1 /*
2 * linux/fs/ext4/crypto_policy.c
3 *
4 * Copyright (C) 2015, Google, Inc.
5 *
6 * This contains encryption policy functions for ext4
7 *
8 * Written by Michael Halcrow, 2015.
9 */
10
11 #include <linux/random.h>
12 #include <linux/string.h>
13 #include <linux/types.h>
14
15 #include "ext4_jbd2.h"
16 #include "ext4.h"
17 #include "xattr.h"
18
ext4_inode_has_encryption_context(struct inode * inode)19 static int ext4_inode_has_encryption_context(struct inode *inode)
20 {
21 int res = ext4_xattr_get(inode, EXT4_XATTR_INDEX_ENCRYPTION,
22 EXT4_XATTR_NAME_ENCRYPTION_CONTEXT, NULL, 0);
23 return (res > 0);
24 }
25
26 /*
27 * check whether the policy is consistent with the encryption context
28 * for the inode
29 */
ext4_is_encryption_context_consistent_with_policy(struct inode * inode,const struct ext4_encryption_policy * policy)30 static int ext4_is_encryption_context_consistent_with_policy(
31 struct inode *inode, const struct ext4_encryption_policy *policy)
32 {
33 struct ext4_encryption_context ctx;
34 int res = ext4_xattr_get(inode, EXT4_XATTR_INDEX_ENCRYPTION,
35 EXT4_XATTR_NAME_ENCRYPTION_CONTEXT, &ctx,
36 sizeof(ctx));
37 if (res != sizeof(ctx))
38 return 0;
39 return (memcmp(ctx.master_key_descriptor, policy->master_key_descriptor,
40 EXT4_KEY_DESCRIPTOR_SIZE) == 0 &&
41 (ctx.flags ==
42 policy->flags) &&
43 (ctx.contents_encryption_mode ==
44 policy->contents_encryption_mode) &&
45 (ctx.filenames_encryption_mode ==
46 policy->filenames_encryption_mode));
47 }
48
ext4_create_encryption_context_from_policy(struct inode * inode,const struct ext4_encryption_policy * policy)49 static int ext4_create_encryption_context_from_policy(
50 struct inode *inode, const struct ext4_encryption_policy *policy)
51 {
52 struct ext4_encryption_context ctx;
53 handle_t *handle;
54 int res, res2;
55
56 res = ext4_convert_inline_data(inode);
57 if (res)
58 return res;
59
60 ctx.format = EXT4_ENCRYPTION_CONTEXT_FORMAT_V1;
61 memcpy(ctx.master_key_descriptor, policy->master_key_descriptor,
62 EXT4_KEY_DESCRIPTOR_SIZE);
63 if (!ext4_valid_contents_enc_mode(policy->contents_encryption_mode)) {
64 printk(KERN_WARNING
65 "%s: Invalid contents encryption mode %d\n", __func__,
66 policy->contents_encryption_mode);
67 return -EINVAL;
68 }
69 if (!ext4_valid_filenames_enc_mode(policy->filenames_encryption_mode)) {
70 printk(KERN_WARNING
71 "%s: Invalid filenames encryption mode %d\n", __func__,
72 policy->filenames_encryption_mode);
73 return -EINVAL;
74 }
75 if (policy->flags & ~EXT4_POLICY_FLAGS_VALID)
76 return -EINVAL;
77 ctx.contents_encryption_mode = policy->contents_encryption_mode;
78 ctx.filenames_encryption_mode = policy->filenames_encryption_mode;
79 ctx.flags = policy->flags;
80 BUILD_BUG_ON(sizeof(ctx.nonce) != EXT4_KEY_DERIVATION_NONCE_SIZE);
81 get_random_bytes(ctx.nonce, EXT4_KEY_DERIVATION_NONCE_SIZE);
82
83 handle = ext4_journal_start(inode, EXT4_HT_MISC,
84 ext4_jbd2_credits_xattr(inode));
85 if (IS_ERR(handle))
86 return PTR_ERR(handle);
87 res = ext4_xattr_set(inode, EXT4_XATTR_INDEX_ENCRYPTION,
88 EXT4_XATTR_NAME_ENCRYPTION_CONTEXT, &ctx,
89 sizeof(ctx), 0);
90 if (!res) {
91 ext4_set_inode_flag(inode, EXT4_INODE_ENCRYPT);
92 res = ext4_mark_inode_dirty(handle, inode);
