summaryrefslogtreecommitdiff
path: root/fs/crypto/policy.c
blob: 4941fe8471ceff03cea2032890b0e16318eff8fb (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
// SPDX-License-Identifier: GPL-2.0
/*
 * Encryption policy functions for per-file encryption support.
 *
 * Copyright (C) 2015, Google, Inc.
 * Copyright (C) 2015, Motorola Mobility.
 *
 * Written by Michael Halcrow, 2015.
 * Modified by Jaegeuk Kim, 2015.
 */

#include <linux/random.h>
#include <linux/string.h>
#include <linux/mount.h>
#include "fscrypt_private.h"

/*
 * check whether an encryption policy is consistent with an encryption context
 */
static bool is_encryption_context_consistent_with_policy(
				const struct fscrypt_context *ctx,
				const struct fscrypt_policy *policy)
{
	return memcmp(ctx->master_key_descriptor, policy->master_key_descriptor,
		      FS_KEY_DESCRIPTOR_SIZE) == 0 &&
		(ctx->flags == policy->flags) &&
		(ctx->contents_encryption_mode ==
		 policy->contents_encryption_mode) &&
		(ctx->filenames_encryption_mode ==
		 policy->filenames_encryption_mode);
}

static int create_encryption_context_from_policy(struct inode *inode,
				const struct fscrypt_policy *policy)
{
	struct fscrypt_context ctx;

	ctx.format = FS_ENCRYPTION_CONTEXT_FORMAT_V1;
	memcpy(ctx.master_key_descriptor, policy->master_key_descriptor,
					FS_KEY_DESCRIPTOR_SIZE);

	if (!fscrypt_valid_enc_modes(policy->contents_encryption_mode,
				     policy->filenames_encryption_mode))
		return -EINVAL;

	if (policy->flags & ~FS_POLICY_FLAGS_VALID)
		return -EINVAL;

	ctx.contents_encryption_mode = policy->contents_encryption_mode;
	ctx.filenames_encryption_mode = policy->filenames_encryption_mode;
	ctx.flags = policy->flags;
	BUILD_BUG_ON(sizeof(ctx.nonce) != FS_KEY_DERIVATION_NONCE_SIZE);
	get_random_bytes(ctx.nonce, FS_KEY_DERIVATION_NONCE_SIZE);

	return inode->i_sb->s_cop->set_context(inode, &ctx, sizeof(ctx), NULL);
}

int fscrypt_ioctl_set_policy(struct file *filp, const void __user *arg)
{
	struct fscrypt_policy policy;
	struct inode *inode = file_inode(filp);
	int ret;
	struct fscrypt_context ctx;

	if (copy_from_user(&policy, arg, sizeof(policy)))
		return -EFAULT;

	if (!inode_owner_or_capable(inode))
		return -EACCES;

	if (policy.version != 0)
		return -EINVAL;

	ret = mnt_want_write_file(filp);
	if (ret)
		return ret;

	inode_lock(inode);

	ret = inode->i_sb->s_cop->get_context(inode, &ctx, sizeof(ctx));
	if (ret == -ENODATA) {
		if (!S_ISDIR(inode->i_mode))
			ret = -ENOTDIR;
		else if (IS_DEADDIR(inode))
			ret = -ENOENT;
		else if (!inode->i_sb->s_cop->empty_dir(inode))
			ret = -ENOTEMPTY;
		else
			ret = create_encryption_context_from_policy(inode,
								    &policy);
	} else if (ret == sizeof(ctx) &&
		   is_encryption_context_consistent_with_policy(&ctx,
								&policy)) {
		/* The file already uses the same encryption policy. */
		ret = 0;
	} else if (ret >= 0 || ret == -ERANGE) {
		/* The file already uses a different encryption policy. */
		ret = -EEXIST;
	}

	inode_unlock(inode);

	mnt_drop_write_file(filp);
	return ret;
}
EXPORT_SYMBOL(fscrypt_ioctl_set_policy);

int fscrypt_ioctl_get_policy(struct file *filp, void __user *arg)
{
	struct inode *inode = file_inode(filp);
	struct fscrypt_context ctx;
	struct fscrypt_policy policy;
	int res;

	if (!IS_ENCRYPTED(inode))
		return -ENODATA;

	res = inode->i_sb->s_cop->get_context(inode, &ctx, sizeof(ctx));
	if (res < 0 && res != -ERANGE)
		return res;
	if (res != sizeof(ctx))
		return -EINVAL;
	if (ctx.format != FS_ENCRYPTION_CONTEXT_FORMAT_V1)
		return -EINVAL;

	policy.version = 0;
	policy.contents_encryption_mode = ctx.contents_encryption_mode;
	policy.filenames_encryption_mode = ctx.filenames_encryption_mode;
	policy.flags = ctx.flags;
	memcpy(policy.master_key_descriptor, ctx.master_key_descriptor,
				FS_KEY_DESCRIPTOR_SIZE);

	if (copy_to_user(arg, &policy, sizeof(policy)))
		return -EFAULT;
	return 0;
}
EXPORT_SYMBOL(fscrypt_ioctl_get_policy);

