1 | // SPDX-License-Identifier: GPL-2.0-or-later |
2 | /* Verify the signature on a PKCS#7 message. |
3 | * |
4 | * Copyright (C) 2012 Red Hat, Inc. All Rights Reserved. |
5 | * Written by David Howells (dhowells@redhat.com) |
6 | */ |
7 | |
8 | #define pr_fmt(fmt) "PKCS7: "fmt |
9 | #include <linux/kernel.h> |
10 | #include <linux/export.h> |
11 | #include <linux/slab.h> |
12 | #include <linux/err.h> |
13 | #include <linux/asn1.h> |
14 | #include <crypto/hash.h> |
15 | #include <crypto/hash_info.h> |
16 | #include <crypto/public_key.h> |
17 | #include "pkcs7_parser.h" |
18 | |
19 | /* |
20 | * Digest the relevant parts of the PKCS#7 data |
21 | */ |
22 | static int pkcs7_digest(struct pkcs7_message *pkcs7, |
23 | struct pkcs7_signed_info *sinfo) |
24 | { |
25 | struct public_key_signature *sig = sinfo->sig; |
26 | struct crypto_shash *tfm; |
27 | struct shash_desc *desc; |
28 | size_t desc_size; |
29 | int ret; |
30 | |
31 | kenter(",%u,%s" , sinfo->index, sinfo->sig->hash_algo); |
32 | |
33 | /* The digest was calculated already. */ |
34 | if (sig->digest) |
35 | return 0; |
36 | |
37 | if (!sinfo->sig->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(alg_name: sinfo->sig->hash_algo, type: 0, mask: 0); |
44 | if (IS_ERR(ptr: tfm)) |
45 | return (PTR_ERR(ptr: tfm) == -ENOENT) ? -ENOPKG : PTR_ERR(ptr: tfm); |
46 | |
47 | desc_size = crypto_shash_descsize(tfm) + sizeof(*desc); |
48 | sig->digest_size = crypto_shash_digestsize(tfm); |
49 | |
50 | ret = -ENOMEM; |
51 | sig->digest = kmalloc(size: sig->digest_size, GFP_KERNEL); |
52 | if (!sig->digest) |
53 | goto error_no_desc; |
54 | |
55 | desc = kzalloc(size: desc_size, GFP_KERNEL); |
56 | if (!desc) |
57 | goto error_no_desc; |
58 | |
59 | desc->tfm = tfm; |
60 | |
61 | /* Digest the message [RFC2315 9.3] */ |
62 | ret = crypto_shash_digest(desc, data: pkcs7->data, len: pkcs7->data_len, |
63 | out: sig->digest); |
64 | if (ret < 0) |
65 | goto error; |
66 | pr_devel("MsgDigest = [%*ph]\n" , 8, sig->digest); |
67 | |
68 | /* However, if there are authenticated attributes, there must be a |
69 | * message digest attribute amongst them which corresponds to the |
70 | * digest we just calculated. |
71 | */ |
72 | if (sinfo->authattrs) { |
73 | u8 tag; |
74 | |
75 | if (!sinfo->msgdigest) { |
76 | pr_warn("Sig %u: No messageDigest\n" , sinfo->index); |
77 | ret = -EKEYREJECTED; |
78 | goto error; |
79 | } |
80 | |
81 | if (sinfo->msgdigest_len != sig->digest_size) { |
82 | pr_warn("Sig %u: Invalid digest size (%u)\n" , |
83 | sinfo->index, sinfo->msgdigest_len); |
84 | ret = -EBADMSG; |
85 | goto error; |
86 | } |
87 | |
88 | if (memcmp(p: sig->digest, q: sinfo->msgdigest, |
89 | size: sinfo->msgdigest_len) != 0) { |
90 | pr_warn("Sig %u: Message digest doesn't match\n" , |
91 | sinfo->index); |
92 | ret = -EKEYREJECTED; |
93 | goto error; |
94 | } |
95 | |
96 | /* We then calculate anew, using the authenticated attributes |
97 | * as the contents of the digest instead. Note that we need to |
98 | * convert the attributes from a CONT.0 into a SET before we |
99 | * hash it. |
100 | */ |
101 | memset(sig->digest, 0, sig->digest_size); |
102 | |
103 | ret = crypto_shash_init(desc); |
104 | if (ret < 0) |
105 | goto error; |
106 | tag = ASN1_CONS_BIT | ASN1_SET; |
