policy.c (1bdd3e05a0a3b4a97ea88bc46fef8fb265c8b94c) policy.c (6e1918cfb263acacd3fc9239127732b69de64695)
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/random.h>
14#include <linux/string.h>
15#include <linux/mount.h>
16#include "fscrypt_private.h"
17
18/**
19 * fscrypt_policies_equal - check whether two encryption policies are the same
20 *
21 * Return: %true if equal, else %false
22 */
23bool fscrypt_policies_equal(const union fscrypt_policy *policy1,
24 const union fscrypt_policy *policy2)
25{
26 if (policy1->version != policy2->version)
27 return false;
28
29 return !memcmp(policy1, policy2, fscrypt_policy_size(policy1));
30}
31
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/random.h>
14#include <linux/string.h>
15#include <linux/mount.h>
16#include "fscrypt_private.h"
17
18/**
19 * fscrypt_policies_equal - check whether two encryption policies are the same
20 *
21 * Return: %true if equal, else %false
22 */
23bool fscrypt_policies_equal(const union fscrypt_policy *policy1,
24 const union fscrypt_policy *policy2)
25{
26 if (policy1->version != policy2->version)
27 return false;
28
29 return !memcmp(policy1, policy2, fscrypt_policy_size(policy1));
30}
31
32static bool fscrypt_valid_enc_modes(u32 contents_mode, u32 filenames_mode)
33{
34 if (contents_mode == FSCRYPT_MODE_AES_256_XTS &&
35 filenames_mode == FSCRYPT_MODE_AES_256_CTS)
36 return true;
37
38 if (contents_mode == FSCRYPT_MODE_AES_128_CBC &&
39 filenames_mode == FSCRYPT_MODE_AES_128_CTS)
40 return true;
41
42 if (contents_mode == FSCRYPT_MODE_ADIANTUM &&
43 filenames_mode == FSCRYPT_MODE_ADIANTUM)
44 return true;
45
46 return false;
47}
48
49static bool supported_direct_key_modes(const struct inode *inode,
50 u32 contents_mode, u32 filenames_mode)
51{
52 const struct fscrypt_mode *mode;
53
54 if (contents_mode != filenames_mode) {
55 fscrypt_warn(inode,
56 "Direct key flag not allowed with different contents and filenames modes");
57 return false;
58 }
59 mode = &fscrypt_modes[contents_mode];
60
61 if (mode->ivsize < offsetofend(union fscrypt_iv, nonce)) {
62 fscrypt_warn(inode, "Direct key flag not allowed with %s",
63 mode->friendly_name);
64 return false;
65 }
66 return true;
67}
68
32static bool supported_iv_ino_lblk_64_policy(
33 const struct fscrypt_policy_v2 *policy,
34 const struct inode *inode)
35{
36 struct super_block *sb = inode->i_sb;
37 int ino_bits = 64, lblk_bits = 64;
38
39 if (policy->flags & FSCRYPT_POLICY_FLAG_DIRECT_KEY) {
40 fscrypt_warn(inode,
41 "The DIRECT_KEY and IV_INO_LBLK_64 flags are mutually exclusive");
42 return false;
43 }
44 /*
45 * It's unsafe to include inode numbers in the IVs if the filesystem can
46 * potentially renumber inodes, e.g. via filesystem shrinking.
47 */
48 if (!sb->s_cop->has_stable_inodes ||
49 !sb->s_cop->has_stable_inodes(sb)) {
50 fscrypt_warn(inode,
51 "Can't use IV_INO_LBLK_64 policy on filesystem '%s' because it doesn't have stable inode numbers",
52 sb->s_id);
53 return false;
54 }
55 if (sb->s_cop->get_ino_and_lblk_bits)
56 sb->s_cop->get_ino_and_lblk_bits(sb, &ino_bits, &lblk_bits);
57 if (ino_bits > 32 || lblk_bits > 32) {
58 fscrypt_warn(inode,
59 "Can't use IV_INO_LBLK_64 policy on filesystem '%s' because it doesn't use 32-bit inode and block numbers",
60 sb->s_id);
61 return false;
62 }
63 return true;
64}
65
69static bool supported_iv_ino_lblk_64_policy(
70 const struct fscrypt_policy_v2 *policy,
71 const struct inode *inode)
72{
73 struct super_block *sb = inode->i_sb;
74 int ino_bits = 64, lblk_bits = 64;
75
76 if (policy->flags & FSCRYPT_POLICY_FLAG_DIRECT_KEY) {
77 fscrypt_warn(inode,
78 "The DIRECT_KEY and IV_INO_LBLK_64 flags are mutually exclusive");
79 return false;
80 }
81 /*
82 * It's unsafe to include inode numbers in the IVs if the filesystem can
83 * potentially renumber inodes, e.g. via filesystem shrinking.
