xref: /openbmc/linux/fs/crypto/policy.c (revision 4f205687)
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 
15 static 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  */
26 static 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 
48 static 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 
95 int 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 }
116 EXPORT_SYMBOL(fscrypt_process_policy);
117 
118 int 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 }
141 EXPORT_SYMBOL(fscrypt_get_policy);
142 
143 int 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 }
179 EXPORT_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  */
190 int 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 }
229 EXPORT_SYMBOL(fscrypt_inherit_context);
230