107 | ret = crypto_shash_update(desc, data: &tag, len: 1); |
108 | if (ret < 0) |
109 | goto error; |
110 | ret = crypto_shash_finup(desc, data: sinfo->authattrs, |
111 | len: sinfo->authattrs_len, out: sig->digest); |
112 | if (ret < 0) |
113 | goto error; |
114 | pr_devel("AADigest = [%*ph]\n" , 8, sig->digest); |
115 | } |
116 | |
117 | error: |
118 | kfree(objp: desc); |
119 | error_no_desc: |
120 | crypto_free_shash(tfm); |
121 | kleave(" = %d" , ret); |
122 | return ret; |
123 | } |
124 | |
125 | int pkcs7_get_digest(struct pkcs7_message *pkcs7, const u8 **buf, u32 *len, |
126 | enum hash_algo *hash_algo) |
127 | { |
128 | struct pkcs7_signed_info *sinfo = pkcs7->signed_infos; |
129 | int i, ret; |
130 | |
131 | /* |
132 | * This function doesn't support messages with more than one signature. |
133 | */ |
134 | if (sinfo == NULL || sinfo->next != NULL) |
135 | return -EBADMSG; |
136 | |
137 | ret = pkcs7_digest(pkcs7, sinfo); |
138 | if (ret) |
139 | return ret; |
140 | |
141 | *buf = sinfo->sig->digest; |
142 | *len = sinfo->sig->digest_size; |
143 | |
144 | i = match_string(array: hash_algo_name, n: HASH_ALGO__LAST, |
145 | string: sinfo->sig->hash_algo); |
146 | if (i >= 0) |
147 | *hash_algo = i; |
148 | |
149 | return 0; |
150 | } |
151 | |
152 | /* |
153 | * Find the key (X.509 certificate) to use to verify a PKCS#7 message. PKCS#7 |
154 | * uses the issuer's name and the issuing certificate serial number for |
155 | * matching purposes. These must match the certificate issuer's name (not |
156 | * subject's name) and the certificate serial number [RFC 2315 6.7]. |
157 | */ |
158 | static int pkcs7_find_key(struct pkcs7_message *pkcs7, |
159 | struct pkcs7_signed_info *sinfo) |
160 | { |
161 | struct x509_certificate *x509; |
162 | unsigned certix = 1; |
163 | |
164 | kenter("%u" , sinfo->index); |
165 | |
166 | for (x509 = pkcs7->certs; x509; x509 = x509->next, certix++) { |
167 | /* I'm _assuming_ that the generator of the PKCS#7 message will |
168 | * encode the fields from the X.509 cert in the same way in the |
169 | * PKCS#7 message - but I can't be 100% sure of that. It's |
170 | * possible this will need element-by-element comparison. |
171 | */ |
172 | if (!asymmetric_key_id_same(kid1: x509->id, kid2: sinfo->sig->auth_ids[0])) |
173 | continue; |
174 | pr_devel("Sig %u: Found cert serial match X.509[%u]\n" , |
175 | sinfo->index, certix); |
176 | |
177 | sinfo->signer = x509; |
178 | return 0; |
179 | } |
180 | |
181 | /* The relevant X.509 cert isn't found here, but it might be found in |
182 | * the trust keyring. |
183 | */ |
184 | pr_debug("Sig %u: Issuing X.509 cert not found (#%*phN)\n" , |
185 | sinfo->index, |
186 | sinfo->sig->auth_ids[0]->len, sinfo->sig->auth_ids[0]->data); |
187 | return 0; |
188 | } |
189 | |
190 | /* |
191 | * Verify the internal certificate chain as best we can. |
192 | */ |
193 | static int pkcs7_verify_sig_chain(struct pkcs7_message *pkcs7, |
194 | struct pkcs7_signed_info *sinfo) |
195 | { |
196 | struct public_key_signature *sig; |
197 | struct x509_certificate *x509 = sinfo->signer, *p; |
198 | struct asymmetric_key_id *auth; |
199 | int ret; |
200 | |
201 | kenter("" ); |
202 | |
203 | for (p = pkcs7->certs; p; p = p->next) |
