1 // SPDX-License-Identifier: GPL-2.0
3 * Encryption policy functions for per-file encryption support.
5 * Copyright (C) 2015, Google, Inc.
6 * Copyright (C) 2015, Motorola Mobility.
8 * Originally written by Michael Halcrow, 2015.
9 * Modified by Jaegeuk Kim, 2015.
10 * Modified by Eric Biggers, 2019 for v2 policy support.
13 #include <linux/random.h>
14 #include <linux/string.h>
15 #include <linux/mount.h>
16 #include "fscrypt_private.h"
19 * fscrypt_policies_equal - check whether two encryption policies are the same
21 * Return: %true if equal, else %false
23 bool fscrypt_policies_equal(const union fscrypt_policy *policy1,
24 const union fscrypt_policy *policy2)
26 if (policy1->version != policy2->version)
29 return !memcmp(policy1, policy2, fscrypt_policy_size(policy1));
32 static bool fscrypt_valid_enc_modes(u32 contents_mode, u32 filenames_mode)
34 if (contents_mode == FSCRYPT_MODE_AES_256_XTS &&
35 filenames_mode == FSCRYPT_MODE_AES_256_CTS)
38 if (contents_mode == FSCRYPT_MODE_AES_128_CBC &&
39 filenames_mode == FSCRYPT_MODE_AES_128_CTS)
42 if (contents_mode == FSCRYPT_MODE_ADIANTUM &&
43 filenames_mode == FSCRYPT_MODE_ADIANTUM)
49 static bool supported_direct_key_modes(const struct inode *inode,
50 u32 contents_mode, u32 filenames_mode)
52 const struct fscrypt_mode *mode;
54 if (contents_mode != filenames_mode) {
56 "Direct key flag not allowed with different contents and filenames modes");
59 mode = &fscrypt_modes[contents_mode];
61 if (mode->ivsize < offsetofend(union fscrypt_iv, nonce)) {
62 fscrypt_warn(inode, "Direct key flag not allowed with %s",
69 static bool supported_iv_ino_lblk_64_policy(
70 const struct fscrypt_policy_v2 *policy,
71 const struct inode *inode)
73 struct super_block *sb = inode->i_sb;
74 int ino_bits = 64, lblk_bits = 64;
76 if (policy->flags & FSCRYPT_POLICY_FLAG_DIRECT_KEY) {
78 "The DIRECT_KEY and IV_INO_LBLK_64 flags are mutually exclusive");
82 * It's unsafe to include inode numbers in the IVs if the filesystem can
83 * potentially renumber inodes, e.g. via filesystem shrinking.
85 if (!sb->s_cop->has_stable_inodes ||
86 !sb->s_cop->has_stable_inodes(sb)) {
88 "Can't use IV_INO_LBLK_64 policy on filesystem '%s' because it doesn't have stable inode numbers",
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) {
96 "Can't use IV_INO_LBLK_64 policy on filesystem '%s' because it doesn't use 32-bit inode and block numbers",
103 static bool fscrypt_supported_v1_policy(const struct fscrypt_policy_v1 *policy,
104 const struct inode *inode)
106 if (!fscrypt_valid_enc_modes(policy->contents_encryption_mode,
107 policy->filenames_encryption_mode)) {
109 "Unsupported encryption modes (contents %d, filenames %d)",
110 policy->contents_encryption_mode,
111 policy->filenames_encryption_mode);
115 if (policy->flags & ~(FSCRYPT_POLICY_FLAGS_PAD_MASK |
116 FSCRYPT_POLICY_FLAG_DIRECT_KEY)) {
117 fscrypt_warn(inode, "Unsupported encryption flags (0x%02x)",
122 if ((policy->flags & FSCRYPT_POLICY_FLAG_DIRECT_KEY) &&
123 !supported_direct_key_modes(inode, policy->contents_encryption_mode,
124 policy->filenames_encryption_mode))
127 if (IS_CASEFOLDED(inode)) {
128 /* With v1, there's no way to derive dirhash keys. */
130 "v1 policies can't be used on casefolded directories");
137 static bool fscrypt_supported_v2_policy(const struct fscrypt_policy_v2 *policy,
138 const struct inode *inode)
140 if (!fscrypt_valid_enc_modes(policy->contents_encryption_mode,
141 policy->filenames_encryption_mode)) {
143 "Unsupported encryption modes (contents %d, filenames %d)",
144 policy->contents_encryption_mode,
145 policy->filenames_encryption_mode);
149 if (policy->flags & ~FSCRYPT_POLICY_FLAGS_VALID) {
150 fscrypt_warn(inode, "Unsupported encryption flags (0x%02x)",
155 if ((policy->flags & FSCRYPT_POLICY_FLAG_DIRECT_KEY) &&
156 !supported_direct_key_modes(inode, policy->contents_encryption_mode,
157 policy->filenames_encryption_mode))
160 if ((policy->flags & FSCRYPT_POLICY_FLAG_IV_INO_LBLK_64) &&
161 !supported_iv_ino_lblk_64_policy(policy, inode))
164 if (memchr_inv(policy->__reserved, 0, sizeof(policy->__reserved))) {
165 fscrypt_warn(inode, "Reserved bits set in encryption policy");
173 * fscrypt_supported_policy - check whether an encryption policy is supported
175 * Given an encryption policy, check whether all its encryption modes and other
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.)