84 */
85 if (!sb->s_cop->has_stable_inodes ||
86 !sb->s_cop->has_stable_inodes(sb)) {
87 fscrypt_warn(inode,
88 "Can't use IV_INO_LBLK_64 policy on filesystem '%s' because it doesn't have stable inode numbers",
89 sb->s_id);
90 return false;
91 }
92 if (sb->s_cop->get_ino_and_lblk_bits)
93 sb->s_cop->get_ino_and_lblk_bits(sb, &ino_bits, &lblk_bits);
94 if (ino_bits > 32 || lblk_bits > 32) {
95 fscrypt_warn(inode,
96 "Can't use IV_INO_LBLK_64 policy on filesystem '%s' because it doesn't use 32-bit inode and block numbers",
97 sb->s_id);
98 return false;
99 }
100 return true;
101}
102
103static bool fscrypt_supported_v1_policy(const struct fscrypt_policy_v1 *policy,
104 const struct inode *inode)
105{
106 if (!fscrypt_valid_enc_modes(policy->contents_encryption_mode,
107 policy->filenames_encryption_mode)) {
108 fscrypt_warn(inode,
109 "Unsupported encryption modes (contents %d, filenames %d)",
110 policy->contents_encryption_mode,
111 policy->filenames_encryption_mode);
112 return false;
113 }
114
115 if (policy->flags & ~(FSCRYPT_POLICY_FLAGS_PAD_MASK |
116 FSCRYPT_POLICY_FLAG_DIRECT_KEY)) {
117 fscrypt_warn(inode, "Unsupported encryption flags (0x%02x)",
118 policy->flags);
119 return false;
120 }
121
122 if ((policy->flags & FSCRYPT_POLICY_FLAG_DIRECT_KEY) &&
123 !supported_direct_key_modes(inode, policy->contents_encryption_mode,
124 policy->filenames_encryption_mode))
125 return false;
126
127 if (IS_CASEFOLDED(inode)) {
128 /* With v1, there's no way to derive dirhash keys. */
129 fscrypt_warn(inode,
130 "v1 policies can't be used on casefolded directories");
131 return false;
132 }
133
134 return true;
135}
136
137static bool fscrypt_supported_v2_policy(const struct fscrypt_policy_v2 *policy,
138 const struct inode *inode)
139{
140 if (!fscrypt_valid_enc_modes(policy->contents_encryption_mode,
141 policy->filenames_encryption_mode)) {
142 fscrypt_warn(inode,
143 "Unsupported encryption modes (contents %d, filenames %d)",
144 policy->contents_encryption_mode,
145 policy->filenames_encryption_mode);
146 return false;
147 }
148
149 if (policy->flags & ~FSCRYPT_POLICY_FLAGS_VALID) {
150 fscrypt_warn(inode, "Unsupported encryption flags (0x%02x)",
151 policy->flags);
152 return false;
153 }
154
155 if ((policy->flags & FSCRYPT_POLICY_FLAG_DIRECT_KEY) &&
156 !supported_direct_key_modes(inode, policy->contents_encryption_mode,
157 policy->filenames_encryption_mode))
158 return false;
159
160 if ((policy->flags & FSCRYPT_POLICY_FLAG_IV_INO_LBLK_64) &&
161 !supported_iv_ino_lblk_64_policy(policy, inode))
162 return false;
163
164 if (memchr_inv(policy->__reserved, 0, sizeof(policy->__reserved))) {
165 fscrypt_warn(inode, "Reserved bits set in encryption policy");
166 return false;
167 }
168
169 return true;
170}
171
66/**
67 * fscrypt_supported_policy - check whether an encryption policy is supported
68 *
69 * Given an encryption policy, check whether all its encryption modes and other
172/**
173 * fscrypt_supported_policy - check whether an encryption policy is supported
174 *
175 * Given an encryption policy, check whether all its encryption modes and other
70 * settings are supported by this kernel. (But we don't currently don't check
71 * for crypto API support here, so attempting to use an algorithm not configured
72 * into the crypto API will still fail later.)
176 * settings are supported by this kernel on the given inode. (But we don't
177 * currently don't check for crypto API support here, so attempting to use an
178 * algorithm not configured into the crypto API will still fail later.)