204 | p->seen = false; |
205 | |
206 | for (;;) { |
207 | pr_debug("verify %s: %*phN\n" , |
208 | x509->subject, |
209 | x509->raw_serial_size, x509->raw_serial); |
210 | x509->seen = true; |
211 | |
212 | if (x509->blacklisted) { |
213 | /* If this cert is blacklisted, then mark everything |
214 | * that depends on this as blacklisted too. |
215 | */ |
216 | sinfo->blacklisted = true; |
217 | for (p = sinfo->signer; p != x509; p = p->signer) |
218 | p->blacklisted = true; |
219 | pr_debug("- blacklisted\n" ); |
220 | return 0; |
221 | } |
222 | |
223 | pr_debug("- issuer %s\n" , x509->issuer); |
224 | sig = x509->sig; |
225 | if (sig->auth_ids[0]) |
226 | pr_debug("- authkeyid.id %*phN\n" , |
227 | sig->auth_ids[0]->len, sig->auth_ids[0]->data); |
228 | if (sig->auth_ids[1]) |
229 | pr_debug("- authkeyid.skid %*phN\n" , |
230 | sig->auth_ids[1]->len, sig->auth_ids[1]->data); |
231 | |
232 | if (x509->self_signed) { |
233 | /* If there's no authority certificate specified, then |
234 | * the certificate must be self-signed and is the root |
235 | * of the chain. Likewise if the cert is its own |
236 | * authority. |
237 | */ |
238 | if (x509->unsupported_sig) |
239 | goto unsupported_sig_in_x509; |
240 | x509->signer = x509; |
241 | pr_debug("- self-signed\n" ); |
242 | return 0; |
243 | } |
244 | |
245 | /* Look through the X.509 certificates in the PKCS#7 message's |
246 | * list to see if the next one is there. |
247 | */ |
248 | auth = sig->auth_ids[0]; |
249 | if (auth) { |
250 | pr_debug("- want %*phN\n" , auth->len, auth->data); |
251 | for (p = pkcs7->certs; p; p = p->next) { |
252 | pr_debug("- cmp [%u] %*phN\n" , |
253 | p->index, p->id->len, p->id->data); |
254 | if (asymmetric_key_id_same(kid1: p->id, kid2: auth)) |
255 | goto found_issuer_check_skid; |
256 | } |
257 | } else if (sig->auth_ids[1]) { |
258 | auth = sig->auth_ids[1]; |
259 | pr_debug("- want %*phN\n" , auth->len, auth->data); |
260 | for (p = pkcs7->certs; p; p = p->next) { |
261 | if (!p->skid) |
262 | continue; |
263 | pr_debug("- cmp [%u] %*phN\n" , |
264 | p->index, p->skid->len, p->skid->data); |
265 | if (asymmetric_key_id_same(kid1: p->skid, kid2: auth)) |
266 | goto found_issuer; |
267 | } |
268 | } |
269 | |
270 | /* We didn't find the root of this chain */ |
271 | pr_debug("- top\n" ); |
272 | return 0; |
273 | |
274 | found_issuer_check_skid: |
275 | /* We matched issuer + serialNumber, but if there's an |
276 | * authKeyId.keyId, that must match the CA subjKeyId also. |
277 | */ |
278 | if (sig->auth_ids[1] && |
279 | !asymmetric_key_id_same(kid1: p->skid, kid2: sig->auth_ids[1])) { |
280 | pr_warn("Sig %u: X.509 chain contains auth-skid nonmatch (%u->%u)\n" , |
281 | sinfo->index, x509->index, p->index); |
282 | return -EKEYREJECTED; |
283 | } |
284 | found_issuer: |
285 | pr_debug("- subject %s\n" , p->subject); |
286 | if (p->seen) { |
287 | pr_warn("Sig %u: X.509 chain contains loop\n" , |
288 | sinfo->index); |
289 | return 0; |
290 | } |
291 | ret = public_key_verify_signature(pkey: p->pub, sig: x509->sig); |
292 | if (ret < 0) |
293 | return ret; |
294 | x509->signer = p; |
295 | if (x509 == p) { |
296 | pr_debug("- self-signed\n" ); |
297 | return 0; |
298 | } |
299 | x509 = p; |
300 | might_sleep(); |
