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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 */
20static 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
33static 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
58int 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 (!inode->i_sb->s_cop->empty_dir(inode))
85 ret = -ENOTEMPTY;
86 else
87 ret = create_encryption_context_from_policy(inode,
88 &policy);
89 } else if (ret == sizeof(ctx) &&
90 is_encryption_context_consistent_with_policy(&ctx,
91 &policy)) {
92 /* The file already uses the same encryption policy. */
93 ret = 0;
94 } else if (ret >= 0 || ret == -ERANGE) {
95 /* The file already uses a different encryption policy. */
96 ret = -EEXIST;
97 }
98
99 inode_unlock(inode);
100
101 mnt_drop_write_file(filp);
102 return ret;
103}
104EXPORT_SYMBOL(fscrypt_ioctl_set_policy);
105
106int fscrypt_ioctl_get_policy(struct file *filp, void __user *arg)
107{
108 struct inode *inode = file_inode(filp);
109 struct fscrypt_context ctx;
110 struct fscrypt_policy policy;
111 int res;
112
113 if (!IS_ENCRYPTED(inode))
114 return -ENODATA;
115
116 res = inode->i_sb->s_cop->get_context(inode, &ctx, sizeof(ctx));
117 if (res < 0 && res != -ERANGE)
118 return res;
119 if (res != sizeof(ctx))
120 return -EINVAL;
121 if (ctx.format != FS_ENCRYPTION_CONTEXT_FORMAT_V1)
122 return -EINVAL;
123
124 policy.version = 0;
125 policy.contents_encryption_mode = ctx.contents_encryption_mode;
126 policy.filenames_encryption_mode = ctx.filenames_encryption_mode;
127 policy.flags = ctx.flags;
128 memcpy(policy.master_key_descriptor, ctx.master_key_descriptor,
129 FS_KEY_DESCRIPTOR_SIZE);
130
131 if (copy_to_user(arg, &policy, sizeof(policy)))
132 return -EFAULT;
133 return 0;
134}
135EXPORT_SYMBOL(fscrypt_ioctl_get_policy);
136
137/**
138 * fscrypt_has_permitted_context() - is a file's encryption policy permitted
139 * within its directory?
140 *
141 * @parent: inode for parent directory
142 * @child: inode for file being looked up, opened, or linked into @parent
143 *
144 * Filesystems must call this before permitting access to an inode in a
145 * situation where the parent directory is encrypted (either before allowing
146 * ->lookup() to succeed, or for a regular file before allowing it to be opened)
147 * and before any operation that involves linking an inode into an encrypted
148 * directory, including link, rename, and cross rename. It enforces the
149 * constraint that within a given encrypted directory tree, all files use the
150 * same encryption policy. The pre-access check is needed to detect potentially
151 * malicious offline violations of this constraint, while the link and rename
152 * checks are needed to prevent online violations of this constraint.
153 *
154 * Return: 1 if permitted, 0 if forbidden. If forbidden, the caller must fail
155 * the filesystem operation with EPERM.
156 */
157int fscrypt_has_permitted_context(struct inode *parent, struct inode *child)
158{
159 const struct fscrypt_operations *cops = parent->i_sb->s_cop;
160 const struct fscrypt_info *parent_ci, *child_ci;
161 struct fscrypt_context parent_ctx, child_ctx;
162 int res;
163
164 /* No restrictions on file types which are never encrypted */
165 if (!S_ISREG(child->i_mode) && !S_ISDIR(child->i_mode) &&
166 !S_ISLNK(child->i_mode))
167 return 1;
168
169 /* No restrictions if the parent directory is unencrypted */
170 if (!IS_ENCRYPTED(parent))
171 return 1;
172
173 /* Encrypted directories must not contain unencrypted files */
174 if (!IS_ENCRYPTED(child))
175 return 0;
176
177 /*
178 * Both parent and child are encrypted, so verify they use the same
179 * encryption policy. Compare the fscrypt_info structs if the keys are
180 * available, otherwise retrieve and compare the fscrypt_contexts.
181 *
182 * Note that the fscrypt_context retrieval will be required frequently
183 * when accessing an encrypted directory tree without the key.
