Merge branch 'keys-trust' into keys-next

Here's a set of patches that changes how certificates/keys are determined
to be trusted.  That's currently a two-step process:

 (1) Up until recently, when an X.509 certificate was parsed - no matter
     the source - it was judged against the keys in .system_keyring,
     assuming those keys to be trusted if they have KEY_FLAG_TRUSTED set
     upon them.

     This has just been changed such that any key in the .ima_mok keyring,
     if configured, may also be used to judge the trustworthiness of a new
     certificate, whether or not the .ima_mok keyring is meant to be
     consulted for whatever process is being undertaken.

     If a certificate is determined to be trustworthy, KEY_FLAG_TRUSTED
     will be set upon a key it is loaded into (if it is loaded into one),
     no matter what the key is going to be loaded for.

 (2) If an X.509 certificate is loaded into a key, then that key - if
     KEY_FLAG_TRUSTED gets set upon it - can be linked into any keyring
     with KEY_FLAG_TRUSTED_ONLY set upon it.  This was meant to be the
     system keyring only, but has been extended to various IMA keyrings.
     A user can at will link any key marked KEY_FLAG_TRUSTED into any
     keyring marked KEY_FLAG_TRUSTED_ONLY if the relevant permissions masks
     permit it.

These patches change that:

 (1) Trust becomes a matter of consulting the ring of trusted keys supplied
     when the trust is evaluated only.

 (2) Every keyring can be supplied with its own manager function to
     restrict what may be added to that keyring.  This is called whenever a
     key is to be linked into the keyring to guard against a key being
     created in one keyring and then linked across.

     This function is supplied with the keyring and the key type and
     payload[*] of the key being linked in for use in its evaluation.  It
     is permitted to use other data also, such as the contents of other
     keyrings such as the system keyrings.

     [*] The type and payload are supplied instead of a key because as an
         optimisation this function may be called whilst creating a key and
         so may reject the proposed key between preparse and allocation.

 (3) A default manager function is provided that permits keys to be
     restricted to only asymmetric keys that are vouched for by the
     contents of the system keyring.

     A second manager function is provided that just rejects with EPERM.

 (4) A key allocation flag, KEY_ALLOC_BYPASS_RESTRICTION, is made available
     so that the kernel can initialise keyrings with keys that form the
     root of the trust relationship.

 (5) KEY_FLAG_TRUSTED and KEY_FLAG_TRUSTED_ONLY are removed, along with
     key_preparsed_payload::trusted.

This change also makes it possible in future for userspace to create a private
set of trusted keys and then to have it sealed by setting a manager function
where the private set is wholly independent of the kernel's trust
relationships.

Further changes in the set involve extracting certain IMA special keyrings
and making them generally global:

 (*) .system_keyring is renamed to .builtin_trusted_keys and remains read
     only.  It carries only keys built in to the kernel.  It may be where
     UEFI keys should be loaded - though that could better be the new
     secondary keyring (see below) or a separate UEFI keyring.

 (*) An optional secondary system keyring (called .secondary_trusted_keys)
     is added to replace the IMA MOK keyring.

     (*) Keys can be added to the secondary keyring by root if the keys can
         be vouched for by either ring of system keys.

 (*) Module signing and kexec only use .builtin_trusted_keys and do not use
     the new secondary keyring.

 (*) Config option SYSTEM_TRUSTED_KEYS now depends on ASYMMETRIC_KEY_TYPE as
     that's the only type currently permitted on the system keyrings.

 (*) A new config option, IMA_KEYRINGS_PERMIT_SIGNED_BY_BUILTIN_OR_SECONDARY,
     is provided to allow keys to be added to IMA keyrings, subject to the
     restriction that such keys are validly signed by a key already in the
     system keyrings.

     If this option is enabled, but secondary keyrings aren't, additions to
     the IMA keyrings will be restricted to signatures verifiable by keys in
     the builtin system keyring only.

