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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 * Written by Michael Halcrow, 2015.
9 * Modified by Jaegeuk Kim, 2015.
10 */
11
12#include <linux/random.h>
13#include <linux/string.h>
14#include <linux/mount.h>
15#include "fscrypt_private.h"
16
17/*
18 * check whether an encryption policy is consistent with an encryption context
19 */
20static bool is_encryption_context_consistent_with_policy(
21 const struct fscrypt_context *ctx,
22 const struct fscrypt_policy *policy)
23{
24 return memcmp(ctx->master_key_descriptor, policy->master_key_descriptor,
25 FS_KEY_DESCRIPTOR_SIZE) == 0 &&
26 (ctx->flags == policy->flags) &&
27 (ctx->contents_encryption_mode ==
28 policy->contents_encryption_mode) &&
29 (ctx->filenames_encryption_mode ==
30 policy->filenames_encryption_mode);
31}
32
33static int create_encryption_context_from_policy(struct inode *inode,
34 const struct fscrypt_policy *policy)
35{
36 struct fscrypt_context ctx;
37
38 ctx.format = FS_ENCRYPTION_CONTEXT_FORMAT_V1;
39 memcpy(ctx.master_key_descriptor, policy->master_key_descriptor,
40 FS_KEY_DESCRIPTOR_SIZE);
41
42 if (!fscrypt_valid_enc_modes(policy->contents_encryption_mode,
43 policy->filenames_encryption_mode))
44 return -EINVAL;
45
46 if (policy->flags & ~FS_POLICY_FLAGS_VALID)
47 return -EINVAL;
48
49 ctx.contents_encryption_mode = policy->contents_encryption_mode;
50 ctx.filenames_encryption_mode = policy->filenames_encryption_mode;
51 ctx.flags = policy->flags;
52 BUILD_BUG_ON(sizeof(ctx.nonce) != FS_KEY_DERIVATION_NONCE_SIZE);
53 get_random_bytes(ctx.nonce, FS_KEY_DERIVATION_NONCE_SIZE);
54
55 return inode->i_sb->s_cop->set_context(inode, &ctx, sizeof(ctx), NULL);
56}
57
58int fscrypt_ioctl_set_policy(struct file *filp, const void __user *arg)
59{
60 struct fscrypt_policy policy;
61 struct inode *inode = file_inode(filp);
62 int ret;
63 struct fscrypt_context ctx;
64
65 if (copy_from_user(&policy, arg, sizeof(policy)))
66 return -EFAULT;
67
68 if (!inode_owner_or_capable(inode))
69 return -EACCES;
70
71 if (policy.version != 0)
72 return -EINVAL;
73
74 ret = mnt_want_write_file(filp);
75 if (ret)
76 return ret;
77
78 inode_lock(inode);
79
80 ret = inode->i_sb->s_cop->get_context(inode, &ctx, sizeof(ctx));
81 if (ret == -ENODATA) {
82 if (!S_ISDIR(inode->i_mode))
83 ret = -ENOTDIR;
84 else if (!inode->i_sb->s_cop->empty_dir(inode))
85 ret = -ENOTEMPTY;
86 else
87 ret = create_encryption_context_from_policy(inode,
88 &policy);
89 } else if (ret == sizeof(ctx) &&
90 is_encryption_context_consistent_with_policy(&ctx,
91 &policy)) {
92 /* The file already uses the same encryption policy. */
93 ret = 0;
94 } else if (ret >= 0 || ret == -ERANGE) {
95 /* The file already uses a different encryption policy. */
96 ret = -EEXIST;
97 }
98
99 inode_unlock(inode);
100
101 mnt_drop_write_file(filp);
102 return ret;
103}
104EXPORT_SYMBOL(fscrypt_ioctl_set_policy);
105
106int fscrypt_ioctl_get_policy(struct file *filp, void __user *arg)
107{
108 struct inode *inode = file_inode(filp);
109 struct fscrypt_context ctx;
110 struct fscrypt_policy policy;
111 int res;
112
113 if (!IS_ENCRYPTED(inode))
114 return -ENODATA;
115
116 res = inode->i_sb->s_cop->get_context(inode, &ctx, sizeof(ctx));
117 if (res < 0 && res != -ERANGE)
118 return res;
119 if (res != sizeof(ctx))
120 return -EINVAL;
121 if (ctx.format != FS_ENCRYPTION_CONTEXT_FORMAT_V1)
122 return -EINVAL;
123
124 policy.version = 0;
125 policy.contents_encryption_mode = ctx.contents_encryption_mode;
126 policy.filenames_encryption_mode = ctx.filenames_encryption_mode;
127 policy.flags = ctx.flags;
128 memcpy(policy.master_key_descriptor, ctx.master_key_descriptor,
129 FS_KEY_DESCRIPTOR_SIZE);
130
131 if (copy_to_user(arg, &policy, sizeof(policy)))
132 return -EFAULT;
133 return 0;
134}
135EXPORT_SYMBOL(fscrypt_ioctl_get_policy);
136
137/**
138 * fscrypt_has_permitted_context() - is a file's encryption policy permitted
139 * within its directory?
