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Jaegeuk Kim0b81d072015-05-15 16:26:10 -07001/*
2 * Encryption policy functions for per-file encryption support.
3 *
4 * Copyright (C) 2015, Google, Inc.
5 * Copyright (C) 2015, Motorola Mobility.
6 *
7 * Written by Michael Halcrow, 2015.
8 * Modified by Jaegeuk Kim, 2015.
9 */
10
11#include <linux/random.h>
12#include <linux/string.h>
Eric Biggersba63f232016-09-08 14:20:38 -070013#include <linux/mount.h>
Hyojun Kim63da4202017-10-06 17:10:08 -070014#include "fscrypt_private.h"
Jaegeuk Kim0b81d072015-05-15 16:26:10 -070015
16/*
Hyojun Kim63da4202017-10-06 17:10:08 -070017 * check whether an encryption policy is consistent with an encryption context
Jaegeuk Kim0b81d072015-05-15 16:26:10 -070018 */
Hyojun Kim63da4202017-10-06 17:10:08 -070019static bool is_encryption_context_consistent_with_policy(
20 const struct fscrypt_context *ctx,
Jaegeuk Kim0b81d072015-05-15 16:26:10 -070021 const struct fscrypt_policy *policy)
22{
Hyojun Kim63da4202017-10-06 17:10:08 -070023 return memcmp(ctx->master_key_descriptor, policy->master_key_descriptor,
24 FS_KEY_DESCRIPTOR_SIZE) == 0 &&
25 (ctx->flags == policy->flags) &&
26 (ctx->contents_encryption_mode ==
27 policy->contents_encryption_mode) &&
28 (ctx->filenames_encryption_mode ==
29 policy->filenames_encryption_mode);
Jaegeuk Kim0b81d072015-05-15 16:26:10 -070030}
31
32static int create_encryption_context_from_policy(struct inode *inode,
33 const struct fscrypt_policy *policy)
34{
35 struct fscrypt_context ctx;
Jaegeuk Kim0b81d072015-05-15 16:26:10 -070036
37 ctx.format = FS_ENCRYPTION_CONTEXT_FORMAT_V1;
38 memcpy(ctx.master_key_descriptor, policy->master_key_descriptor,
39 FS_KEY_DESCRIPTOR_SIZE);
40
Hyojun Kim63da4202017-10-06 17:10:08 -070041 if (!fscrypt_valid_enc_modes(policy->contents_encryption_mode,
42 policy->filenames_encryption_mode))
Jaegeuk Kim0b81d072015-05-15 16:26:10 -070043 return -EINVAL;
Jaegeuk Kim0b81d072015-05-15 16:26:10 -070044
45 if (policy->flags & ~FS_POLICY_FLAGS_VALID)
46 return -EINVAL;
47
48 ctx.contents_encryption_mode = policy->contents_encryption_mode;
49 ctx.filenames_encryption_mode = policy->filenames_encryption_mode;
50 ctx.flags = policy->flags;
51 BUILD_BUG_ON(sizeof(ctx.nonce) != FS_KEY_DERIVATION_NONCE_SIZE);
52 get_random_bytes(ctx.nonce, FS_KEY_DERIVATION_NONCE_SIZE);
53
54 return inode->i_sb->s_cop->set_context(inode, &ctx, sizeof(ctx), NULL);
55}
56
Hyojun Kim63da4202017-10-06 17:10:08 -070057int fscrypt_ioctl_set_policy(struct file *filp, const void __user *arg)
Jaegeuk Kim0b81d072015-05-15 16:26:10 -070058{
Hyojun Kim63da4202017-10-06 17:10:08 -070059 struct fscrypt_policy policy;
Eric Biggersba63f232016-09-08 14:20:38 -070060 struct inode *inode = file_inode(filp);
61 int ret;
Hyojun Kim63da4202017-10-06 17:10:08 -070062 struct fscrypt_context ctx;
63
64 if (copy_from_user(&policy, arg, sizeof(policy)))
65 return -EFAULT;
Eric Biggersba63f232016-09-08 14:20:38 -070066
Eric Biggers163ae1c2016-09-08 10:57:08 -070067 if (!inode_owner_or_capable(inode))
68 return -EACCES;
69
Hyojun Kim63da4202017-10-06 17:10:08 -070070 if (policy.version != 0)
Jaegeuk Kim0b81d072015-05-15 16:26:10 -070071 return -EINVAL;
72
