crypto/asymmetric_keys/pkcs7_verify.c

0001 // SPDX-License-Identifier: GPL-2.0-or-later
0002 /* Verify the signature on a PKCS#7 message.
0003  *
0004  * Copyright (C) 2012 Red Hat, Inc. All Rights Reserved.
0005  * Written by David Howells (dhowells@redhat.com)
0006  */
0007
0008 #define pr_fmt(fmt) "PKCS7: "fmt
0009 #include <linux/kernel.h>
0010 #include <linux/export.h>
0011 #include <linux/slab.h>
0012 #include <linux/err.h>
0013 #include <linux/asn1.h>
0014 #include <crypto/hash.h>
0015 #include <crypto/hash_info.h>
0016 #include <crypto/public_key.h>
0017 #include "pkcs7_parser.h"
0018
0019 /*
0020  * Digest the relevant parts of the PKCS#7 data
0021  */
0022 static int pkcs7_digest(struct pkcs7_message *pkcs7,
0023             struct pkcs7_signed_info *sinfo)
0024 {
0025     struct public_key_signature *sig = sinfo->sig;
0026     struct crypto_shash *tfm;
0027     struct shash_desc *desc;
0028     size_t desc_size;
0029     int ret;
0030
0031     kenter(",%u,%s", sinfo->index, sinfo->sig->hash_algo);
0032
0033     /* The digest was calculated already. */
0034     if (sig->digest)
0035         return 0;
0036
0037     if (!sinfo->sig->hash_algo)
0038         return -ENOPKG;
0039
0040     /* Allocate the hashing algorithm we're going to need and find out how
0041      * big the hash operational data will be.
0042      */
0043     tfm = crypto_alloc_shash(sinfo->sig->hash_algo, 0, 0);
0044     if (IS_ERR(tfm))
0045         return (PTR_ERR(tfm) == -ENOENT) ? -ENOPKG : PTR_ERR(tfm);
0046
0047     desc_size = crypto_shash_descsize(tfm) + sizeof(*desc);
0048     sig->digest_size = crypto_shash_digestsize(tfm);
0049
0050     ret = -ENOMEM;
0051     sig->digest = kmalloc(sig->digest_size, GFP_KERNEL);
0052     if (!sig->digest)
0053         goto error_no_desc;
0054
0055     desc = kzalloc(desc_size, GFP_KERNEL);
0056     if (!desc)
0057         goto error_no_desc;
0058
0059     desc->tfm   = tfm;
0060
0061     /* Digest the message [RFC2315 9.3] */
0062     ret = crypto_shash_digest(desc, pkcs7->data, pkcs7->data_len,
0063                   sig->digest);
0064     if (ret < 0)
0065         goto error;
0066     pr_devel("MsgDigest = [%*ph]\n", 8, sig->digest);
0067
0068     /* However, if there are authenticated attributes, there must be a
0069      * message digest attribute amongst them which corresponds to the
0070      * digest we just calculated.
0071      */
0072     if (sinfo->authattrs) {
0073         u8 tag;
0074
0075         if (!sinfo->msgdigest) {
0076             pr_warn("Sig %u: No messageDigest\n", sinfo->index);
0077             ret = -EKEYREJECTED;
0078             goto error;
0079         }
0080
0081         if (sinfo->msgdigest_len != sig->digest_size) {
0082             pr_debug("Sig %u: Invalid digest size (%u)\n",
0083                  sinfo->index, sinfo->msgdigest_len);
0084             ret = -EBADMSG;
0085             goto error;
0086         }
0087
0088         if (memcmp(sig->digest, sinfo->msgdigest,
0089                sinfo->msgdigest_len) != 0) {
0090             pr_debug("Sig %u: Message digest doesn't match\n",
0091                  sinfo->index);
0092             ret = -EKEYREJECTED;
0093             goto error;
0094         }
0095
0096         /* We then calculate anew, using the authenticated attributes
0097          * as the contents of the digest instead.  Note that we need to
0098          * convert the attributes from a CONT.0 into a SET before we
0099          * hash it.
0100          */
0101         memset(sig->digest, 0, sig->digest_size);
0102
0103         ret = crypto_shash_init(desc);
0104         if (ret < 0)
0105             goto error;
0106         tag = ASN1_CONS_BIT | ASN1_SET;
0107         ret = crypto_shash_update(desc, &tag, 1);
0108         if (ret < 0)
0109             goto error;
0110         ret = crypto_shash_finup(desc, sinfo->authattrs,
0111                      sinfo->authattrs_len, sig->digest);
0112         if (ret < 0)
0113             goto error;
0114         pr_devel("AADigest = [%*ph]\n", 8, sig->digest);
0115     }
0116
0117 error:
0118     kfree(desc);
0119 error_no_desc:
0120     crypto_free_shash(tfm);
0121     kleave(" = %d", ret);
0122     return ret;
0123 }
0124
0125 int pkcs7_get_digest(struct pkcs7_message *pkcs7, const u8 **buf, u32 *len,
0126              enum hash_algo *hash_algo)
0127 {
0128     struct pkcs7_signed_info *sinfo = pkcs7->signed_infos;
0129     int i, ret;
0130
0131     /*
0132      * This function doesn't support messages with more than one signature.
