certs: Add a secondary system keyring that can be added to dynamically

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>

diff --git a/certs/Kconfig b/certs/Kconfig
index 743d480..fc5955f 100644 (file)
--- 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 e460d00..50979d6 100644 (file)
--- a/certs/system_keyring.c
+++ b/certs/system_keyring.c
@@ -18,41 +18,88 @@
 #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;
 
 /**
- * restrict_link_by_builtin_trusted - Restrict keyring addition by system CA
+ * 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 system keyring.
+ * 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(system_trusted_keyring,
-                                         type, payload);
+       return restrict_link_by_signature(builtin_trusted_keys, type, payload);
 }
 
+#ifdef CONFIG_SECONDARY_TRUSTED_KEYRING
+/**
+ * restrict_link_by_builtin_and_secondary_trusted - Restrict keyring
+ *   addition by both builtin and secondary keyrings
+ *
+ * Restrict the addition of keys into a keyring based on the key-to-be-added
+ * being vouched for by a key in either the built-in or the secondary system
+ * keyrings.
+ */
+int restrict_link_by_builtin_and_secondary_trusted(
+       struct key *keyring,
+       const struct key_type *type,
+       const union key_payload *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.
+        */
+       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);
+}
+#endif
+
 /*
- * 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,
-                             restrict_link_by_builtin_trusted, NULL);
-       if (IS_ERR(system_trusted_keyring))
-               panic("Can't allocate system trusted keyring\n");
+                             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_builtin_and_secondary_trusted,
+                             NULL);
+       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 +135,7 @@ 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 +172,8 @@ 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 +205,15 @@ 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 c72330a..6144240 100644 (file)
--- a/include/keys/system_keyring.h
+++ b/include/keys/system_keyring.h
@@ -24,6 +24,15 @@ extern int restrict_link_by_builtin_trusted(struct key *keyring,
 #define restrict_link_by_builtin_trusted restrict_link_reject
 #endif
 
+#ifdef CONFIG_SECONDARY_TRUSTED_KEYRING
+extern int restrict_link_by_builtin_and_secondary_trusted(
+       struct key *keyring,
+       const struct key_type *type,
+       const union key_payload *payload);
+#else
+#define restrict_link_by_builtin_and_secondary_trusted restrict_link_by_builtin_trusted
+#endif
+
 #ifdef CONFIG_IMA_MOK_KEYRING
 extern struct key *ima_mok_keyring;
 extern struct key *ima_blacklist_keyring;