Eric Biggersba63f232016-09-08 14:20:38 -070073 ret = mnt_want_write_file(filp);
74 if (ret)
75 return ret;
76
Eric Biggers8906a822016-10-15 09:48:50 -040077 inode_lock(inode);
78
Hyojun Kim63da4202017-10-06 17:10:08 -070079 ret = inode->i_sb->s_cop->get_context(inode, &ctx, sizeof(ctx));
80 if (ret == -ENODATA) {
Eric Biggers002ced42016-09-08 11:36:39 -070081 if (!S_ISDIR(inode->i_mode))
Hyojun Kim63da4202017-10-06 17:10:08 -070082 ret = -ENOTDIR;
Eric Biggersba63f232016-09-08 14:20:38 -070083 else if (!inode->i_sb->s_cop->empty_dir(inode))
84 ret = -ENOTEMPTY;
85 else
86 ret = create_encryption_context_from_policy(inode,
Hyojun Kim63da4202017-10-06 17:10:08 -070087 &policy);
88 } else if (ret == sizeof(ctx) &&
89 is_encryption_context_consistent_with_policy(&ctx,
90 &policy)) {
91 /* The file already uses the same encryption policy. */
92 ret = 0;
93 } else if (ret >= 0 || ret == -ERANGE) {
94 /* The file already uses a different encryption policy. */
95 ret = -EEXIST;
Jaegeuk Kim0b81d072015-05-15 16:26:10 -070096 }
97
Eric Biggers8906a822016-10-15 09:48:50 -040098 inode_unlock(inode);
99
Eric Biggersba63f232016-09-08 14:20:38 -0700100 mnt_drop_write_file(filp);
101 return ret;
Jaegeuk Kim0b81d072015-05-15 16:26:10 -0700102}
Hyojun Kim63da4202017-10-06 17:10:08 -0700103EXPORT_SYMBOL(fscrypt_ioctl_set_policy);
Jaegeuk Kim0b81d072015-05-15 16:26:10 -0700104
Hyojun Kim63da4202017-10-06 17:10:08 -0700105int fscrypt_ioctl_get_policy(struct file *filp, void __user *arg)
Jaegeuk Kim0b81d072015-05-15 16:26:10 -0700106{
Hyojun Kim63da4202017-10-06 17:10:08 -0700107 struct inode *inode = file_inode(filp);
Jaegeuk Kim0b81d072015-05-15 16:26:10 -0700108 struct fscrypt_context ctx;
Hyojun Kim63da4202017-10-06 17:10:08 -0700109 struct fscrypt_policy policy;
Jaegeuk Kim0b81d072015-05-15 16:26:10 -0700110 int res;
111
Jaegeuk Kim8dec0742017-06-22 12:14:40 -0700112 if (!IS_ENCRYPTED(inode))
Jaegeuk Kim0b81d072015-05-15 16:26:10 -0700113 return -ENODATA;
114
115 res = inode->i_sb->s_cop->get_context(inode, &ctx, sizeof(ctx));
Hyojun Kim63da4202017-10-06 17:10:08 -0700116 if (res < 0 && res != -ERANGE)
117 return res;
Jaegeuk Kim0b81d072015-05-15 16:26:10 -0700118 if (res != sizeof(ctx))
Hyojun Kim63da4202017-10-06 17:10:08 -0700119 return -EINVAL;
Jaegeuk Kim0b81d072015-05-15 16:26:10 -0700120 if (ctx.format != FS_ENCRYPTION_CONTEXT_FORMAT_V1)
121 return -EINVAL;
122
Hyojun Kim63da4202017-10-06 17:10:08 -0700123 policy.version = 0;
124 policy.contents_encryption_mode = ctx.contents_encryption_mode;
125 policy.filenames_encryption_mode = ctx.filenames_encryption_mode;
126 policy.flags = ctx.flags;
127 memcpy(policy.master_key_descriptor, ctx.master_key_descriptor,
Jaegeuk Kim0b81d072015-05-15 16:26:10 -0700128 FS_KEY_DESCRIPTOR_SIZE);
Hyojun Kim63da4202017-10-06 17:10:08 -0700129
130 if (copy_to_user(arg, &policy, sizeof(policy)))
131 return -EFAULT;
Jaegeuk Kim0b81d072015-05-15 16:26:10 -0700132 return 0;
133}
Hyojun Kim63da4202017-10-06 17:10:08 -0700134EXPORT_SYMBOL(fscrypt_ioctl_get_policy);
Jaegeuk Kim0b81d072015-05-15 16:26:10 -0700135
Eric Biggers64a599a2017-04-07 10:58:37 -0700136/**
137 * fscrypt_has_permitted_context() - is a file's encryption policy permitted
138 * within its directory?