73 *
74 * Return: %true if supported, else %false
75 */
76bool fscrypt_supported_policy(const union fscrypt_policy *policy_u,
77 const struct inode *inode)
78{
79 switch (policy_u->version) {
179 *
180 * Return: %true if supported, else %false
181 */
182bool fscrypt_supported_policy(const union fscrypt_policy *policy_u,
183 const struct inode *inode)
184{
185 switch (policy_u->version) {
80 case FSCRYPT_POLICY_V1: {
81 const struct fscrypt_policy_v1 *policy = &policy_u->v1;
82
83 if (!fscrypt_valid_enc_modes(policy->contents_encryption_mode,
84 policy->filenames_encryption_mode)) {
85 fscrypt_warn(inode,
86 "Unsupported encryption modes (contents %d, filenames %d)",
87 policy->contents_encryption_mode,
88 policy->filenames_encryption_mode);
89 return false;
90 }
91
92 if (policy->flags & ~(FSCRYPT_POLICY_FLAGS_PAD_MASK |
93 FSCRYPT_POLICY_FLAG_DIRECT_KEY)) {
94 fscrypt_warn(inode,
95 "Unsupported encryption flags (0x%02x)",
96 policy->flags);
97 return false;
98 }
99
100 return true;
186 case FSCRYPT_POLICY_V1:
187 return fscrypt_supported_v1_policy(&policy_u->v1, inode);
188 case FSCRYPT_POLICY_V2:
189 return fscrypt_supported_v2_policy(&policy_u->v2, inode);
101 }
190 }
102 case FSCRYPT_POLICY_V2: {
103 const struct fscrypt_policy_v2 *policy = &policy_u->v2;
104
105 if (!fscrypt_valid_enc_modes(policy->contents_encryption_mode,
106 policy->filenames_encryption_mode)) {
107 fscrypt_warn(inode,
108 "Unsupported encryption modes (contents %d, filenames %d)",
109 policy->contents_encryption_mode,
110 policy->filenames_encryption_mode);
111 return false;
112 }
113
114 if (policy->flags & ~FSCRYPT_POLICY_FLAGS_VALID) {
115 fscrypt_warn(inode,
116 "Unsupported encryption flags (0x%02x)",
117 policy->flags);
118 return false;
119 }
120
121 if ((policy->flags & FSCRYPT_POLICY_FLAG_IV_INO_LBLK_64) &&
122 !supported_iv_ino_lblk_64_policy(policy, inode))
123 return false;
124
125 if (memchr_inv(policy->__reserved, 0,
126 sizeof(policy->__reserved))) {
127 fscrypt_warn(inode,
128 "Reserved bits set in encryption policy");
129 return false;
130 }
131
132 return true;
133 }
134 }
135 return false;
136}
137
138/**
139 * fscrypt_new_context_from_policy - create a new fscrypt_context from a policy
140 *
141 * Create an fscrypt_context for an inode that is being assigned the given
142 * encryption policy. A new nonce is randomly generated.
143 *
144 * Return: the size of the new context in bytes.
145 */
146static int fscrypt_new_context_from_policy(union fscrypt_context *ctx_u,
147 const union fscrypt_policy *policy_u)
148{
149 memset(ctx_u, 0, sizeof(*ctx_u));
150
151 switch (policy_u->version) {
152 case FSCRYPT_POLICY_V1: {
153 const struct fscrypt_policy_v1 *policy = &policy_u->v1;
154 struct fscrypt_context_v1 *ctx = &ctx_u->v1;
155
156 ctx->version = FSCRYPT_CONTEXT_V1;
157 ctx->contents_encryption_mode =
158 policy->contents_encryption_mode;
159 ctx->filenames_encryption_mode =
160 policy->filenames_encryption_mode;
161 ctx->flags = policy->flags;
162 memcpy(ctx->master_key_descriptor,
163 policy->master_key_descriptor,
164 sizeof(ctx->master_key_descriptor));
165 get_random_bytes(ctx->nonce, sizeof(ctx->nonce));
166 return sizeof(*ctx);
167 }
168 case FSCRYPT_POLICY_V2: {
169 const struct fscrypt_policy_v2 *policy = &policy_u->v2;
170 struct fscrypt_context_v2 *ctx = &ctx_u->v2;
171
172 ctx->version = FSCRYPT_CONTEXT_V2;
173 ctx->contents_encryption_mode =
174 policy->contents_encryption_mode;
175 ctx->filenames_encryption_mode =
176 policy->filenames_encryption_mode;
177 ctx->flags = policy->flags;
178 memcpy(ctx->master_key_identifier,
179 policy->master_key_identifier,
180 sizeof(ctx->master_key_identifier));
181 get_random_bytes(ctx->nonce, sizeof(ctx->nonce));
182 return sizeof(*ctx);
183 }
184 }
185 BUG();
186}
187
188/**
189 * fscrypt_policy_from_context - convert an fscrypt_context to an fscrypt_policy
190 *
191 * Given an fscrypt_context, build the corresponding fscrypt_policy.
192 *
193 * Return: 0 on success, or -EINVAL if the fscrypt_context has an unrecognized
194 * version number or size.
195 *
196 * This does *not* validate the settings within the policy itself, e.g. the
197 * modes, flags, and reserved bits. Use fscrypt_supported_policy() for that.
