp, void __user *arg)
583  {
584  	struct inode *inode = file_inode(filp);
585  	union fscrypt_context ctx;
586  	int ret;
587  
588  	ret = inode->i_sb->s_cop->get_context(inode, &ctx, sizeof(ctx));
589  	if (ret < 0)
590  		return ret;
591  	if (!fscrypt_context_is_valid(&ctx, ret))
592  		return -EINVAL;
593  	if (copy_to_user(arg, fscrypt_context_nonce(&ctx),
594  			 FSCRYPT_FILE_NONCE_SIZE))
595  		return -EFAULT;
596  	return 0;
597  }
598  EXPORT_SYMBOL_GPL(fscrypt_ioctl_get_nonce);
599  
600  /**
601   * fscrypt_has_permitted_context() - is a file's encryption policy permitted
602   *				     within its directory?
603   *
604   * @parent: inode for parent directory
605   * @child: inode for file being looked up, opened, or linked into @parent
606   *
607   * Filesystems must call this before permitting access to an inode in a
608   * situation where the parent directory is encrypted (either before allowing
609   * ->lookup() to succeed, or for a regular file before allowing it to be opened)
610   * and before any operation that involves linking an inode into an encrypted
611   * directory, including link, rename, and cross rename.  It enforces the
612   * constraint that within a given encrypted directory tree, all files use the
613   * same encryption policy.  The pre-access check is needed to detect potentially
614   * malicious offline violations of this constraint, while the link and rename
615   * checks are needed to prevent online violations of this constraint.
616   *
617   * Return: 1 if permitted, 0 if forbidden.
618   */
619  int fscrypt_has_permitted_context(struct inode *parent, struct inode *child)
620  {
621  	union fscrypt_policy parent_policy, child_policy;
622  	int err, err1, err2;
623  
624  	/* No restrictions on file types which are never encrypted */
625  	if (!S_ISREG(child->i_mode) && !S_ISDIR(child->i_mode) &&
626  	    !S_ISLNK(child->i_mode))
627  		return 1;
628  
629  	/* No restrictions if the parent directory is unencrypted */
630  	if (!IS_ENCRYPTED(parent))
631  		return 1;
632  
633  	/* Encrypted directories must not contain unencrypted files */
634  	if (!IS_ENCRYPTED(child))
635  		return 0;
636  
637  	/*
638  	 * Both parent and child are encrypted, so verify they use the same
639  	 * encryption policy.  Compare the fscrypt_info structs if the keys are
640  	 * available, otherwise retrieve and compare the fscrypt_contexts.
641  	 *
642  	 * Note that the fscrypt_context retrieval will be required frequently
643  	 * when accessing an encrypted directory tree without the key.
644  	 * Performance-wise this is not a big deal because we already don't
645  	 * really optimize for file access without the key (to the extent that
646  	 * such access is even possible), given that any attempted access
647  	 * already causes a fscrypt_context retrieval and keyring search.
648  	 *
649  	 * In any case, if an unexpected error occurs, fall back to "forbidden".
650  	 */
651  
652  	err = fscrypt_get_encryption_info(parent, true);
653  	if (err)
654  		return 0;
655  	err = fscrypt_get_encryption_info(child, true);
656  	if (err)
657  		return 0;
658  
659  	err1 = fscrypt_get_policy(parent, &parent_policy);
660  	err2 = fscrypt_get_policy(child, &child_policy);
661  
662  	/*
663  	 * Allow the case where the parent and child both have an unrecognized
664  	 * encryption policy, so that files with an unrecognized encryption
665  	 * policy can be deleted.
666  	 */
667  	if (err1 == -EINVAL && err2 == -EINVAL)
668  		return 1;
669  
670  	if (err1 || err2)
671  		return 0;
672  
673  	return fscrypt_policies_equal(&parent_policy, &child_policy);
674  }
675  EXPORT_SYMBOL(fscrypt_has_permitted_context);
676  
677  /*
678   * Return the encryption policy that new files in the directory will inherit, or
679   * NULL if none, or an ERR_PTR() on error.  If the directory is encrypted, also
680   * ensure that its key is set up, so that the new filename can be encrypted.