139 *
140 * @parent: inode for parent directory
141 * @child: inode for file being looked up, opened, or linked into @parent
142 *
143 * Filesystems must call this before permitting access to an inode in a
144 * situation where the parent directory is encrypted (either before allowing
145 * ->lookup() to succeed, or for a regular file before allowing it to be opened)
146 * and before any operation that involves linking an inode into an encrypted
147 * directory, including link, rename, and cross rename. It enforces the
148 * constraint that within a given encrypted directory tree, all files use the
149 * same encryption policy. The pre-access check is needed to detect potentially
150 * malicious offline violations of this constraint, while the link and rename
151 * checks are needed to prevent online violations of this constraint.
152 *
153 * Return: 1 if permitted, 0 if forbidden. If forbidden, the caller must fail
154 * the filesystem operation with EPERM.
155 */
Jaegeuk Kim0b81d072015-05-15 16:26:10 -0700156int fscrypt_has_permitted_context(struct inode *parent, struct inode *child)
157{
Eric Biggers64a599a2017-04-07 10:58:37 -0700158 const struct fscrypt_operations *cops = parent->i_sb->s_cop;
159 const struct fscrypt_info *parent_ci, *child_ci;
160 struct fscrypt_context parent_ctx, child_ctx;
Jaegeuk Kim0b81d072015-05-15 16:26:10 -0700161 int res;
162
Eric Biggersd259b682016-12-19 14:20:13 -0800163 /* No restrictions on file types which are never encrypted */
164 if (!S_ISREG(child->i_mode) && !S_ISDIR(child->i_mode) &&
165 !S_ISLNK(child->i_mode))
166 return 1;
167
Eric Biggers64a599a2017-04-07 10:58:37 -0700168 /* No restrictions if the parent directory is unencrypted */
Jaegeuk Kim8dec0742017-06-22 12:14:40 -0700169 if (!IS_ENCRYPTED(parent))
Jaegeuk Kim0b81d072015-05-15 16:26:10 -0700170 return 1;
Eric Biggers64a599a2017-04-07 10:58:37 -0700171
172 /* Encrypted directories must not contain unencrypted files */
Jaegeuk Kim8dec0742017-06-22 12:14:40 -0700173 if (!IS_ENCRYPTED(child))
Jaegeuk Kim0b81d072015-05-15 16:26:10 -0700174 return 0;
Eric Biggers64a599a2017-04-07 10:58:37 -0700175
176 /*
177 * Both parent and child are encrypted, so verify they use the same
178 * encryption policy. Compare the fscrypt_info structs if the keys are
179 * available, otherwise retrieve and compare the fscrypt_contexts.
180 *
181 * Note that the fscrypt_context retrieval will be required frequently
182 * when accessing an encrypted directory tree without the key.
183 * Performance-wise this is not a big deal because we already don't
184 * really optimize for file access without the key (to the extent that
185 * such access is even possible), given that any attempted access
186 * already causes a fscrypt_context retrieval and keyring search.
187 *
188 * In any case, if an unexpected error occurs, fall back to "forbidden".