198 */
199int fscrypt_policy_from_context(union fscrypt_policy *policy_u,
200 const union fscrypt_context *ctx_u,
201 int ctx_size)
202{
203 memset(policy_u, 0, sizeof(*policy_u));
204
205 if (ctx_size <= 0 || ctx_size != fscrypt_context_size(ctx_u))
206 return -EINVAL;
207
208 switch (ctx_u->version) {
209 case FSCRYPT_CONTEXT_V1: {
210 const struct fscrypt_context_v1 *ctx = &ctx_u->v1;
211 struct fscrypt_policy_v1 *policy = &policy_u->v1;
212
213 policy->version = FSCRYPT_POLICY_V1;
214 policy->contents_encryption_mode =
215 ctx->contents_encryption_mode;
216 policy->filenames_encryption_mode =
217 ctx->filenames_encryption_mode;
218 policy->flags = ctx->flags;
219 memcpy(policy->master_key_descriptor,
220 ctx->master_key_descriptor,
221 sizeof(policy->master_key_descriptor));
222 return 0;
223 }
224 case FSCRYPT_CONTEXT_V2: {
225 const struct fscrypt_context_v2 *ctx = &ctx_u->v2;
226 struct fscrypt_policy_v2 *policy = &policy_u->v2;
227
228 policy->version = FSCRYPT_POLICY_V2;
229 policy->contents_encryption_mode =
230 ctx->contents_encryption_mode;
231 policy->filenames_encryption_mode =
232 ctx->filenames_encryption_mode;
233 policy->flags = ctx->flags;
234 memcpy(policy->__reserved, ctx->__reserved,
235 sizeof(policy->__reserved));
236 memcpy(policy->master_key_identifier,
237 ctx->master_key_identifier,
238 sizeof(policy->master_key_identifier));
239 return 0;
240 }
241 }
242 /* unreachable */
243 return -EINVAL;
244}
245
246/* Retrieve an inode's encryption policy */
247static int fscrypt_get_policy(struct inode *inode, union fscrypt_policy *policy)
248{
249 const struct fscrypt_info *ci;
250 union fscrypt_context ctx;
251 int ret;
252
253 ci = READ_ONCE(inode->i_crypt_info);
254 if (ci) {
255 /* key available, use the cached policy */
256 *policy = ci->ci_policy;
257 return 0;
258 }
259
260 if (!IS_ENCRYPTED(inode))
261 return -ENODATA;
262
263 ret = inode->i_sb->s_cop->get_context(inode, &ctx, sizeof(ctx));
264 if (ret < 0)
265 return (ret == -ERANGE) ? -EINVAL : ret;
266
267 return fscrypt_policy_from_context(policy, &ctx, ret);
268}
269
270static int set_encryption_policy(struct inode *inode,
271 const union fscrypt_policy *policy)
272{
273 union fscrypt_context ctx;
274 int ctxsize;
275 int err;
276
277 if (!fscrypt_supported_policy(policy, inode))
278 return -EINVAL;
279
280 switch (policy->version) {
281 case FSCRYPT_POLICY_V1:
282 /*
283 * The original encryption policy version provided no way of
284 * verifying that the correct master key was supplied, which was
285 * insecure in scenarios where multiple users have access to the
286 * same encrypted files (even just read-only access). The new
287 * encryption policy version fixes this and also implies use of
288 * an improved key derivation function and allows non-root users
289 * to securely remove keys. So as long as compatibility with
290 * old kernels isn't required, it is recommended to use the new
291 * policy version for all new encrypted directories.
292 */
293 pr_warn_once("%s (pid %d) is setting deprecated v1 encryption policy; recommend upgrading to v2.\n",
294 current->comm, current->pid);
295 break;
296 case FSCRYPT_POLICY_V2:
297 err = fscrypt_verify_key_added(inode->i_sb,
298 policy->v2.master_key_identifier);
299 if (err)
300 return err;
301 break;
302 default:
303 WARN_ON(1);
304 return -EINVAL;
305 }
306
307 ctxsize = fscrypt_new_context_from_policy(&ctx, policy);
308
309 return inode->i_sb->s_cop->set_context(inode, &ctx, ctxsize, NULL);
310}
311
312int fscrypt_ioctl_set_policy(struct file *filp, const void __user *arg)
313{
314 union fscrypt_policy policy;
315 union fscrypt_policy existing_policy;
316 struct inode *inode = file_inode(filp);
317 u8 version;
318 int size;
319 int ret;
320
321 if (get_user(policy.version, (const u8 __user *)arg))
322 return -EFAULT;
323
324 size = fscrypt_policy_size(&policy);
325 if (size <= 0)
326 return -EINVAL;
327
328 /*
329 * We should just copy the remaining 'size - 1' bytes here, but a
330 * bizarre bug in gcc 7 and earlier (fixed by gcc r255731) causes gcc to
331 * think that size can be 0 here (despite the check above!) *and* that
332 * it's a compile-time constant. Thus it would think copy_from_user()
333 * is passed compile-time constant ULONG_MAX, causing the compile-time
334 * buffer overflow check to fail, breaking the build. This only occurred
335 * when building an i386 kernel with -Os and branch profiling enabled.
336 *
337 * Work around it by just copying the first byte again...