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

1 files changed, 33 insertions, 11 deletions

diff --git a/include/linux/key.h b/include/linux/key.h
index 5f5b1129dc92..722914798f37 100644
--- a/include/linux/key.h
+++ b/include/linux/key.h
@@ -173,11 +173,9 @@ struct key {
 #define KEY_FLAG_NEGATIVE	5	/* set if key is negative */
 #define KEY_FLAG_ROOT_CAN_CLEAR	6	/* set if key can be cleared by root without permission */
 #define KEY_FLAG_INVALIDATED	7	/* set if key has been invalidated */
-#define KEY_FLAG_TRUSTED	8	/* set if key is trusted */
-#define KEY_FLAG_TRUSTED_ONLY	9	/* set if keyring only accepts links to trusted keys */
-#define KEY_FLAG_BUILTIN	10	/* set if key is builtin */
-#define KEY_FLAG_ROOT_CAN_INVAL	11	/* set if key can be invalidated by root without permission */
-#define KEY_FLAG_KEEP		12	/* set if key should not be removed */
+#define KEY_FLAG_BUILTIN	8	/* set if key is built in to the kernel */
+#define KEY_FLAG_ROOT_CAN_INVAL	9	/* set if key can be invalidated by root without permission */
+#define KEY_FLAG_KEEP		10	/* set if key should not be removed */
 
 	/* the key type and key description string
 	 * - the desc is used to match a key against search criteria
@@ -205,6 +203,20 @@ struct key {
 		};
 		int reject_error;
 	};
+
+	/* This is set on a keyring to restrict the addition of a link to a key
+	 * to it.  If this method isn't provided then it is assumed that the
+	 * keyring is open to any addition.  It is ignored for non-keyring
+	 * keys.
+	 *
+	 * This is intended for use with rings of trusted keys whereby addition
+	 * to the keyring needs to be controlled.  KEY_ALLOC_BYPASS_RESTRICTION
+	 * overrides this, allowing the kernel to add extra keys without
+	 * restriction.
+	 */
+	int (*restrict_link)(struct key *keyring,
+			     const struct key_type *type,
+			     const union key_payload *payload);
 };
 
 extern struct key *key_alloc(struct key_type *type,
@@ -212,14 +224,17 @@ extern struct key *key_alloc(struct key_type *type,
 			     kuid_t uid, kgid_t gid,
 			     const struct cred *cred,
 			     key_perm_t perm,
-			     unsigned long flags);
+			     unsigned long flags,
+			     int (*restrict_link)(struct key *,
+						  const struct key_type *,
+						  const union key_payload *));
 
 
-#define KEY_ALLOC_IN_QUOTA	0x0000	/* add to quota, reject if would overrun */
-#define KEY_ALLOC_QUOTA_OVERRUN	0x0001	/* add to quota, permit even if overrun */
-#define KEY_ALLOC_NOT_IN_QUOTA	0x0002	/* not in quota */
-#define KEY_ALLOC_TRUSTED	0x0004	/* Key should be flagged as trusted */
-#define KEY_ALLOC_BUILT_IN	0x0008	/* Key is built into kernel */
+#define KEY_ALLOC_IN_QUOTA		0x0000	/* add to quota, reject if would overrun */
+#define KEY_ALLOC_QUOTA_OVERRUN		0x0001	/* add to quota, permit even if overrun */
+#define KEY_ALLOC_NOT_IN_QUOTA		0x0002	/* not in quota */
+#define KEY_ALLOC_BUILT_IN		0x0004	/* Key is built into kernel */
+#define KEY_ALLOC_BYPASS_RESTRICTION	0x0008	/* Override the check on restricted keyrings */
 
 extern void key_revoke(struct key *key);
 extern void key_invalidate(struct key *key);
@@ -288,8 +303,15 @@ extern struct key *keyring_alloc(const char *description, kuid_t uid, kgid_t gid
 				 const struct cred *cred,
 				 key_perm_t perm,
 				 unsigned long flags,
+				 int (*restrict_link)(struct key *,
+						      const struct key_type *,
+						      const union key_payload *),
 				 struct key *dest);
 
+extern int restrict_link_reject(struct key *keyring,
+				const struct key_type *type,
+				const union key_payload *payload);
+
 extern int keyring_clear(struct key *keyring);
 
 extern key_ref_t keyring_search(key_ref_t keyring,