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![Eric Biggers](/assets/img/avatar_default.png)
If none of the certificates in a SignerInfo's certificate chain match a
trusted key, nor is the last certificate signed by a trusted key, then
pkcs7_validate_trust_one() tries to check whether the SignerInfo's
signature was made directly by a trusted key. But, it actually fails to
set the 'sig' variable correctly, so it actually verifies the last
signature seen. That will only be the SignerInfo's signature if the
certificate chain is empty; otherwise it will actually be the last
certificate's signature.
This is not by itself a security problem, since verifying any of the
certificates in the chain should be sufficient to verify the SignerInfo.
Still, it's not working as intended so it should be fixed.
Fix it by setting 'sig' correctly for the direct verification case.
Fixes: 757932e6da
("PKCS#7: Handle PKCS#7 messages that contain no X.509 certs")
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: David Howells <dhowells@redhat.com>
192 lines
4.8 KiB
C
192 lines
4.8 KiB
C
/* Validate the trust chain of 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 (dhowells@redhat.com)
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public Licence
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* as published by the Free Software Foundation; either version
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* 2 of the Licence, or (at your option) any later version.
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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 <linux/key.h>
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#include <keys/asymmetric-type.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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* Check the trust on one PKCS#7 SignedInfo block.
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*/
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static int pkcs7_validate_trust_one(struct pkcs7_message *pkcs7,
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struct pkcs7_signed_info *sinfo,
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struct key *trust_keyring)
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{
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struct public_key_signature *sig = sinfo->sig;
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struct x509_certificate *x509, *last = NULL, *p;
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struct key *key;
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int ret;
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kenter(",%u,", sinfo->index);
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if (sinfo->unsupported_crypto) {
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kleave(" = -ENOPKG [cached]");
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return -ENOPKG;
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}
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for (x509 = sinfo->signer; x509; x509 = x509->signer) {
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if (x509->seen) {
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if (x509->verified)
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goto verified;
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kleave(" = -ENOKEY [cached]");
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return -ENOKEY;
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}
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x509->seen = true;
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/* Look to see if this certificate is present in the trusted
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* keys.
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*/
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key = find_asymmetric_key(trust_keyring,
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x509->id, x509->skid, false);
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if (!IS_ERR(key)) {
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/* One of the X.509 certificates in the PKCS#7 message
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* is apparently the same as one we already trust.
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* Verify that the trusted variant can also validate
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* the signature on the descendant.
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*/
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pr_devel("sinfo %u: Cert %u as key %x\n",
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sinfo->index, x509->index, key_serial(key));
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goto matched;
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}
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if (key == ERR_PTR(-ENOMEM))
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return -ENOMEM;
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/* Self-signed certificates form roots of their own, and if we
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* don't know them, then we can't accept them.
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*/
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if (x509->signer == x509) {
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kleave(" = -ENOKEY [unknown self-signed]");
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return -ENOKEY;
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}
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might_sleep();
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last = x509;
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sig = last->sig;
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}
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/* No match - see if the root certificate has a signer amongst the
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* trusted keys.
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*/
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if (last && (last->sig->auth_ids[0] || last->sig->auth_ids[1])) {
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key = find_asymmetric_key(trust_keyring,
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last->sig->auth_ids[0],
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last->sig->auth_ids[1],
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false);
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if (!IS_ERR(key)) {
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x509 = last;
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pr_devel("sinfo %u: Root cert %u signer is key %x\n",
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sinfo->index, x509->index, key_serial(key));
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goto matched;
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}
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if (PTR_ERR(key) != -ENOKEY)
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return PTR_ERR(key);
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}
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/* As a last resort, see if we have a trusted public key that matches
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* the signed info directly.
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*/
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key = find_asymmetric_key(trust_keyring,
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sinfo->sig->auth_ids[0], NULL, false);
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if (!IS_ERR(key)) {
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pr_devel("sinfo %u: Direct signer is key %x\n",
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sinfo->index, key_serial(key));
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x509 = NULL;
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sig = sinfo->sig;
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goto matched;
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}
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if (PTR_ERR(key) != -ENOKEY)
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return PTR_ERR(key);
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kleave(" = -ENOKEY [no backref]");
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return -ENOKEY;
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matched:
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ret = verify_signature(key, sig);
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key_put(key);
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if (ret < 0) {
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if (ret == -ENOMEM)
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return ret;
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kleave(" = -EKEYREJECTED [verify %d]", ret);
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return -EKEYREJECTED;
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}
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verified:
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if (x509) {
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x509->verified = true;
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for (p = sinfo->signer; p != x509; p = p->signer)
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p->verified = true;
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}
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kleave(" = 0");
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return 0;
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}
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/**
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* pkcs7_validate_trust - Validate PKCS#7 trust chain
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* @pkcs7: The PKCS#7 certificate to validate
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* @trust_keyring: Signing certificates to use as starting points
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*
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* Validate that the certificate chain inside the PKCS#7 message intersects
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* keys we already know and trust.
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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 signature failed to match for which we have a valid
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* key, or:
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*
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* (*) 0 if at least one signature chain intersects with the keys in the trust
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* keyring, or:
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*
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* (*) -ENOPKG if a suitable crypto module couldn't be found for a check on a
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* chain.
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*
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* (*) -ENOKEY if we couldn't find a match for any of the signature chains in
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* the message.
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*
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* May also return -ENOMEM.
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*/
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int pkcs7_validate_trust(struct pkcs7_message *pkcs7,
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struct key *trust_keyring)
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{
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struct pkcs7_signed_info *sinfo;
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struct x509_certificate *p;
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int cached_ret = -ENOKEY;
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int ret;
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for (p = pkcs7->certs; p; p = p->next)
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p->seen = false;
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for (sinfo = pkcs7->signed_infos; sinfo; sinfo = sinfo->next) {
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ret = pkcs7_validate_trust_one(pkcs7, sinfo, trust_keyring);
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switch (ret) {
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case -ENOKEY:
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continue;
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case -ENOPKG:
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if (cached_ret == -ENOKEY)
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cached_ret = -ENOPKG;
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continue;
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case 0:
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cached_ret = 0;
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continue;
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default:
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return ret;
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}
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}
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return cached_ret;
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}
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EXPORT_SYMBOL_GPL(pkcs7_validate_trust);
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