140 *
141 * @parent: inode for parent directory
142 * @child: inode for file being looked up, opened, or linked into @parent
143 *
144 * Filesystems must call this before permitting access to an inode in a
145 * situation where the parent directory is encrypted (either before allowing
146 * ->lookup() to succeed, or for a regular file before allowing it to be opened)
147 * and before any operation that involves linking an inode into an encrypted
148 * directory, including link, rename, and cross rename. It enforces the
149 * constraint that within a given encrypted directory tree, all files use the
150 * same encryption policy. The pre-access check is needed to detect potentially
151 * malicious offline violations of this constraint, while the link and rename
152 * checks are needed to prevent online violations of this constraint.
153 *
154 * Return: 1 if permitted, 0 if forbidden. If forbidden, the caller must fail
155 * the filesystem operation with EPERM.
156 */
157int fscrypt_has_permitted_context(struct inode *parent, struct inode *child)
158{
159 const struct fscrypt_operations *cops = parent->i_sb->s_cop;
160 const struct fscrypt_info *parent_ci, *child_ci;
161 struct fscrypt_context parent_ctx, child_ctx;
162 int res;
163
164 /* No restrictions on file types which are never encrypted */
165 if (!S_ISREG(child->i_mode) && !S_ISDIR(child->i_mode) &&
166 !S_ISLNK(child->i_mode))
167 return 1;
168
169 /* No restrictions if the parent directory is unencrypted */
170 if (!IS_ENCRYPTED(parent))
171 return 1;
172
173 /* Encrypted directories must not contain unencrypted files */
174 if (!IS_ENCRYPTED(child))
175 return 0;
176
177 /*
178 * Both parent and child are encrypted, so verify they use the same
179 * encryption policy. Compare the fscrypt_info structs if the keys are
180 * available, otherwise retrieve and compare the fscrypt_contexts.
181 *
182 * Note that the fscrypt_context retrieval will be required frequently
183 * when accessing an encrypted directory tree without the key.
184 * Performance-wise this is not a big deal because we already don't
185 * really optimize for file access without the key (to the extent that
186 * such access is even possible), given that any attempted access
187 * already causes a fscrypt_context retrieval and keyring search.
188 *
189 * In any case, if an unexpected error occurs, fall back to "forbidden".
