From patchwork Wed Dec 25 12:51:51 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Alexey Gladkov X-Patchwork-Id: 11310259 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id E2CAA138C for ; Wed, 25 Dec 2019 13:03:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id CB9C92075E for ; Wed, 25 Dec 2019 13:03:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726415AbfLYNDN (ORCPT ); Wed, 25 Dec 2019 08:03:13 -0500 Received: from monster.unsafe.ru ([5.9.28.80]:36100 "EHLO mail.unsafe.ru" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726289AbfLYNDM (ORCPT ); Wed, 25 Dec 2019 08:03:12 -0500 Received: from localhost.localdomain (ip-89-102-33-211.net.upcbroadband.cz [89.102.33.211]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.unsafe.ru (Postfix) with ESMTPSA id A2A82C61B17; Wed, 25 Dec 2019 12:53:28 +0000 (UTC) From: Alexey Gladkov To: LKML , Kernel Hardening , Linux API , Linux FS Devel , Linux Security Module Cc: Akinobu Mita , Alexander Viro , Alexey Dobriyan , Alexey Gladkov , Andrew Morton , Andy Lutomirski , Daniel Micay , Djalal Harouni , "Dmitry V . Levin" , "Eric W . Biederman" , Greg Kroah-Hartman , Ingo Molnar , "J . Bruce Fields" , Jeff Layton , Jonathan Corbet , Kees Cook , Linus Torvalds , Oleg Nesterov , Solar Designer , Stephen Rothwell Subject: [PATCH v6 10/10] docs: proc: add documentation for "hidepid=3" and "pidonly" options and new mount behavior Date: Wed, 25 Dec 2019 13:51:51 +0100 Message-Id: <20191225125151.1950142-11-gladkov.alexey@gmail.com> X-Mailer: git-send-email 2.24.1 In-Reply-To: <20191225125151.1950142-1-gladkov.alexey@gmail.com> References: <20191225125151.1950142-1-gladkov.alexey@gmail.com> MIME-Version: 1.0 Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org Signed-off-by: Alexey Gladkov --- Documentation/filesystems/proc.txt | 53 ++++++++++++++++++++++++++++++ 1 file changed, 53 insertions(+) diff --git a/Documentation/filesystems/proc.txt b/Documentation/filesystems/proc.txt index 99ca040e3f90..6a62ae20a181 100644 --- a/Documentation/filesystems/proc.txt +++ b/Documentation/filesystems/proc.txt @@ -50,6 +50,8 @@ Table of Contents 4 Configuring procfs 4.1 Mount options + 5 Filesystem behavior + ------------------------------------------------------------------------------ Preface ------------------------------------------------------------------------------ @@ -2021,6 +2023,7 @@ The following mount options are supported: hidepid= Set /proc// access mode. gid= Set the group authorized to learn processes information. + pidonly= Show only task related subset of procfs. hidepid=0 means classic mode - everybody may access all /proc// directories (default). @@ -2042,6 +2045,56 @@ information about running processes, whether some daemon runs with elevated privileges, whether other user runs some sensitive program, whether other users run any program at all, etc. +hidepid=3 means that procfs should only contain /proc// directories +that the caller can ptrace. + gid= defines a group authorized to learn processes information otherwise prohibited by hidepid=. If you use some daemon like identd which needs to learn information about processes information, just add identd to this group. + +The pidonly=1 hides all top level files and directories in the procfs that +are not related to tasks. + +------------------------------------------------------------------------------ +5 Filesystem behavior +------------------------------------------------------------------------------ + +Originally, before the advent of pid namepsace, procfs was a global file +system. It means that there was only one procfs instance in the system. + +When pid namespace was added, a separate procfs instance was mounted in +each pid namespace. So, procfs mount options are global among all +mountpoints within the same namespace. + +# grep ^proc /proc/mounts +proc /proc proc rw,relatime,hidepid=2 0 0 + +# strace -e mount mount -o hidepid=1 -t proc proc /tmp/proc +mount("proc", "/tmp/proc", "proc", 0, "hidepid=1") = 0 ++++ exited with 0 +++ + +# grep ^proc /proc/mounts +proc /proc proc rw,relatime,hidepid=2 0 0 +proc /tmp/proc proc rw,relatime,hidepid=2 0 0 + +and only after remounting procfs mount options will change at all +mountpoints. + +# mount -o remount,hidepid=1 -t proc proc /tmp/proc + +# grep ^proc /proc/mounts +proc /proc proc rw,relatime,hidepid=1 0 0 +proc /tmp/proc proc rw,relatime,hidepid=1 0 0 + +This behavior is different from the behavior of other filesystems. + +The new procfs behavior is more like other filesystems. Each procfs mount +creates a new procfs instance. Mount options affect own procfs instance. +It means that it became possible to have several procfs instances +displaying tasks with different filtering options in one pid namespace. + +# mount -o hidepid=2 -t proc proc /proc +# mount -o hidepid=1 -t proc proc /tmp/proc +# grep ^proc /proc/mounts +proc /proc proc rw,relatime,hidepid=2 0 0 +proc /tmp/proc proc rw,relatime,hidepid=1 0 0