338 */
339 version = policy.version;
340 if (copy_from_user(&policy, arg, size))
341 return -EFAULT;
342 policy.version = version;
343
344 if (!inode_owner_or_capable(inode))
345 return -EACCES;
346
347 ret = mnt_want_write_file(filp);
348 if (ret)
349 return ret;
350
351 inode_lock(inode);
352
353 ret = fscrypt_get_policy(inode, &existing_policy);
354 if (ret == -ENODATA) {
355 if (!S_ISDIR(inode->i_mode))
356 ret = -ENOTDIR;
357 else if (IS_DEADDIR(inode))
358 ret = -ENOENT;
359 else if (!inode->i_sb->s_cop->empty_dir(inode))
360 ret = -ENOTEMPTY;
361 else
362 ret = set_encryption_policy(inode, &policy);
363 } else if (ret == -EINVAL ||
364 (ret == 0 && !fscrypt_policies_equal(&policy,
365 &existing_policy))) {
366 /* The file already uses a different encryption policy. */
367 ret = -EEXIST;
368 }
369
370 inode_unlock(inode);
371
372 mnt_drop_write_file(filp);
373 return ret;
374}
375EXPORT_SYMBOL(fscrypt_ioctl_set_policy);
376
377/* Original ioctl version; can only get the original policy version */
378int fscrypt_ioctl_get_policy(struct file *filp, void __user *arg)
379{
380 union fscrypt_policy policy;
381 int err;
382
383 err = fscrypt_get_policy(file_inode(filp), &policy);
384 if (err)
385 return err;
386
387 if (policy.version != FSCRYPT_POLICY_V1)
388 return -EINVAL;
389
390 if (copy_to_user(arg, &policy, sizeof(policy.v1)))
391 return -EFAULT;
392 return 0;
393}
394EXPORT_SYMBOL(fscrypt_ioctl_get_policy);
395
396/* Extended ioctl version; can get policies of any version */
397int fscrypt_ioctl_get_policy_ex(struct file *filp, void __user *uarg)
398{
399 struct fscrypt_get_policy_ex_arg arg;
400 union fscrypt_policy *policy = (union fscrypt_policy *)&arg.policy;
401 size_t policy_size;
402 int err;
403
404 /* arg is policy_size, then policy */
405 BUILD_BUG_ON(offsetof(typeof(arg), policy_size) != 0);
406 BUILD_BUG_ON(offsetofend(typeof(arg), policy_size) !=
407 offsetof(typeof(arg), policy));
408 BUILD_BUG_ON(sizeof(arg.policy) != sizeof(*policy));
409
410 err = fscrypt_get_policy(file_inode(filp), policy);
411 if (err)
412 return err;
413 policy_size = fscrypt_policy_size(policy);
414
415 if (copy_from_user(&arg, uarg, sizeof(arg.policy_size)))
416 return -EFAULT;
417
418 if (policy_size > arg.policy_size)
419 return -EOVERFLOW;
420 arg.policy_size = policy_size;
421
422 if (copy_to_user(uarg, &arg, sizeof(arg.policy_size) + policy_size))
423 return -EFAULT;
424 return 0;
425}
426EXPORT_SYMBOL_GPL(fscrypt_ioctl_get_policy_ex);
427
428/**
429 * fscrypt_has_permitted_context() - is a file's encryption policy permitted
430 * within its directory?
431 *
432 * @parent: inode for parent directory
433 * @child: inode for file being looked up, opened, or linked into @parent
434 *
435 * Filesystems must call this before permitting access to an inode in a
436 * situation where the parent directory is encrypted (either before allowing
437 * ->lookup() to succeed, or for a regular file before allowing it to be opened)
438 * and before any operation that involves linking an inode into an encrypted
439 * directory, including link, rename, and cross rename. It enforces the
440 * constraint that within a given encrypted directory tree, all files use the
441 * same encryption policy. The pre-access check is needed to detect potentially
442 * malicious offline violations of this constraint, while the link and rename
443 * checks are needed to prevent online violations of this constraint.
444 *
445 * Return: 1 if permitted, 0 if forbidden.
446 */
447int fscrypt_has_permitted_context(struct inode *parent, struct inode *child)
448{
449 union fscrypt_policy parent_policy, child_policy;
450 int err;
451
452 /* No restrictions on file types which are never encrypted */
453 if (!S_ISREG(child->i_mode) && !S_ISDIR(child->i_mode) &&
454 !S_ISLNK(child->i_mode))
455 return 1;
456
457 /* No restrictions if the parent directory is unencrypted */
458 if (!IS_ENCRYPTED(parent))
459 return 1;
460
461 /* Encrypted directories must not contain unencrypted files */
462 if (!IS_ENCRYPTED(child))
463 return 0;
464
465 /*
466 * Both parent and child are encrypted, so verify they use the same
467 * encryption policy. Compare the fscrypt_info structs if the keys are
468 * available, otherwise retrieve and compare the fscrypt_contexts.
469 *
470 * Note that the fscrypt_context retrieval will be required frequently
471 * when accessing an encrypted directory tree without the key.
472 * Performance-wise this is not a big deal because we already don't
473 * really optimize for file access without the key (to the extent that
474 * such access is even possible), given that any attempted access
475 * already causes a fscrypt_context retrieval and keyring search.
476 *
477 * In any case, if an unexpected error occurs, fall back to "forbidden".
478 */
479
480 err = fscrypt_get_encryption_info(parent);
481 if (err)
482 return 0;
483 err = fscrypt_get_encryption_info(child);
484 if (err)
485 return 0;
486
487 err = fscrypt_get_policy(parent, &parent_policy);
488 if (err)
489 return 0;
490
491 err = fscrypt_get_policy(child, &child_policy);
492 if (err)
493 return 0;
494
495 return fscrypt_policies_equal(&parent_policy, &child_policy);
496}
497EXPORT_SYMBOL(fscrypt_has_permitted_context);
498
499/**
500 * fscrypt_inherit_context() - Sets a child context from its parent
501 * @parent: Parent inode from which the context is inherited.
502 * @child: Child inode that inherits the context from @parent.
503 * @fs_data: private data given by FS.