301 | } |
302 | |
303 | unsupported_sig_in_x509: |
304 | /* Just prune the certificate chain at this point if we lack some |
305 | * crypto module to go further. Note, however, we don't want to set |
306 | * sinfo->unsupported_crypto as the signed info block may still be |
307 | * validatable against an X.509 cert lower in the chain that we have a |
308 | * trusted copy of. |
309 | */ |
310 | return 0; |
311 | } |
312 | |
313 | /* |
314 | * Verify one signed information block from a PKCS#7 message. |
315 | */ |
316 | static int pkcs7_verify_one(struct pkcs7_message *pkcs7, |
317 | struct pkcs7_signed_info *sinfo) |
318 | { |
319 | int ret; |
320 | |
321 | kenter(",%u" , sinfo->index); |
322 | |
323 | /* First of all, digest the data in the PKCS#7 message and the |
324 | * signed information block |
325 | */ |
326 | ret = pkcs7_digest(pkcs7, sinfo); |
327 | if (ret < 0) |
328 | return ret; |
329 | |
330 | /* Find the key for the signature if there is one */ |
331 | ret = pkcs7_find_key(pkcs7, sinfo); |
332 | if (ret < 0) |
333 | return ret; |
334 | |
335 | if (!sinfo->signer) |
336 | return 0; |
337 | |
338 | pr_devel("Using X.509[%u] for sig %u\n" , |
339 | sinfo->signer->index, sinfo->index); |
340 | |
341 | /* Check that the PKCS#7 signing time is valid according to the X.509 |
342 | * certificate. We can't, however, check against the system clock |
343 | * since that may not have been set yet and may be wrong. |
344 | */ |
345 | if (test_bit(sinfo_has_signing_time, &sinfo->aa_set)) { |
346 | if (sinfo->signing_time < sinfo->signer->valid_from || |
347 | sinfo->signing_time > sinfo->signer->valid_to) { |
348 | pr_warn("Message signed outside of X.509 validity window\n" ); |
349 | return -EKEYREJECTED; |
350 | } |
351 | } |
352 | |
353 | /* Verify the PKCS#7 binary against the key */ |
354 | ret = public_key_verify_signature(pkey: sinfo->signer->pub, sig: sinfo->sig); |
355 | if (ret < 0) |
356 | return ret; |
357 | |
358 | pr_devel("Verified signature %u\n" , sinfo->index); |
359 | |
360 | /* Verify the internal certificate chain */ |
361 | return pkcs7_verify_sig_chain(pkcs7, sinfo); |
362 | } |
363 | |
364 | /** |
365 | * pkcs7_verify - Verify a PKCS#7 message |
366 | * @pkcs7: The PKCS#7 message to be verified |
367 | * @usage: The use to which the key is being put |
368 | * |
369 | * Verify a PKCS#7 message is internally consistent - that is, the data digest |
370 | * matches the digest in the AuthAttrs and any signature in the message or one |
371 | * of the X.509 certificates it carries that matches another X.509 cert in the |
372 | * message can be verified. |
373 | * |
374 | * This does not look to match the contents of the PKCS#7 message against any |
375 | * external public keys. |
376 | * |
377 | * Returns, in order of descending priority: |
378 | * |
379 | * (*) -EKEYREJECTED if a key was selected that had a usage restriction at |
380 | * odds with the specified usage, or: |
381 | * |
382 | * (*) -EKEYREJECTED if a signature failed to match for which we found an |
383 | * appropriate X.509 certificate, or: |
384 | * |
385 | * (*) -EBADMSG if some part of the message was invalid, or: |
386 | * |
387 | * (*) 0 if a signature chain passed verification, or: |
388 | * |
