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9f0d3314 DH |
1 | /* Verify the signature on a PKCS#7 message. |
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 | #define pr_fmt(fmt) "PKCS7: "fmt | |
13 | #include <linux/kernel.h> | |
14 | #include <linux/export.h> | |
15 | #include <linux/slab.h> | |
16 | #include <linux/err.h> | |
17 | #include <linux/asn1.h> | |
18 | #include <crypto/hash.h> | |
19 | #include "public_key.h" | |
20 | #include "pkcs7_parser.h" | |
21 | ||
22 | /* | |
23 | * Digest the relevant parts of the PKCS#7 data | |
24 | */ | |
25 | static int pkcs7_digest(struct pkcs7_message *pkcs7, | |
26 | struct pkcs7_signed_info *sinfo) | |
27 | { | |
28 | struct crypto_shash *tfm; | |
29 | struct shash_desc *desc; | |
30 | size_t digest_size, desc_size; | |
31 | void *digest; | |
32 | int ret; | |
33 | ||
34 | kenter(",%u,%u", sinfo->index, sinfo->sig.pkey_hash_algo); | |
35 | ||
36 | if (sinfo->sig.pkey_hash_algo >= PKEY_HASH__LAST || | |
37 | !hash_algo_name[sinfo->sig.pkey_hash_algo]) | |
38 | return -ENOPKG; | |
39 | ||
40 | /* Allocate the hashing algorithm we're going to need and find out how | |
41 | * big the hash operational data will be. | |
42 | */ | |
43 | tfm = crypto_alloc_shash(hash_algo_name[sinfo->sig.pkey_hash_algo], | |
44 | 0, 0); | |
45 | if (IS_ERR(tfm)) | |
46 | return (PTR_ERR(tfm) == -ENOENT) ? -ENOPKG : PTR_ERR(tfm); | |
47 | ||
48 | desc_size = crypto_shash_descsize(tfm) + sizeof(*desc); | |
49 | sinfo->sig.digest_size = digest_size = crypto_shash_digestsize(tfm); | |
50 | ||
51 | ret = -ENOMEM; | |
52 | digest = kzalloc(digest_size + desc_size, GFP_KERNEL); | |
53 | if (!digest) | |
54 | goto error_no_desc; | |
55 | ||
56 | desc = digest + digest_size; | |
57 | desc->tfm = tfm; | |
58 | desc->flags = CRYPTO_TFM_REQ_MAY_SLEEP; | |
59 | ||
60 | /* Digest the message [RFC2315 9.3] */ | |
61 | ret = crypto_shash_init(desc); | |
62 | if (ret < 0) | |
63 | goto error; | |
64 | ret = crypto_shash_finup(desc, pkcs7->data, pkcs7->data_len, digest); | |
65 | if (ret < 0) | |
66 | goto error; | |
67 | pr_devel("MsgDigest = [%*ph]\n", 8, digest); | |
68 | ||
69 | /* However, if there are authenticated attributes, there must be a | |
70 | * message digest attribute amongst them which corresponds to the | |
71 | * digest we just calculated. | |
72 | */ | |
73 | if (sinfo->msgdigest) { | |
74 | u8 tag; | |
75 | ||
76 | if (sinfo->msgdigest_len != sinfo->sig.digest_size) { | |
77 | pr_debug("Sig %u: Invalid digest size (%u)\n", | |
78 | sinfo->index, sinfo->msgdigest_len); | |
79 | ret = -EBADMSG; | |
80 | goto error; | |
81 | } | |
82 | ||
83 | if (memcmp(digest, sinfo->msgdigest, sinfo->msgdigest_len) != 0) { | |
84 | pr_debug("Sig %u: Message digest doesn't match\n", | |
85 | sinfo->index); | |
86 | ret = -EKEYREJECTED; | |
87 | goto error; | |
88 | } | |
89 | ||
90 | /* We then calculate anew, using the authenticated attributes | |
91 | * as the contents of the digest instead. Note that we need to | |
92 | * convert the attributes from a CONT.0 into a SET before we | |
93 | * hash it. | |
94 | */ | |
95 | memset(digest, 0, sinfo->sig.digest_size); | |
96 | ||
97 | ret = crypto_shash_init(desc); | |
98 | if (ret < 0) | |