504 * @preload: preload child i_crypt_info if true
505 *
506 * Return: 0 on success, -errno on failure
507 */
508int fscrypt_inherit_context(struct inode *parent, struct inode *child,
509 void *fs_data, bool preload)
510{
511 union fscrypt_context ctx;
512 int ctxsize;
513 struct fscrypt_info *ci;
514 int res;
515
516 res = fscrypt_get_encryption_info(parent);
517 if (res < 0)
518 return res;
519
520 ci = READ_ONCE(parent->i_crypt_info);
521 if (ci == NULL)
522 return -ENOKEY;
523
524 ctxsize = fscrypt_new_context_from_policy(&ctx, &ci->ci_policy);
525
526 BUILD_BUG_ON(sizeof(ctx) != FSCRYPT_SET_CONTEXT_MAX_SIZE);
527 res = parent->i_sb->s_cop->set_context(child, &ctx, ctxsize, fs_data);
528 if (res)
529 return res;
530 return preload ? fscrypt_get_encryption_info(child): 0;
531}
532EXPORT_SYMBOL(fscrypt_inherit_context);
191 return false;
192}
193
194/**
195 * fscrypt_new_context_from_policy - create a new fscrypt_context from a policy
196 *
197 * Create an fscrypt_context for an inode that is being assigned the given
198 * encryption policy. A new nonce is randomly generated.
199 *
200 * Return: the size of the new context in bytes.
201 */
202static int fscrypt_new_context_from_policy(union fscrypt_context *ctx_u,
203 const union fscrypt_policy *policy_u)
204{
205 memset(ctx_u, 0, sizeof(*ctx_u));
206
207 switch (policy_u->version) {
208 case FSCRYPT_POLICY_V1: {
209 const struct fscrypt_policy_v1 *policy = &policy_u->v1;
210 struct fscrypt_context_v1 *ctx = &ctx_u->v1;
211
212 ctx->version = FSCRYPT_CONTEXT_V1;
213 ctx->contents_encryption_mode =
214 policy->contents_encryption_mode;
215 ctx->filenames_encryption_mode =
216 policy->filenames_encryption_mode;
217 ctx->flags = policy->flags;
218 memcpy(ctx->master_key_descriptor,
219 policy->master_key_descriptor,
220 sizeof(ctx->master_key_descriptor));
221 get_random_bytes(ctx->nonce, sizeof(ctx->nonce));
222 return sizeof(*ctx);
223 }
224 case FSCRYPT_POLICY_V2: {
225 const struct fscrypt_policy_v2 *policy = &policy_u->v2;
226 struct fscrypt_context_v2 *ctx = &ctx_u->v2;
227
228 ctx->version = FSCRYPT_CONTEXT_V2;
229 ctx->contents_encryption_mode =
230 policy->contents_encryption_mode;
231 ctx->filenames_encryption_mode =
232 policy->filenames_encryption_mode;
233 ctx->flags = policy->flags;
234 memcpy(ctx->master_key_identifier,
235 policy->master_key_identifier,
236 sizeof(ctx->master_key_identifier));
237 get_random_bytes(ctx->nonce, sizeof(ctx->nonce));
238 return sizeof(*ctx);
239 }
240 }
241 BUG();
242}
243
244/**
245 * fscrypt_policy_from_context - convert an fscrypt_context to an fscrypt_policy
246 *
247 * Given an fscrypt_context, build the corresponding fscrypt_policy.
248 *
249 * Return: 0 on success, or -EINVAL if the fscrypt_context has an unrecognized
250 * version number or size.
251 *
252 * This does *not* validate the settings within the policy itself, e.g. the
253 * modes, flags, and reserved bits. Use fscrypt_supported_policy() for that.
254 */
255int fscrypt_policy_from_context(union fscrypt_policy *policy_u,
256 const union fscrypt_context *ctx_u,
257 int ctx_size)
258{
259 memset(policy_u, 0, sizeof(*policy_u));
260
261 if (ctx_size <= 0 || ctx_size != fscrypt_context_size(ctx_u))
262 return -EINVAL;
263
264 switch (ctx_u->version) {
265 case FSCRYPT_CONTEXT_V1: {
266 const struct fscrypt_context_v1 *ctx = &ctx_u->v1;
267 struct fscrypt_policy_v1 *policy = &policy_u->v1;
268
269 policy->version = FSCRYPT_POLICY_V1;
270 policy->contents_encryption_mode =
271 ctx->contents_encryption_mode;
272 policy->filenames_encryption_mode =
273 ctx->filenames_encryption_mode;
274 policy->flags = ctx->flags;
275 memcpy(policy->master_key_descriptor,
276 ctx->master_key_descriptor,
277 sizeof(policy->master_key_descriptor));
278 return 0;
279 }
280 case FSCRYPT_CONTEXT_V2: {
281 const struct fscrypt_context_v2 *ctx = &ctx_u->v2;
282 struct fscrypt_policy_v2 *policy = &policy_u->v2;
283
284 policy->version = FSCRYPT_POLICY_V2;
285 policy->contents_encryption_mode =
286 ctx->contents_encryption_mode;
287 policy->filenames_encryption_mode =
288 ctx->filenames_encryption_mode;
289 policy->flags = ctx->flags;
290 memcpy(policy->__reserved, ctx->__reserved,
291 sizeof(policy->__reserved));
292 memcpy(policy->master_key_identifier,
293 ctx->master_key_identifier,
294 sizeof(policy->master_key_identifier));
295 return 0;
296 }
297 }
298 /* unreachable */
299 return -EINVAL;
300}
301
302/* Retrieve an inode's encryption policy */
303static int fscrypt_get_policy(struct inode *inode, union fscrypt_policy *policy)
304{
305 const struct fscrypt_info *ci;
306 union fscrypt_context ctx;
307 int ret;
308
309 ci = READ_ONCE(inode->i_crypt_info);
310 if (ci) {
311 /* key available, use the cached policy */
312 *policy = ci->ci_policy;
313 return 0;
314 }
315
316 if (!IS_ENCRYPTED(inode))
317 return -ENODATA;
318
319 ret = inode->i_sb->s_cop->get_context(inode, &ctx, sizeof(ctx));
320 if (ret < 0)
321 return (ret == -ERANGE) ? -EINVAL : ret;
322
323 return fscrypt_policy_from_context(policy, &ctx, ret);
324}
325
326static int set_encryption_policy(struct inode *inode,
327 const union fscrypt_policy *policy)
328{
329 union fscrypt_context ctx;
330 int ctxsize;
331 int err;
332
333 if (!fscrypt_supported_policy(policy, inode))
334 return -EINVAL;
335
336 switch (policy->version) {
337 case FSCRYPT_POLICY_V1:
338 /*
339 * The original encryption policy version provided no way of
340 * verifying that the correct master key was supplied, which was
341 * insecure in scenarios where multiple users have access to the
342 * same encrypted files (even just read-only access). The new
343 * encryption policy version fixes this and also implies use of
344 * an improved key derivation function and allows non-root users
345 * to securely remove keys. So as long as compatibility with
346 * old kernels isn't required, it is recommended to use the new
347 * policy version for all new encrypted directories.
