From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-11.6 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 24554C433DB for ; Tue, 9 Feb 2021 06:16:18 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D148964DED for ; Tue, 9 Feb 2021 06:16:17 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229704AbhBIGQB (ORCPT ); Tue, 9 Feb 2021 01:16:01 -0500 Received: from mail.kernel.org ([198.145.29.99]:41380 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229464AbhBIGP4 (ORCPT ); Tue, 9 Feb 2021 01:15:56 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id EF97264EB8; Tue, 9 Feb 2021 06:15:14 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1612851315; bh=a7ndhO7sYv1/e3+bqD0RFzvVKWKeRKjNuOSPf7QgqyA=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=Fv4UohDKldrz01lbMyNhgCf3pU8u0aPY+GosGBrpYYhMmLvTbzMos8nACFtxJOZ+1 jHqyH9EgExWph4B+q82Oxx7CYh3MV6hj2CGcN9zwWRTzheSNPY3IKnYS6In5EIS4S8 I9uFeyU6Je4gga/E5JhAYrlvW7dByMzCEIdDxuSGyTQT04jKhdGg8Ozu7KGAUPIzII FxjKXSrCkOfPvoDxuFWUKr+jzmBWLcb5EnTpa4uf48ex5ebCZOXTqHHLC4CrmLaO3N 4Tymi+b4yxrGAXTrUjYzDHfteDrpbN+U4LHyR6umr8p0yi1DcrxiOQppeHV30TjWzr Kcz/jJTA/qdAQ== Date: Tue, 9 Feb 2021 08:15:11 +0200 From: Leon Romanovsky To: Jakub Kicinski Cc: Arjun Roy , davem@davemloft.net, netdev@vger.kernel.org, arjunroy@google.com, edumazet@google.com, soheil@google.com, David Ahern Subject: Re: [net-next v2] tcp: Explicitly mark reserved field in tcp_zerocopy_receive args. Message-ID: <20210209061511.GI20265@unreal> References: <20210206203648.609650-1-arjunroy.kdev@gmail.com> <20210206152828.6610da2b@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com> <20210207082654.GC4656@unreal> <20210208104143.60a6d730@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210208104143.60a6d730@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com> Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Mon, Feb 08, 2021 at 10:41:43AM -0800, Jakub Kicinski wrote: > On Sun, 7 Feb 2021 10:26:54 +0200 Leon Romanovsky wrote: > > On Sat, Feb 06, 2021 at 03:28:28PM -0800, Jakub Kicinski wrote: > > > On Sat, 6 Feb 2021 12:36:48 -0800 Arjun Roy wrote: > > > > From: Arjun Roy > > > > > > > > Explicitly define reserved field and require it to be 0-valued. > > > > > > > diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c > > > > index e1a17c6b473c..c8469c579ed8 100644 > > > > --- a/net/ipv4/tcp.c > > > > +++ b/net/ipv4/tcp.c > > > > @@ -4159,6 +4159,8 @@ static int do_tcp_getsockopt(struct sock *sk, int level, > > > > } > > > > if (copy_from_user(&zc, optval, len)) > > > > return -EFAULT; > > > > + if (zc.reserved) > > > > + return -EINVAL; > > > > lock_sock(sk); > > > > err = tcp_zerocopy_receive(sk, &zc, &tss); > > > > release_sock(sk); > > > > > > I was expecting we'd also throw in a check_zeroed_user(). > > > Either we can check if the buffer is zeroed all the way, > > > or we can't and we shouldn't validate reserved either > > > > > > check_zeroed_user(optval + offsetof(reserved), > > > len - offsetof(reserved)) > > > ? > > > > There is a check that len is not larger than zs and users can't give > > large buffer. > > > > I would say that is pretty safe to write "if (zc.reserved)". > > Which check? There's a check which truncates (writes back to user space > len = min(len, sizeof(zc)). Application can still pass garbage beyond > sizeof(zc) and syscall may start failing in the future if sizeof(zc) > changes. At least in my tree, we have the length check: 4155 if (len > sizeof(zc)) { 4156 len = sizeof(zc); 4157 if (put_user(len, optlen)) 4158 return -EFAULT; 4159 } Ad David wrote below, the "if (zc.reserved)" is enough. We have following options: 1. Old kernel that have sizeof(sz) upto .reserved and old userspace -> len <= sizeof(sz) - works correctly. 2. Old kernel that have sizeof(sz) upto .reserved and new userspace that sends larger struct -> "f (len > sizeof(zc))" will return -EFAULT 3. New kernel that have sizeof(sz) beyond reserved and old userspace -> any new added field to struct sz should be checked and anyway it is the same as item 1. 4. New kernel and new userspace -> standard flow. Thanks