KEYS: verify a certificate is signed by a 'trusted' key

Only public keys, with certificates signed by an existing
'trusted' key on the system trusted keyring, should be added
to a trusted keyring.  This patch adds support for verifying
a certificate's signature.

This is derived from David Howells pkcs7_request_asymmetric_key() patch.

Changelog v6:
- on error free key - Dmitry
- validate trust only for not already trusted keys - Dmitry
- formatting cleanup

Changelog:
- define get_system_trusted_keyring() to fix kbuild issues

Signed-off-by: Mimi Zohar <zohar@linux.vnet.ibm.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: Dmitry Kasatkin <dmitry.kasatkin@gmail.com>

diff --git a/crypto/asymmetric_keys/x509_public_key.c b/crypto/asymmetric_keys/x509_public_key.c
index 382ef0d2ff2e5e030c0068d1076155364d48f43d..436fbd8552fc4c06ffc8b1464bb1b3fa18e2d253 100644 (file)
--- a/crypto/asymmetric_keys/x509_public_key.c
+++ b/crypto/asymmetric_keys/x509_public_key.c
@@ -18,11 +18,61 @@
 #include <linux/asn1_decoder.h>
 #include <keys/asymmetric-subtype.h>
 #include <keys/asymmetric-parser.h>
+#include <keys/system_keyring.h>
 #include <crypto/hash.h>
 #include "asymmetric_keys.h"
 #include "public_key.h"
 #include "x509_parser.h"
 
+/*
+ * Find a key in the given keyring by issuer and authority.
+ */
+static struct key *x509_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;
+
+       /* 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);
+}
+
 /*
  * Set up the signature parameters in an X.509 certificate.  This involves
  * digesting the signed data and extracting the signature.
@@ -102,6 +152,37 @@ int x509_check_signature(const struct public_key *pub,
 }
 EXPORT_SYMBOL_GPL(x509_check_signature);
 
+/*
+ * Check the new certificate against the ones in the trust keyring.  If one of
+ * those is the signing key and validates the new certificate, then mark the
+ * new certificate as being trusted.
+ *
+ * Return 0 if the new certificate was successfully validated, 1 if we couldn't
+ * find a matching parent certificate in the trusted list and an error if there
+ * is a matching certificate but the signature check fails.
+ */
+static int x509_validate_trust(struct x509_certificate *cert,
+                              struct key *trust_keyring)
+{
+       const struct public_key *pk;
+       struct key *key;
+       int ret = 1;
+
+       if (!trust_keyring)
+               return -EOPNOTSUPP;
+
+       key = x509_request_asymmetric_key(trust_keyring,
+                                         cert->issuer, strlen(cert->issuer),
+                                         cert->authority,
+                                         strlen(cert->authority));
+       if (!IS_ERR(key))  {
+               pk = key->payload.data;
+               ret = x509_check_signature(pk, cert);
+               key_put(key);
+       }
+       return ret;
+}
+
 /*
  * Attempt to parse a data blob for a key as an X509 certificate.
  */
@@ -155,9 +236,13 @@ static int x509_key_preparse(struct key_preparsed_payload *prep)
        /* Check the signature on the key if it appears to be self-signed */
        if (!cert->authority ||
            strcmp(cert->fingerprint, cert->authority) == 0) {
-               ret = x509_check_signature(cert->pub, cert);
+               ret = x509_check_signature(cert->pub, cert); /* self-signed */
                if (ret < 0)
                        goto error_free_cert;
+       } else if (!prep->trusted) {
+               ret = x509_validate_trust(cert, get_system_trusted_keyring());
+               if (!ret)
+                       prep->trusted = 1;
        }
 
        /* Propose a description */

diff --git a/include/keys/system_keyring.h b/include/keys/system_keyring.h
index 8dabc399bd1d156d9ced4d371ba8b8136deea5f4..72665eb8069269f4e1b6726c8cd2d04374405ab8 100644 (file)
--- a/include/keys/system_keyring.h
+++ b/include/keys/system_keyring.h
@@ -17,7 +17,15 @@
 #include <linux/key.h>
 
 extern struct key *system_trusted_keyring;
-
+static inline struct key *get_system_trusted_keyring(void)
+{
+       return system_trusted_keyring;
+}
+#else
+static inline struct key *get_system_trusted_keyring(void)
+{
+       return NULL;
+}
 #endif
 
 #endif /* _KEYS_SYSTEM_KEYRING_H */