0133      */
0134     if (sinfo == NULL || sinfo->next != NULL)
0135         return -EBADMSG;
0136
0137     ret = pkcs7_digest(pkcs7, sinfo);
0138     if (ret)
0139         return ret;
0140
0141     *buf = sinfo->sig->digest;
0142     *len = sinfo->sig->digest_size;
0143
0144     i = match_string(hash_algo_name, HASH_ALGO__LAST,
0145              sinfo->sig->hash_algo);
0146     if (i >= 0)
0147         *hash_algo = i;
0148
0149     return 0;
0150 }
0151
0152 /*
0153  * Find the key (X.509 certificate) to use to verify a PKCS#7 message.  PKCS#7
0154  * uses the issuer's name and the issuing certificate serial number for
0155  * matching purposes.  These must match the certificate issuer's name (not
0156  * subject's name) and the certificate serial number [RFC 2315 6.7].
0157  */
0158 static int pkcs7_find_key(struct pkcs7_message *pkcs7,
0159               struct pkcs7_signed_info *sinfo)
0160 {
0161     struct x509_certificate *x509;
0162     unsigned certix = 1;
0163
0164     kenter("%u", sinfo->index);
0165
0166     for (x509 = pkcs7->certs; x509; x509 = x509->next, certix++) {
0167         /* I'm _assuming_ that the generator of the PKCS#7 message will
0168          * encode the fields from the X.509 cert in the same way in the
0169          * PKCS#7 message - but I can't be 100% sure of that.  It's
0170          * possible this will need element-by-element comparison.
0171          */
0172         if (!asymmetric_key_id_same(x509->id, sinfo->sig->auth_ids[0]))
0173             continue;
0174         pr_devel("Sig %u: Found cert serial match X.509[%u]\n",
0175              sinfo->index, certix);
0176
0177         sinfo->signer = x509;
0178         return 0;
0179     }
0180
0181     /* The relevant X.509 cert isn't found here, but it might be found in
0182      * the trust keyring.
0183      */
0184     pr_debug("Sig %u: Issuing X.509 cert not found (#%*phN)\n",
0185          sinfo->index,
0186          sinfo->sig->auth_ids[0]->len, sinfo->sig->auth_ids[0]->data);
0187     return 0;
0188 }
0189
0190 /*
0191  * Verify the internal certificate chain as best we can.
0192  */
0193 static int pkcs7_verify_sig_chain(struct pkcs7_message *pkcs7,
0194                   struct pkcs7_signed_info *sinfo)
0195 {
0196     struct public_key_signature *sig;
0197     struct x509_certificate *x509 = sinfo->signer, *p;
0198     struct asymmetric_key_id *auth;
0199     int ret;
0200
0201     kenter("");
0202
0203     for (p = pkcs7->certs; p; p = p->next)
0204         p->seen = false;
0205
0206     for (;;) {
0207         pr_debug("verify %s: %*phN\n",
0208              x509->subject,
0209              x509->raw_serial_size, x509->raw_serial);
0210         x509->seen = true;
0211
0212         if (x509->blacklisted) {
0213             /* If this cert is blacklisted, then mark everything
0214              * that depends on this as blacklisted too.
0215              */
0216             sinfo->blacklisted = true;
0217             for (p = sinfo->signer; p != x509; p = p->signer)
0218                 p->blacklisted = true;
0219             pr_debug("- blacklisted\n");
0220             return 0;
0221         }
0222
0223         pr_debug("- issuer %s\n", x509->issuer);
0224         sig = x509->sig;
0225         if (sig->auth_ids[0])
0226             pr_debug("- authkeyid.id %*phN\n",
0227                  sig->auth_ids[0]->len, sig->auth_ids[0]->data);
0228         if (sig->auth_ids[1])
0229             pr_debug("- authkeyid.skid %*phN\n",
0230                  sig->auth_ids[1]->len, sig->auth_ids[1]->data);
0231
0232         if (x509->self_signed) {
0233             /* If there's no authority certificate specified, then
0234              * the certificate must be self-signed and is the root
0235              * of the chain.  Likewise if the cert is its own
0236              * authority.
0237              */
0238             if (x509->unsupported_sig)
0239                 goto unsupported_sig_in_x509;
0240             x509->signer = x509;
0241             pr_debug("- self-signed\n");
0242             return 0;
0243         }
0244
0245         /* Look through the X.509 certificates in the PKCS#7 message's
0246          * list to see if the next one is there.
