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487 lines
13 KiB
487 lines
13 KiB
// SPDX-License-Identifier: GPL-2.0-or-later |
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/* Verify the signature on a PKCS#7 message. |
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* |
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* Copyright (C) 2012 Red Hat, Inc. All Rights Reserved. |
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* Written by David Howells ([email protected]) |
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*/ |
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|
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#define pr_fmt(fmt) "PKCS7: "fmt |
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#include <linux/kernel.h> |
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#include <linux/export.h> |
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#include <linux/slab.h> |
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#include <linux/err.h> |
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#include <linux/asn1.h> |
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#include <crypto/hash.h> |
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#include <crypto/hash_info.h> |
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#include <crypto/public_key.h> |
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#include "pkcs7_parser.h" |
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|
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/* |
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* Digest the relevant parts of the PKCS#7 data |
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*/ |
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static int pkcs7_digest(struct pkcs7_message *pkcs7, |
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struct pkcs7_signed_info *sinfo) |
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{ |
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struct public_key_signature *sig = sinfo->sig; |
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struct crypto_shash *tfm; |
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struct shash_desc *desc; |
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size_t desc_size; |
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int ret; |
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kenter(",%u,%s", sinfo->index, sinfo->sig->hash_algo); |
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/* The digest was calculated already. */ |
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if (sig->digest) |
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return 0; |
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if (!sinfo->sig->hash_algo) |
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return -ENOPKG; |
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/* Allocate the hashing algorithm we're going to need and find out how |
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* big the hash operational data will be. |
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*/ |
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tfm = crypto_alloc_shash(sinfo->sig->hash_algo, 0, 0); |
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if (IS_ERR(tfm)) |
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return (PTR_ERR(tfm) == -ENOENT) ? -ENOPKG : PTR_ERR(tfm); |
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desc_size = crypto_shash_descsize(tfm) + sizeof(*desc); |
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sig->digest_size = crypto_shash_digestsize(tfm); |
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ret = -ENOMEM; |
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sig->digest = kmalloc(sig->digest_size, GFP_KERNEL); |
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if (!sig->digest) |
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goto error_no_desc; |
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desc = kzalloc(desc_size, GFP_KERNEL); |
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if (!desc) |
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goto error_no_desc; |
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desc->tfm = tfm; |
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/* Digest the message [RFC2315 9.3] */ |
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ret = crypto_shash_digest(desc, pkcs7->data, pkcs7->data_len, |
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sig->digest); |
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if (ret < 0) |
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goto error; |
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pr_devel("MsgDigest = [%*ph]\n", 8, sig->digest); |
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|
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/* However, if there are authenticated attributes, there must be a |
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* message digest attribute amongst them which corresponds to the |
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* digest we just calculated. |
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*/ |
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if (sinfo->authattrs) { |
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u8 tag; |
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if (!sinfo->msgdigest) { |
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pr_warn("Sig %u: No messageDigest\n", sinfo->index); |
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ret = -EKEYREJECTED; |
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goto error; |
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} |
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if (sinfo->msgdigest_len != sig->digest_size) { |
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pr_debug("Sig %u: Invalid digest size (%u)\n", |
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sinfo->index, sinfo->msgdigest_len); |
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ret = -EBADMSG; |
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goto error; |
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} |
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if (memcmp(sig->digest, sinfo->msgdigest, |
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sinfo->msgdigest_len) != 0) { |
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pr_debug("Sig %u: Message digest doesn't match\n", |
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sinfo->index); |
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ret = -EKEYREJECTED; |
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goto error; |
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} |
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|
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/* We then calculate anew, using the authenticated attributes |
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* as the contents of the digest instead. Note that we need to |
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* convert the attributes from a CONT.0 into a SET before we |
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* hash it. |
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*/ |
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memset(sig->digest, 0, sig->digest_size); |
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ret = crypto_shash_init(desc); |
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if (ret < 0) |
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goto error; |
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tag = ASN1_CONS_BIT | ASN1_SET; |
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ret = crypto_shash_update(desc, &tag, 1); |
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if (ret < 0) |
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goto error; |
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ret = crypto_shash_finup(desc, sinfo->authattrs, |
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sinfo->authattrs_len, sig->digest); |
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if (ret < 0) |
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goto error; |
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pr_devel("AADigest = [%*ph]\n", 8, sig->digest); |
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} |
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error: |
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kfree(desc); |
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error_no_desc: |
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crypto_free_shash(tfm); |
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kleave(" = %d", ret); |
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return ret; |
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} |
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int pkcs7_get_digest(struct pkcs7_message *pkcs7, const u8 **buf, u32 *len, |
