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 */
is_encryption_context_consistent_with_policy(const struct fscrypt_context * ctx,const struct fscrypt_policy * policy)20 static 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
create_encryption_context_from_policy(struct inode * inode,const struct fscrypt_policy * policy)33 static 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
fscrypt_ioctl_set_policy(struct file * filp,const void __user * arg)58 int 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 (IS_DEADDIR(inode))
85 ret = -ENOENT;
86 else if (!inode->i_sb->s_cop->empty_dir(inode))
87 ret = -ENOTEMPTY;
88 else
89 ret = create_encryption_context_from_policy(inode,
90 &policy);
91 } else if (ret == sizeof(ctx) &&
92 is_encryption_context_consistent_with_policy(&ctx,
93 &policy)) {
94 /* The file already uses the same encryption policy. */
95 ret = 0;
96 } else if (ret >= 0 || ret == -ERANGE) {
97 /* The file already uses a different encryption policy. */
98 ret = -EEXIST;
99 }
100
101 inode_unlock(inode);
102
103 mnt_drop_write_file(filp);
104 return ret;
105 }
106 EXPORT_SYMBOL(fscrypt_ioctl_set_policy);
107
fscrypt_ioctl_get_policy(struct file * filp,void __user * arg)108 int fscrypt_ioctl_get_policy(struct file *filp, void __user *arg)
109 {
110 struct inode *inode = file_inode(filp);
111 struct fscrypt_context ctx;
112 struct fscrypt_policy policy;
113 int res;
114
115 if (!IS_ENCRYPTED(inode))
116 return -ENODATA;
117
118 res = inode->i_sb->s_cop->get_context(inode, &ctx, sizeof(ctx));
119 if (res < 0 && res != -ERANGE)
120 return res;
121 if (res != sizeof(ctx))
122 return -EINVAL;
123 if (ctx.format != FS_ENCRYPTION_CONTEXT_FORMAT_V1)
124 return -EINVAL;
125
126 policy.version = 0;
127 policy.contents_encryption_mode = ctx.contents_encryption_mode;
128 policy.filenames_encryption_mode = ctx.filenames_encryption_mode;
129 policy.flags = ctx.flags;
130 memcpy(policy.master_key_descriptor, ctx.master_key_descriptor,
131 FS_KEY_DESCRIPTOR_SIZE);
132
133 if (copy_to_user(arg, &policy, sizeof(policy)))
134 return -EFAULT;
135 return 0;
136 }
137 EXPORT_SYMBOL(fscrypt_ioctl_get_policy);
138
139 /**
140 * fscrypt_has_permitted_context() - is a file's encryption policy permitted
141 * within its directory?
142 *
143 * @parent: inode for parent directory
144 * @child: inode for file being looked up, opened, or linked into @parent
145 *
146 * Filesystems must call this before permitting access to an inode in a
147 * situation where the parent directory is encrypted (either before allowing
148 * ->lookup() to succeed, or for a regular file before allowing it to be opened)
149 * and before any operation that involves linking an inode into an encrypted
150 * directory, including link, rename, and cross rename. It enforces the
151 * constraint that within a given encrypted directory tree, all files use the
152 * same encryption policy. The pre-access check is needed to detect potentially
153 * malicious offline violations of this constraint, while the link and rename
154 * checks are needed to prevent online violations of this constraint.
155 *
156 * Return: 1 if permitted, 0 if forbidden.
157 */
fscrypt_has_permitted_context(struct inode * parent,struct inode * child)158 int fscrypt_has_permitted_context(struct inode *parent, struct inode *child)
159 {
160 const struct fscrypt_operations *cops = parent->i_sb->s_cop;
161 const struct fscrypt_info *parent_ci, *child_ci;
162 struct fscrypt_context parent_ctx, child_ctx;
163 int res;
164
165 /* No restrictions on file types which are never encrypted */
166 if (!S_ISREG(child->i_mode) && !S_ISDIR(child->i_mode) &&
167 !S_ISLNK(child->i_mode))
168 return 1;
169
170 /* No restrictions if the parent directory is unencrypted */
171 if (!IS_ENCRYPTED(parent))
172 return 1;
173
174 /* Encrypted directories must not contain unencrypted files */
175 if (!IS_ENCRYPTED(child))
176 return 0;
177
178 /*
179 * Both parent and child are encrypted, so verify they use the same
180 * encryption policy. Compare the fscrypt_info structs if the keys are
181 * available, otherwise retrieve and compare the fscrypt_contexts.