681   */
682  const union fscrypt_policy *fscrypt_policy_to_inherit(struct inode *dir)
683  {
684  	int err;
685  
686  	if (IS_ENCRYPTED(dir)) {
687  		err = fscrypt_require_key(dir);
688  		if (err)
689  			return ERR_PTR(err);
690  		return &dir->i_crypt_info->ci_policy;
691  	}
692  
693  	return fscrypt_get_dummy_policy(dir->i_sb);
694  }
695  
696  /**
697   * fscrypt_context_for_new_inode() - create an encryption context for a new inode
698   * @ctx: where context should be written
699   * @inode: inode from which to fetch policy and nonce
700   *
701   * Given an in-core "prepared" (via fscrypt_prepare_new_inode) inode,
702   * generate a new context and write it to ctx. ctx _must_ be at least
703   * FSCRYPT_SET_CONTEXT_MAX_SIZE bytes.
704   *
705   * Return: size of the resulting context or a negative error code.
706   */
707  int fscrypt_context_for_new_inode(void *ctx, struct inode *inode)
708  {
709  	struct fscrypt_info *ci = inode->i_crypt_info;
710  
711  	BUILD_BUG_ON(sizeof(union fscrypt_context) !=
712  			FSCRYPT_SET_CONTEXT_MAX_SIZE);
713  
714  	/* fscrypt_prepare_new_inode() should have set up the key already. */
715  	if (WARN_ON_ONCE(!ci))
716  		return -ENOKEY;
717  
718  	return fscrypt_new_context(ctx, &ci->ci_policy, ci->ci_nonce);
719  }
720  EXPORT_SYMBOL_GPL(fscrypt_context_for_new_inode);
721  
722  /**
723   * fscrypt_set_context() - Set the fscrypt context of a new inode
724   * @inode: a new inode
725   * @fs_data: private data given by FS and passed to ->set_context()
726   *
727   * This should be called after fscrypt_prepare_new_inode(), generally during a
728   * filesystem transaction.  Everything here must be %GFP_NOFS-safe.
729   *
730   * Return: 0 on success, -errno on failure
731   */
732  int fscrypt_set_context(struct inode *inode, void *fs_data)
733  {
734  	struct fscrypt_info *ci = inode->i_crypt_info;
735  	union fscrypt_context ctx;
736  	int ctxsize;
737  
738  	ctxsize = fscrypt_context_for_new_inode(&ctx, inode);
739  	if (ctxsize < 0)
740  		return ctxsize;
741  
742  	/*
743  	 * This may be the first time the inode number is available, so do any
744  	 * delayed key setup that requires the inode number.
745  	 */
746  	if (ci->ci_policy.version == FSCRYPT_POLICY_V2 &&
747  	    (ci->ci_policy.v2.flags & FSCRYPT_POLICY_FLAG_IV_INO_LBLK_32))
748  		fscrypt_hash_inode_number(ci, ci->ci_master_key);
749  
750  	return inode->i_sb->s_cop->set_context(inode, &ctx, ctxsize, fs_data);
751  }
752  EXPORT_SYMBOL_GPL(fscrypt_set_context);
753  
754  /**
755   * fscrypt_parse_test_dummy_encryption() - parse the test_dummy_encryption mount option
756   * @param: the mount option
757   * @dummy_policy: (input/output) the place to write the dummy policy that will
758   *	result from parsing the option.  Zero-initialize this.  If a policy is
759   *	already set here (due to test_dummy_encryption being given multiple
760   *	times), then this function will verify that the policies are the same.
761   *
762   * Return: 0 on success; -EINVAL if the argument is invalid; -EEXIST if the
763   *	   argument conflicts with one already specified; or -ENOMEM.
