KEYS: Move the point of trust determination to __key_link()

Move the point at which a key is determined to be trustworthy to
__key_link() so that we use the contents of the keyring being linked in to
to determine whether the key being linked in is trusted or not.

What is 'trusted' then becomes a matter of what's in the keyring.

Currently, the test is done when the key is parsed, but given that at that
point we can only sensibly refer to the contents of the system trusted
keyring, we can only use that as the basis for working out the
trustworthiness of a new key.

With this change, a trusted keyring is a set of keys that once the
trusted-only flag is set cannot be added to except by verification through
one of the contained keys.

Further, adding a key into a trusted keyring, whilst it might grant
trustworthiness in the context of that keyring, does not automatically
grant trustworthiness in the context of a second keyring to which it could
be secondarily linked.

To accomplish this, the authentication data associated with the key source
must now be retained.  For an X.509 cert, this means the contents of the
AuthorityKeyIdentifier and the signature data.


If system keyrings are disabled then restrict_link_by_builtin_trusted()
resolves to restrict_link_reject().  The integrity digital signature code
still works correctly with this as it was previously using
KEY_FLAG_TRUSTED_ONLY, which doesn't permit anything to be added if there
is no system keyring against which trust can be determined.

Signed-off-by: David Howells <dhowells@redhat.com>

2 files changed, 35 insertions, 4 deletions

diff --git a/security/integrity/digsig.c b/security/integrity/digsig.c
index 659566c..d647178 100644
--- a/security/integrity/digsig.c
+++ b/security/integrity/digsig.c
@@ -18,6 +18,8 @@
 #include <linux/cred.h>
 #include <linux/key-type.h>
 #include <linux/digsig.h>
+#include <crypto/public_key.h>
+#include <keys/system_keyring.h>
 
 #include "integrity.h"
 
@@ -40,6 +42,35 @@ static bool init_keyring __initdata = true;
 static bool init_keyring __initdata;
 #endif
 
+#ifdef CONFIG_SYSTEM_TRUSTED_KEYRING
+/*
+ * Restrict the addition of keys into the IMA keyring.
+ *
+ * Any key that needs to go in .ima keyring must be signed by CA in
+ * either .system or .ima_mok keyrings.
+ */
+static int restrict_link_by_ima_mok(struct key *keyring,
+				    const struct key_type *type,
+				    unsigned long flags,
+				    const union key_payload *payload)
+{
+	int ret;
+
+	ret = restrict_link_by_builtin_trusted(keyring, type, flags, payload);
+	if (ret != -ENOKEY)
+		return ret;
+
+	return restrict_link_by_signature(get_ima_mok_keyring(),
+					  type, payload);
+}
+#else
+/*
+ * If there's no system trusted keyring, then keys cannot be loaded into
+ * .ima_mok and added keys cannot be marked trusted.
+ */
+#define restrict_link_by_ima_mok restrict_link_reject
+#endif
+
 int integrity_digsig_verify(const unsigned int id, const char *sig, int siglen,
 			    const char *digest, int digestlen)
 {
@@ -84,7 +115,7 @@ int __init integrity_init_keyring(const unsigned int id)
 				     KEY_USR_VIEW | KEY_USR_READ |
 				     KEY_USR_WRITE | KEY_USR_SEARCH),
 				    KEY_ALLOC_NOT_IN_QUOTA,
-				    NULL, NULL);
+				    restrict_link_by_ima_mok, NULL);
 	if (IS_ERR(keyring[id])) {
 		err = PTR_ERR(keyring[id]);
 		pr_info("Can't allocate %s keyring (%d)\n",
diff --git a/security/integrity/ima/ima_mok.c b/security/integrity/ima/ima_mok.c
index ef91248..2988726 100644
--- a/security/integrity/ima/ima_mok.c
+++ b/security/integrity/ima/ima_mok.c
@@ -17,7 +17,7 @@
 #include <linux/cred.h>
 #include <linux/err.h>
 #include <linux/init.h>
-#include <keys/asymmetric-type.h>
+#include <keys/system_keyring.h>
 
 
 struct key *ima_mok_keyring;
@@ -36,7 +36,7 @@ __init int ima_mok_init(void)
 			      KEY_USR_VIEW | KEY_USR_READ |
 			      KEY_USR_WRITE | KEY_USR_SEARCH,
 			      KEY_ALLOC_NOT_IN_QUOTA,
-			      keyring_restrict_trusted_only, NULL);
+			      restrict_link_by_builtin_trusted, NULL);
 
 	ima_blacklist_keyring = keyring_alloc(".ima_blacklist",
 				KUIDT_INIT(0), KGIDT_INIT(0), current_cred(),
@@ -44,7 +44,7 @@ __init int ima_mok_init(void)
 				KEY_USR_VIEW | KEY_USR_READ |
 				KEY_USR_WRITE | KEY_USR_SEARCH,
 				KEY_ALLOC_NOT_IN_QUOTA,
-				keyring_restrict_trusted_only, NULL);
+				restrict_link_by_builtin_trusted, NULL);
 
 	if (IS_ERR(ima_mok_keyring) || IS_ERR(ima_blacklist_keyring))
 		panic("Can't allocate IMA MOK or blacklist keyrings.");