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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 | /* |
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 | |
134 | kenter("%u", sinfo->index); |
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 | */ |
142 | if (!asymmetric_key_id_same(x509->id, sinfo->signing_cert_id)) |
143 | continue; |
144 | pr_devel("Sig %u: Found cert serial match X.509[%u]\n", |
145 | sinfo->index, certix); |
146 | |
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 | } |
156 | |
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; |
164 | } |
165 | |
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 (;;) { |
181 | pr_debug("verify %s: %*phN\n", |
182 | x509->subject, |
183 | x509->raw_serial_size, x509->raw_serial); |
184 | x509->seen = true; |
185 | ret = x509_get_sig_params(x509); |
186 | if (ret < 0) |
187 | goto maybe_missing_crypto_in_x509; |
188 | |
189 | pr_debug("- issuer %s\n", x509->issuer); |
190 | if (x509->authority) |
191 | pr_debug("- authkeyid %*phN\n", |
192 | x509->authority->len, x509->authority->data); |
193 | |
194 | if (!x509->authority || |
195 | strcmp(x509->subject, x509->issuer) == 0) { |
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) |
209 | goto maybe_missing_crypto_in_x509; |
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 | */ |
218 | pr_debug("- want %*phN\n", |
219 | x509->authority->len, x509->authority->data); |
220 | for (p = pkcs7->certs; p; p = p->next) { |
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)) |
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: |
234 | pr_debug("- subject %s\n", p->subject); |
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 | } |
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; |
262 | } |
263 | |
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 | |
281 | /* Find the key for the signature if there is one */ |
282 | ret = pkcs7_find_key(pkcs7, sinfo); |
283 | if (ret < 0) |
284 | return ret; |
285 | |
286 | if (!sinfo->signer) |
287 | return 0; |
288 | |
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 | |
299 | /* Verify the internal certificate chain */ |
300 | return pkcs7_verify_sig_chain(pkcs7, sinfo); |
301 | } |
302 | |
303 | /** |
304 | * pkcs7_verify - Verify a PKCS#7 message |
305 | * @pkcs7: The PKCS#7 message to be verified |
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: |
327 | */ |
328 | int pkcs7_verify(struct pkcs7_message *pkcs7) |
329 | { |
330 | struct pkcs7_signed_info *sinfo; |
331 | struct x509_certificate *x509; |
332 | int enopkg = -ENOPKG; |
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; |
341 | pr_debug("X.509[%u] %*phN\n", |
342 | n, x509->authority->len, x509->authority->data); |
343 | } |
344 | |
345 | for (sinfo = pkcs7->signed_infos; sinfo; sinfo = sinfo->next) { |
346 | ret = pkcs7_verify_one(pkcs7, sinfo); |
347 | if (ret < 0) { |
348 | if (ret == -ENOPKG) { |
349 | sinfo->unsupported_crypto = true; |
350 | continue; |
351 | } |
352 | kleave(" = %d", ret); |
353 | return ret; |
354 | } |
355 | enopkg = 0; |
356 | } |
357 | |
358 | kleave(" = %d", enopkg); |
359 | return enopkg; |
360 | } |
361 | EXPORT_SYMBOL_GPL(pkcs7_verify); |
362 |
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