99 | goto error; | |
100 | tag = ASN1_CONS_BIT | ASN1_SET; | |
101 | ret = crypto_shash_update(desc, &tag, 1); | |
102 | if (ret < 0) | |
103 | goto error; | |
104 | ret = crypto_shash_finup(desc, sinfo->authattrs, | |
105 | sinfo->authattrs_len, digest); | |
106 | if (ret < 0) | |
107 | goto error; | |
108 | pr_devel("AADigest = [%*ph]\n", 8, digest); | |
109 | } | |
110 | ||
111 | sinfo->sig.digest = digest; | |
112 | digest = NULL; | |
113 | ||
114 | error: | |
115 | kfree(digest); | |
116 | error_no_desc: | |
117 | crypto_free_shash(tfm); | |
118 | kleave(" = %d", ret); | |
119 | return ret; | |
120 | } | |
121 | ||
122 | /* | |
a4730357 DH |
123 | * Find the key (X.509 certificate) to use to verify a PKCS#7 message. PKCS#7 |
124 | * uses the issuer's name and the issuing certificate serial number for | |
125 | * matching purposes. These must match the certificate issuer's name (not | |
126 | * subject's name) and the certificate serial number [RFC 2315 6.7]. | |
127 | */ | |
128 | static int pkcs7_find_key(struct pkcs7_message *pkcs7, | |
129 | struct pkcs7_signed_info *sinfo) | |
130 | { | |
131 | struct x509_certificate *x509; | |
132 | unsigned certix = 1; | |
133 | ||
46963b77 | 134 | kenter("%u", sinfo->index); |
a4730357 DH |
135 | |
136 | for (x509 = pkcs7->certs; x509; x509 = x509->next, certix++) { | |
137 | /* I'm _assuming_ that the generator of the PKCS#7 message will | |
138 | * encode the fields from the X.509 cert in the same way in the | |
139 | * PKCS#7 message - but I can't be 100% sure of that. It's | |
140 | * possible this will need element-by-element comparison. | |
141 | */ | |
46963b77 | 142 | if (!asymmetric_key_id_same(x509->id, sinfo->signing_cert_id)) |
a4730357 DH |
143 | continue; |
144 | pr_devel("Sig %u: Found cert serial match X.509[%u]\n", | |
145 | sinfo->index, certix); | |
146 | ||
a4730357 DH |
147 | if (x509->pub->pkey_algo != sinfo->sig.pkey_algo) { |
148 | pr_warn("Sig %u: X.509 algo and PKCS#7 sig algo don't match\n", | |
149 | sinfo->index); | |
150 | continue; | |
151 | } | |
152 | ||
153 | sinfo->signer = x509; | |
154 | return 0; | |
155 | } | |
46963b77 | 156 | |
757932e6 DH |
157 | /* The relevant X.509 cert isn't found here, but it might be found in |
158 | * the trust keyring. | |
159 | */ | |
160 | pr_debug("Sig %u: Issuing X.509 cert not found (#%*phN)\n", | |
161 | sinfo->index, | |
162 | sinfo->signing_cert_id->len, sinfo->signing_cert_id->data); | |
163 | return 0; | |
a4730357 DH |
164 | } |
165 | ||
8c76d793 DH |
166 | /* |
167 | * Verify the internal certificate chain as best we can. | |
168 | */ | |
169 | static int pkcs7_verify_sig_chain(struct pkcs7_message *pkcs7, | |
170 | struct pkcs7_signed_info *sinfo) | |
171 | { | |
172 | struct x509_certificate *x509 = sinfo->signer, *p; | |
173 | int ret; | |
174 | ||
175 | kenter(""); | |
176 | ||
177 | for (p = pkcs7->certs; p; p = p->next) | |
178 | p->seen = false; | |
179 | ||
180 | for (;;) { | |
46963b77 DH |
181 | pr_debug("verify %s: %*phN\n", |
182 | x509->subject, | |
183 | x509->raw_serial_size, x509->raw_serial); | |
8c76d793 DH |
184 | x509->seen = true; |
185 | ret = x509_get_sig_params(x509); | |
186 | if (ret < 0) | |
41559420 | 187 | goto maybe_missing_crypto_in_x509; |