190 */
191
192 res = fscrypt_get_encryption_info(parent);
193 if (res)
194 return 0;
195 res = fscrypt_get_encryption_info(child);
196 if (res)
197 return 0;
198 parent_ci = parent->i_crypt_info;
199 child_ci = child->i_crypt_info;
200
201 if (parent_ci && child_ci) {
202 return memcmp(parent_ci->ci_master_key, child_ci->ci_master_key,
203 FS_KEY_DESCRIPTOR_SIZE) == 0 &&
204 (parent_ci->ci_data_mode == child_ci->ci_data_mode) &&
205 (parent_ci->ci_filename_mode ==
206 child_ci->ci_filename_mode) &&
207 (parent_ci->ci_flags == child_ci->ci_flags);
208 }
209
210 res = cops->get_context(parent, &parent_ctx, sizeof(parent_ctx));
211 if (res != sizeof(parent_ctx))
212 return 0;
213
214 res = cops->get_context(child, &child_ctx, sizeof(child_ctx));
215 if (res != sizeof(child_ctx))
216 return 0;
217
218 return memcmp(parent_ctx.master_key_descriptor,
219 child_ctx.master_key_descriptor,
220 FS_KEY_DESCRIPTOR_SIZE) == 0 &&
221 (parent_ctx.contents_encryption_mode ==
222 child_ctx.contents_encryption_mode) &&
223 (parent_ctx.filenames_encryption_mode ==
224 child_ctx.filenames_encryption_mode) &&
225 (parent_ctx.flags == child_ctx.flags);
226}
227EXPORT_SYMBOL(fscrypt_has_permitted_context);
228
229/**
230 * fscrypt_inherit_context() - Sets a child context from its parent
231 * @parent: Parent inode from which the context is inherited.
232 * @child: Child inode that inherits the context from @parent.
233 * @fs_data: private data given by FS.
234 * @preload: preload child i_crypt_info if true
235 *
236 * Return: 0 on success, -errno on failure
237 */
238int fscrypt_inherit_context(struct inode *parent, struct inode *child,
239 void *fs_data, bool preload)
240{
241 struct fscrypt_context ctx;
242 struct fscrypt_info *ci;
243 int res;
244
245 res = fscrypt_get_encryption_info(parent);
246 if (res < 0)
247 return res;
248
249 ci = parent->i_crypt_info;
250 if (ci == NULL)
251 return -ENOKEY;
252
253 ctx.format = FS_ENCRYPTION_CONTEXT_FORMAT_V1;
254 ctx.contents_encryption_mode = ci->ci_data_mode;
255 ctx.filenames_encryption_mode = ci->ci_filename_mode;
256 ctx.flags = ci->ci_flags;
257 memcpy(ctx.master_key_descriptor, ci->ci_master_key,
258 FS_KEY_DESCRIPTOR_SIZE);
259 get_random_bytes(ctx.nonce, FS_KEY_DERIVATION_NONCE_SIZE);
260 BUILD_BUG_ON(sizeof(ctx) != FSCRYPT_SET_CONTEXT_MAX_SIZE);
261 res = parent->i_sb->s_cop->set_context(child, &ctx,
262 sizeof(ctx), fs_data);
263 if (res)
264 return res;
265 return preload ? fscrypt_get_encryption_info(child): 0;
266}
267EXPORT_SYMBOL(fscrypt_inherit_context);
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
32/**
33 * fscrypt_supported_policy - check whether an encryption policy is supported
34 *
35 * Given an encryption policy, check whether all its encryption modes and other
36 * settings are supported by this kernel. (But we don't currently don't check
37 * for crypto API support here, so attempting to use an algorithm not configured
38 * into the crypto API will still fail later.)