180 * Return: %true if supported, else %false
182 bool fscrypt_supported_policy(const union fscrypt_policy *policy_u,
183 const struct inode *inode)
185 switch (policy_u->version) {
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);
195 * fscrypt_new_context_from_policy - create a new fscrypt_context from a policy
197 * Create an fscrypt_context for an inode that is being assigned the given
198 * encryption policy. A new nonce is randomly generated.
200 * Return: the size of the new context in bytes.
202 static int fscrypt_new_context_from_policy(union fscrypt_context *ctx_u,
203 const union fscrypt_policy *policy_u)
205 memset(ctx_u, 0, sizeof(*ctx_u));
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;
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));
224 case FSCRYPT_POLICY_V2: {
225 const struct fscrypt_policy_v2 *policy = &policy_u->v2;
226 struct fscrypt_context_v2 *ctx = &ctx_u->v2;
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));
245 * fscrypt_policy_from_context - convert an fscrypt_context to an fscrypt_policy
247 * Given an fscrypt_context, build the corresponding fscrypt_policy.
249 * Return: 0 on success, or -EINVAL if the fscrypt_context has an unrecognized
250 * version number or size.
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.
255 int fscrypt_policy_from_context(union fscrypt_policy *policy_u,
256 const union fscrypt_context *ctx_u,
259 memset(policy_u, 0, sizeof(*policy_u));
261 if (ctx_size <= 0 || ctx_size != fscrypt_context_size(ctx_u))
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;
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));
280 case FSCRYPT_CONTEXT_V2: {
281 const struct fscrypt_context_v2 *ctx = &ctx_u->v2;
282 struct fscrypt_policy_v2 *policy = &policy_u->v2;
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));
302 /* Retrieve an inode's encryption policy */
303 static int fscrypt_get_policy(struct inode *inode, union fscrypt_policy *policy)
305 const struct fscrypt_info *ci;
306 union fscrypt_context ctx;
309 ci = READ_ONCE(inode->i_crypt_info);
311 /* key available, use the cached policy */
312 *policy = ci->ci_policy;
316 if (!IS_ENCRYPTED(inode))
319 ret = inode->i_sb->s_cop->get_context(inode, &ctx, sizeof(ctx));
321 return (ret == -ERANGE) ? -EINVAL : ret;
323 return fscrypt_policy_from_context(policy, &ctx, ret);
326 static int set_encryption_policy(struct inode *inode,
327 const union fscrypt_policy *policy)
329 union fscrypt_context ctx;
333 if (!fscrypt_supported_policy(policy, inode))
336 switch (policy->version) {
337 case FSCRYPT_POLICY_V1:
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.