184 * Performance-wise this is not a big deal because we already don't
185 * really optimize for file access without the key (to the extent that
186 * such access is even possible), given that any attempted access
187 * already causes a fscrypt_context retrieval and keyring search.
188 *
189 * In any case, if an unexpected error occurs, fall back to "forbidden".
190 */
191
192 res = fscrypt_get_encryption_info(parent);
193 if (res)
194 return 0;
195 res = fscrypt_get_encryption_info(child);
196 if (res)
197 return 0;
198 parent_ci = parent->i_crypt_info;
199 child_ci = child->i_crypt_info;
200
201 if (parent_ci && child_ci) {
202 return memcmp(parent_ci->ci_master_key, child_ci->ci_master_key,
203 FS_KEY_DESCRIPTOR_SIZE) == 0 &&
204 (parent_ci->ci_data_mode == child_ci->ci_data_mode) &&
205 (parent_ci->ci_filename_mode ==
206 child_ci->ci_filename_mode) &&
207 (parent_ci->ci_flags == child_ci->ci_flags);
208 }
209
210 res = cops->get_context(parent, &parent_ctx, sizeof(parent_ctx));
211 if (res != sizeof(parent_ctx))
212 return 0;
213
214 res = cops->get_context(child, &child_ctx, sizeof(child_ctx));
215 if (res != sizeof(child_ctx))
216 return 0;
217
218 return memcmp(parent_ctx.master_key_descriptor,
219 child_ctx.master_key_descriptor,
220 FS_KEY_DESCRIPTOR_SIZE) == 0 &&
221 (parent_ctx.contents_encryption_mode ==
222 child_ctx.contents_encryption_mode) &&
223 (parent_ctx.filenames_encryption_mode ==
224 child_ctx.filenames_encryption_mode) &&
225 (parent_ctx.flags == child_ctx.flags);
226}
227EXPORT_SYMBOL(fscrypt_has_permitted_context);
228
229/**
230 * fscrypt_inherit_context() - Sets a child context from its parent
231 * @parent: Parent inode from which the context is inherited.
232 * @child: Child inode that inherits the context from @parent.
233 * @fs_data: private data given by FS.
234 * @preload: preload child i_crypt_info if true
235 *
236 * Return: 0 on success, -errno on failure
237 */
238int fscrypt_inherit_context(struct inode *parent, struct inode *child,
239 void *fs_data, bool preload)
240{
241 struct fscrypt_context ctx;
242 struct fscrypt_info *ci;
243 int res;
244
245 res = fscrypt_get_encryption_info(parent);
246 if (res < 0)
247 return res;
248
249 ci = parent->i_crypt_info;
250 if (ci == NULL)
251 return -ENOKEY;
252
253 ctx.format = FS_ENCRYPTION_CONTEXT_FORMAT_V1;
254 ctx.contents_encryption_mode = ci->ci_data_mode;
255 ctx.filenames_encryption_mode = ci->ci_filename_mode;
256 ctx.flags = ci->ci_flags;
257 memcpy(ctx.master_key_descriptor, ci->ci_master_key,
258 FS_KEY_DESCRIPTOR_SIZE);
259 get_random_bytes(ctx.nonce, FS_KEY_DERIVATION_NONCE_SIZE);
260 BUILD_BUG_ON(sizeof(ctx) != FSCRYPT_SET_CONTEXT_MAX_SIZE);
261 res = parent->i_sb->s_cop->set_context(child, &ctx,
262 sizeof(ctx), fs_data);
263 if (res)
264 return res;
265 return preload ? fscrypt_get_encryption_info(child): 0;
266}
267EXPORT_SYMBOL(fscrypt_inherit_context);
1/*
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>
13#include <linux/fscrypto.h>
14
15static int inode_has_encryption_context(struct inode *inode)
16{
17 if (!inode->i_sb->s_cop->get_context)
18 return 0;
19 return (inode->i_sb->s_cop->get_context(inode, NULL, 0L) > 0);
20}
21
22/*
