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-rw-r--r--kernel/crypto/asymmetric_keys/pkcs7_trust.c200
1 files changed, 200 insertions, 0 deletions
diff --git a/kernel/crypto/asymmetric_keys/pkcs7_trust.c b/kernel/crypto/asymmetric_keys/pkcs7_trust.c
new file mode 100644
index 000000000..1d2937607
--- /dev/null
+++ b/kernel/crypto/asymmetric_keys/pkcs7_trust.c
@@ -0,0 +1,200 @@
+/* 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"
+
+/**
+ * Check the trust on one PKCS#7 SignedInfo block.
+ */
+static 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);
+
+ if (sinfo->unsupported_crypto) {
+ kleave(" = -ENOPKG [cached]");
+ return -ENOPKG;
+ }
+
+ 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 = x509_request_asymmetric_key(trust_keyring, x509->id,
+ false);
+ 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.
+ */
+ pr_devel("sinfo %u: Cert %u as key %x\n",
+ sinfo->index, x509->index, key_serial(key));
+ 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->authority) {
+ key = x509_request_asymmetric_key(trust_keyring, last->authority,
+ false);
+ if (!IS_ERR(key)) {
+ x509 = last;
+ pr_devel("sinfo %u: Root cert %u signer is key %x\n",
+ sinfo->index, x509->index, key_serial(key));
+ goto matched;
+ }
+ if (PTR_ERR(key) != -ENOKEY)
+ return PTR_ERR(key);
+ }
+
+ /* As a last resort, see if we have a trusted public key that matches
+ * the signed info directly.
+ */
+ key = x509_request_asymmetric_key(trust_keyring,
+ sinfo->signing_cert_id,
+ false);
+ if (!IS_ERR(key)) {
+ pr_devel("sinfo %u: Direct signer is key %x\n",
+ sinfo->index, key_serial(key));
+ x509 = NULL;
+ goto matched;
+ }
+ if (PTR_ERR(key) != -ENOKEY)
+ return PTR_ERR(key);
+
+ kleave(" = -ENOKEY [no backref]");
+ return -ENOKEY;
+
+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:
+ if (x509) {
+ 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 = -ENOKEY;
+ int 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);
+ switch (ret) {
+ case -ENOKEY:
+ continue;
+ case -ENOPKG:
+ if (cached_ret == -ENOKEY)
+ cached_ret = -ENOPKG;
+ continue;
+ case 0:
+ *_trusted |= sinfo->trusted;
+ cached_ret = 0;
+ continue;
+ default:
+ return ret;
+ }
+ }
+
+ return cached_ret;
+}
+EXPORT_SYMBOL_GPL(pkcs7_validate_trust);