389 | * (*) -EKEYREJECTED if a blacklisted key was encountered, or: |
390 | * |
391 | * (*) -ENOPKG if none of the signature chains are verifiable because suitable |
392 | * crypto modules couldn't be found. |
393 | */ |
394 | int pkcs7_verify(struct pkcs7_message *pkcs7, |
395 | enum key_being_used_for usage) |
396 | { |
397 | struct pkcs7_signed_info *sinfo; |
398 | int actual_ret = -ENOPKG; |
399 | int ret; |
400 | |
401 | kenter("" ); |
402 | |
403 | switch (usage) { |
404 | case VERIFYING_MODULE_SIGNATURE: |
405 | if (pkcs7->data_type != OID_data) { |
406 | pr_warn("Invalid module sig (not pkcs7-data)\n" ); |
407 | return -EKEYREJECTED; |
408 | } |
409 | if (pkcs7->have_authattrs) { |
410 | pr_warn("Invalid module sig (has authattrs)\n" ); |
411 | return -EKEYREJECTED; |
412 | } |
413 | break; |
414 | case VERIFYING_FIRMWARE_SIGNATURE: |
415 | if (pkcs7->data_type != OID_data) { |
416 | pr_warn("Invalid firmware sig (not pkcs7-data)\n" ); |
417 | return -EKEYREJECTED; |
418 | } |
419 | if (!pkcs7->have_authattrs) { |
420 | pr_warn("Invalid firmware sig (missing authattrs)\n" ); |
421 | return -EKEYREJECTED; |
422 | } |
423 | break; |
424 | case VERIFYING_KEXEC_PE_SIGNATURE: |
425 | if (pkcs7->data_type != OID_msIndirectData) { |
426 | pr_warn("Invalid kexec sig (not Authenticode)\n" ); |
427 | return -EKEYREJECTED; |
428 | } |
429 | /* Authattr presence checked in parser */ |
430 | break; |
431 | case VERIFYING_UNSPECIFIED_SIGNATURE: |
432 | if (pkcs7->data_type != OID_data) { |
433 | pr_warn("Invalid unspecified sig (not pkcs7-data)\n" ); |
434 | return -EKEYREJECTED; |
435 | } |
436 | break; |
437 | default: |
438 | return -EINVAL; |
439 | } |
440 | |
441 | for (sinfo = pkcs7->signed_infos; sinfo; sinfo = sinfo->next) { |
442 | ret = pkcs7_verify_one(pkcs7, sinfo); |
443 | if (sinfo->blacklisted) { |
444 | if (actual_ret == -ENOPKG) |
445 | actual_ret = -EKEYREJECTED; |
446 | continue; |
447 | } |
448 | if (ret < 0) { |
449 | if (ret == -ENOPKG) { |
450 | sinfo->unsupported_crypto = true; |
451 | continue; |
452 | } |
453 | kleave(" = %d" , ret); |
454 | return ret; |
455 | } |
456 | actual_ret = 0; |
457 | } |
458 | |
459 | kleave(" = %d" , actual_ret); |
460 | return actual_ret; |
461 | } |
462 | EXPORT_SYMBOL_GPL(pkcs7_verify); |
463 | |
464 | /** |
465 | * pkcs7_supply_detached_data - Supply the data needed to verify a PKCS#7 message |
466 | * @pkcs7: The PKCS#7 message |
467 | * @data: The data to be verified |
468 | * @datalen: The amount of data |
469 | * |
470 | * Supply the detached data needed to verify a PKCS#7 message. Note that no |
471 | * attempt to retain/pin the data is made. That is left to the caller. The |
472 | * data will not be modified by pkcs7_verify() and will not be freed when the |
473 | * PKCS#7 message is freed. |
474 | * |
475 | * Returns -EINVAL if data is already supplied in the message, 0 otherwise. |
476 | */ |
477 | int pkcs7_supply_detached_data(struct pkcs7_message *pkcs7, |
478 | const void *data, size_t datalen) |
479 | { |
480 | if (pkcs7->data) { |
481 | pr_warn("Data already supplied\n" ); |
482 | return -EINVAL; |
483 | } |
484 | pkcs7->data = data; |
485 | pkcs7->data_len = datalen; |
486 | return 0; |
487 | } |
488 | EXPORT_SYMBOL_GPL(pkcs7_supply_detached_data); |
489 | |