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Linux/crypto/asymmetric_keys/pkcs7_verify.c

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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 <crypto/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 public_key_signature *sig = sinfo->sig;
 29         struct crypto_shash *tfm;
 30         struct shash_desc *desc;
 31         size_t desc_size;
 32         int ret;
 33 
 34         kenter(",%u,%s", sinfo->index, sinfo->sig->hash_algo);
 35 
 36         if (!sinfo->sig->hash_algo)
 37                 return -ENOPKG;
 38 
 39         /* Allocate the hashing algorithm we're going to need and find out how
 40          * big the hash operational data will be.
 41          */
 42         tfm = crypto_alloc_shash(sinfo->sig->hash_algo, 0, 0);
 43         if (IS_ERR(tfm))
 44                 return (PTR_ERR(tfm) == -ENOENT) ? -ENOPKG : PTR_ERR(tfm);
 45 
 46         desc_size = crypto_shash_descsize(tfm) + sizeof(*desc);
 47         sig->digest_size = crypto_shash_digestsize(tfm);
 48 
 49         ret = -ENOMEM;
 50         sig->digest = kmalloc(sig->digest_size, GFP_KERNEL);
 51         if (!sig->digest)
 52                 goto error_no_desc;
 53 
 54         desc = kzalloc(desc_size, GFP_KERNEL);
 55         if (!desc)
 56                 goto error_no_desc;
 57 
 58         desc->tfm   = tfm;
 59         desc->flags = CRYPTO_TFM_REQ_MAY_SLEEP;
 60 
 61         /* Digest the message [RFC2315 9.3] */
 62         ret = crypto_shash_init(desc);
 63         if (ret < 0)
 64                 goto error;
 65         ret = crypto_shash_finup(desc, pkcs7->data, pkcs7->data_len,
 66                                  sig->digest);
 67         if (ret < 0)
 68                 goto error;
 69         pr_devel("MsgDigest = [%*ph]\n", 8, sig->digest);
 70 
 71         /* However, if there are authenticated attributes, there must be a
 72          * message digest attribute amongst them which corresponds to the
 73          * digest we just calculated.
 74          */
 75         if (sinfo->authattrs) {
 76                 u8 tag;
 77 
 78                 if (!sinfo->msgdigest) {
 79                         pr_warn("Sig %u: No messageDigest\n", sinfo->index);
 80                         ret = -EKEYREJECTED;
 81                         goto error;
 82                 }
 83 
 84                 if (sinfo->msgdigest_len != sig->digest_size) {
 85                         pr_debug("Sig %u: Invalid digest size (%u)\n",
 86                                  sinfo->index, sinfo->msgdigest_len);
 87                         ret = -EBADMSG;
 88                         goto error;
 89                 }
 90 
 91                 if (memcmp(sig->digest, sinfo->msgdigest,
 92                            sinfo->msgdigest_len) != 0) {
 93                         pr_debug("Sig %u: Message digest doesn't match\n",
 94                                  sinfo->index);
 95                         ret = -EKEYREJECTED;
 96                         goto error;
 97                 }
 98 
 99                 /* We then calculate anew, using the authenticated attributes
100                  * as the contents of the digest instead.  Note that we need to
101                  * convert the attributes from a CONT.0 into a SET before we
102                  * hash it.
103                  */
104                 memset(sig->digest, 0, sig->digest_size);
105 
106                 ret = crypto_shash_init(desc);
107                 if (ret < 0)
108                         goto error;
109                 tag = ASN1_CONS_BIT | ASN1_SET;
110                 ret = crypto_shash_update(desc, &tag, 1);
111                 if (ret < 0)
112                         goto error;
113                 ret = crypto_shash_finup(desc, sinfo->authattrs,
114                                          sinfo->authattrs_len, sig->digest);
115                 if (ret < 0)
116                         goto error;
117                 pr_devel("AADigest = [%*ph]\n", 8, sig->digest);
118         }
119 
120 error:
121         kfree(desc);
122 error_no_desc:
123         crypto_free_shash(tfm);
124         kleave(" = %d", ret);
125         return ret;
126 }
127 
128 /*
129  * Find the key (X.509 certificate) to use to verify a PKCS#7 message.  PKCS#7
130  * uses the issuer's name and the issuing certificate serial number for
131  * matching purposes.  These must match the certificate issuer's name (not
132  * subject's name) and the certificate serial number [RFC 2315 6.7].
