CacheFiles: Fix error handling in cachefiles_determine_cache_security()

cachefiles_determine_cache_security() is expected to return with a
security override in place.  However, if set_create_files_as() fails, we
fail to do this.  In this case, we should just reinstate the security
override that was set by the caller.

Furthermore, if set_create_files_as() fails, we should dispose of the
new credentials we were in the process of creating.

Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/cachefiles/security.c

@@ -77,6 +77,8 @@ static int cachefiles_check_cache_dir(struct cachefiles_cache *cache,
 /*
  * check the security details of the on-disk cache
  * - must be called with security override in force
+ * - must return with a security override in force - even in the case of an
+ *   error
  */
 int cachefiles_determine_cache_security(struct cachefiles_cache *cache,
 					struct dentry *root,
@@ -99,6 +101,8 @@ int cachefiles_determine_cache_security(struct cachefiles_cache *cache,
 	 * which create files */
 	ret = set_create_files_as(new, root->d_inode);
 	if (ret < 0) {
+		abort_creds(new);
+		cachefiles_begin_secure(cache, _saved_cred);
 		_leave(" = %d [cfa]", ret);
 		return ret;
 	}