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=-13.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED,USER_AGENT_MUTT 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 1EA18C43387 for ; Wed, 2 Jan 2019 18:28:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id F3F58218E2 for ; Wed, 2 Jan 2019 18:28:38 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727968AbfABS2h (ORCPT ); Wed, 2 Jan 2019 13:28:37 -0500 Received: from mx2.suse.de ([195.135.220.15]:57742 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1727749AbfABS2h (ORCPT ); Wed, 2 Jan 2019 13:28:37 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay1.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id A3845AF13; Wed, 2 Jan 2019 18:28:35 +0000 (UTC) Received: by ds.suse.cz (Postfix, from userid 10065) id 1C7DBDA781; Wed, 2 Jan 2019 19:28:07 +0100 (CET) Date: Wed, 2 Jan 2019 19:28:07 +0100 From: David Sterba To: Filipe Manana Cc: Anand Jain , linux-btrfs Subject: Re: [PATCH] Btrfs: do not overwrite error return value in the balance ioctl Message-ID: <20190102182806.GF23615@twin.jikos.cz> Reply-To: dsterba@suse.cz Mail-Followup-To: dsterba@suse.cz, Filipe Manana , Anand Jain , linux-btrfs References: <20181214194541.21891-1-fdmanana@kernel.org> <9c378108-591d-e275-8898-3c67d97156fa@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.23.1 (2014-03-12) Sender: linux-btrfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org On Mon, Dec 17, 2018 at 09:24:43AM +0000, Filipe Manana wrote: > On Mon, Dec 17, 2018 at 8:25 AM Anand Jain wrote: > > > > > > > > On 12/15/2018 03:45 AM, fdmanana@kernel.org wrote: > > > From: Filipe Manana > > > > > > If the call to btrfs_balance() failed we would overwrite the error > > > returned to user space with -EFAULT if the call to copy_to_user() failed > > > as well. Fix that by calling copy_to_user() only if btrfs_balance() > > > returned success. > > > > > > Signed-off-by: Filipe Manana > > > --- > > > fs/btrfs/ioctl.c | 2 +- > > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > > > diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c > > > index abe45fd97ab5..4ad7288f77d0 100644 > > > --- a/fs/btrfs/ioctl.c > > > +++ b/fs/btrfs/ioctl.c > > > @@ -4707,7 +4707,7 @@ static long btrfs_ioctl_balance(struct file *file, void __user *arg) > > > ret = btrfs_balance(fs_info, bctl, bargs); > > > bctl = NULL; > > > > > > - if (arg) { > > > + if (ret == 0 && arg) { > > > if (copy_to_user(arg, bargs, sizeof(*bargs))) > > > ret = -EFAULT; > > > } > > > > > > > This changes the BTRFS_IOC_BALANCE_V2 semantics. > > > > Originally, if BTRFS_IOC_BALANCE_V2 is failed/canceled we do update > > bargs [1] and copy to user land, but after this patch we copy only > > if the ioctl is successful. I doubt if David is OK with that. > > I thought about that. But that logic, if it's really in use by someone > (something) out there then they must be treating -EFAULT differently > from any other error. > Because if copy_to_user() fails it means it didn't copy all bytes it > was so supposed to (its return value is number of bytes not copied), > so the arguments structure ends up in an inconsistent state. The balance ioctl as used in btrfs-progs expects valid contents of the bargs even if the ioctl returns negative value, with errno set to ECANCELED: https://github.com/kdave/btrfs-progs/blob/master/cmds-balance.c#L458 So the condition would need to take that into account if ((ret == 0 || ret == -ECANCELED) && arg) I haven't found any other error that would need to be whitelisted here.