133  */
134 static int pkcs7_find_key(struct pkcs7_message *pkcs7,
135                           struct pkcs7_signed_info *sinfo)
136 {
137         struct x509_certificate *x509;
138         unsigned certix = 1;
139 
140         kenter("%u", sinfo->index);
141 
142         for (x509 = pkcs7->certs; x509; x509 = x509->next, certix++) {
143                 /* I'm _assuming_ that the generator of the PKCS#7 message will
144                  * encode the fields from the X.509 cert in the same way in the
145                  * PKCS#7 message - but I can't be 100% sure of that.  It's
146                  * possible this will need element-by-element comparison.
147                  */
148                 if (!asymmetric_key_id_same(x509->id, sinfo->sig->auth_ids[0]))
149                         continue;
150                 pr_devel("Sig %u: Found cert serial match X.509[%u]\n",
151                          sinfo->index, certix);
152 
153                 if (x509->pub->pkey_algo != sinfo->sig->pkey_algo) {
154                         pr_warn("Sig %u: X.509 algo and PKCS#7 sig algo don't match\n",
155                                 sinfo->index);
156                         continue;
157                 }
158 
159                 sinfo->signer = x509;
160                 return 0;
161         }
162 
163         /* The relevant X.509 cert isn't found here, but it might be found in
164          * the trust keyring.
165          */
166         pr_debug("Sig %u: Issuing X.509 cert not found (#%*phN)\n",
167                  sinfo->index,
168                  sinfo->sig->auth_ids[0]->len, sinfo->sig->auth_ids[0]->data);
169         return 0;
170 }
171 
172 /*
173  * Verify the internal certificate chain as best we can.
174  */
175 static int pkcs7_verify_sig_chain(struct pkcs7_message *pkcs7,
176                                   struct pkcs7_signed_info *sinfo)
177 {
178         struct public_key_signature *sig;
179         struct x509_certificate *x509 = sinfo->signer, *p;
180         struct asymmetric_key_id *auth;
181         int ret;
182 
183         kenter("");
184 
185         for (p = pkcs7->certs; p; p = p->next)
186                 p->seen = false;
187 
188         for (;;) {
189                 pr_debug("verify %s: %*phN\n",
190                          x509->subject,
191                          x509->raw_serial_size, x509->raw_serial);
192                 x509->seen = true;
193                 if (x509->unsupported_key)
194                         goto unsupported_crypto_in_x509;
195 
196                 pr_debug("- issuer %s\n", x509->issuer);
197                 sig = x509->sig;
198                 if (sig->auth_ids[0])
199                         pr_debug("- authkeyid.id %*phN\n",
200                                  sig->auth_ids[0]->len, sig->auth_ids[0]->data);
201                 if (sig->auth_ids[1])
202                         pr_debug("- authkeyid.skid %*phN\n",
203                                  sig->auth_ids[1]->len, sig->auth_ids[1]->data);
204 
205                 if (x509->self_signed) {
206                         /* If there's no authority certificate specified, then
207                          * the certificate must be self-signed and is the root
208                          * of the chain.  Likewise if the cert is its own
209                          * authority.
210                          */
211                         if (x509->unsupported_sig)
212                                 goto unsupported_crypto_in_x509;
213                         x509->signer = x509;
214                         pr_debug("- self-signed\n");
215                         return 0;
216                 }
217 
218                 /* Look through the X.509 certificates in the PKCS#7 message's
219                  * list to see if the next one is there.