39 *
40 * Return: %true if supported, else %false
41 */
42bool fscrypt_supported_policy(const union fscrypt_policy *policy_u,
43 const struct inode *inode)
44{
45 switch (policy_u->version) {
46 case FSCRYPT_POLICY_V1: {
47 const struct fscrypt_policy_v1 *policy = &policy_u->v1;
48
49 if (!fscrypt_valid_enc_modes(policy->contents_encryption_mode,
50 policy->filenames_encryption_mode)) {
51 fscrypt_warn(inode,
52 "Unsupported encryption modes (contents %d, filenames %d)",
53 policy->contents_encryption_mode,
54 policy->filenames_encryption_mode);
55 return false;
56 }
57
58 if (policy->flags & ~FSCRYPT_POLICY_FLAGS_VALID) {
59 fscrypt_warn(inode,
60 "Unsupported encryption flags (0x%02x)",
61 policy->flags);
62 return false;
63 }
64
65 return true;
66 }
67 case FSCRYPT_POLICY_V2: {
68 const struct fscrypt_policy_v2 *policy = &policy_u->v2;
69
70 if (!fscrypt_valid_enc_modes(policy->contents_encryption_mode,
71 policy->filenames_encryption_mode)) {
72 fscrypt_warn(inode,
73 "Unsupported encryption modes (contents %d, filenames %d)",
74 policy->contents_encryption_mode,
75 policy->filenames_encryption_mode);
76 return false;
77 }
78
79 if (policy->flags & ~FSCRYPT_POLICY_FLAGS_VALID) {
80 fscrypt_warn(inode,
81 "Unsupported encryption flags (0x%02x)",
82 policy->flags);
83 return false;
84 }
85
86 if (memchr_inv(policy->__reserved, 0,
87 sizeof(policy->__reserved))) {
88 fscrypt_warn(inode,
89 "Reserved bits set in encryption policy");
90 return false;
91 }
92
93 return true;
94 }
95 }
96 return false;
97}
98
99/**
100 * fscrypt_new_context_from_policy - create a new fscrypt_context from a policy
101 *
102 * Create an fscrypt_context for an inode that is being assigned the given
103 * encryption policy. A new nonce is randomly generated.
104 *
105 * Return: the size of the new context in bytes.
106 */
107static int fscrypt_new_context_from_policy(union fscrypt_context *ctx_u,
108 const union fscrypt_policy *policy_u)
109{
110 memset(ctx_u, 0, sizeof(*ctx_u));
111
112 switch (policy_u->version) {
113 case FSCRYPT_POLICY_V1: {
114 const struct fscrypt_policy_v1 *policy = &policy_u->v1;
115 struct fscrypt_context_v1 *ctx = &ctx_u->v1;
116
117 ctx->version = FSCRYPT_CONTEXT_V1;
118 ctx->contents_encryption_mode =
119 policy->contents_encryption_mode;
120 ctx->filenames_encryption_mode =
121 policy->filenames_encryption_mode;
122 ctx->flags = policy->flags;
123 memcpy(ctx->master_key_descriptor,
124 policy->master_key_descriptor,
125 sizeof(ctx->master_key_descriptor));
126 get_random_bytes(ctx->nonce, sizeof(ctx->nonce));
127 return sizeof(*ctx);
128 }
129 case FSCRYPT_POLICY_V2: {
130 const struct fscrypt_policy_v2 *policy = &policy_u->v2;
131 struct fscrypt_context_v2 *ctx = &ctx_u->v2;
132
133 ctx->version = FSCRYPT_CONTEXT_V2;
134 ctx->contents_encryption_mode =
135 policy->contents_encryption_mode;
136 ctx->filenames_encryption_mode =
137 policy->filenames_encryption_mode;
138 ctx->flags = policy->flags;
139 memcpy(ctx->master_key_identifier,
140 policy->master_key_identifier,
141 sizeof(ctx->master_key_identifier));
142 get_random_bytes(ctx->nonce, sizeof(ctx->nonce));
143 return sizeof(*ctx);
144 }
145 }
146 BUG();
147}
148
149/**
150 * fscrypt_policy_from_context - convert an fscrypt_context to an fscrypt_policy
151 *
152 * Given an fscrypt_context, build the corresponding fscrypt_policy.
153 *
154 * Return: 0 on success, or -EINVAL if the fscrypt_context has an unrecognized
155 * version number or size.
156 *
157 * This does *not* validate the settings within the policy itself, e.g. the
158 * modes, flags, and reserved bits. Use fscrypt_supported_policy() for that.