182 *
183 * Note that the fscrypt_context retrieval will be required frequently
184 * when accessing an encrypted directory tree without the key.
185 * Performance-wise this is not a big deal because we already don't
186 * really optimize for file access without the key (to the extent that
187 * such access is even possible), given that any attempted access
188 * already causes a fscrypt_context retrieval and keyring search.
189 *
190 * In any case, if an unexpected error occurs, fall back to "forbidden".
191 */
192
193 res = fscrypt_get_encryption_info(parent);
194 if (res)
195 return 0;
196 res = fscrypt_get_encryption_info(child);
197 if (res)
198 return 0;
199 parent_ci = parent->i_crypt_info;
200 child_ci = child->i_crypt_info;
201
202 if (parent_ci && child_ci) {
203 return memcmp(parent_ci->ci_master_key, child_ci->ci_master_key,
204 FS_KEY_DESCRIPTOR_SIZE) == 0 &&
205 (parent_ci->ci_data_mode == child_ci->ci_data_mode) &&
206 (parent_ci->ci_filename_mode ==
207 child_ci->ci_filename_mode) &&
208 (parent_ci->ci_flags == child_ci->ci_flags);
209 }
210
211 res = cops->get_context(parent, &parent_ctx, sizeof(parent_ctx));
212 if (res != sizeof(parent_ctx))
213 return 0;
214
215 res = cops->get_context(child, &child_ctx, sizeof(child_ctx));
216 if (res != sizeof(child_ctx))
217 return 0;
218
219 return memcmp(parent_ctx.master_key_descriptor,
220 child_ctx.master_key_descriptor,
221 FS_KEY_DESCRIPTOR_SIZE) == 0 &&
222 (parent_ctx.contents_encryption_mode ==
223 child_ctx.contents_encryption_mode) &&
224 (parent_ctx.filenames_encryption_mode ==
225 child_ctx.filenames_encryption_mode) &&
226 (parent_ctx.flags == child_ctx.flags);
227 }
228 EXPORT_SYMBOL(fscrypt_has_permitted_context);
229
230 /**
231 * fscrypt_inherit_context() - Sets a child context from its parent
232 * @parent: Parent inode from which the context is inherited.
233 * @child: Child inode that inherits the context from @parent.
234 * @fs_data: private data given by FS.
235 * @preload: preload child i_crypt_info if true
236 *
237 * Return: 0 on success, -errno on failure
238 */
fscrypt_inherit_context(struct inode * parent,struct inode * child,void * fs_data,bool preload)239 int fscrypt_inherit_context(struct inode *parent, struct inode *child,
240 void *fs_data, bool preload)
241 {
242 struct fscrypt_context ctx;
243 struct fscrypt_info *ci;
244 int res;
245
246 res = fscrypt_get_encryption_info(parent);
247 if (res < 0)
248 return res;
249
250 ci = parent->i_crypt_info;
251 if (ci == NULL)
252 return -ENOKEY;
253
254 ctx.format = FS_ENCRYPTION_CONTEXT_FORMAT_V1;
255 ctx.contents_encryption_mode = ci->ci_data_mode;
256 ctx.filenames_encryption_mode = ci->ci_filename_mode;
257 ctx.flags = ci->ci_flags;
258 memcpy(ctx.master_key_descriptor, ci->ci_master_key,
259 FS_KEY_DESCRIPTOR_SIZE);
260 get_random_bytes(ctx.nonce, FS_KEY_DERIVATION_NONCE_SIZE);
261 BUILD_BUG_ON(sizeof(ctx) != FSCRYPT_SET_CONTEXT_MAX_SIZE);
262 res = parent->i_sb->s_cop->set_context(child, &ctx,
263 sizeof(ctx), fs_data);
264 if (res)
265 return res;
266 return preload ? fscrypt_get_encryption_info(child): 0;
267 }
268 EXPORT_SYMBOL(fscrypt_inherit_context);
269