220                  */
221                 auth = sig->auth_ids[0];
222                 if (auth) {
223                         pr_debug("- want %*phN\n", auth->len, auth->data);
224                         for (p = pkcs7->certs; p; p = p->next) {
225                                 pr_debug("- cmp [%u] %*phN\n",
226                                          p->index, p->id->len, p->id->data);
227                                 if (asymmetric_key_id_same(p->id, auth))
228                                         goto found_issuer_check_skid;
229                         }
230                 } else if (sig->auth_ids[1]) {
231                         auth = sig->auth_ids[1];
232                         pr_debug("- want %*phN\n", auth->len, auth->data);
233                         for (p = pkcs7->certs; p; p = p->next) {
234                                 if (!p->skid)
235                                         continue;
236                                 pr_debug("- cmp [%u] %*phN\n",
237                                          p->index, p->skid->len, p->skid->data);
238                                 if (asymmetric_key_id_same(p->skid, auth))
239                                         goto found_issuer;
240                         }
241                 }
242 
243                 /* We didn't find the root of this chain */
244                 pr_debug("- top\n");
245                 return 0;
246 
247         found_issuer_check_skid:
248                 /* We matched issuer + serialNumber, but if there's an
249                  * authKeyId.keyId, that must match the CA subjKeyId also.
250                  */
251                 if (sig->auth_ids[1] &&
252                     !asymmetric_key_id_same(p->skid, sig->auth_ids[1])) {
253                         pr_warn("Sig %u: X.509 chain contains auth-skid nonmatch (%u->%u)\n",
254                                 sinfo->index, x509->index, p->index);
255                         return -EKEYREJECTED;
256                 }
257         found_issuer:
258                 pr_debug("- subject %s\n", p->subject);
259                 if (p->seen) {
260                         pr_warn("Sig %u: X.509 chain contains loop\n",
261                                 sinfo->index);
262                         return 0;
263                 }
264                 ret = public_key_verify_signature(p->pub, p->sig);
265                 if (ret < 0)
266                         return ret;
267                 x509->signer = p;
268                 if (x509 == p) {
269                         pr_debug("- self-signed\n");
270                         return 0;
271                 }
272                 x509 = p;
273                 might_sleep();
274         }
275 
276 unsupported_crypto_in_x509:
277         /* Just prune the certificate chain at this point if we lack some
278          * crypto module to go further.  Note, however, we don't want to set
279          * sinfo->unsupported_crypto as the signed info block may still be
280          * validatable against an X.509 cert lower in the chain that we have a
281          * trusted copy of.
282          */
283         return 0;
284 }
285 
286 /*
287  * Verify one signed information block from a PKCS#7 message.
288  */
289 static int pkcs7_verify_one(struct pkcs7_message *pkcs7,
290                             struct pkcs7_signed_info *sinfo)
291 {
292         int ret;
293 
294         kenter(",%u", sinfo->index);
295 
296         /* First of all, digest the data in the PKCS#7 message and the
297          * signed information block
298          */
299         ret = pkcs7_digest(pkcs7, sinfo);
300         if (ret < 0)
301                 return ret;
302 
303         /* Find the key for the signature if there is one */
304         ret = pkcs7_find_key(pkcs7, sinfo);
305         if (ret < 0)
306                 return ret;
307 
308         if (!sinfo->signer)
309                 return 0;
310 
311         pr_devel("Using X.509[%u] for sig %u\n",
312                  sinfo->signer->index, sinfo->index);
313 
314         /* Check that the PKCS#7 signing time is valid according to the X.509
315          * certificate.  We can't, however, check against the system clock
316          * since that may not have been set yet and may be wrong.
317          */
318         if (test_bit(sinfo_has_signing_time, &sinfo->aa_set)) {
319                 if (sinfo->signing_time < sinfo->signer->valid_from ||
320                     sinfo->signing_time > sinfo->signer->valid_to) {
321                         pr_warn("Message signed outside of X.509 validity window\n");
322                         return -EKEYREJECTED;
323                 }
324         }
325 
326         /* Verify the PKCS#7 binary against the key */
327         ret = public_key_verify_signature(sinfo->signer->pub, sinfo->sig);
328         if (ret < 0)
329                 return ret;
330 
331         pr_devel("Verified signature %u\n", sinfo->index);
332 
333         /* Verify the internal certificate chain */
334         return pkcs7_verify_sig_chain(pkcs7, sinfo);
335 }
336 
337 /**
338  * pkcs7_verify - Verify a PKCS#7 message
339  * @pkcs7: The PKCS#7 message to be verified
340  * @usage: The use to which the key is being put
341  *
342  * Verify a PKCS#7 message is internally consistent - that is, the data digest
343  * matches the digest in the AuthAttrs and any signature in the message or one
344  * of the X.509 certificates it carries that matches another X.509 cert in the
345  * message can be verified.
