PKCS#7: Find intersection between PKCS#7 message and known, trusted keys
Find the intersection between the X.509 certificate chain contained in a PKCS#7 message and a set of keys that we already know and trust. Signed-off-by: David Howells <dhowells@redhat.com> Acked-by: Vivek Goyal <vgoyal@redhat.com> Reviewed-by: Kees Cook <keescook@chromium.org>
This commit is contained in:
David Howells
parent
8c76d79393
commit
08815b62d7
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@ -33,6 +33,7 @@ obj-$(CONFIG_PKCS7_MESSAGE_PARSER) += pkcs7_message.o
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pkcs7_message-y := \
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pkcs7-asn1.o \
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pkcs7_parser.o \
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pkcs7_trust.o \
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pkcs7_verify.o
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$(obj)/pkcs7_parser.o: $(obj)/pkcs7-asn1.h
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@ -0,0 +1,219 @@
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/* 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 "public_key.h"
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#include "pkcs7_parser.h"
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/*
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* Request an asymmetric key.
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*/
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static struct key *pkcs7_request_asymmetric_key(
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struct key *keyring,
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const char *signer, size_t signer_len,
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const char *authority, size_t auth_len)
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{
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key_ref_t key;
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char *id;
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kenter(",%zu,,%zu", signer_len, auth_len);
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/* Construct an identifier. */
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id = kmalloc(signer_len + 2 + auth_len + 1, GFP_KERNEL);
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if (!id)
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return ERR_PTR(-ENOMEM);
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memcpy(id, signer, signer_len);
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id[signer_len + 0] = ':';
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id[signer_len + 1] = ' ';
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memcpy(id + signer_len + 2, authority, auth_len);
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id[signer_len + 2 + auth_len] = 0;
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pr_debug("Look up: \"%s\"\n", id);
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key = keyring_search(make_key_ref(keyring, 1),
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&key_type_asymmetric, id);
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if (IS_ERR(key))
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pr_debug("Request for module key '%s' err %ld\n",
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id, PTR_ERR(key));
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kfree(id);
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if (IS_ERR(key)) {
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switch (PTR_ERR(key)) {
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/* Hide some search errors */
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case -EACCES:
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case -ENOTDIR:
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case -EAGAIN:
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return ERR_PTR(-ENOKEY);
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default:
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return ERR_CAST(key);
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}
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}
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pr_devel("<==%s() = 0 [%x]\n", __func__, key_serial(key_ref_to_ptr(key)));
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return key_ref_to_ptr(key);
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}
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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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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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bool trusted;
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int ret;
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kenter(",%u,", sinfo->index);
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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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trusted = x509->trusted;
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goto verified;
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}
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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 = pkcs7_request_asymmetric_key(
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trust_keyring,
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x509->subject, strlen(x509->subject),
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x509->fingerprint, strlen(x509->fingerprint));
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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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goto matched;
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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->next == 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->issuer || !last->authority) {
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kleave(" = -ENOKEY [no backref]");
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return -ENOKEY;
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}
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key = pkcs7_request_asymmetric_key(
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trust_keyring,
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last->issuer, strlen(last->issuer),
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last->authority, strlen(last->authority));
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if (IS_ERR(key))
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return PTR_ERR(key) == -ENOMEM ? -ENOMEM : -ENOKEY;
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x509 = last;
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matched:
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ret = verify_signature(key, sig);
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trusted = test_bit(KEY_FLAG_TRUSTED, &key->flags);
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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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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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p->trusted = trusted;
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}
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sinfo->trusted = trusted;
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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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* @_trusted: Set to true if trustworth, false otherwise
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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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bool *_trusted)
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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 = 0, 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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if (ret < 0) {
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if (ret == -ENOPKG) {
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cached_ret = -ENOPKG;
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} else if (ret == -ENOKEY) {
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if (cached_ret == 0)
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cached_ret = -ENOKEY;
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} else {
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return ret;
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}
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}
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*_trusted |= sinfo->trusted;
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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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@ -9,6 +9,7 @@
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* 2 of the Licence, or (at your option) any later version.
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*/
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struct key;
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struct pkcs7_message;
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/*
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@ -22,6 +23,13 @@ extern int pkcs7_get_content_data(const struct pkcs7_message *pkcs7,
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const void **_data, size_t *_datalen,
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bool want_wrapper);
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/*
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* pkcs7_trust.c
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*/
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extern int pkcs7_validate_trust(struct pkcs7_message *pkcs7,
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struct key *trust_keyring,
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bool *_trusted);
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/*
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* pkcs7_verify.c
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*/
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