159 */
160int fscrypt_policy_from_context(union fscrypt_policy *policy_u,
161 const union fscrypt_context *ctx_u,
162 int ctx_size)
163{
164 memset(policy_u, 0, sizeof(*policy_u));
165
166 if (ctx_size <= 0 || ctx_size != fscrypt_context_size(ctx_u))
167 return -EINVAL;
168
169 switch (ctx_u->version) {
170 case FSCRYPT_CONTEXT_V1: {
171 const struct fscrypt_context_v1 *ctx = &ctx_u->v1;
172 struct fscrypt_policy_v1 *policy = &policy_u->v1;
173
174 policy->version = FSCRYPT_POLICY_V1;
175 policy->contents_encryption_mode =
176 ctx->contents_encryption_mode;
177 policy->filenames_encryption_mode =
178 ctx->filenames_encryption_mode;
179 policy->flags = ctx->flags;
180 memcpy(policy->master_key_descriptor,
181 ctx->master_key_descriptor,
182 sizeof(policy->master_key_descriptor));
183 return 0;
184 }
185 case FSCRYPT_CONTEXT_V2: {
186 const struct fscrypt_context_v2 *ctx = &ctx_u->v2;
187 struct fscrypt_policy_v2 *policy = &policy_u->v2;
188
189 policy->version = FSCRYPT_POLICY_V2;
190 policy->contents_encryption_mode =
191 ctx->contents_encryption_mode;
192 policy->filenames_encryption_mode =
193 ctx->filenames_encryption_mode;
194 policy->flags = ctx->flags;
195 memcpy(policy->__reserved, ctx->__reserved,
196 sizeof(policy->__reserved));
197 memcpy(policy->master_key_identifier,
198 ctx->master_key_identifier,
199 sizeof(policy->master_key_identifier));
200 return 0;
201 }
202 }
203 /* unreachable */
204 return -EINVAL;
205}
206
207/* Retrieve an inode's encryption policy */
208static int fscrypt_get_policy(struct inode *inode, union fscrypt_policy *policy)
209{
210 const struct fscrypt_info *ci;
211 union fscrypt_context ctx;
212 int ret;
213
214 ci = READ_ONCE(inode->i_crypt_info);
215 if (ci) {
216 /* key available, use the cached policy */
217 *policy = ci->ci_policy;
218 return 0;
219 }
220
221 if (!IS_ENCRYPTED(inode))
222 return -ENODATA;
223
224 ret = inode->i_sb->s_cop->get_context(inode, &ctx, sizeof(ctx));
225 if (ret < 0)
226 return (ret == -ERANGE) ? -EINVAL : ret;
227
228 return fscrypt_policy_from_context(policy, &ctx, ret);
229}
230
231static int set_encryption_policy(struct inode *inode,
232 const union fscrypt_policy *policy)
233{
234 union fscrypt_context ctx;
235 int ctxsize;
236 int err;
237
238 if (!fscrypt_supported_policy(policy, inode))
239 return -EINVAL;
240
241 switch (policy->version) {
242 case FSCRYPT_POLICY_V1:
243 /*
244 * The original encryption policy version provided no way of
245 * verifying that the correct master key was supplied, which was
246 * insecure in scenarios where multiple users have access to the
247 * same encrypted files (even just read-only access). The new
248 * encryption policy version fixes this and also implies use of
249 * an improved key derivation function and allows non-root users
250 * to securely remove keys. So as long as compatibility with
251 * old kernels isn't required, it is recommended to use the new
252 * policy version for all new encrypted directories.
253 */
254 pr_warn_once("%s (pid %d) is setting deprecated v1 encryption policy; recommend upgrading to v2.\n",
255 current->comm, current->pid);
256 break;
257 case FSCRYPT_POLICY_V2:
258 err = fscrypt_verify_key_added(inode->i_sb,
259 policy->v2.master_key_identifier);
260 if (err)
261 return err;
262 break;
263 default:
264 WARN_ON(1);
265 return -EINVAL;
266 }
267
268 ctxsize = fscrypt_new_context_from_policy(&ctx, policy);
269
270 return inode->i_sb->s_cop->set_context(inode, &ctx, ctxsize, NULL);
271}
272
273int fscrypt_ioctl_set_policy(struct file *filp, const void __user *arg)
274{
275 union fscrypt_policy policy;
276 union fscrypt_policy existing_policy;
277 struct inode *inode = file_inode(filp);
278 u8 version;
279 int size;
280 int ret;
281
282 if (get_user(policy.version, (const u8 __user *)arg))
283 return -EFAULT;
284
285 size = fscrypt_policy_size(&policy);
286 if (size <= 0)
287 return -EINVAL;
288
289 /*
290 * We should just copy the remaining 'size - 1' bytes here, but a
291 * bizarre bug in gcc 7 and earlier (fixed by gcc r255731) causes gcc to
292 * think that size can be 0 here (despite the check above!) *and* that
293 * it's a compile-time constant. Thus it would think copy_from_user()
294 * is passed compile-time constant ULONG_MAX, causing the compile-time
295 * buffer overflow check to fail, breaking the build. This only occurred
296 * when building an i386 kernel with -Os and branch profiling enabled.
