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 2014-07-01 16:40:20 +01:00
parent 8c76d79393
commit 08815b62d7
3 changed files with 228 additions and 0 deletions

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@ -33,6 +33,7 @@ obj-$(CONFIG_PKCS7_MESSAGE_PARSER) += pkcs7_message.o
pkcs7_message-y := \
pkcs7-asn1.o \
pkcs7_parser.o \
pkcs7_trust.o \
pkcs7_verify.o
$(obj)/pkcs7_parser.o: $(obj)/pkcs7-asn1.h

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@ -0,0 +1,219 @@
/* Validate the trust chain of a PKCS#7 message.
*
* Copyright (C) 2012 Red Hat, Inc. All Rights Reserved.
* Written by David Howells (dhowells@redhat.com)
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public Licence
* as published by the Free Software Foundation; either version
* 2 of the Licence, or (at your option) any later version.
*/
#define pr_fmt(fmt) "PKCS7: "fmt
#include <linux/kernel.h>
#include <linux/export.h>
#include <linux/slab.h>
#include <linux/err.h>
#include <linux/asn1.h>
#include <linux/key.h>
#include <keys/asymmetric-type.h>
#include "public_key.h"
#include "pkcs7_parser.h"
/*
* Request an asymmetric key.
*/
static struct key *pkcs7_request_asymmetric_key(
struct key *keyring,
const char *signer, size_t signer_len,
const char *authority, size_t auth_len)
{
key_ref_t key;
char *id;
kenter(",%zu,,%zu", signer_len, auth_len);
/* Construct an identifier. */
id = kmalloc(signer_len + 2 + auth_len + 1, GFP_KERNEL);
if (!id)
return ERR_PTR(-ENOMEM);
memcpy(id, signer, signer_len);
id[signer_len + 0] = ':';
id[signer_len + 1] = ' ';
memcpy(id + signer_len + 2, authority, auth_len);
id[signer_len + 2 + auth_len] = 0;
pr_debug("Look up: \"%s\"\n", id);
key = keyring_search(make_key_ref(keyring, 1),
&key_type_asymmetric, id);
if (IS_ERR(key))
pr_debug("Request for module key '%s' err %ld\n",
id, PTR_ERR(key));
kfree(id);
if (IS_ERR(key)) {
switch (PTR_ERR(key)) {
/* Hide some search errors */
case -EACCES:
case -ENOTDIR:
case -EAGAIN:
return ERR_PTR(-ENOKEY);
default:
return ERR_CAST(key);
}
}
pr_devel("<==%s() = 0 [%x]\n", __func__, key_serial(key_ref_to_ptr(key)));
return key_ref_to_ptr(key);
}
/**
* Check the trust on one PKCS#7 SignedInfo block.
*/
int pkcs7_validate_trust_one(struct pkcs7_message *pkcs7,
struct pkcs7_signed_info *sinfo,
struct key *trust_keyring)
{
struct public_key_signature *sig = &sinfo->sig;
struct x509_certificate *x509, *last = NULL, *p;
struct key *key;
bool trusted;
int ret;
kenter(",%u,", sinfo->index);
for (x509 = sinfo->signer; x509; x509 = x509->signer) {
if (x509->seen) {
if (x509->verified) {
trusted = x509->trusted;
goto verified;
}
kleave(" = -ENOKEY [cached]");
return -ENOKEY;
}
x509->seen = true;
/* Look to see if this certificate is present in the trusted
* keys.
*/
key = pkcs7_request_asymmetric_key(
trust_keyring,
x509->subject, strlen(x509->subject),
x509->fingerprint, strlen(x509->fingerprint));
if (!IS_ERR(key))
/* One of the X.509 certificates in the PKCS#7 message
* is apparently the same as one we already trust.
* Verify that the trusted variant can also validate
* the signature on the descendant.
*/
goto matched;
if (key == ERR_PTR(-ENOMEM))
return -ENOMEM;
/* Self-signed certificates form roots of their own, and if we
* don't know them, then we can't accept them.
*/
if (x509->next == x509) {
kleave(" = -ENOKEY [unknown self-signed]");
return -ENOKEY;
}
might_sleep();
last = x509;
sig = &last->sig;
}
/* No match - see if the root certificate has a signer amongst the
* trusted keys.
*/
if (!last || !last->issuer || !last->authority) {
kleave(" = -ENOKEY [no backref]");
return -ENOKEY;
}
key = pkcs7_request_asymmetric_key(
trust_keyring,
last->issuer, strlen(last->issuer),
last->authority, strlen(last->authority));
if (IS_ERR(key))
return PTR_ERR(key) == -ENOMEM ? -ENOMEM : -ENOKEY;
x509 = last;
matched:
ret = verify_signature(key, sig);
trusted = test_bit(KEY_FLAG_TRUSTED, &key->flags);
key_put(key);
if (ret < 0) {
if (ret == -ENOMEM)
return ret;
kleave(" = -EKEYREJECTED [verify %d]", ret);
return -EKEYREJECTED;
}
verified:
x509->verified = true;
for (p = sinfo->signer; p != x509; p = p->signer) {
p->verified = true;
p->trusted = trusted;
}
sinfo->trusted = trusted;
kleave(" = 0");
return 0;
}
/**
* pkcs7_validate_trust - Validate PKCS#7 trust chain
* @pkcs7: The PKCS#7 certificate to validate
* @trust_keyring: Signing certificates to use as starting points
* @_trusted: Set to true if trustworth, false otherwise
*
* Validate that the certificate chain inside the PKCS#7 message intersects
* keys we already know and trust.
*
* Returns, in order of descending priority:
*
* (*) -EKEYREJECTED if a signature failed to match for which we have a valid
* key, or:
*
* (*) 0 if at least one signature chain intersects with the keys in the trust
* keyring, or:
*
* (*) -ENOPKG if a suitable crypto module couldn't be found for a check on a
* chain.
*
* (*) -ENOKEY if we couldn't find a match for any of the signature chains in
* the message.
*
* May also return -ENOMEM.
*/
int pkcs7_validate_trust(struct pkcs7_message *pkcs7,
struct key *trust_keyring,
bool *_trusted)
{
struct pkcs7_signed_info *sinfo;
struct x509_certificate *p;
int cached_ret = 0, ret;
for (p = pkcs7->certs; p; p = p->next)
p->seen = false;
for (sinfo = pkcs7->signed_infos; sinfo; sinfo = sinfo->next) {
ret = pkcs7_validate_trust_one(pkcs7, sinfo, trust_keyring);
if (ret < 0) {
if (ret == -ENOPKG) {
cached_ret = -ENOPKG;
} else if (ret == -ENOKEY) {
if (cached_ret == 0)
cached_ret = -ENOKEY;
} else {
return ret;
}
}
*_trusted |= sinfo->trusted;
}
return cached_ret;
}
EXPORT_SYMBOL_GPL(pkcs7_validate_trust);

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@ -9,6 +9,7 @@
* 2 of the Licence, or (at your option) any later version.
*/
struct key;
struct pkcs7_message;
/*
@ -22,6 +23,13 @@ extern int pkcs7_get_content_data(const struct pkcs7_message *pkcs7,
const void **_data, size_t *_datalen,
bool want_wrapper);
/*
* pkcs7_trust.c
*/
extern int pkcs7_validate_trust(struct pkcs7_message *pkcs7,
struct key *trust_keyring,
bool *_trusted);
/*
* pkcs7_verify.c
*/