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enum hash_algo *hash_algo) |
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{ |
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struct pkcs7_signed_info *sinfo = pkcs7->signed_infos; |
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int i, ret; |
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/* |
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* This function doesn't support messages with more than one signature. |
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*/ |
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if (sinfo == NULL || sinfo->next != NULL) |
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return -EBADMSG; |
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ret = pkcs7_digest(pkcs7, sinfo); |
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if (ret) |
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return ret; |
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*buf = sinfo->sig->digest; |
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*len = sinfo->sig->digest_size; |
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i = match_string(hash_algo_name, HASH_ALGO__LAST, |
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sinfo->sig->hash_algo); |
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if (i >= 0) |
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*hash_algo = i; |
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return 0; |
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} |
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/* |
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* Find the key (X.509 certificate) to use to verify a PKCS#7 message. PKCS#7 |
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* uses the issuer's name and the issuing certificate serial number for |
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* matching purposes. These must match the certificate issuer's name (not |
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* subject's name) and the certificate serial number [RFC 2315 6.7]. |
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*/ |
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static int pkcs7_find_key(struct pkcs7_message *pkcs7, |
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struct pkcs7_signed_info *sinfo) |
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{ |
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struct x509_certificate *x509; |
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unsigned certix = 1; |
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kenter("%u", sinfo->index); |
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for (x509 = pkcs7->certs; x509; x509 = x509->next, certix++) { |
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/* I'm _assuming_ that the generator of the PKCS#7 message will |
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* encode the fields from the X.509 cert in the same way in the |
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* PKCS#7 message - but I can't be 100% sure of that. It's |
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* possible this will need element-by-element comparison. |
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*/ |
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if (!asymmetric_key_id_same(x509->id, sinfo->sig->auth_ids[0])) |
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continue; |
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pr_devel("Sig %u: Found cert serial match X.509[%u]\n", |
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sinfo->index, certix); |
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sinfo->signer = x509; |
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return 0; |
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} |
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/* The relevant X.509 cert isn't found here, but it might be found in |
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* the trust keyring. |
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*/ |
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pr_debug("Sig %u: Issuing X.509 cert not found (#%*phN)\n", |
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sinfo->index, |
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sinfo->sig->auth_ids[0]->len, sinfo->sig->auth_ids[0]->data); |
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return 0; |
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} |
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/* |
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* Verify the internal certificate chain as best we can. |
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*/ |
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static int pkcs7_verify_sig_chain(struct pkcs7_message *pkcs7, |
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struct pkcs7_signed_info *sinfo) |
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{ |
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struct public_key_signature *sig; |
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struct x509_certificate *x509 = sinfo->signer, *p; |
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struct asymmetric_key_id *auth; |
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int ret; |
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kenter(""); |
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for (p = pkcs7->certs; p; p = p->next) |
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p->seen = false; |
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for (;;) { |
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pr_debug("verify %s: %*phN\n", |
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x509->subject, |
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x509->raw_serial_size, x509->raw_serial); |
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x509->seen = true; |
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if (x509->blacklisted) { |
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/* If this cert is blacklisted, then mark everything |
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* that depends on this as blacklisted too. |
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*/ |
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sinfo->blacklisted = true; |
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for (p = sinfo->signer; p != x509; p = p->signer) |
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p->blacklisted = true; |
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pr_debug("- blacklisted\n"); |
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return 0; |
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} |
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pr_debug("- issuer %s\n", x509->issuer); |
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sig = x509->sig; |
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if (sig->auth_ids[0]) |
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pr_debug("- authkeyid.id %*phN\n", |
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sig->auth_ids[0]->len, sig->auth_ids[0]->data); |
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if (sig->auth_ids[1]) |
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pr_debug("- authkeyid.skid %*phN\n", |
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sig->auth_ids[1]->len, sig->auth_ids[1]->data); |
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if (x509->self_signed) { |
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/* If there's no authority certificate specified, then |
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* the certificate must be self-signed and is the root |
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* of the chain. Likewise if the cert is its own |
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* authority. |
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*/ |
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if (x509->unsupported_sig) |
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goto unsupported_sig_in_x509; |
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x509->signer = x509; |
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pr_debug("- self-signed\n"); |
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return 0; |
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} |
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/* Look through the X.509 certificates in the PKCS#7 message's |
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* list to see if the next one is there. |
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*/ |
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auth = sig->auth_ids[0]; |
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if (auth) { |
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pr_debug("- want %*phN\n", auth->len, auth->data); |
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for (p = pkcs7->certs; p; p = p->next) { |
