[RFC PATCH 11/12] certs: Add a secondary system keyring that can be added to dynamically [ver #2]

[David Howells <dhowells@redhat.com>]

Add a secondary system keyring that can be added to by root whilst the
system is running - provided the key being added is vouched for by a key
built into the kernel or already added to the secondary keyring.

Rename .system_keyring to .builtin_trusted_keys to distinguish it more
obviously from the new keyring (called .secondary_trusted_keys).

The new keyring needs to be enabled with CONFIG_SECONDARY_TRUSTED_KEYRING.

If the secondary keyring is enabled, a link is created from that to
.builtin_trusted_keys so that the the latter will automatically be searched
too if the secondary keyring is searched.

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

 certs/Kconfig                 |    8 ++++
 certs/system_keyring.c        |   79 ++++++++++++++++++++++++++++++++++-------
 include/keys/system_keyring.h |    4 ++
 3 files changed, 78 insertions(+), 13 deletions(-)

diff --git a/certs/Kconfig b/certs/Kconfig
index 743d480f5f6f..fc5955f5fc8a 100644
--- a/certs/Kconfig
+++ b/certs/Kconfig
@@ -56,4 +56,12 @@ config SYSTEM_EXTRA_CERTIFICATE_SIZE
 	  This is the number of bytes reserved in the kernel image for a
 	  certificate to be inserted.
 
+config SECONDARY_TRUSTED_KEYRING
+	bool "Provide a keyring to which extra trustable keys may be added"
+	depends on SYSTEM_TRUSTED_KEYRING
+	help
+	  If set, provide a keyring to which extra keys may be added, provided
+	  those keys are not blacklisted and are vouched for by a key built
+	  into the kernel or already in the secondary trusted keyring.
+
 endmenu
diff --git a/certs/system_keyring.c b/certs/system_keyring.c
index 3cfc88c76aee..9700f37350ff 100644
--- a/certs/system_keyring.c
+++ b/certs/system_keyring.c
@@ -18,7 +18,10 @@
 #include <keys/system_keyring.h>
 #include <crypto/pkcs7.h>
 
-static struct key *system_trusted_keyring;
+static struct key *builtin_trusted_keys;
+#ifdef CONFIG_SECONDARY_TRUSTED_KEYRING
+static struct key *secondary_trusted_keys;
+#endif
 
 extern __initconst const u8 system_certificate_list[];
 extern __initconst const unsigned long system_certificate_list_size;
@@ -33,26 +36,68 @@ int restrict_link_by_system_trusted(struct key *keyring,
 				    const struct key_type *type,
 				    const union key_payload *payload)
 {
-	return restrict_link_by_signature(system_trusted_keyring,
-					  type, payload);
+	/* If we have a secondary trusted keyring, then that contains a link
+	 * through to the builtin keyring and the search will follow that link.
+	 */
+#ifdef CONFIG_SECONDARY_TRUSTED_KEYRING
+	if (type == &key_type_keyring &&
+	    keyring == secondary_trusted_keys &&
+	    payload == &builtin_trusted_keys->payload)
+		/* Allow the builtin keyring to be added to the secondary */
+		return 0;
+
+	return restrict_link_by_signature(secondary_trusted_keys, type, payload);
+#else
+	return restrict_link_by_signature(builtin_trusted_keys, type, payload);
+#endif
+}
+
+/**
+ * restrict_link_to_builtin_trusted - Restrict keyring addition by built in CA
+ *
+ * Restrict the addition of keys into a keyring based on the key-to-be-added
+ * being vouched for by a key in the built in system keyring.
+ */
+int restrict_link_by_builtin_trusted(struct key *keyring,
+				     const struct key_type *type,
+				     const union key_payload *payload)
+{
+	return restrict_link_by_signature(builtin_trusted_keys, type, payload);
 }
 
 /*
- * Load the compiled-in keys
+ * Create the trusted keyrings
  */
 static __init int system_trusted_keyring_init(void)
 {
-	pr_notice("Initialise system trusted keyring\n");
+	pr_notice("Initialise system trusted keyrings\n");
 