348 */
349 pr_warn_once("%s (pid %d) is setting deprecated v1 encryption policy; recommend upgrading to v2.\n",
350 current->comm, current->pid);
351 break;
352 case FSCRYPT_POLICY_V2:
353 err = fscrypt_verify_key_added(inode->i_sb,
354 policy->v2.master_key_identifier);
355 if (err)
356 return err;
357 break;
358 default:
359 WARN_ON(1);
360 return -EINVAL;
361 }
362
363 ctxsize = fscrypt_new_context_from_policy(&ctx, policy);
364
365 return inode->i_sb->s_cop->set_context(inode, &ctx, ctxsize, NULL);
366}
367
368int fscrypt_ioctl_set_policy(struct file *filp, const void __user *arg)
369{
370 union fscrypt_policy policy;
371 union fscrypt_policy existing_policy;
372 struct inode *inode = file_inode(filp);
373 u8 version;
374 int size;
375 int ret;
376
377 if (get_user(policy.version, (const u8 __user *)arg))
378 return -EFAULT;
379
380 size = fscrypt_policy_size(&policy);
381 if (size <= 0)
382 return -EINVAL;
383
384 /*
385 * We should just copy the remaining 'size - 1' bytes here, but a
386 * bizarre bug in gcc 7 and earlier (fixed by gcc r255731) causes gcc to
387 * think that size can be 0 here (despite the check above!) *and* that
388 * it's a compile-time constant. Thus it would think copy_from_user()
389 * is passed compile-time constant ULONG_MAX, causing the compile-time
390 * buffer overflow check to fail, breaking the build. This only occurred
391 * when building an i386 kernel with -Os and branch profiling enabled.
392 *
393 * Work around it by just copying the first byte again...
394 */
395 version = policy.version;
396 if (copy_from_user(&policy, arg, size))
397 return -EFAULT;
398 policy.version = version;
399
400 if (!inode_owner_or_capable(inode))
401 return -EACCES;
402
403 ret = mnt_want_write_file(filp);
404 if (ret)
405 return ret;
406
407 inode_lock(inode);
408
409 ret = fscrypt_get_policy(inode, &existing_policy);
410 if (ret == -ENODATA) {
411 if (!S_ISDIR(inode->i_mode))
412 ret = -ENOTDIR;
413 else if (IS_DEADDIR(inode))
414 ret = -ENOENT;
415 else if (!inode->i_sb->s_cop->empty_dir(inode))
416 ret = -ENOTEMPTY;
417 else
418 ret = set_encryption_policy(inode, &policy);
419 } else if (ret == -EINVAL ||
420 (ret == 0 && !fscrypt_policies_equal(&policy,
421 &existing_policy))) {
422 /* The file already uses a different encryption policy. */
423 ret = -EEXIST;
424 }
425
426 inode_unlock(inode);
427
428 mnt_drop_write_file(filp);
429 return ret;
430}
431EXPORT_SYMBOL(fscrypt_ioctl_set_policy);
432
433/* Original ioctl version; can only get the original policy version */
434int fscrypt_ioctl_get_policy(struct file *filp, void __user *arg)
435{
436 union fscrypt_policy policy;
437 int err;
438
439 err = fscrypt_get_policy(file_inode(filp), &policy);
440 if (err)
441 return err;
442
443 if (policy.version != FSCRYPT_POLICY_V1)
444 return -EINVAL;
445
446 if (copy_to_user(arg, &policy, sizeof(policy.v1)))
447 return -EFAULT;
448 return 0;
449}
450EXPORT_SYMBOL(fscrypt_ioctl_get_policy);
451
452/* Extended ioctl version; can get policies of any version */
453int fscrypt_ioctl_get_policy_ex(struct file *filp, void __user *uarg)
454{
455 struct fscrypt_get_policy_ex_arg arg;
456 union fscrypt_policy *policy = (union fscrypt_policy *)&arg.policy;
457 size_t policy_size;
458 int err;
459
460 /* arg is policy_size, then policy */
461 BUILD_BUG_ON(offsetof(typeof(arg), policy_size) != 0);
462 BUILD_BUG_ON(offsetofend(typeof(arg), policy_size) !=
463 offsetof(typeof(arg), policy));
464 BUILD_BUG_ON(sizeof(arg.policy) != sizeof(*policy));
465
466 err = fscrypt_get_policy(file_inode(filp), policy);
467 if (err)
468 return err;
469 policy_size = fscrypt_policy_size(policy);
470
471 if (copy_from_user(&arg, uarg, sizeof(arg.policy_size)))
472 return -EFAULT;
473
474 if (policy_size > arg.policy_size)
475 return -EOVERFLOW;
476 arg.policy_size = policy_size;
477
478 if (copy_to_user(uarg, &arg, sizeof(arg.policy_size) + policy_size))
479 return -EFAULT;
480 return 0;
481}
482EXPORT_SYMBOL_GPL(fscrypt_ioctl_get_policy_ex);
483
484/**
485 * fscrypt_has_permitted_context() - is a file's encryption policy permitted
486 * within its directory?