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pr_debug("- cmp [%u] %*phN\n", |
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p->index, p->id->len, p->id->data); |
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if (asymmetric_key_id_same(p->id, auth)) |
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goto found_issuer_check_skid; |
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} |
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} else if (sig->auth_ids[1]) { |
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auth = sig->auth_ids[1]; |
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pr_debug("- want %*phN\n", auth->len, auth->data); |
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for (p = pkcs7->certs; p; p = p->next) { |
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if (!p->skid) |
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continue; |
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pr_debug("- cmp [%u] %*phN\n", |
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p->index, p->skid->len, p->skid->data); |
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if (asymmetric_key_id_same(p->skid, auth)) |
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goto found_issuer; |
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} |
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} |
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/* We didn't find the root of this chain */ |
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pr_debug("- top\n"); |
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return 0; |
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found_issuer_check_skid: |
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/* We matched issuer + serialNumber, but if there's an |
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* authKeyId.keyId, that must match the CA subjKeyId also. |
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*/ |
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if (sig->auth_ids[1] && |
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!asymmetric_key_id_same(p->skid, sig->auth_ids[1])) { |
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pr_warn("Sig %u: X.509 chain contains auth-skid nonmatch (%u->%u)\n", |
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sinfo->index, x509->index, p->index); |
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return -EKEYREJECTED; |
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} |
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found_issuer: |
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pr_debug("- subject %s\n", p->subject); |
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if (p->seen) { |
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pr_warn("Sig %u: X.509 chain contains loop\n", |
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sinfo->index); |
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return 0; |
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} |
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ret = public_key_verify_signature(p->pub, x509->sig); |
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if (ret < 0) |
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return ret; |
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x509->signer = p; |
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if (x509 == p) { |
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pr_debug("- self-signed\n"); |
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return 0; |
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} |
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x509 = p; |
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might_sleep(); |
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} |
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unsupported_sig_in_x509: |
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/* Just prune the certificate chain at this point if we lack some |
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* crypto module to go further. Note, however, we don't want to set |
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* sinfo->unsupported_crypto as the signed info block may still be |
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* validatable against an X.509 cert lower in the chain that we have a |
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* trusted copy of. |
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*/ |
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return 0; |
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} |
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/* |
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* Verify one signed information block from a PKCS#7 message. |
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*/ |
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static int pkcs7_verify_one(struct pkcs7_message *pkcs7, |
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struct pkcs7_signed_info *sinfo) |
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{ |
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int ret; |
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kenter(",%u", sinfo->index); |
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/* First of all, digest the data in the PKCS#7 message and the |
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* signed information block |
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*/ |
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ret = pkcs7_digest(pkcs7, sinfo); |
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if (ret < 0) |
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return ret; |
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/* Find the key for the signature if there is one */ |
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ret = pkcs7_find_key(pkcs7, sinfo); |
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if (ret < 0) |
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return ret; |
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if (!sinfo->signer) |
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return 0; |
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pr_devel("Using X.509[%u] for sig %u\n", |
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sinfo->signer->index, sinfo->index); |
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|
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/* Check that the PKCS#7 signing time is valid according to the X.509 |
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* certificate. We can't, however, check against the system clock |
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* since that may not have been set yet and may be wrong. |
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*/ |
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if (test_bit(sinfo_has_signing_time, &sinfo->aa_set)) { |
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if (sinfo->signing_time < sinfo->signer->valid_from || |
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sinfo->signing_time > sinfo->signer->valid_to) { |
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pr_warn("Message signed outside of X.509 validity window\n"); |
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return -EKEYREJECTED; |
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} |
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} |
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/* Verify the PKCS#7 binary against the key */ |
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ret = public_key_verify_signature(sinfo->signer->pub, sinfo->sig); |
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if (ret < 0) |
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return ret; |
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pr_devel("Verified signature %u\n", sinfo->index); |
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/* Verify the internal certificate chain */ |
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return pkcs7_verify_sig_chain(pkcs7, sinfo); |
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} |
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/** |
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* pkcs7_verify - Verify a PKCS#7 message |
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* @pkcs7: The PKCS#7 message to be verified |
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* @usage: The use to which the key is being put |
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* |
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* Verify a PKCS#7 message is internally consistent - that is, the data digest |
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* matches the digest in the AuthAttrs and any signature in the message or one |
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* of the X.509 certificates it carries that matches another X.509 cert in the |
