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.h"
16#include "xattr.h"
17
18static int ext4_inode_has_encryption_context(struct inode *inode)
19{
20	int res = ext4_xattr_get(inode, EXT4_XATTR_INDEX_ENCRYPTION,
21				 EXT4_XATTR_NAME_ENCRYPTION_CONTEXT, NULL, 0);
22	return (res > 0);
23}
24
25/*
26 * check whether the policy is consistent with the encryption context
27 * for the inode
28 */
29static int ext4_is_encryption_context_consistent_with_policy(
30	struct inode *inode, const struct ext4_encryption_policy *policy)
31{
32	struct ext4_encryption_context ctx;
33	int res = ext4_xattr_get(inode, EXT4_XATTR_INDEX_ENCRYPTION,
34				 EXT4_XATTR_NAME_ENCRYPTION_CONTEXT, &ctx,
35				 sizeof(ctx));
36	if (res != sizeof(ctx))
37		return 0;
38	return (memcmp(ctx.master_key_descriptor, policy->master_key_descriptor,
39			EXT4_KEY_DESCRIPTOR_SIZE) == 0 &&
40		(ctx.flags ==
41		 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 ext4_create_encryption_context_from_policy(
49	struct inode *inode, const struct ext4_encryption_policy *policy)
50{
51	struct ext4_encryption_context ctx;
52	int res = 0;
53
54	ctx.format = EXT4_ENCRYPTION_CONTEXT_FORMAT_V1;
55	memcpy(ctx.master_key_descriptor, policy->master_key_descriptor,
56	       EXT4_KEY_DESCRIPTOR_SIZE);
57	if (!ext4_valid_contents_enc_mode(policy->contents_encryption_mode)) {
58		printk(KERN_WARNING
59		       "%s: Invalid contents encryption mode %d\n", __func__,
60			policy->contents_encryption_mode);
61		return -EINVAL;
62	}
63	if (!ext4_valid_filenames_enc_mode(policy->filenames_encryption_mode)) {
64		printk(KERN_WARNING
65		       "%s: Invalid filenames encryption mode %d\n", __func__,
66			policy->filenames_encryption_mode);
67		return -EINVAL;
68	}
69	if (policy->flags & ~EXT4_POLICY_FLAGS_VALID)
70		return -EINVAL;
71	ctx.contents_encryption_mode = policy->contents_encryption_mode;
72	ctx.filenames_encryption_mode = policy->filenames_encryption_mode;
73	ctx.flags = policy->flags;
74	BUILD_BUG_ON(sizeof(ctx.nonce) != EXT4_KEY_DERIVATION_NONCE_SIZE);
75	get_random_bytes(ctx.nonce, EXT4_KEY_DERIVATION_NONCE_SIZE);
76
77	res = ext4_xattr_set(inode, EXT4_XATTR_INDEX_ENCRYPTION,
78			     EXT4_XATTR_NAME_ENCRYPTION_CONTEXT, &ctx,
79			     sizeof(ctx), 0);
80	if (!res)
81		ext4_set_inode_flag(inode, EXT4_INODE_ENCRYPT);
82	return res;
83}
84
85int ext4_process_policy(const struct ext4_encryption_policy *policy,
86			struct inode *inode)
87{
88	if (policy->version != 0)
89		return -EINVAL;
90
91	if (!ext4_inode_has_encryption_context(inode)) {
92		if (!ext4_empty_dir(inode))
93			return -ENOTEMPTY;
94		return ext4_create_encryption_context_from_policy(inode,
95								  policy);
96	}
97
98	if (ext4_is_encryption_context_consistent_with_policy(inode, policy))
99		return 0;
100
101	printk(KERN_WARNING "%s: Policy inconsistent with encryption context\n",
102	       __func__);
103	return -EINVAL;
104}
105
106int ext4_get_policy(struct inode *inode, struct ext4_encryption_policy *policy)
107{
108	struct ext4_encryption_context ctx;
109
110	int res = ext4_xattr_get(inode, EXT4_XATTR_INDEX_ENCRYPTION,
