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=-9.5 required=3.0 tests=DKIM_ADSP_CUSTOM_MED, FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_GIT autolearn=unavailable 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 82135C2BA16 for ; Fri, 3 Apr 2020 18:07:48 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 605A3206F5 for ; Fri, 3 Apr 2020 18:07:48 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2404553AbgDCSHh (ORCPT ); Fri, 3 Apr 2020 14:07:37 -0400 Received: from raptor.unsafe.ru ([5.9.43.93]:38060 "EHLO raptor.unsafe.ru" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2404463AbgDCSHd (ORCPT ); Fri, 3 Apr 2020 14:07:33 -0400 Received: from comp-core-i7-2640m-0182e6.redhat.com (ip-89-102-33-211.net.upcbroadband.cz [89.102.33.211]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits)) (No client certificate requested) by raptor.unsafe.ru (Postfix) with ESMTPSA id CAFFB209DA; Fri, 3 Apr 2020 18:07:28 +0000 (UTC) From: Alexey Gladkov To: LKML Cc: Kernel Hardening , Linux API , Linux FS Devel , Linux Security Module , 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 , David Howells Subject: [PATCH v11 6/8] docs: proc: add documentation for "hidepid=4" and "subset=pid" options and new mount behavior Date: Fri, 3 Apr 2020 20:06:46 +0200 Message-Id: <20200403180648.721362-7-gladkov.alexey@gmail.com> X-Mailer: git-send-email 2.25.2 In-Reply-To: <20200403180648.721362-1-gladkov.alexey@gmail.com> References: <20200403180648.721362-1-gladkov.alexey@gmail.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Greylist: Sender succeeded SMTP AUTH, not delayed by milter-greylist-4.6.1 (raptor.unsafe.ru [5.9.43.93]); Fri, 03 Apr 2020 18:07:29 +0000 (UTC) Sender: linux-api-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-api@vger.kernel.org Signed-off-by: Alexey Gladkov Reviewed-by: Alexey Dobriyan Reviewed-by: Kees Cook --- Documentation/filesystems/proc.txt | 53 ++++++++++++++++++++++++++++++ 1 file changed, 53 insertions(+) diff --git a/Documentation/filesystems/proc.txt b/Documentation/filesystems/proc.txt index 99ca040e3f90..bd0e0ab85048 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. + subset= Show only the specified 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=4 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. + +subset=pid 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 -- 2.25.2