487 *
488 * @parent: inode for parent directory
489 * @child: inode for file being looked up, opened, or linked into @parent
490 *
491 * Filesystems must call this before permitting access to an inode in a
492 * situation where the parent directory is encrypted (either before allowing
493 * ->lookup() to succeed, or for a regular file before allowing it to be opened)
494 * and before any operation that involves linking an inode into an encrypted
495 * directory, including link, rename, and cross rename. It enforces the
496 * constraint that within a given encrypted directory tree, all files use the
497 * same encryption policy. The pre-access check is needed to detect potentially
498 * malicious offline violations of this constraint, while the link and rename
499 * checks are needed to prevent online violations of this constraint.
500 *
501 * Return: 1 if permitted, 0 if forbidden.
502 */
503int fscrypt_has_permitted_context(struct inode *parent, struct inode *child)
504{
505 union fscrypt_policy parent_policy, child_policy;
506 int err;
507
508 /* No restrictions on file types which are never encrypted */
509 if (!S_ISREG(child->i_mode) && !S_ISDIR(child->i_mode) &&
510 !S_ISLNK(child->i_mode))
511 return 1;
512
513 /* No restrictions if the parent directory is unencrypted */
514 if (!IS_ENCRYPTED(parent))
515 return 1;
516
517 /* Encrypted directories must not contain unencrypted files */
518 if (!IS_ENCRYPTED(child))
519 return 0;
520
521 /*
522 * Both parent and child are encrypted, so verify they use the same
523 * encryption policy. Compare the fscrypt_info structs if the keys are
524 * available, otherwise retrieve and compare the fscrypt_contexts.
525 *
526 * Note that the fscrypt_context retrieval will be required frequently
527 * when accessing an encrypted directory tree without the key.
528 * Performance-wise this is not a big deal because we already don't
529 * really optimize for file access without the key (to the extent that
530 * such access is even possible), given that any attempted access
531 * already causes a fscrypt_context retrieval and keyring search.
532 *
533 * In any case, if an unexpected error occurs, fall back to "forbidden".
534 */
535
536 err = fscrypt_get_encryption_info(parent);
537 if (err)
538 return 0;
539 err = fscrypt_get_encryption_info(child);
540 if (err)
541 return 0;
542
543 err = fscrypt_get_policy(parent, &parent_policy);
544 if (err)
545 return 0;
546
547 err = fscrypt_get_policy(child, &child_policy);
548 if (err)
549 return 0;
550
551 return fscrypt_policies_equal(&parent_policy, &child_policy);
552}
553EXPORT_SYMBOL(fscrypt_has_permitted_context);
554
555/**
556 * fscrypt_inherit_context() - Sets a child context from its parent
557 * @parent: Parent inode from which the context is inherited.
558 * @child: Child inode that inherits the context from @parent.
559 * @fs_data: private data given by FS.
560 * @preload: preload child i_crypt_info if true
561 *
562 * Return: 0 on success, -errno on failure
563 */
564int fscrypt_inherit_context(struct inode *parent, struct inode *child,
565 void *fs_data, bool preload)
566{
567 union fscrypt_context ctx;
568 int ctxsize;
569 struct fscrypt_info *ci;
570 int res;
571
572 res = fscrypt_get_encryption_info(parent);
573 if (res < 0)
574 return res;
575
576 ci = READ_ONCE(parent->i_crypt_info);
577 if (ci == NULL)
578 return -ENOKEY;
579
580 ctxsize = fscrypt_new_context_from_policy(&ctx, &ci->ci_policy);
581
582 BUILD_BUG_ON(sizeof(ctx) != FSCRYPT_SET_CONTEXT_MAX_SIZE);
583 res = parent->i_sb->s_cop->set_context(child, &ctx, ctxsize, fs_data);
584 if (res)
585 return res;
586 return preload ? fscrypt_get_encryption_info(child): 0;
587}
588EXPORT_SYMBOL(fscrypt_inherit_context);