764   */
765  int fscrypt_parse_test_dummy_encryption(const struct fs_parameter *param,
766  				struct fscrypt_dummy_policy *dummy_policy)
767  {
768  	const char *arg = "v2";
769  	union fscrypt_policy *policy;
770  	int err;
771  
772  	if (param->type == fs_value_is_string && *param->string)
773  		arg = param->string;
774  
775  	policy = kzalloc(sizeof(*policy), GFP_KERNEL);
776  	if (!policy)
777  		return -ENOMEM;
778  
779  	if (!strcmp(arg, "v1")) {
780  		policy->version = FSCRYPT_POLICY_V1;
781  		policy->v1.contents_encryption_mode = FSCRYPT_MODE_AES_256_XTS;
782  		policy->v1.filenames_encryption_mode = FSCRYPT_MODE_AES_256_CTS;
783  		memset(policy->v1.master_key_descriptor, 0x42,
784  		       FSCRYPT_KEY_DESCRIPTOR_SIZE);
785  	} else if (!strcmp(arg, "v2")) {
786  		policy->version = FSCRYPT_POLICY_V2;
787  		policy->v2.contents_encryption_mode = FSCRYPT_MODE_AES_256_XTS;
788  		policy->v2.filenames_encryption_mode = FSCRYPT_MODE_AES_256_CTS;
789  		err = fscrypt_get_test_dummy_key_identifier(
790  				policy->v2.master_key_identifier);
791  		if (err)
792  			goto out;
793  	} else {
794  		err = -EINVAL;
795  		goto out;
796  	}
797  
798  	if (dummy_policy->policy) {
799  		if (fscrypt_policies_equal(policy, dummy_policy->policy))
800  			err = 0;
801  		else
802  			err = -EEXIST;
803  		goto out;
804  	}
805  	dummy_policy->policy = policy;
806  	policy = NULL;
807  	err = 0;
808  out:
809  	kfree(policy);
810  	return err;
811  }
812  EXPORT_SYMBOL_GPL(fscrypt_parse_test_dummy_encryption);
813  
814  /**
815   * fscrypt_dummy_policies_equal() - check whether two dummy policies are equal
816   * @p1: the first test dummy policy (may be unset)
817   * @p2: the second test dummy policy (may be unset)
818   *
819   * Return: %true if the dummy policies are both set and equal, or both unset.
820   */
821  bool fscrypt_dummy_policies_equal(const struct fscrypt_dummy_policy *p1,
822  				  const struct fscrypt_dummy_policy *p2)
823  {
824  	if (!p1->policy && !p2->policy)
825  		return true;
826  	if (!p1->policy || !p2->policy)
827  		return false;
828  	return fscrypt_policies_equal(p1->policy, p2->policy);
829  }
830  EXPORT_SYMBOL_GPL(fscrypt_dummy_policies_equal);
831  
832  /**
833   * fscrypt_show_test_dummy_encryption() - show '-o test_dummy_encryption'
834   * @seq: the seq_file to print the option to
835   * @sep: the separator character to use
836   * @sb: the filesystem whose options are being shown
837   *
838   * Show the test_dummy_encryption mount option, if it was specified.
839   * This is mainly used for /proc/mounts.
840   */
841  void fscrypt_show_test_dummy_encryption(struct seq_file *seq, char sep,
842  					struct super_block *sb)
843  {
844  	const union fscrypt_policy *policy = fscrypt_get_dummy_policy(sb);
845  	int vers;
846  
847  	if (!policy)
848  		return;
849  
850  	vers = policy->version;
851  	if (vers == FSCRYPT_POLICY_V1) /* Handle numbering quirk */
852  		vers = 1;
853  
854  	seq_printf(seq, "%ctest_dummy_encryption=v%d", sep, vers);
855  }
856  EXPORT_SYMBOL_GPL(fscrypt_show_test_dummy_encryption);
857