getname_kernel() needs to make sure that ->name != ->iname in long case

missed it in "kill struct filename.separate" several years ago.

Cc: stable@vger.kernel.org
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/namei.c

@@ -222,9 +222,10 @@ getname_kernel(const char * filename)
 	if (len <= EMBEDDED_NAME_MAX) {
 		result->name = (char *)result->iname;
 	} else if (len <= PATH_MAX) {
+		const size_t size = offsetof(struct filename, iname[1]);
 		struct filename *tmp;
 
-		tmp = kmalloc(sizeof(*tmp), GFP_KERNEL);
+		tmp = kmalloc(size, GFP_KERNEL);
 		if (unlikely(!tmp)) {
 			__putname(result);
 			return ERR_PTR(-ENOMEM);