349 pr_warn_once("%s (pid %d) is setting deprecated v1 encryption policy; recommend upgrading to v2.\n",
350 current->comm, current->pid);
352 case FSCRYPT_POLICY_V2:
353 err = fscrypt_verify_key_added(inode->i_sb,
354 policy->v2.master_key_identifier);
363 ctxsize = fscrypt_new_context_from_policy(&ctx, policy);
365 return inode->i_sb->s_cop->set_context(inode, &ctx, ctxsize, NULL);
368 int fscrypt_ioctl_set_policy(struct file *filp, const void __user *arg)
370 union fscrypt_policy policy;
371 union fscrypt_policy existing_policy;
372 struct inode *inode = file_inode(filp);
377 if (get_user(policy.version, (const u8 __user *)arg))
380 size = fscrypt_policy_size(&policy);
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.
393 * Work around it by just copying the first byte again...
395 version = policy.version;
396 if (copy_from_user(&policy, arg, size))
398 policy.version = version;
400 if (!inode_owner_or_capable(inode))
403 ret = mnt_want_write_file(filp);
409 ret = fscrypt_get_policy(inode, &existing_policy);
410 if (ret == -ENODATA) {
411 if (!S_ISDIR(inode->i_mode))
413 else if (IS_DEADDIR(inode))
415 else if (!inode->i_sb->s_cop->empty_dir(inode))
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. */
428 mnt_drop_write_file(filp);
431 EXPORT_SYMBOL(fscrypt_ioctl_set_policy);
433 /* Original ioctl version; can only get the original policy version */
434 int fscrypt_ioctl_get_policy(struct file *filp, void __user *arg)
436 union fscrypt_policy policy;
439 err = fscrypt_get_policy(file_inode(filp), &policy);
443 if (policy.version != FSCRYPT_POLICY_V1)
446 if (copy_to_user(arg, &policy, sizeof(policy.v1)))
450 EXPORT_SYMBOL(fscrypt_ioctl_get_policy);
452 /* Extended ioctl version; can get policies of any version */
453 int fscrypt_ioctl_get_policy_ex(struct file *filp, void __user *uarg)
455 struct fscrypt_get_policy_ex_arg arg;
456 union fscrypt_policy *policy = (union fscrypt_policy *)&arg.policy;
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));
466 err = fscrypt_get_policy(file_inode(filp), policy);
469 policy_size = fscrypt_policy_size(policy);
471 if (copy_from_user(&arg, uarg, sizeof(arg.policy_size)))
474 if (policy_size > arg.policy_size)
476 arg.policy_size = policy_size;
478 if (copy_to_user(uarg, &arg, sizeof(arg.policy_size) + policy_size))
482 EXPORT_SYMBOL_GPL(fscrypt_ioctl_get_policy_ex);
485 * fscrypt_has_permitted_context() - is a file's encryption policy permitted
486 * within its directory?
488 * @parent: inode for parent directory
489 * @child: inode for file being looked up, opened, or linked into @parent
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.
501 * Return: 1 if permitted, 0 if forbidden.
503 int fscrypt_has_permitted_context(struct inode *parent, struct inode *child)
505 union fscrypt_policy parent_policy, child_policy;
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))
513 /* No restrictions if the parent directory is unencrypted */
514 if (!IS_ENCRYPTED(parent))
517 /* Encrypted directories must not contain unencrypted files */
518 if (!IS_ENCRYPTED(child))
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.
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.
533 * In any case, if an unexpected error occurs, fall back to "forbidden".
536 err = fscrypt_get_encryption_info(parent);
539 err = fscrypt_get_encryption_info(child);
543 err = fscrypt_get_policy(parent, &parent_policy);
547 err = fscrypt_get_policy(child, &child_policy);
551 return fscrypt_policies_equal(&parent_policy, &child_policy);
553 EXPORT_SYMBOL(fscrypt_has_permitted_context);
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
562 * Return: 0 on success, -errno on failure
564 int fscrypt_inherit_context(struct inode *parent, struct inode *child,
565 void *fs_data, bool preload)
567 union fscrypt_context ctx;
569 struct fscrypt_info *ci;
572 res = fscrypt_get_encryption_info(parent);
576 ci = READ_ONCE(parent->i_crypt_info);
580 ctxsize = fscrypt_new_context_from_policy(&ctx, &ci->ci_policy);
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);
586 return preload ? fscrypt_get_encryption_info(child): 0;
588 EXPORT_SYMBOL(fscrypt_inherit_context);