From patchwork Thu Apr 23 20:03:14 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Alexey Gladkov X-Patchwork-Id: 11506487 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 84CF7912 for ; Thu, 23 Apr 2020 20:04:45 +0000 (UTC) Received: from mother.openwall.net (mother.openwall.net [195.42.179.200]) by mail.kernel.org (Postfix) with SMTP id EA75E20776 for ; Thu, 23 Apr 2020 20:04:44 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org EA75E20776 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=gmail.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=kernel-hardening-return-18625-patchwork-kernel-hardening=patchwork.kernel.org@lists.openwall.com Received: (qmail 3282 invoked by uid 550); 23 Apr 2020 20:04:03 -0000 Mailing-List: contact kernel-hardening-help@lists.openwall.com; run by ezmlm Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: List-ID: Delivered-To: mailing list kernel-hardening@lists.openwall.com Received: (qmail 3186 invoked from network); 23 Apr 2020 20:04:02 -0000 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 v13 6/8] docs: proc: add documentation for "hidepid=4" and "subset=pid" options and new mount behavior Date: Thu, 23 Apr 2020 22:03:14 +0200 Message-Id: <20200423200316.164518-7-gladkov.alexey@gmail.com> X-Mailer: git-send-email 2.25.3 In-Reply-To: <20200423200316.164518-1-gladkov.alexey@gmail.com> References: <20200423200316.164518-1-gladkov.alexey@gmail.com> MIME-Version: 1.0 X-Greylist: Sender succeeded SMTP AUTH, not delayed by milter-greylist-4.6.1 (raptor.unsafe.ru [5.9.43.93]); Thu, 23 Apr 2020 20:03:45 +0000 (UTC) Signed-off-by: Alexey Gladkov Reviewed-by: Alexey Dobriyan Reviewed-by: Kees Cook --- Documentation/filesystems/proc.rst | 54 ++++++++++++++++++++++++++++++ 1 file changed, 54 insertions(+) diff --git a/Documentation/filesystems/proc.rst b/Documentation/filesystems/proc.rst index 38b606991065..360486c7a992 100644 --- a/Documentation/filesystems/proc.rst +++ b/Documentation/filesystems/proc.rst @@ -51,6 +51,8 @@ fixes/update part 1.1 Stefani Seibold June 9 2009 4 Configuring procfs 4.1 Mount options + 5 Filesystem behavior + Preface ======= @@ -2142,6 +2144,7 @@ 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 @@ -2164,6 +2167,57 @@ 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