23 * check whether the policy is consistent with the encryption context
24 * for the inode
25 */
26static int is_encryption_context_consistent_with_policy(struct inode *inode,
27 const struct fscrypt_policy *policy)
28{
29 struct fscrypt_context ctx;
30 int res;
31
32 if (!inode->i_sb->s_cop->get_context)
33 return 0;
34
35 res = inode->i_sb->s_cop->get_context(inode, &ctx, sizeof(ctx));
36 if (res != sizeof(ctx))
37 return 0;
38
39 return (memcmp(ctx.master_key_descriptor, policy->master_key_descriptor,
40 FS_KEY_DESCRIPTOR_SIZE) == 0 &&
41 (ctx.flags == policy->flags) &&
42 (ctx.contents_encryption_mode ==
43 policy->contents_encryption_mode) &&
44 (ctx.filenames_encryption_mode ==
45 policy->filenames_encryption_mode));
46}
47
48static int create_encryption_context_from_policy(struct inode *inode,
49 const struct fscrypt_policy *policy)
50{
51 struct fscrypt_context ctx;
52 int res;
53
54 if (!inode->i_sb->s_cop->set_context)
55 return -EOPNOTSUPP;
56
57 if (inode->i_sb->s_cop->prepare_context) {
58 res = inode->i_sb->s_cop->prepare_context(inode);
59 if (res)
60 return res;
61 }
62
63 ctx.format = FS_ENCRYPTION_CONTEXT_FORMAT_V1;
64 memcpy(ctx.master_key_descriptor, policy->master_key_descriptor,
65 FS_KEY_DESCRIPTOR_SIZE);
66
67 if (!fscrypt_valid_contents_enc_mode(
68 policy->contents_encryption_mode)) {
69 printk(KERN_WARNING
70 "%s: Invalid contents encryption mode %d\n", __func__,
71 policy->contents_encryption_mode);
72 return -EINVAL;
73 }
74
75 if (!fscrypt_valid_filenames_enc_mode(
76 policy->filenames_encryption_mode)) {
77 printk(KERN_WARNING
78 "%s: Invalid filenames encryption mode %d\n", __func__,
79 policy->filenames_encryption_mode);
80 return -EINVAL;
81 }
82
83 if (policy->flags & ~FS_POLICY_FLAGS_VALID)
84 return -EINVAL;
85
86 ctx.contents_encryption_mode = policy->contents_encryption_mode;
87 ctx.filenames_encryption_mode = policy->filenames_encryption_mode;
88 ctx.flags = policy->flags;
89 BUILD_BUG_ON(sizeof(ctx.nonce) != FS_KEY_DERIVATION_NONCE_SIZE);
90 get_random_bytes(ctx.nonce, FS_KEY_DERIVATION_NONCE_SIZE);
91
92 return inode->i_sb->s_cop->set_context(inode, &ctx, sizeof(ctx), NULL);
93}
94
95int fscrypt_process_policy(struct inode *inode,
96 const struct fscrypt_policy *policy)
97{
98 if (policy->version != 0)
99 return -EINVAL;
100
101 if (!inode_has_encryption_context(inode)) {
102 if (!inode->i_sb->s_cop->empty_dir)
103 return -EOPNOTSUPP;
104 if (!inode->i_sb->s_cop->empty_dir(inode))
105 return -ENOTEMPTY;
106 return create_encryption_context_from_policy(inode, policy);
107 }
108
109 if (is_encryption_context_consistent_with_policy(inode, policy))
110 return 0;
111
112 printk(KERN_WARNING "%s: Policy inconsistent with encryption context\n",
113 __func__);
114 return -EINVAL;
115}
116EXPORT_SYMBOL(fscrypt_process_policy);
117
118int fscrypt_get_policy(struct inode *inode, struct fscrypt_policy *policy)
119{
120 struct fscrypt_context ctx;
121 int res;
122
123 if (!inode->i_sb->s_cop->get_context ||
124 !inode->i_sb->s_cop->is_encrypted(inode))
125 return -ENODATA;
126
127 res = inode->i_sb->s_cop->get_context(inode, &ctx, sizeof(ctx));
128 if (res != sizeof(ctx))
129 return -ENODATA;
130 if (ctx.format != FS_ENCRYPTION_CONTEXT_FORMAT_V1)
131 return -EINVAL;