8c76d793 | 188 | |
412eccba | 189 | pr_debug("- issuer %s\n", x509->issuer); |
8c76d793 | 190 | if (x509->authority) |
46963b77 DH |
191 | pr_debug("- authkeyid %*phN\n", |
192 | x509->authority->len, x509->authority->data); | |
8c76d793 DH |
193 | |
194 | if (!x509->authority || | |
412eccba | 195 | strcmp(x509->subject, x509->issuer) == 0) { |
8c76d793 DH |
196 | /* If there's no authority certificate specified, then |
197 | * the certificate must be self-signed and is the root | |
198 | * of the chain. Likewise if the cert is its own | |
199 | * authority. | |
200 | */ | |
201 | pr_debug("- no auth?\n"); | |
202 | if (x509->raw_subject_size != x509->raw_issuer_size || | |
203 | memcmp(x509->raw_subject, x509->raw_issuer, | |
204 | x509->raw_issuer_size) != 0) | |
205 | return 0; | |
206 | ||
207 | ret = x509_check_signature(x509->pub, x509); | |
208 | if (ret < 0) | |
41559420 | 209 | goto maybe_missing_crypto_in_x509; |
8c76d793 DH |
210 | x509->signer = x509; |
211 | pr_debug("- self-signed\n"); | |
212 | return 0; | |
213 | } | |
214 | ||
215 | /* Look through the X.509 certificates in the PKCS#7 message's | |
216 | * list to see if the next one is there. | |
217 | */ | |
46963b77 DH |
218 | pr_debug("- want %*phN\n", |
219 | x509->authority->len, x509->authority->data); | |
8c76d793 | 220 | for (p = pkcs7->certs; p; p = p->next) { |
46963b77 DH |
221 | if (!p->skid) |
222 | continue; | |
223 | pr_debug("- cmp [%u] %*phN\n", | |
224 | p->index, p->skid->len, p->skid->data); | |
225 | if (asymmetric_key_id_same(p->skid, x509->authority)) | |
8c76d793 DH |
226 | goto found_issuer; |
227 | } | |
228 | ||
229 | /* We didn't find the root of this chain */ | |
230 | pr_debug("- top\n"); | |
231 | return 0; | |
232 | ||
233 | found_issuer: | |
46963b77 | 234 | pr_debug("- subject %s\n", p->subject); |
8c76d793 DH |
235 | if (p->seen) { |
236 | pr_warn("Sig %u: X.509 chain contains loop\n", | |
237 | sinfo->index); | |
238 | return 0; | |
239 | } | |
240 | ret = x509_check_signature(p->pub, x509); | |
241 | if (ret < 0) | |
242 | return ret; | |
243 | x509->signer = p; | |
244 | if (x509 == p) { | |
245 | pr_debug("- self-signed\n"); | |
246 | return 0; | |
247 | } | |
248 | x509 = p; | |
249 | might_sleep(); | |
250 | } | |
41559420 DH |
251 | |
252 | maybe_missing_crypto_in_x509: | |
253 | /* Just prune the certificate chain at this point if we lack some | |
254 | * crypto module to go further. Note, however, we don't want to set | |
255 | * sinfo->missing_crypto as the signed info block may still be | |
256 | * validatable against an X.509 cert lower in the chain that we have a | |
257 | * trusted copy of. | |
258 | */ | |
259 | if (ret == -ENOPKG) | |
260 | return 0; | |
261 | return ret; | |
8c76d793 DH |
262 | } |
263 | ||
9f0d3314 DH |
264 | /* |
265 | * Verify one signed information block from a PKCS#7 message. | |
266 | */ | |
267 | static int pkcs7_verify_one(struct pkcs7_message *pkcs7, | |
268 | struct pkcs7_signed_info *sinfo) | |
269 | { | |
270 | int ret; | |
271 | ||
272 | kenter(",%u", sinfo->index); | |
273 | ||
274 | /* First of all, digest the data in the PKCS#7 message and the | |
275 | * signed information block | |
