1 /* Module signature checker
2 *
3 * Copyright (C) 2012 Red Hat, Inc. All Rights Reserved.
4 * Written by David Howells (dhowells@redhat.com)
5 *
6 * This program is free software; you can redistribute it and/or
7 * modify it under the terms of the GNU General Public Licence
8 * as published by the Free Software Foundation; either version
9 * 2 of the Licence, or (at your option) any later version.
10 */
11
12 #include <linux/kernel.h>
13 #include <linux/err.h>
14 #include <crypto/public_key.h>
15 #include <crypto/hash.h>
16 #include <keys/asymmetric-type.h>
17 #include <keys/system_keyring.h>
18 #include "module-internal.h"
19
20 /*
21 * Module signature information block.
22 *
23 * The constituents of the signature section are, in order:
24 *
25 * - Signer's name
26 * - Key identifier
27 * - Signature data
28 * - Information block
29 */
30 struct module_signature {
31 u8 algo; /* Public-key crypto algorithm [enum pkey_algo] */
32 u8 hash; /* Digest algorithm [enum pkey_hash_algo] */
33 u8 id_type; /* Key identifier type [enum pkey_id_type] */
34 u8 signer_len; /* Length of signer's name */
35 u8 key_id_len; /* Length of key identifier */
36 u8 __pad[3];
37 __be32 sig_len; /* Length of signature data */
38 };
39
40 /*
41 * Digest the module contents.
42 */
mod_make_digest(enum pkey_hash_algo hash,const void * mod,unsigned long modlen)43 static struct public_key_signature *mod_make_digest(enum pkey_hash_algo hash,
44 const void *mod,
45 unsigned long modlen)
46 {
47 struct public_key_signature *pks;
48 struct crypto_shash *tfm;
49 struct shash_desc *desc;
50 size_t digest_size, desc_size;
51 int ret;
52
53 pr_devel("==>%s()\n", __func__);
54
55 /* Allocate the hashing algorithm we're going to need and find out how
56 * big the hash operational data will be.
57 */
58 tfm = crypto_alloc_shash(pkey_hash_algo[hash], 0, 0);
59 if (IS_ERR(tfm))
60 return (PTR_ERR(tfm) == -ENOENT) ? ERR_PTR(-ENOPKG) : ERR_CAST(tfm);
61
62 desc_size = crypto_shash_descsize(tfm) + sizeof(*desc);
63 digest_size = crypto_shash_digestsize(tfm);
64
65 /* We allocate the hash operational data storage on the end of our
66 * context data and the digest output buffer on the end of that.
67 */
68 ret = -ENOMEM;
69 pks = kzalloc(digest_size + sizeof(*pks) + desc_size, GFP_KERNEL);
70 if (!pks)
71 goto error_no_pks;
72
73 pks->pkey_hash_algo = hash;
74 pks->digest = (u8 *)pks + sizeof(*pks) + desc_size;
75 pks->digest_size = digest_size;
76
77 desc = (void *)pks + sizeof(*pks);
78 desc->tfm = tfm;
79 desc->flags = CRYPTO_TFM_REQ_MAY_SLEEP;
80
81 ret = crypto_shash_init(desc);
82 if (ret < 0)
83 goto error;
84
85 ret = crypto_shash_finup(desc, mod, modlen, pks->digest);
86 if (ret < 0)
87 goto error;
88
89 crypto_free_shash(tfm);
90 pr_devel("<==%s() = ok\n", __func__);
91 return pks;
92
93 error:
94 kfree(pks);
95 error_no_pks:
96 crypto_free_shash(tfm);
97 pr_devel("<==%s() = %d\n", __func__, ret);
98 return ERR_PTR(ret);
99 }
100
101 /*
102 * Extract an MPI array from the signature data. This represents the actual
103 * signature. Each raw MPI is prefaced by a BE 2-byte value indicating the
104 * size of the MPI in bytes.
105 *
106 * RSA signatures only have one MPI, so currently we only read one.
107 */
mod_extract_mpi_array(struct public_key_signature * pks,const void * data,size_t len)108 static int mod_extract_mpi_array(struct public_key_signature *pks,
109 const void *data, size_t len)
110 {
111 size_t nbytes;
112 MPI mpi;
113
114 if (len < 3)
115 return -EBADMSG;
116 nbytes = ((const u8 *)data)[0] << 8 | ((const u8 *)data)[1];
117 data += 2;
118 len -= 2;
119 if (len != nbytes)
120 return -EBADMSG;
121
122 mpi = mpi_read_raw_data(data, nbytes);
123 if (!mpi)
124 return -ENOMEM;
125 pks->mpi[0] = mpi;
126 pks->nr_mpi = 1;
127 return 0;
128 }
129
130 /*
131 * Request an asymmetric key.