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* message can be verified. |
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* |
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* This does not look to match the contents of the PKCS#7 message against any |
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* external public keys. |
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* |
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* Returns, in order of descending priority: |
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* |
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* (*) -EKEYREJECTED if a key was selected that had a usage restriction at |
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* odds with the specified usage, or: |
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* |
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* (*) -EKEYREJECTED if a signature failed to match for which we found an |
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* appropriate X.509 certificate, or: |
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* |
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* (*) -EBADMSG if some part of the message was invalid, or: |
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* |
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* (*) 0 if a signature chain passed verification, or: |
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* |
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* (*) -EKEYREJECTED if a blacklisted key was encountered, or: |
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* |
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* (*) -ENOPKG if none of the signature chains are verifiable because suitable |
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* crypto modules couldn't be found. |
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*/ |
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int pkcs7_verify(struct pkcs7_message *pkcs7, |
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enum key_being_used_for usage) |
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{ |
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struct pkcs7_signed_info *sinfo; |
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int actual_ret = -ENOPKG; |
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int ret; |
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kenter(""); |
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switch (usage) { |
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case VERIFYING_MODULE_SIGNATURE: |
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if (pkcs7->data_type != OID_data) { |
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pr_warn("Invalid module sig (not pkcs7-data)\n"); |
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return -EKEYREJECTED; |
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} |
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if (pkcs7->have_authattrs) { |
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pr_warn("Invalid module sig (has authattrs)\n"); |
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return -EKEYREJECTED; |
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} |
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break; |
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case VERIFYING_FIRMWARE_SIGNATURE: |
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if (pkcs7->data_type != OID_data) { |
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pr_warn("Invalid firmware sig (not pkcs7-data)\n"); |
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return -EKEYREJECTED; |
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} |
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if (!pkcs7->have_authattrs) { |
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pr_warn("Invalid firmware sig (missing authattrs)\n"); |
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return -EKEYREJECTED; |
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} |
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break; |
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case VERIFYING_KEXEC_PE_SIGNATURE: |
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if (pkcs7->data_type != OID_msIndirectData) { |
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pr_warn("Invalid kexec sig (not Authenticode)\n"); |
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return -EKEYREJECTED; |
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} |
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/* Authattr presence checked in parser */ |
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break; |
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case VERIFYING_UNSPECIFIED_SIGNATURE: |
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if (pkcs7->data_type != OID_data) { |
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pr_warn("Invalid unspecified sig (not pkcs7-data)\n"); |
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return -EKEYREJECTED; |
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} |
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break; |
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default: |
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return -EINVAL; |
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} |
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for (sinfo = pkcs7->signed_infos; sinfo; sinfo = sinfo->next) { |
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ret = pkcs7_verify_one(pkcs7, sinfo); |
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if (sinfo->blacklisted) { |
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if (actual_ret == -ENOPKG) |
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actual_ret = -EKEYREJECTED; |
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continue; |
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} |
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if (ret < 0) { |
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if (ret == -ENOPKG) { |
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sinfo->unsupported_crypto = true; |
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continue; |
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} |
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kleave(" = %d", ret); |
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return ret; |
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} |
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actual_ret = 0; |
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} |
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kleave(" = %d", actual_ret); |
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return actual_ret; |
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} |
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EXPORT_SYMBOL_GPL(pkcs7_verify); |
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/** |
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* pkcs7_supply_detached_data - Supply the data needed to verify a PKCS#7 message |
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* @pkcs7: The PKCS#7 message |
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* @data: The data to be verified |
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* @datalen: The amount of data |
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* |
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* Supply the detached data needed to verify a PKCS#7 message. Note that no |
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* attempt to retain/pin the data is made. That is left to the caller. The |
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* data will not be modified by pkcs7_verify() and will not be freed when the |
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* PKCS#7 message is freed. |
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* |
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* Returns -EINVAL if data is already supplied in the message, 0 otherwise. |
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*/ |
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int pkcs7_supply_detached_data(struct pkcs7_message *pkcs7, |
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const void *data, size_t datalen) |
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{ |
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if (pkcs7->data) { |
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pr_debug("Data already supplied\n"); |
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return -EINVAL; |
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} |
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pkcs7->data = data; |
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pkcs7->data_len = datalen; |
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return 0; |
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}
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