132
133 policy->version = 0;
134 policy->contents_encryption_mode = ctx.contents_encryption_mode;
135 policy->filenames_encryption_mode = ctx.filenames_encryption_mode;
136 policy->flags = ctx.flags;
137 memcpy(&policy->master_key_descriptor, ctx.master_key_descriptor,
138 FS_KEY_DESCRIPTOR_SIZE);
139 return 0;
140}
141EXPORT_SYMBOL(fscrypt_get_policy);
142
143int fscrypt_has_permitted_context(struct inode *parent, struct inode *child)
144{
145 struct fscrypt_info *parent_ci, *child_ci;
146 int res;
147
148 if ((parent == NULL) || (child == NULL)) {
149 printk(KERN_ERR "parent %p child %p\n", parent, child);
150 BUG_ON(1);
151 }
152
153 /* no restrictions if the parent directory is not encrypted */
154 if (!parent->i_sb->s_cop->is_encrypted(parent))
155 return 1;
156 /* if the child directory is not encrypted, this is always a problem */
157 if (!parent->i_sb->s_cop->is_encrypted(child))
158 return 0;
159 res = fscrypt_get_encryption_info(parent);
160 if (res)
161 return 0;
162 res = fscrypt_get_encryption_info(child);
163 if (res)
164 return 0;
165 parent_ci = parent->i_crypt_info;
166 child_ci = child->i_crypt_info;
167 if (!parent_ci && !child_ci)
168 return 1;
169 if (!parent_ci || !child_ci)
170 return 0;
171
172 return (memcmp(parent_ci->ci_master_key,
173 child_ci->ci_master_key,
174 FS_KEY_DESCRIPTOR_SIZE) == 0 &&
175 (parent_ci->ci_data_mode == child_ci->ci_data_mode) &&
176 (parent_ci->ci_filename_mode == child_ci->ci_filename_mode) &&
177 (parent_ci->ci_flags == child_ci->ci_flags));
178}
179EXPORT_SYMBOL(fscrypt_has_permitted_context);
180
181/**
182 * fscrypt_inherit_context() - Sets a child context from its parent
183 * @parent: Parent inode from which the context is inherited.
184 * @child: Child inode that inherits the context from @parent.
185 * @fs_data: private data given by FS.
186 * @preload: preload child i_crypt_info
187 *
188 * Return: Zero on success, non-zero otherwise
189 */
190int fscrypt_inherit_context(struct inode *parent, struct inode *child,
191 void *fs_data, bool preload)
192{
193 struct fscrypt_context ctx;
194 struct fscrypt_info *ci;
195 int res;
196
197 if (!parent->i_sb->s_cop->set_context)
198 return -EOPNOTSUPP;
199
200 res = fscrypt_get_encryption_info(parent);
201 if (res < 0)
202 return res;
203
204 ci = parent->i_crypt_info;
205 if (ci == NULL)
206 return -ENOKEY;
207
208 ctx.format = FS_ENCRYPTION_CONTEXT_FORMAT_V1;
209 if (fscrypt_dummy_context_enabled(parent)) {
210 ctx.contents_encryption_mode = FS_ENCRYPTION_MODE_AES_256_XTS;
211 ctx.filenames_encryption_mode = FS_ENCRYPTION_MODE_AES_256_CTS;
212 ctx.flags = 0;
213 memset(ctx.master_key_descriptor, 0x42, FS_KEY_DESCRIPTOR_SIZE);
214 res = 0;
215 } else {
216 ctx.contents_encryption_mode = ci->ci_data_mode;
217 ctx.filenames_encryption_mode = ci->ci_filename_mode;
218 ctx.flags = ci->ci_flags;
219 memcpy(ctx.master_key_descriptor, ci->ci_master_key,
220 FS_KEY_DESCRIPTOR_SIZE);
221 }
222 get_random_bytes(ctx.nonce, FS_KEY_DERIVATION_NONCE_SIZE);
223 res = parent->i_sb->s_cop->set_context(child, &ctx,
224 sizeof(ctx), fs_data);
225 if (res)
226 return res;
227 return preload ? fscrypt_get_encryption_info(child): 0;
228}
229EXPORT_SYMBOL(fscrypt_inherit_context);