132 */
request_asymmetric_key(const char * signer,size_t signer_len,const u8 * key_id,size_t key_id_len)133 static struct key *request_asymmetric_key(const char *signer, size_t signer_len,
134 const u8 *key_id, size_t key_id_len)
135 {
136 key_ref_t key;
137 size_t i;
138 char *id, *q;
139
140 pr_devel("==>%s(,%zu,,%zu)\n", __func__, signer_len, key_id_len);
141
142 /* Construct an identifier. */
143 id = kmalloc(signer_len + 2 + key_id_len * 2 + 1, GFP_KERNEL);
144 if (!id)
145 return ERR_PTR(-ENOKEY);
146
147 memcpy(id, signer, signer_len);
148
149 q = id + signer_len;
150 *q++ = ':';
151 *q++ = ' ';
152 for (i = 0; i < key_id_len; i++) {
153 *q++ = hex_asc[*key_id >> 4];
154 *q++ = hex_asc[*key_id++ & 0x0f];
155 }
156
157 *q = 0;
158
159 pr_debug("Look up: \"%s\"\n", id);
160
161 key = keyring_search(make_key_ref(system_trusted_keyring, 1),
162 &key_type_asymmetric, id);
163 if (IS_ERR(key))
164 pr_warn("Request for unknown module key '%s' err %ld\n",
165 id, PTR_ERR(key));
166 kfree(id);
167
168 if (IS_ERR(key)) {
169 switch (PTR_ERR(key)) {
170 /* Hide some search errors */
171 case -EACCES:
172 case -ENOTDIR:
173 case -EAGAIN:
174 return ERR_PTR(-ENOKEY);
175 default:
176 return ERR_CAST(key);
177 }
178 }
179
180 pr_devel("<==%s() = 0 [%x]\n", __func__, key_serial(key_ref_to_ptr(key)));
181 return key_ref_to_ptr(key);
182 }
183
184 /*
185 * Verify the signature on a module.
186 */
mod_verify_sig(const void * mod,unsigned long * _modlen)187 int mod_verify_sig(const void *mod, unsigned long *_modlen)
188 {
189 struct public_key_signature *pks;
190 struct module_signature ms;
191 struct key *key;
192 const void *sig;
193 size_t modlen = *_modlen, sig_len;
194 int ret;
195
196 pr_devel("==>%s(,%zu)\n", __func__, modlen);
197
198 if (modlen <= sizeof(ms))
199 return -EBADMSG;
200
201 memcpy(&ms, mod + (modlen - sizeof(ms)), sizeof(ms));
202 modlen -= sizeof(ms);
203
204 sig_len = be32_to_cpu(ms.sig_len);
205 if (sig_len >= modlen)
206 return -EBADMSG;
207 modlen -= sig_len;
208 if ((size_t)ms.signer_len + ms.key_id_len >= modlen)
209 return -EBADMSG;
210 modlen -= (size_t)ms.signer_len + ms.key_id_len;
211
212 *_modlen = modlen;
213 sig = mod + modlen;
214
215 /* For the moment, only support RSA and X.509 identifiers */
216 if (ms.algo != PKEY_ALGO_RSA ||
217 ms.id_type != PKEY_ID_X509)
218 return -ENOPKG;
219
220 if (ms.hash >= PKEY_HASH__LAST ||
221 !pkey_hash_algo[ms.hash])
222 return -ENOPKG;
223
224 key = request_asymmetric_key(sig, ms.signer_len,
225 sig + ms.signer_len, ms.key_id_len);
226 if (IS_ERR(key))
227 return PTR_ERR(key);
228
229 pks = mod_make_digest(ms.hash, mod, modlen);
230 if (IS_ERR(pks)) {
231 ret = PTR_ERR(pks);
232 goto error_put_key;
233 }
234
235 ret = mod_extract_mpi_array(pks, sig + ms.signer_len + ms.key_id_len,
236 sig_len);
237 if (ret < 0)
238 goto error_free_pks;
239
240 ret = verify_signature(key, pks);
241 pr_devel("verify_signature() = %d\n", ret);
242
243 error_free_pks:
244 mpi_free(pks->rsa.s);
245 kfree(pks);
246 error_put_key:
247 key_put(key);
248 pr_devel("<==%s() = %d\n", __func__, ret);
249 return ret;
250 }
251