276 | */ | |
277 | ret = pkcs7_digest(pkcs7, sinfo); | |
278 | if (ret < 0) | |
279 | return ret; | |
280 | ||
757932e6 | 281 | /* Find the key for the signature if there is one */ |
a4730357 DH |
282 | ret = pkcs7_find_key(pkcs7, sinfo); |
283 | if (ret < 0) | |
284 | return ret; | |
285 | ||
757932e6 DH |
286 | if (!sinfo->signer) |
287 | return 0; | |
288 | ||
a4730357 DH |
289 | pr_devel("Using X.509[%u] for sig %u\n", |
290 | sinfo->signer->index, sinfo->index); | |
291 | ||
292 | /* Verify the PKCS#7 binary against the key */ | |
293 | ret = public_key_verify_signature(sinfo->signer->pub, &sinfo->sig); | |
294 | if (ret < 0) | |
295 | return ret; | |
296 | ||
297 | pr_devel("Verified signature %u\n", sinfo->index); | |
298 | ||
8c76d793 DH |
299 | /* Verify the internal certificate chain */ |
300 | return pkcs7_verify_sig_chain(pkcs7, sinfo); | |
9f0d3314 DH |
301 | } |
302 | ||
303 | /** | |
304 | * pkcs7_verify - Verify a PKCS#7 message | |
305 | * @pkcs7: The PKCS#7 message to be verified | |
41559420 DH |
306 | * |
307 | * Verify a PKCS#7 message is internally consistent - that is, the data digest | |
308 | * matches the digest in the AuthAttrs and any signature in the message or one | |
309 | * of the X.509 certificates it carries that matches another X.509 cert in the | |
310 | * message can be verified. | |
311 | * | |
312 | * This does not look to match the contents of the PKCS#7 message against any | |
313 | * external public keys. | |
314 | * | |
315 | * Returns, in order of descending priority: | |
316 | * | |
317 | * (*) -EKEYREJECTED if a signature failed to match for which we found an | |
318 | * appropriate X.509 certificate, or: | |
319 | * | |
320 | * (*) -EBADMSG if some part of the message was invalid, or: | |
321 | * | |
322 | * (*) -ENOPKG if none of the signature chains are verifiable because suitable | |
323 | * crypto modules couldn't be found, or: | |
324 | * | |
325 | * (*) 0 if all the signature chains that don't incur -ENOPKG can be verified | |
326 | * (note that a signature chain may be of zero length), or: | |
9f0d3314 DH |
327 | */ |
328 | int pkcs7_verify(struct pkcs7_message *pkcs7) | |
329 | { | |
330 | struct pkcs7_signed_info *sinfo; | |
331 | struct x509_certificate *x509; | |
41559420 | 332 | int enopkg = -ENOPKG; |
9f0d3314 DH |
333 | int ret, n; |
334 | ||
335 | kenter(""); | |
336 | ||
337 | for (n = 0, x509 = pkcs7->certs; x509; x509 = x509->next, n++) { | |
338 | ret = x509_get_sig_params(x509); | |
339 | if (ret < 0) | |
340 | return ret; | |
46963b77 DH |
341 | pr_debug("X.509[%u] %*phN\n", |
342 | n, x509->authority->len, x509->authority->data); | |
9f0d3314 DH |
343 | } |
344 | ||
345 | for (sinfo = pkcs7->signed_infos; sinfo; sinfo = sinfo->next) { | |
346 | ret = pkcs7_verify_one(pkcs7, sinfo); | |
347 | if (ret < 0) { | |
41559420 DH |
348 | if (ret == -ENOPKG) { |
349 | sinfo->unsupported_crypto = true; | |
350 | continue; | |
351 | } | |
9f0d3314 DH |
352 | kleave(" = %d", ret); |
353 | return ret; | |
354 | } | |
41559420 | 355 | enopkg = 0; |
9f0d3314 DH |
356 | } |
357 | ||
41559420 DH |
358 | kleave(" = %d", enopkg); |
359 | return enopkg; | |
9f0d3314 DH |
360 | } |
361 | EXPORT_SYMBOL_GPL(pkcs7_verify); |