93 if (res)
94 EXT4_ERROR_INODE(inode, "Failed to mark inode dirty");
95 }
96 res2 = ext4_journal_stop(handle);
97 if (!res)
98 res = res2;
99 return res;
100 }
101
ext4_process_policy(const struct ext4_encryption_policy * policy,struct inode * inode)102 int ext4_process_policy(const struct ext4_encryption_policy *policy,
103 struct inode *inode)
104 {
105 if (!inode_owner_or_capable(inode))
106 return -EACCES;
107
108 if (policy->version != 0)
109 return -EINVAL;
110
111 if (!ext4_inode_has_encryption_context(inode)) {
112 if (!S_ISDIR(inode->i_mode))
113 return -EINVAL;
114 if (!ext4_empty_dir(inode))
115 return -ENOTEMPTY;
116 return ext4_create_encryption_context_from_policy(inode,
117 policy);
118 }
119
120 if (ext4_is_encryption_context_consistent_with_policy(inode, policy))
121 return 0;
122
123 printk(KERN_WARNING "%s: Policy inconsistent with encryption context\n",
124 __func__);
125 return -EINVAL;
126 }
127
ext4_get_policy(struct inode * inode,struct ext4_encryption_policy * policy)128 int ext4_get_policy(struct inode *inode, struct ext4_encryption_policy *policy)
129 {
130 struct ext4_encryption_context ctx;
131
132 int res = ext4_xattr_get(inode, EXT4_XATTR_INDEX_ENCRYPTION,
133 EXT4_XATTR_NAME_ENCRYPTION_CONTEXT,
134 &ctx, sizeof(ctx));
135 if (res != sizeof(ctx))
136 return -ENOENT;
137 if (ctx.format != EXT4_ENCRYPTION_CONTEXT_FORMAT_V1)
138 return -EINVAL;
139 policy->version = 0;
140 policy->contents_encryption_mode = ctx.contents_encryption_mode;
141 policy->filenames_encryption_mode = ctx.filenames_encryption_mode;
142 policy->flags = ctx.flags;
143 memcpy(&policy->master_key_descriptor, ctx.master_key_descriptor,
144 EXT4_KEY_DESCRIPTOR_SIZE);
145 return 0;
146 }
147
ext4_is_child_context_consistent_with_parent(struct inode * parent,struct inode * child)148 int ext4_is_child_context_consistent_with_parent(struct inode *parent,
149 struct inode *child)
150 {
151 const struct ext4_crypt_info *parent_ci, *child_ci;
152 struct ext4_encryption_context parent_ctx, child_ctx;
153 int res;
154
155 /* No restrictions on file types which are never encrypted */
156 if (!S_ISREG(child->i_mode) && !S_ISDIR(child->i_mode) &&
157 !S_ISLNK(child->i_mode))
158 return 1;
159
160 /* No restrictions if the parent directory is unencrypted */
161 if (!ext4_encrypted_inode(parent))
162 return 1;
163
164 /* Encrypted directories must not contain unencrypted files */
165 if (!ext4_encrypted_inode(child))
166 return 0;
167
168 /*
169 * Both parent and child are encrypted, so verify they use the same
170 * encryption policy. Compare the fscrypt_info structs if the keys are
171 * available, otherwise retrieve and compare the fscrypt_contexts.
172 *
173 * Note that the fscrypt_context retrieval will be required frequently
174 * when accessing an encrypted directory tree without the key.
175 * Performance-wise this is not a big deal because we already don't
176 * really optimize for file access without the key (to the extent that
177 * such access is even possible), given that any attempted access
178 * already causes a fscrypt_context retrieval and keyring search.
179 *
180 * In any case, if an unexpected error occurs, fall back to "forbidden".
