->permission() sanitizing: MAY_NOT_BLOCK

Duplicate the flags argument into mask bitmap.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/fs/namei.c b/fs/namei.c
index c5af0f3..723a3fe 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -318,13 +318,16 @@
 {
 	int ret;
 	struct user_namespace *ns = inode_userns(inode);
+	int mask = MAY_EXEC;
+	if (flags & IPERM_FLAG_RCU)
+		mask |= MAY_NOT_BLOCK;
 
 	if (inode->i_op->permission) {
-		ret = inode->i_op->permission(inode, MAY_EXEC, flags);
+		ret = inode->i_op->permission(inode, mask, flags);
 		if (likely(!ret))
 			goto ok;
 	} else {
-		ret = acl_permission_check(inode, MAY_EXEC, flags);
+		ret = acl_permission_check(inode, mask, flags);
 		if (likely(!ret))
 			goto ok;
 		if (ret != -EACCES)