/**
 * fscrypt_has_permitted_context() - is a file's encryption policy permitted
 *				     within its directory?
 *
 * @parent: inode for parent directory
 * @child: inode for file being looked up, opened, or linked into @parent
 *
 * Filesystems must call this before permitting access to an inode in a
 * situation where the parent directory is encrypted (either before allowing
 * ->lookup() to succeed, or for a regular file before allowing it to be opened)
 * and before any operation that involves linking an inode into an encrypted
 * directory, including link, rename, and cross rename.  It enforces the
 * constraint that within a given encrypted directory tree, all files use the
 * same encryption policy.  The pre-access check is needed to detect potentially
 * malicious offline violations of this constraint, while the link and rename
 * checks are needed to prevent online violations of this constraint.
 *
 * Return: 1 if permitted, 0 if forbidden.
 */
int fscrypt_has_permitted_context(struct inode *parent, struct inode *child)
{
	const struct fscrypt_operations *cops = parent->i_sb->s_cop;
	const struct fscrypt_info *parent_ci, *child_ci;
	struct fscrypt_context parent_ctx, child_ctx;
	int res;

	/* No restrictions on file types which are never encrypted */
	if (!S_ISREG(child->i_mode) && !S_ISDIR(child->i_mode) &&
	    !S_ISLNK(child->i_mode))
		return 1;

	/* No restrictions if the parent directory is unencrypted */
	if (!IS_ENCRYPTED(parent))
		return 1;

	/* Encrypted directories must not contain unencrypted files */
	if (!IS_ENCRYPTED(child))
		return 0;

	/*
	 * Both parent and child are encrypted, so verify they use the same
	 * encryption policy.  Compare the fscrypt_info structs if the keys are
	 * available, otherwise retrieve and compare the fscrypt_contexts.
	 *
	 * Note that the fscrypt_context retrieval will be required frequently
	 * when accessing an encrypted directory tree without the key.
	 * Performance-wise this is not a big deal because we already don't
	 * really optimize for file access without the key (to the extent that
	 * such access is even possible), given that any attempted access
	 * already causes a fscrypt_context retrieval and keyring search.
	 *
	 * In any case, if an unexpected error occurs, fall back to "forbidden".
	 */

	res = fscrypt_get_encryption_info(parent);
	if (res)
		return 0;
	res = fscrypt_get_encryption_info(child);
	if (res)
		return 0;
	parent_ci = READ_ONCE(parent->i_crypt_info);
	child_ci = READ_ONCE(child->i_crypt_info);

	if (parent_ci && child_ci) {
		return memcmp(parent_ci->ci_master_key_descriptor,
			      child_ci->ci_master_key_descriptor,
			      FS_KEY_DESCRIPTOR_SIZE) == 0 &&
			(parent_ci->ci_data_mode == child_ci->ci_data_mode) &&
			(parent_ci->ci_filename_mode ==
			 child_ci->ci_filename_mode) &&
			(parent_ci->ci_flags == child_ci->ci_flags);
	}

	res = cops->get_context(parent, &parent_ctx, sizeof(parent_ctx));
	if (res != sizeof(parent_ctx))
		return 0;

	res = cops->get_context(child, &child_ctx, sizeof(child_ctx));
	if (res != sizeof(child_ctx))
		return 0;

	return memcmp(parent_ctx.master_key_descriptor,
		      child_ctx.master_key_descriptor,
		      FS_KEY_DESCRIPTOR_SIZE) == 0 &&
		(parent_ctx.contents_encryption_mode ==
		 child_ctx.contents_encryption_mode) &&
		(parent_ctx.filenames_encryption_mode ==
		 child_ctx.filenames_encryption_mode) &&
		(parent_ctx.flags == child_ctx.flags);
}
EXPORT_SYMBOL(fscrypt_has_permitted_context);

/**
 * fscrypt_inherit_context() - Sets a child context from its parent
 * @parent: Parent inode from which the context is inherited.
 * @child:  Child inode that inherits the context from @parent.
 * @fs_data:  private data given by FS.
 * @preload:  preload child i_crypt_info if true
 *
 * Return: 0 on success, -errno on failure
 */
int fscrypt_inherit_context(struct inode *parent, struct inode *child,
						void *fs_data, bool preload)
{
	struct fscrypt_context ctx;
	struct fscrypt_info *ci;
	int res;

	res = fscrypt_get_encryption_info(parent);
	if (res < 0)
		return res;

	ci = READ_ONCE(parent->i_crypt_info);
	if (ci == NULL)
		return -ENOKEY;

	ctx.format = FS_ENCRYPTION_CONTEXT_FORMAT_V1;
	ctx.contents_encryption_mode = ci->ci_data_mode;
	ctx.filenames_encryption_mode = ci->ci_filename_mode;
	ctx.flags = ci->ci_flags;
	memcpy(ctx.master_key_descriptor, ci->ci_master_key_descriptor,
	       FS_KEY_DESCRIPTOR_SIZE);
	get_random_bytes(ctx.nonce, FS_KEY_DERIVATION_NONCE_SIZE);
	BUILD_BUG_ON(sizeof(ctx) != FSCRYPT_SET_CONTEXT_MAX_SIZE);
	res = parent->i_sb->s_cop->set_context(child, &ctx,
						sizeof(ctx), fs_data);
	if (res)
		return res;
	return preload ? fscrypt_get_encryption_info(child): 0;
}
EXPORT_SYMBOL(fscrypt_inherit_context);