0247          */
0248         auth = sig->auth_ids[0];
0249         if (auth) {
0250             pr_debug("- want %*phN\n", auth->len, auth->data);
0251             for (p = pkcs7->certs; p; p = p->next) {
0252                 pr_debug("- cmp [%u] %*phN\n",
0253                      p->index, p->id->len, p->id->data);
0254                 if (asymmetric_key_id_same(p->id, auth))
0255                     goto found_issuer_check_skid;
0256             }
0257         } else if (sig->auth_ids[1]) {
0258             auth = sig->auth_ids[1];
0259             pr_debug("- want %*phN\n", auth->len, auth->data);
0260             for (p = pkcs7->certs; p; p = p->next) {
0261                 if (!p->skid)
0262                     continue;
0263                 pr_debug("- cmp [%u] %*phN\n",
0264                      p->index, p->skid->len, p->skid->data);
0265                 if (asymmetric_key_id_same(p->skid, auth))
0266                     goto found_issuer;
0267             }
0268         }
0269
0270         /* We didn't find the root of this chain */
0271         pr_debug("- top\n");
0272         return 0;
0273
0274     found_issuer_check_skid:
0275         /* We matched issuer + serialNumber, but if there's an
0276          * authKeyId.keyId, that must match the CA subjKeyId also.
0277          */
0278         if (sig->auth_ids[1] &&
0279             !asymmetric_key_id_same(p->skid, sig->auth_ids[1])) {
0280             pr_warn("Sig %u: X.509 chain contains auth-skid nonmatch (%u->%u)\n",
0281                 sinfo->index, x509->index, p->index);
0282             return -EKEYREJECTED;
0283         }
0284     found_issuer:
0285         pr_debug("- subject %s\n", p->subject);
0286         if (p->seen) {
0287             pr_warn("Sig %u: X.509 chain contains loop\n",
0288                 sinfo->index);
0289             return 0;
0290         }
0291         ret = public_key_verify_signature(p->pub, x509->sig);
0292         if (ret < 0)
0293             return ret;
0294         x509->signer = p;
0295         if (x509 == p) {
0296             pr_debug("- self-signed\n");
0297             return 0;
0298         }
0299         x509 = p;
0300         might_sleep();
0301     }
0302
0303 unsupported_sig_in_x509:
0304     /* Just prune the certificate chain at this point if we lack some
0305      * crypto module to go further.  Note, however, we don't want to set
0306      * sinfo->unsupported_crypto as the signed info block may still be
0307      * validatable against an X.509 cert lower in the chain that we have a
0308      * trusted copy of.
0309      */
0310     return 0;
0311 }
0312
0313 /*
0314  * Verify one signed information block from a PKCS#7 message.
0315  */
0316 static int pkcs7_verify_one(struct pkcs7_message *pkcs7,
0317                 struct pkcs7_signed_info *sinfo)
0318 {
0319     int ret;
0320
0321     kenter(",%u", sinfo->index);
0322
0323     /* First of all, digest the data in the PKCS#7 message and the
0324      * signed information block
0325      */
0326     ret = pkcs7_digest(pkcs7, sinfo);
0327     if (ret < 0)
0328         return ret;
0329
0330     /* Find the key for the signature if there is one */
0331     ret = pkcs7_find_key(pkcs7, sinfo);
0332     if (ret < 0)
0333         return ret;
0334
0335     if (!sinfo->signer)
0336         return 0;
0337
0338     pr_devel("Using X.509[%u] for sig %u\n",
0339          sinfo->signer->index, sinfo->index);
0340
0341     /* Check that the PKCS#7 signing time is valid according to the X.509
0342      * certificate.  We can't, however, check against the system clock
0343      * since that may not have been set yet and may be wrong.
0344      */
0345     if (test_bit(sinfo_has_signing_time, &sinfo->aa_set)) {
0346         if (sinfo->signing_time < sinfo->signer->valid_from ||
0347             sinfo->signing_time > sinfo->signer->valid_to) {
0348             pr_warn("Message signed outside of X.509 validity window\n");
0349             return -EKEYREJECTED;
0350         }
0351     }
0352
0353     /* Verify the PKCS#7 binary against the key */
0354     ret = public_key_verify_signature(sinfo->signer->pub, sinfo->sig);
0355     if (ret < 0)
0356         return ret;
0357
0358     pr_devel("Verified signature %u\n", sinfo->index);
0359
0360     /* Verify the internal certificate chain */
0361     return pkcs7_verify_sig_chain(pkcs7, sinfo);
0362 }
0363
0364 /**
0365  * pkcs7_verify - Verify a PKCS#7 message
0366  * @pkcs7: The PKCS#7 message to be verified
0367  * @usage: The use to which the key is being put
0368  *
0369  * Verify a PKCS#7 message is internally consistent - that is, the data digest
0370  * matches the digest in the AuthAttrs and any signature in the message or one
0371  * of the X.509 certificates it carries that matches another X.509 cert in the
0372  * message can be verified.