181 */
182
183 res = ext4_get_encryption_info(parent);
184 if (res)
185 return 0;
186 res = ext4_get_encryption_info(child);
187 if (res)
188 return 0;
189 parent_ci = EXT4_I(parent)->i_crypt_info;
190 child_ci = EXT4_I(child)->i_crypt_info;
191 if (parent_ci && child_ci) {
192 return memcmp(parent_ci->ci_master_key, child_ci->ci_master_key,
193 EXT4_KEY_DESCRIPTOR_SIZE) == 0 &&
194 (parent_ci->ci_data_mode == child_ci->ci_data_mode) &&
195 (parent_ci->ci_filename_mode ==
196 child_ci->ci_filename_mode) &&
197 (parent_ci->ci_flags == child_ci->ci_flags);
198 }
199
200 res = ext4_xattr_get(parent, EXT4_XATTR_INDEX_ENCRYPTION,
201 EXT4_XATTR_NAME_ENCRYPTION_CONTEXT,
202 &parent_ctx, sizeof(parent_ctx));
203 if (res != sizeof(parent_ctx))
204 return 0;
205
206 res = ext4_xattr_get(child, EXT4_XATTR_INDEX_ENCRYPTION,
207 EXT4_XATTR_NAME_ENCRYPTION_CONTEXT,
208 &child_ctx, sizeof(child_ctx));
209 if (res != sizeof(child_ctx))
210 return 0;
211
212 return memcmp(parent_ctx.master_key_descriptor,
213 child_ctx.master_key_descriptor,
214 EXT4_KEY_DESCRIPTOR_SIZE) == 0 &&
215 (parent_ctx.contents_encryption_mode ==
216 child_ctx.contents_encryption_mode) &&
217 (parent_ctx.filenames_encryption_mode ==
218 child_ctx.filenames_encryption_mode) &&
219 (parent_ctx.flags == child_ctx.flags);
220 }
221
222 /**
223 * ext4_inherit_context() - Sets a child context from its parent
224 * @parent: Parent inode from which the context is inherited.
225 * @child: Child inode that inherits the context from @parent.
226 *
227 * Return: Zero on success, non-zero otherwise
228 */
ext4_inherit_context(struct inode * parent,struct inode * child)229 int ext4_inherit_context(struct inode *parent, struct inode *child)
230 {
231 struct ext4_encryption_context ctx;
232 struct ext4_crypt_info *ci;
233 int res;
234
235 res = ext4_get_encryption_info(parent);
236 if (res < 0)
237 return res;
238 ci = EXT4_I(parent)->i_crypt_info;
239 if (ci == NULL)
240 return -ENOKEY;
241
242 ctx.format = EXT4_ENCRYPTION_CONTEXT_FORMAT_V1;
243 if (DUMMY_ENCRYPTION_ENABLED(EXT4_SB(parent->i_sb))) {
244 ctx.contents_encryption_mode = EXT4_ENCRYPTION_MODE_AES_256_XTS;
245 ctx.filenames_encryption_mode =
246 EXT4_ENCRYPTION_MODE_AES_256_CTS;
247 ctx.flags = 0;
248 memset(ctx.master_key_descriptor, 0x42,
249 EXT4_KEY_DESCRIPTOR_SIZE);
250 res = 0;
251 } else {
252 ctx.contents_encryption_mode = ci->ci_data_mode;
253 ctx.filenames_encryption_mode = ci->ci_filename_mode;
254 ctx.flags = ci->ci_flags;
255 memcpy(ctx.master_key_descriptor, ci->ci_master_key,
256 EXT4_KEY_DESCRIPTOR_SIZE);
257 }
258 get_random_bytes(ctx.nonce, EXT4_KEY_DERIVATION_NONCE_SIZE);
259 res = ext4_xattr_set(child, EXT4_XATTR_INDEX_ENCRYPTION,
260 EXT4_XATTR_NAME_ENCRYPTION_CONTEXT, &ctx,
261 sizeof(ctx), 0);
262 if (!res) {
263 ext4_set_inode_flag(child, EXT4_INODE_ENCRYPT);
264 ext4_clear_inode_state(child, EXT4_STATE_MAY_INLINE_DATA);
265 res = ext4_get_encryption_info(child);
266 }
267 return res;
268 }
269