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=-1.7 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED 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 4E748C43441 for ; Sun, 18 Nov 2018 17:45:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 190A620817 for ; Sun, 18 Nov 2018 17:45:35 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="IURlL1tv" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 190A620817 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org 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 S1727343AbeKSEGZ (ORCPT ); Sun, 18 Nov 2018 23:06:25 -0500 Received: from mail.kernel.org ([198.145.29.99]:41678 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726366AbeKSEGZ (ORCPT ); Sun, 18 Nov 2018 23:06:25 -0500 Received: from mail-wm1-f43.google.com (mail-wm1-f43.google.com [209.85.128.43]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id F279820869 for ; Sun, 18 Nov 2018 17:45:31 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1542563132; bh=MlYcTA+pxCgRlLmkq7p10271XiJ9hbticyJ1njnyFsQ=; h=References:In-Reply-To:From:Date:Subject:To:Cc:From; b=IURlL1tvEjBqbGeborq7K5QglZ4Wlv0EaaB/ebnCijfgZ167g5ONgZHGjr0qVxday 7zQ0I99mjgUbu37x+8XTTJpVeeRBEuqUQ+eUlS5bqeemZzzTUkNYOiyW2EwziNixnf Bt3IMJKe8GXacD9JYES7ahdEzQ+T4yxU6unS9o/M= Received: by mail-wm1-f43.google.com with SMTP id s11so3092095wmh.1 for ; Sun, 18 Nov 2018 09:45:31 -0800 (PST) X-Gm-Message-State: AA+aEWZQmAVtwEjCyAe+lWpeGjztOwcoZfkSAINsIWvFOEvZGH6uVaEW hsfo3VciIYCGXlHQo55P04U8vzywqY6wunIhFT9xlw== X-Google-Smtp-Source: AJdET5d2h7VKi4CG5DuHDqLhl9nCvGXdRxQ47ppG1zriGIaTeyWGDWElkNryTkn02fZwjl5IQiQsiQ4IBTooQDJNFAU= X-Received: by 2002:a7b:ce11:: with SMTP id m17mr5018311wmc.74.1542563130440; Sun, 18 Nov 2018 09:45:30 -0800 (PST) MIME-Version: 1.0 References: <20181118111751.6142-1-christian@brauner.io> <875zwu46z1.fsf@xmission.com> In-Reply-To: <875zwu46z1.fsf@xmission.com> From: Andy Lutomirski Date: Sun, 18 Nov 2018 09:45:18 -0800 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH] proc: allow killing processes via file descriptors To: "Eric W. Biederman" Cc: Daniel Colascione , Andrew Lutomirski , Christian Brauner , LKML , "Serge E. Hallyn" , Jann Horn , Andrew Morton , Oleg Nesterov , Aleksa Sarai , Al Viro , Linux FS Devel , Linux API , Tim Murray , Kees Cook Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, Nov 18, 2018 at 9:43 AM Eric W. Biederman wrote: > > Daniel Colascione writes: > > > On Sun, Nov 18, 2018 at 9:13 AM, Andy Lutomirski wrote: > >> On Sun, Nov 18, 2018 at 8:29 AM Daniel Colascione wrote: > >>> > >>> On Sun, Nov 18, 2018 at 8:17 AM, Andy Lutomirski wrote: > >>> > On Sun, Nov 18, 2018 at 7:53 AM Daniel Colascione wrote: > >>> >> > >>> >> On Sun, Nov 18, 2018 at 7:38 AM, Andy Lutomirski wrote: > >>> >> > I fully agree that a more comprehensive, less expensive API for > >>> >> > managing processes would be nice. But I also think that this patch > >>> >> > (using the directory fd and ioctl) is better from a security > >>> >> > perspective than using a new file in /proc. > >>> >> > >>> >> That's an assertion, not an argument. And I'm not opposed to an > >>> >> operation on the directory FD, now that it's clear Linus has banned > >>> >> "write(2)-as-a-command" APIs. I just insist that we implement the API > >>> >> with a system call instead of a less-reliable ioctl due to the > >>> >> inherent namespace collision issues in ioctl command names. > >>> > > >>> > Linus banned it because of bugs iike the ones in the patch. > >>> > >>> Maybe: he didn't provide a reason. What's your point? > >> > >> My point is that an API that involves a file like /proc/PID/kill is > >> very tricky to get right. Here are some considerations: > > > > Moot. write(2) for this interface is off the table anyway. The right > > approach here is a system call that accepts a /proc/pid directory file > > descriptor, a signal number, and a signal information field (as in > > sigqueue(2)). > > If we did not have the permission check challenges and could perform > the permission checks in open, write(2) would be on the table. > Performing write(2) would only be concrend about data. > > Unfortunately we have setresuid and exec which make that infeasible > for the kill operations. setresuid() should be irrelevant. If you had permission to kill a process and the process calls setresuid(), you should still have permission to kill it. For execve(), we could make execve() invalidate the fd. (See other email.)