0373  *
0374  * This does not look to match the contents of the PKCS#7 message against any
0375  * external public keys.
0376  *
0377  * Returns, in order of descending priority:
0378  *
0379  *  (*) -EKEYREJECTED if a key was selected that had a usage restriction at
0380  *      odds with the specified usage, or:
0381  *
0382  *  (*) -EKEYREJECTED if a signature failed to match for which we found an
0383  *  appropriate X.509 certificate, or:
0384  *
0385  *  (*) -EBADMSG if some part of the message was invalid, or:
0386  *
0387  *  (*) 0 if a signature chain passed verification, or:
0388  *
0389  *  (*) -EKEYREJECTED if a blacklisted key was encountered, or:
0390  *
0391  *  (*) -ENOPKG if none of the signature chains are verifiable because suitable
0392  *  crypto modules couldn't be found.
0393  */
0394 int pkcs7_verify(struct pkcs7_message *pkcs7,
0395          enum key_being_used_for usage)
0396 {
0397     struct pkcs7_signed_info *sinfo;
0398     int actual_ret = -ENOPKG;
0399     int ret;
0400
0401     kenter("");
0402
0403     switch (usage) {
0404     case VERIFYING_MODULE_SIGNATURE:
0405         if (pkcs7->data_type != OID_data) {
0406             pr_warn("Invalid module sig (not pkcs7-data)\n");
0407             return -EKEYREJECTED;
0408         }
0409         if (pkcs7->have_authattrs) {
0410             pr_warn("Invalid module sig (has authattrs)\n");
0411             return -EKEYREJECTED;
0412         }
0413         break;
0414     case VERIFYING_FIRMWARE_SIGNATURE:
0415         if (pkcs7->data_type != OID_data) {
0416             pr_warn("Invalid firmware sig (not pkcs7-data)\n");
0417             return -EKEYREJECTED;
0418         }
0419         if (!pkcs7->have_authattrs) {
0420             pr_warn("Invalid firmware sig (missing authattrs)\n");
0421             return -EKEYREJECTED;
0422         }
0423         break;
0424     case VERIFYING_KEXEC_PE_SIGNATURE:
0425         if (pkcs7->data_type != OID_msIndirectData) {
0426             pr_warn("Invalid kexec sig (not Authenticode)\n");
0427             return -EKEYREJECTED;
0428         }
0429         /* Authattr presence checked in parser */
0430         break;
0431     case VERIFYING_UNSPECIFIED_SIGNATURE:
0432         if (pkcs7->data_type != OID_data) {
0433             pr_warn("Invalid unspecified sig (not pkcs7-data)\n");
0434             return -EKEYREJECTED;
0435         }
0436         break;
0437     default:
0438         return -EINVAL;
0439     }
0440
0441     for (sinfo = pkcs7->signed_infos; sinfo; sinfo = sinfo->next) {
0442         ret = pkcs7_verify_one(pkcs7, sinfo);
0443         if (sinfo->blacklisted) {
0444             if (actual_ret == -ENOPKG)
0445                 actual_ret = -EKEYREJECTED;
0446             continue;
0447         }
0448         if (ret < 0) {
0449             if (ret == -ENOPKG) {
0450                 sinfo->unsupported_crypto = true;
0451                 continue;
0452             }
0453             kleave(" = %d", ret);
0454             return ret;
0455         }
0456         actual_ret = 0;
0457     }
0458
0459     kleave(" = %d", actual_ret);
0460     return actual_ret;
0461 }
0462 EXPORT_SYMBOL_GPL(pkcs7_verify);
0463
0464 /**
0465  * pkcs7_supply_detached_data - Supply the data needed to verify a PKCS#7 message
0466  * @pkcs7: The PKCS#7 message
0467  * @data: The data to be verified
0468  * @datalen: The amount of data
0469  *
0470  * Supply the detached data needed to verify a PKCS#7 message.  Note that no
0471  * attempt to retain/pin the data is made.  That is left to the caller.  The
0472  * data will not be modified by pkcs7_verify() and will not be freed when the
0473  * PKCS#7 message is freed.
0474  *
0475  * Returns -EINVAL if data is already supplied in the message, 0 otherwise.
0476  */
0477 int pkcs7_supply_detached_data(struct pkcs7_message *pkcs7,
0478                    const void *data, size_t datalen)
0479 {
0480     if (pkcs7->data) {
0481         pr_debug("Data already supplied\n");
0482         return -EINVAL;
0483     }
0484     pkcs7->data = data;
0485     pkcs7->data_len = datalen;
0486     return 0;
0487 }