From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753231AbeBEPEA (ORCPT ); Mon, 5 Feb 2018 10:04:00 -0500 Received: from shards.monkeyblade.net ([184.105.139.130]:54826 "EHLO shards.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752920AbeBEPDt (ORCPT ); Mon, 5 Feb 2018 10:03:49 -0500 Date: Mon, 05 Feb 2018 10:03:47 -0500 (EST) Message-Id: <20180205.100347.176614123780866781.davem@davemloft.net> To: keescook@chromium.org Cc: syzbot+e2d6cfb305e9f3911dea@syzkaller.appspotmail.com, linux-kernel@vger.kernel.org, netdev@vger.kernel.org, ebiggers3@gmail.com, james.morse@arm.com, keun-o.park@darkmatter.ae, labbott@redhat.com, linux-mm@kvack.org, mingo@kernel.org Subject: Re: [PATCH v2] socket: Provide put_cmsg_whitelist() for constant size copies From: David Miller In-Reply-To: <20180202102749.GA34019@beast> References: <20180202102749.GA34019@beast> X-Mailer: Mew version 6.7 on Emacs 25.3 / Mule 6.0 (HANACHIRUSATO) Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Kees Cook Date: Fri, 2 Feb 2018 02:27:49 -0800 > @@ -343,6 +343,14 @@ struct ucred { > > extern int move_addr_to_kernel(void __user *uaddr, int ulen, struct sockaddr_storage *kaddr); > extern int put_cmsg(struct msghdr*, int level, int type, int len, void *data); > +/* > + * Provide a bounce buffer for copying cmsg data to userspace when the > + * target memory isn't already whitelisted for hardened usercopy. > + */ > +#define put_cmsg_whitelist(_msg, _level, _type, _ptr) ({ \ > + typeof(*(_ptr)) _val = *(_ptr); \ > + put_cmsg(_msg, _level, _type, sizeof(_val), &_val); \ > + }) I understand what you are trying to achieve, but it's at a real cost here. Some of these objects are structures, for example the struct sock_extended_err is 16 bytes. And now we're going to copy it twice, once into the on-stack copy, and then once again into the CMSG blob. Please find a way to make hardened user copy happy without adding new overhead. Thank you.