-	system_trusted_keyring =
-		keyring_alloc(".system_keyring",
+	builtin_trusted_keys =
+		keyring_alloc(".builtin_trusted_keys",
 			      KUIDT_INIT(0), KGIDT_INIT(0), current_cred(),
 			      ((KEY_POS_ALL & ~KEY_POS_SETATTR) |
 			      KEY_USR_VIEW | KEY_USR_READ | KEY_USR_SEARCH),
 			      KEY_ALLOC_NOT_IN_QUOTA,
+			      NULL, NULL);
+	if (IS_ERR(builtin_trusted_keys))
+		panic("Can't allocate builtin trusted keyring\n");
+
+#ifdef CONFIG_SECONDARY_TRUSTED_KEYRING
+	secondary_trusted_keys =
+		keyring_alloc(".secondary_trusted_keys",
+			      KUIDT_INIT(0), KGIDT_INIT(0), current_cred(),
+			      ((KEY_POS_ALL & ~KEY_POS_SETATTR) |
+			       KEY_USR_VIEW | KEY_USR_READ | KEY_USR_SEARCH |
+			       KEY_USR_WRITE),
+			      KEY_ALLOC_NOT_IN_QUOTA,
 			      restrict_link_by_system_trusted, NULL);
-	if (IS_ERR(system_trusted_keyring))
-		panic("Can't allocate system trusted keyring\n");
+	if (IS_ERR(secondary_trusted_keys))
+		panic("Can't allocate secondary trusted keyring\n");
+
+	if (key_link(secondary_trusted_keys, builtin_trusted_keys) < 0)
+		panic("Can't link trusted keyrings\n");
+#endif
+
 	return 0;
 }
 
@@ -88,7 +133,7 @@ static __init int load_system_certificate_list(void)
 		if (plen > end - p)
 			goto dodgy_cert;
 
-		key = key_create_or_update(make_key_ref(system_trusted_keyring, 1),
+		key = key_create_or_update(make_key_ref(builtin_trusted_keys, 1),
 					   "asymmetric",
 					   NULL,
 					   p,
@@ -125,7 +170,8 @@ late_initcall(load_system_certificate_list);
  * @len: Size of @data.
  * @raw_pkcs7: The PKCS#7 message that is the signature.
  * @pkcs7_len: The size of @raw_pkcs7.
- * @trusted_keys: Trusted keys to use (NULL for system_trusted_keyring).
+ * @trusted_keys: Trusted keys to use (NULL for builtin trusted keys only,
+ *					(void *)1UL for all trusted keys).
  * @usage: The use to which the key is being put.
  * @view_content: Callback to gain access to content.
  * @ctx: Context for callback.
@@ -157,8 +203,15 @@ int verify_pkcs7_signature(const void *data, size_t len,
 	if (ret < 0)
 		goto error;
 
-	if (!trusted_keys)
-		trusted_keys = system_trusted_keyring;
+	if (!trusted_keys) {
+		trusted_keys = builtin_trusted_keys;
+	} else if (trusted_keys == (void *)1UL) {
+#ifdef CONFIG_SECONDARY_TRUSTED_KEYRING
+		trusted_keys = secondary_trusted_keys;
+#else
+		trusted_keys = builtin_trusted_keys;
+#endif
+	}
 	ret = pkcs7_validate_trust(pkcs7, trusted_keys);
 	if (ret < 0) {
 		if (ret == -ENOKEY)
diff --git a/include/keys/system_keyring.h b/include/keys/system_keyring.h
index 71f3e2523767..c6c05f1513f5 100644
--- a/include/keys/system_keyring.h
+++ b/include/keys/system_keyring.h
@@ -19,9 +19,13 @@
 extern int restrict_link_by_system_trusted(struct key *keyring,
 					   const struct key_type *type,
 					   const union key_payload *payload);
+extern int restrict_link_by_builtin_trusted(struct key *keyring,
+					    const struct key_type *type,
+					    const union key_payload *payload);
 
 #else
 #define restrict_link_by_system_trusted restrict_link_reject
+#define restrict_link_by_builtin_trusted restrict_link_reject
 #endif
 
 #ifdef CONFIG_IMA_MOK_KEYRING