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=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,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 9F7FBECDE44 for ; Wed, 31 Oct 2018 15:10:13 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7125E205F4 for ; Wed, 31 Oct 2018 15:10:13 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 7125E205F4 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729615AbeKAAIg (ORCPT ); Wed, 31 Oct 2018 20:08:36 -0400 Received: from mx1.redhat.com ([209.132.183.28]:47336 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728649AbeKAAIf (ORCPT ); Wed, 31 Oct 2018 20:08:35 -0400 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 29BBA330788; Wed, 31 Oct 2018 15:10:11 +0000 (UTC) Received: from dhcp-27-174.brq.redhat.com (unknown [10.43.17.31]) by smtp.corp.redhat.com (Postfix) with SMTP id 7AB5365918; Wed, 31 Oct 2018 15:10:09 +0000 (UTC) Received: by dhcp-27-174.brq.redhat.com (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Wed, 31 Oct 2018 16:10:10 +0100 (CET) Date: Wed, 31 Oct 2018 16:10:07 +0100 From: Oleg Nesterov To: Daniel Colascione Cc: "Eric W. Biederman" , linux-kernel , Tim Murray , Joel Fernandes , Suren Baghdasaryan , Kees Cook , Christian Brauner Subject: Re: [RFC PATCH] Implement /proc/pid/kill Message-ID: <20181031151007.GA21207@redhat.com> References: <20181029221037.87724-1-dancol@google.com> <87bm7a3et9.fsf@xmission.com> <20181031124435.GA9007@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.24 (2015-08-30) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.26]); Wed, 31 Oct 2018 15:10:11 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 10/31, Daniel Colascione wrote: > > > perhaps it would be simpler to do > > > > my_cred = override_creds(file->f_cred); > > kill_pid(...); > > revert_creds(my_cred); > > Thanks for the suggestion. That looks neat, but it's not quite enough. > The problem is that check_kill_permission looks for > same_thread_group(current, t) _before_ checking kill_of_by_cred, Yes, you are right. Looks like kill_pid_info_as_cred() can find another user, but probably it needs some changes with or without /proc/pid/kill ... > There's another problem though: say we open /proc/pid/5/kill *, with > proc 5 being an ordinary unprivileged process, e.g., the shell. At > open(2) time, the access check passes. Now suppose PID 5 execve(2)s > into a setuid process. The kill FD is still open, so the kill FD's > holder can send a signal Confused... why? kill_ok_by_cred() should fail? Oleg.