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 Received: from lists1p.gnu.org (lists1p.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id E6113C5AD4E for ; Mon, 10 Aug 2026 09:59:12 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists1p.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1wtMmF-0001oA-HI; Mon, 10 Aug 2026 05:58:39 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists1p.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1wtMm9-0001nl-DJ for qemu-devel@nongnu.org; Mon, 10 Aug 2026 05:58:35 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1wtMm7-0001Ea-5H for qemu-devel@nongnu.org; Mon, 10 Aug 2026 05:58:33 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1786355909; h=from:from:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=goUfrKlN1mp9xiTSk0RK8nHSArkxqJtqRDwcPz2xjTw=; b=S59hk+zZzL5GHA4ox8d4BiQTSLYfzdJ1Lr25cQv8uAsS4tTCwKy9PQpzRPji79l1Y6Yf5p c0bzLR/xferOhoOV51rdzVqPYi+yTRjAC+vVvwwTaGDnhZdaK2vQl2Sdc49rVGDOuoGB8s U0wNWjRsuD12eG3WPCg3PTv/eCXrDbE= Received: from mx-prod-mc-03.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-479--re7WYINNSO-uEVrqaPjwQ-1; Mon, 10 Aug 2026 05:58:26 -0400 X-MC-Unique: -re7WYINNSO-uEVrqaPjwQ-1 X-Mimecast-MFC-AGG-ID: -re7WYINNSO-uEVrqaPjwQ_1786355905 Received: from mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.17]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 0873A1956045; Mon, 10 Aug 2026 09:58:25 +0000 (UTC) Received: from redhat.com (headnet03.pony-001.prod.iad2.dc.redhat.com [10.2.32.114]) by mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id A9B1119560AB; Mon, 10 Aug 2026 09:58:23 +0000 (UTC) Date: Mon, 10 Aug 2026 10:58:20 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Kostiantyn Kostiuk Cc: Valentino Paulon , qemu-devel@nongnu.org, yvugenfi@redhat.com, michael.roth@amd.com Subject: Re: [PATCH] qga: Do not follow symlink in guest-ssh-* commands Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/2.4.0 (2026-06-19) X-Scanned-By: MIMEDefang 3.0 on 10.30.177.17 Received-SPF: pass client-ip=170.10.129.124; envelope-from=berrange@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: 4 X-Spam_score: 0.4 X-Spam_bar: / X-Spam_report: (0.4 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.827, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=0.001, RCVD_IN_SBL_CSS=3.335, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=no autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: qemu development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On Mon, Aug 10, 2026 at 12:33:39PM +0300, Kostiantyn Kostiuk wrote: > On Mon, Aug 10, 2026 at 12:28 PM Daniel P. Berrangé > wrote: > > > On Mon, Aug 10, 2026 at 11:58:44AM +0300, Kostiantyn Kostiuk wrote: > > > On Mon, Aug 10, 2026 at 11:55 AM Daniel P. Berrangé > > > > > wrote: > > > > > > > On Mon, Aug 10, 2026 at 11:37:34AM +0300, Kostiantyn Kostiuk wrote: > > > > > On Mon, Aug 10, 2026 at 11:20 AM Daniel P. Berrangé < > > berrange@redhat.com > > > > > > > > > > wrote: > > > > > > > > > > > On Mon, Aug 10, 2026 at 11:06:27AM +0300, Kostiantyn Kostiuk wrote: > > > > > > > Hi Valentino, > > > > > > > > > > > > > > Sorry for the long delay. > > > > > > > I have a question for you > > > > > > > > > > > > > > On Tue, Jul 14, 2026 at 7:10 PM Valentino Paulon < > > > > > > > valentino.paulon88@gmail.com> wrote: > > > > > > > > > > > > > > > > > So, you propose to call seteuid/setegid before any I/O > > > > operation? > > > > > > > > > > > > > > > > > > Yes, specifically for the SSH commands, because they're > > unusual > > > > in > > > > > > > > > that we're doing stuff on behalf of an unprivileged user. > > > > > > > > > > > > > > > > +1 on the euid/egid direction -- as the reporter that's the > > > > outcome I > > > > > > > > was hoping for. It confines every step (read, mkdir, create, > > > > rename, > > > > > > > > chown) to what the target user could already do himself, which > > > > removes > > > > > > > > the whole TOCTOU class instead of chasing one instance of it. > > > > > > > > > > > > > > > > A few implementation details that tend to bite with this > > pattern, > > > > in > > > > > > > > case they save a round-trip: > > > > > > > > > > > > > > > > - drop the supplementary groups too, not just egid: > > initgroups() > > > > (or > > > > > > > > setgroups() with the user's list) while still root, otherwise > > the > > > > > > > > agent's effective access won't match the user's in either > > direction > > > > > > > > > > > > > > > > > > > > > > Technically, there is no limitation to running QGA in > > unprivileged > > > > mode. > > > > > > > Normally, it is a system daemon, but this is not mandatory. > > > > > > > In this case, we can not call initgroups because the caller must > > > > > > > have CAP_SETGID. > > > > > > > We can call initgroups only when QGA runs as root. What do you > > think? > > > > > > > > > > > > In any practical sense it is a system daemon given the set of > > commands > > > > > > it is exposing. Thus, IMHO, deploying as an unprivileged user > > should > > > > > > be considered a broken deployment. We could make that explicit by > > > > > > refusing to launch. > > > > > > > > > > > > > > > > Makes sense, but we have one more issue with QGA unit tests in this > > case. > > > > > They are called by an unprivileged user (build user), and initgroups > > > > broke > > > > > it. > > > > > Is it possible to enter the namespace automatically by the test > > engine? > > > > > > > > We can't assume that is possible todo in all build/test environments. > > > > > > > > Doing things as different user accounts feels pretty dubious for the > > > > scope of a unit test too - that is really functional or integration > > > > testing. > > > > > > > > Can we somehow restructure the tests and/or agent code to avoid the > > > > changing groups stuff in unit tests. > > > > > > > > > > There are two possible options: > > > 1. add #ifdef QGA_BUILD_UNIT_TEST into qmp_guest_ssh_* functions > > > 2. check the current uid and skip initgroups if it is zero (my initial > > > question) > > > > Surely you mean "if it is non-zero" here, as it is with uid!=0 that > > the UID changes will fail. > > > > yes. So what sounds better: "ifdef" or "uid!=0"? I'd be inclined to #ifdef so we know it doesn't affect production deployments, only tests. With regards, Daniel -- |: https://berrange.com ~~ https://hachyderm.io/@berrange :| |: https://libvirt.org ~~ https://entangle-photo.org :| |: https://pixelfed.art/berrange ~~ https://fstop138.berrange.com :|