297 *
298 * Work around it by just copying the first byte again...
299 */
300 version = policy.version;
301 if (copy_from_user(&policy, arg, size))
302 return -EFAULT;
303 policy.version = version;
304
305 if (!inode_owner_or_capable(inode))
306 return -EACCES;
307
308 ret = mnt_want_write_file(filp);
309 if (ret)
310 return ret;
311
312 inode_lock(inode);
313
314 ret = fscrypt_get_policy(inode, &existing_policy);
315 if (ret == -ENODATA) {
316 if (!S_ISDIR(inode->i_mode))
317 ret = -ENOTDIR;
318 else if (IS_DEADDIR(inode))
319 ret = -ENOENT;
320 else if (!inode->i_sb->s_cop->empty_dir(inode))
321 ret = -ENOTEMPTY;
322 else
323 ret = set_encryption_policy(inode, &policy);
324 } else if (ret == -EINVAL ||
325 (ret == 0 && !fscrypt_policies_equal(&policy,
326 &existing_policy))) {
327 /* The file already uses a different encryption policy. */
328 ret = -EEXIST;
329 }
330
331 inode_unlock(inode);
332
333 mnt_drop_write_file(filp);
334 return ret;
335}
336EXPORT_SYMBOL(fscrypt_ioctl_set_policy);
337
338/* Original ioctl version; can only get the original policy version */
339int fscrypt_ioctl_get_policy(struct file *filp, void __user *arg)
340{
341 union fscrypt_policy policy;
342 int err;
343
344 err = fscrypt_get_policy(file_inode(filp), &policy);
345 if (err)
346 return err;
347
348 if (policy.version != FSCRYPT_POLICY_V1)
349 return -EINVAL;
350
351 if (copy_to_user(arg, &policy, sizeof(policy.v1)))
352 return -EFAULT;
353 return 0;
354}
355EXPORT_SYMBOL(fscrypt_ioctl_get_policy);
356
357/* Extended ioctl version; can get policies of any version */
358int fscrypt_ioctl_get_policy_ex(struct file *filp, void __user *uarg)
359{
360 struct fscrypt_get_policy_ex_arg arg;
361 union fscrypt_policy *policy = (union fscrypt_policy *)&arg.policy;
362 size_t policy_size;
363 int err;
364
365 /* arg is policy_size, then policy */
366 BUILD_BUG_ON(offsetof(typeof(arg), policy_size) != 0);
367 BUILD_BUG_ON(offsetofend(typeof(arg), policy_size) !=
368 offsetof(typeof(arg), policy));
369 BUILD_BUG_ON(sizeof(arg.policy) != sizeof(*policy));
370
371 err = fscrypt_get_policy(file_inode(filp), policy);
372 if (err)
373 return err;
374 policy_size = fscrypt_policy_size(policy);
375
376 if (copy_from_user(&arg, uarg, sizeof(arg.policy_size)))
377 return -EFAULT;
378
379 if (policy_size > arg.policy_size)
380 return -EOVERFLOW;
381 arg.policy_size = policy_size;
382
383 if (copy_to_user(uarg, &arg, sizeof(arg.policy_size) + policy_size))
384 return -EFAULT;
385 return 0;
386}
387EXPORT_SYMBOL_GPL(fscrypt_ioctl_get_policy_ex);
388
389/**
390 * fscrypt_has_permitted_context() - is a file's encryption policy permitted
391 * within its directory?