346  *
347  * This does not look to match the contents of the PKCS#7 message against any
348  * external public keys.
349  *
350  * Returns, in order of descending priority:
351  *
352  *  (*) -EKEYREJECTED if a key was selected that had a usage restriction at
353  *      odds with the specified usage, or:
354  *
355  *  (*) -EKEYREJECTED if a signature failed to match for which we found an
356  *      appropriate X.509 certificate, or:
357  *
358  *  (*) -EBADMSG if some part of the message was invalid, or:
359  *
360  *  (*) -ENOPKG if none of the signature chains are verifiable because suitable
361  *      crypto modules couldn't be found, or:
362  *
363  *  (*) 0 if all the signature chains that don't incur -ENOPKG can be verified
364  *      (note that a signature chain may be of zero length), or:
365  */
366 int pkcs7_verify(struct pkcs7_message *pkcs7,
367                  enum key_being_used_for usage)
368 {
369         struct pkcs7_signed_info *sinfo;
370         int enopkg = -ENOPKG;
371         int ret;
372 
373         kenter("");
374 
375         switch (usage) {
376         case VERIFYING_MODULE_SIGNATURE:
377                 if (pkcs7->data_type != OID_data) {
378                         pr_warn("Invalid module sig (not pkcs7-data)\n");
379                         return -EKEYREJECTED;
380                 }
381                 if (pkcs7->have_authattrs) {
382                         pr_warn("Invalid module sig (has authattrs)\n");
383                         return -EKEYREJECTED;
384                 }
385                 break;
386         case VERIFYING_FIRMWARE_SIGNATURE:
387                 if (pkcs7->data_type != OID_data) {
388                         pr_warn("Invalid firmware sig (not pkcs7-data)\n");
389                         return -EKEYREJECTED;
390                 }
391                 if (!pkcs7->have_authattrs) {
392                         pr_warn("Invalid firmware sig (missing authattrs)\n");
393                         return -EKEYREJECTED;
394                 }
395                 break;
396         case VERIFYING_KEXEC_PE_SIGNATURE:
397                 if (pkcs7->data_type != OID_msIndirectData) {
398                         pr_warn("Invalid kexec sig (not Authenticode)\n");
399                         return -EKEYREJECTED;
400                 }
401                 /* Authattr presence checked in parser */
402                 break;
403         case VERIFYING_UNSPECIFIED_SIGNATURE:
404                 if (pkcs7->data_type != OID_data) {
405                         pr_warn("Invalid unspecified sig (not pkcs7-data)\n");
406                         return -EKEYREJECTED;
407                 }
408                 break;
409         default:
410                 return -EINVAL;
411         }
412 
413         for (sinfo = pkcs7->signed_infos; sinfo; sinfo = sinfo->next) {
414                 ret = pkcs7_verify_one(pkcs7, sinfo);
415                 if (ret < 0) {
416                         if (ret == -ENOPKG) {
417                                 sinfo->unsupported_crypto = true;
418                                 continue;
419                         }
420                         kleave(" = %d", ret);
421                         return ret;
422                 }
423                 enopkg = 0;
424         }
425 
426         kleave(" = %d", enopkg);
427         return enopkg;
428 }
429 EXPORT_SYMBOL_GPL(pkcs7_verify);
430 
431 /**
432  * pkcs7_supply_detached_data - Supply the data needed to verify a PKCS#7 message
433  * @pkcs7: The PKCS#7 message
434  * @data: The data to be verified
435  * @datalen: The amount of data
436  *
437  * Supply the detached data needed to verify a PKCS#7 message.  Note that no
438  * attempt to retain/pin the data is made.  That is left to the caller.  The
439  * data will not be modified by pkcs7_verify() and will not be freed when the
440  * PKCS#7 message is freed.
441  *
442  * Returns -EINVAL if data is already supplied in the message, 0 otherwise.
443  */
444 int pkcs7_supply_detached_data(struct pkcs7_message *pkcs7,
445                                const void *data, size_t datalen)
446 {
447         if (pkcs7->data) {
448                 pr_debug("Data already supplied\n");
449                 return -EINVAL;
450         }
451         pkcs7->data = data;
452         pkcs7->data_len = datalen;
453         return 0;
454 }
455 

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