111				 EXT4_XATTR_NAME_ENCRYPTION_CONTEXT,
112				 &ctx, sizeof(ctx));
113	if (res != sizeof(ctx))
114		return -ENOENT;
115	if (ctx.format != EXT4_ENCRYPTION_CONTEXT_FORMAT_V1)
116		return -EINVAL;
117	policy->version = 0;
118	policy->contents_encryption_mode = ctx.contents_encryption_mode;
119	policy->filenames_encryption_mode = ctx.filenames_encryption_mode;
120	policy->flags = ctx.flags;
121	memcpy(&policy->master_key_descriptor, ctx.master_key_descriptor,
122	       EXT4_KEY_DESCRIPTOR_SIZE);
123	return 0;
124}
125
126int ext4_is_child_context_consistent_with_parent(struct inode *parent,
127						 struct inode *child)
128{
129	struct ext4_encryption_context parent_ctx, child_ctx;
130	int res;
131
132	if ((parent == NULL) || (child == NULL)) {
133		pr_err("parent %p child %p\n", parent, child);
134		BUG_ON(1);
135	}
136	/* no restrictions if the parent directory is not encrypted */
137	if (!ext4_encrypted_inode(parent))
138		return 1;
139	res = ext4_xattr_get(parent, EXT4_XATTR_INDEX_ENCRYPTION,
140			     EXT4_XATTR_NAME_ENCRYPTION_CONTEXT,
141			     &parent_ctx, sizeof(parent_ctx));
142	if (res != sizeof(parent_ctx))
143		return 0;
144	/* if the child directory is not encrypted, this is always a problem */
145	if (!ext4_encrypted_inode(child))
146		return 0;
147	res = ext4_xattr_get(child, EXT4_XATTR_INDEX_ENCRYPTION,
148			     EXT4_XATTR_NAME_ENCRYPTION_CONTEXT,
149			     &child_ctx, sizeof(child_ctx));
150	if (res != sizeof(child_ctx))
151		return 0;
152	return (memcmp(parent_ctx.master_key_descriptor,
153		       child_ctx.master_key_descriptor,
154		       EXT4_KEY_DESCRIPTOR_SIZE) == 0 &&
155		(parent_ctx.contents_encryption_mode ==
156		 child_ctx.contents_encryption_mode) &&
157		(parent_ctx.filenames_encryption_mode ==
158		 child_ctx.filenames_encryption_mode));
159}
160
161/**
162 * ext4_inherit_context() - Sets a child context from its parent
163 * @parent: Parent inode from which the context is inherited.
164 * @child:  Child inode that inherits the context from @parent.
165 *
166 * Return: Zero on success, non-zero otherwise
167 */
168int ext4_inherit_context(struct inode *parent, struct inode *child)
169{
170	struct ext4_encryption_context ctx;
171	int res = ext4_xattr_get(parent, EXT4_XATTR_INDEX_ENCRYPTION,
172				 EXT4_XATTR_NAME_ENCRYPTION_CONTEXT,
173				 &ctx, sizeof(ctx));
174
175	if (res != sizeof(ctx)) {
176		if (DUMMY_ENCRYPTION_ENABLED(EXT4_SB(parent->i_sb))) {
177			ctx.format = EXT4_ENCRYPTION_CONTEXT_FORMAT_V1;
178			ctx.contents_encryption_mode =
179				EXT4_ENCRYPTION_MODE_AES_256_XTS;
180			ctx.filenames_encryption_mode =
181				EXT4_ENCRYPTION_MODE_AES_256_CTS;
182			ctx.flags = 0;
183			memset(ctx.master_key_descriptor, 0x42,
184			       EXT4_KEY_DESCRIPTOR_SIZE);
185			res = 0;
186		} else {
187			goto out;
188		}
189	}
190	get_random_bytes(ctx.nonce, EXT4_KEY_DERIVATION_NONCE_SIZE);
191	res = ext4_xattr_set(child, EXT4_XATTR_INDEX_ENCRYPTION,
192			     EXT4_XATTR_NAME_ENCRYPTION_CONTEXT, &ctx,
193			     sizeof(ctx), 0);
194out:
195	if (!res)
196		ext4_set_inode_flag(child, EXT4_INODE_ENCRYPT);
197	return res;
198}
199