189 */
190
Jaegeuk Kim0b81d072015-05-15 16:26:10 -0700191 res = fscrypt_get_encryption_info(parent);
192 if (res)
193 return 0;
194 res = fscrypt_get_encryption_info(child);
195 if (res)
196 return 0;
197 parent_ci = parent->i_crypt_info;
198 child_ci = child->i_crypt_info;
Eric Biggers64a599a2017-04-07 10:58:37 -0700199
200 if (parent_ci && child_ci) {
201 return memcmp(parent_ci->ci_master_key, child_ci->ci_master_key,
202 FS_KEY_DESCRIPTOR_SIZE) == 0 &&
203 (parent_ci->ci_data_mode == child_ci->ci_data_mode) &&
204 (parent_ci->ci_filename_mode ==
205 child_ci->ci_filename_mode) &&
206 (parent_ci->ci_flags == child_ci->ci_flags);
207 }
208
209 res = cops->get_context(parent, &parent_ctx, sizeof(parent_ctx));
210 if (res != sizeof(parent_ctx))
Jaegeuk Kim0b81d072015-05-15 16:26:10 -0700211 return 0;
212
Eric Biggers64a599a2017-04-07 10:58:37 -0700213 res = cops->get_context(child, &child_ctx, sizeof(child_ctx));
214 if (res != sizeof(child_ctx))
215 return 0;
216
217 return memcmp(parent_ctx.master_key_descriptor,
218 child_ctx.master_key_descriptor,
219 FS_KEY_DESCRIPTOR_SIZE) == 0 &&
220 (parent_ctx.contents_encryption_mode ==
221 child_ctx.contents_encryption_mode) &&
222 (parent_ctx.filenames_encryption_mode ==
223 child_ctx.filenames_encryption_mode) &&
224 (parent_ctx.flags == child_ctx.flags);
Jaegeuk Kim0b81d072015-05-15 16:26:10 -0700225}
226EXPORT_SYMBOL(fscrypt_has_permitted_context);
227
228/**
229 * fscrypt_inherit_context() - Sets a child context from its parent
230 * @parent: Parent inode from which the context is inherited.
231 * @child: Child inode that inherits the context from @parent.
232 * @fs_data: private data given by FS.
Hyojun Kim63da4202017-10-06 17:10:08 -0700233 * @preload: preload child i_crypt_info if true
Jaegeuk Kim0b81d072015-05-15 16:26:10 -0700234 *
Hyojun Kim63da4202017-10-06 17:10:08 -0700235 * Return: 0 on success, -errno on failure
Jaegeuk Kim0b81d072015-05-15 16:26:10 -0700236 */
237int fscrypt_inherit_context(struct inode *parent, struct inode *child,
238 void *fs_data, bool preload)
239{
240 struct fscrypt_context ctx;
241 struct fscrypt_info *ci;
242 int res;
243
Jaegeuk Kim0b81d072015-05-15 16:26:10 -0700244 res = fscrypt_get_encryption_info(parent);
245 if (res < 0)
246 return res;
247
248 ci = parent->i_crypt_info;
249 if (ci == NULL)
250 return -ENOKEY;
251
252 ctx.format = FS_ENCRYPTION_CONTEXT_FORMAT_V1;
Hyojun Kim63da4202017-10-06 17:10:08 -0700253 ctx.contents_encryption_mode = ci->ci_data_mode;
254 ctx.filenames_encryption_mode = ci->ci_filename_mode;
255 ctx.flags = ci->ci_flags;
256 memcpy(ctx.master_key_descriptor, ci->ci_master_key,
257 FS_KEY_DESCRIPTOR_SIZE);
Jaegeuk Kim0b81d072015-05-15 16:26:10 -0700258 get_random_bytes(ctx.nonce, FS_KEY_DERIVATION_NONCE_SIZE);
259 res = parent->i_sb->s_cop->set_context(child, &ctx,
260 sizeof(ctx), fs_data);
261 if (res)
262 return res;
263 return preload ? fscrypt_get_encryption_info(child): 0;
264}
265EXPORT_SYMBOL(fscrypt_inherit_context);