Merge tag 'keys-acl-20190703' of git://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs

Pull keyring ACL support from David Howells:
 "This changes the permissions model used by keys and keyrings to be
  based on an internal ACL by the following means:

   - Replace the permissions mask internally with an ACL that contains a
     list of ACEs, each with a specific subject with a permissions mask.
     Potted default ACLs are available for new keys and keyrings.

     ACE subjects can be macroised to indicate the UID and GID specified
     on the key (which remain). Future commits will be able to add
     additional subject types, such as specific UIDs or domain
     tags/namespaces.

     Also split a number of permissions to give finer control. Examples
     include splitting the revocation permit from the change-attributes
     permit, thereby allowing someone to be granted permission to revoke
     a key without allowing them to change the owner; also the ability
     to join a keyring is split from the ability to link to it, thereby
     stopping a process accessing a keyring by joining it and thus
     acquiring use of possessor permits.

   - Provide a keyctl to allow the granting or denial of one or more
     permits to a specific subject. Direct access to the ACL is not
     granted, and the ACL cannot be viewed"

* tag 'keys-acl-20190703' of git://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs:
  keys: Provide KEYCTL_GRANT_PERMISSION
  keys: Replace uid/gid/perm permissions checking with an ACL

security/keys/keyring.c

@@ -515,11 +515,19 @@ static long keyring_read(const struct key *keyring,
 	return ret;
 }
 
-/*
- * Allocate a keyring and link into the destination keyring.
+/**
+ * keyring_alloc - Allocate a keyring and link into the destination
+ * @description: The key description to allow the key to be searched out.
+ * @uid: The owner of the new key.
+ * @gid: The group ID for the new key's group permissions.
+ * @cred: The credentials specifying UID namespace.
+ * @acl: The ACL to attach to the new key.
+ * @flags: Flags specifying quota properties.
+ * @restrict_link: Optional link restriction for new keyrings.
+ * @dest: Destination keyring.
  */
 struct key *keyring_alloc(const char *description, kuid_t uid, kgid_t gid,
-			  const struct cred *cred, key_perm_t perm,
+			  const struct cred *cred, struct key_acl *acl,
 			  unsigned long flags,
 			  struct key_restriction *restrict_link,
 			  struct key *dest)
@@ -528,7 +536,7 @@ struct key *keyring_alloc(const char *description, kuid_t uid, kgid_t gid,
 	int ret;
 
 	keyring = key_alloc(&key_type_keyring, description,
-			    uid, gid, cred, perm, flags, restrict_link);
+			    uid, gid, cred, acl, flags, restrict_link);
 	if (!IS_ERR(keyring)) {
 		ret = key_instantiate_and_link(keyring, NULL, 0, dest, NULL);
 		if (ret < 0) {
@@ -1132,10 +1140,11 @@ found:
 /*
  * Find a keyring with the specified name.
  *
- * Only keyrings that have nonzero refcount, are not revoked, and are owned by a
- * user in the current user namespace are considered.  If @uid_keyring is %true,
- * the keyring additionally must have been allocated as a user or user session
- * keyring; otherwise, it must grant Search permission directly to the caller.
+ * Only keyrings that have nonzero refcount, are not revoked, and are owned by
+ * a user in the current user namespace are considered.  If @uid_keyring is
+ * %true, the keyring additionally must have been allocated as a user or user
+ * session keyring; otherwise, it must grant JOIN permission directly to the
+ * caller (ie. not through possession).
  *
  * Returns a pointer to the keyring with the keyring's refcount having being
  * incremented on success.  -ENOKEY is returned if a key could not be found.
@@ -1169,7 +1178,7 @@ struct key *find_keyring_by_name(const char *name, bool uid_keyring)
 				continue;
 		} else {
 			if (key_permission(make_key_ref(keyring, 0),
-					   KEY_NEED_SEARCH) < 0)
+					   KEY_NEED_JOIN) < 0)
 				continue;
 		}