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