392 *
393 * @parent: inode for parent directory
394 * @child: inode for file being looked up, opened, or linked into @parent
395 *
396 * Filesystems must call this before permitting access to an inode in a
397 * situation where the parent directory is encrypted (either before allowing
398 * ->lookup() to succeed, or for a regular file before allowing it to be opened)
399 * and before any operation that involves linking an inode into an encrypted
400 * directory, including link, rename, and cross rename. It enforces the
401 * constraint that within a given encrypted directory tree, all files use the
402 * same encryption policy. The pre-access check is needed to detect potentially
403 * malicious offline violations of this constraint, while the link and rename
404 * checks are needed to prevent online violations of this constraint.
405 *
406 * Return: 1 if permitted, 0 if forbidden.
407 */
408int fscrypt_has_permitted_context(struct inode *parent, struct inode *child)
409{
410 union fscrypt_policy parent_policy, child_policy;
411 int err;
412
413 /* No restrictions on file types which are never encrypted */
414 if (!S_ISREG(child->i_mode) && !S_ISDIR(child->i_mode) &&
415 !S_ISLNK(child->i_mode))
416 return 1;
417
418 /* No restrictions if the parent directory is unencrypted */
419 if (!IS_ENCRYPTED(parent))
420 return 1;
421
422 /* Encrypted directories must not contain unencrypted files */
423 if (!IS_ENCRYPTED(child))
424 return 0;
425
426 /*
427 * Both parent and child are encrypted, so verify they use the same
428 * encryption policy. Compare the fscrypt_info structs if the keys are
429 * available, otherwise retrieve and compare the fscrypt_contexts.
430 *
431 * Note that the fscrypt_context retrieval will be required frequently
432 * when accessing an encrypted directory tree without the key.
433 * Performance-wise this is not a big deal because we already don't
434 * really optimize for file access without the key (to the extent that
435 * such access is even possible), given that any attempted access
436 * already causes a fscrypt_context retrieval and keyring search.
437 *
438 * In any case, if an unexpected error occurs, fall back to "forbidden".
439 */
440
441 err = fscrypt_get_encryption_info(parent);
442 if (err)
443 return 0;
444 err = fscrypt_get_encryption_info(child);
445 if (err)
446 return 0;
447
448 err = fscrypt_get_policy(parent, &parent_policy);
449 if (err)
450 return 0;
451
452 err = fscrypt_get_policy(child, &child_policy);
453 if (err)
454 return 0;
455
456 return fscrypt_policies_equal(&parent_policy, &child_policy);
457}
458EXPORT_SYMBOL(fscrypt_has_permitted_context);
459
460/**
461 * fscrypt_inherit_context() - Sets a child context from its parent
462 * @parent: Parent inode from which the context is inherited.
463 * @child: Child inode that inherits the context from @parent.
464 * @fs_data: private data given by FS.
465 * @preload: preload child i_crypt_info if true
466 *
467 * Return: 0 on success, -errno on failure
468 */
469int fscrypt_inherit_context(struct inode *parent, struct inode *child,
470 void *fs_data, bool preload)
471{
472 union fscrypt_context ctx;
473 int ctxsize;
474 struct fscrypt_info *ci;
475 int res;
476
477 res = fscrypt_get_encryption_info(parent);
478 if (res < 0)
479 return res;
480
481 ci = READ_ONCE(parent->i_crypt_info);
482 if (ci == NULL)
483 return -ENOKEY;
484
485 ctxsize = fscrypt_new_context_from_policy(&ctx, &ci->ci_policy);
486
487 BUILD_BUG_ON(sizeof(ctx) != FSCRYPT_SET_CONTEXT_MAX_SIZE);
488 res = parent->i_sb->s_cop->set_context(child, &ctx, ctxsize, fs_data);
489 if (res)
490 return res;
491 return preload ? fscrypt_get_encryption_info(child): 0;
492}
493EXPORT_SYMBOL(fscrypt_inherit_context);