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=-7.0 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED autolearn=no 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 A0B81C433E3 for ; Fri, 24 Jul 2020 16:09:46 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7D922206C1 for ; Fri, 24 Jul 2020 16:09:46 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="amrFECy6" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728620AbgGXQJq (ORCPT ); Fri, 24 Jul 2020 12:09:46 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:34576 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728550AbgGXQJp (ORCPT ); Fri, 24 Jul 2020 12:09:45 -0400 Received: from mail-oo1-xc44.google.com (mail-oo1-xc44.google.com [IPv6:2607:f8b0:4864:20::c44]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D38B9C0619D3 for ; Fri, 24 Jul 2020 09:09:44 -0700 (PDT) Received: by mail-oo1-xc44.google.com with SMTP id g18so1062189ooa.0 for ; Fri, 24 Jul 2020 09:09:44 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=RN4PaFKgTuwx2nAu04ml5n4WptsVE0BbHCXhZ2ECARM=; b=amrFECy6Q0B94H96yfm9cqa3mULOA4SSBFcKckFClRO6fjgxwUTUQvl7Jt5tQ0Pn8Q XRVXz7Hod42YRUv7k1EY3sCZTxstQ/4KhJ6/V3IV2LIPrLMLIMIoCU37NXAG6JYU+wye ALYj5O0pqm68FT2qdZzVNzi8p1IELEo8n54mKkHrXoR1cHgViZGAsk5O73D4Qsxe42uJ Fp+zfAMmi518fe7lya3Ey6u8YC3XTwUQ/2liOLKMpISx6hG9g9MFAw8ZuqbJkN28rsHo qHCvfpOw6jL6pKGFa5XaiY71l8Jt/z+gX3smUocwCNEqXcknTBfpPP5EQpEZx8BBaSSH nNTQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=RN4PaFKgTuwx2nAu04ml5n4WptsVE0BbHCXhZ2ECARM=; b=D/Fwfc5lY5jATTZytVRHuyBPkHZJblqua9EbhcYxRqrSU/6b39qyz0ypdOOLIupCER JixEoTMJzg1GR8xwh7Q8uij8y+15fhljJ061tAjoOMkTuT47CtylqAVyVfG3S0O33+z9 RgUA/V05XeDh2EksPegH0Ka3J0RWNdfZMmaM82UDzBnOMlXed1Beqeu3GGz6qAhq1MiZ NNAywN0m22cEr2/z+WG0LF775gMAQqahzEzlbM97KI0qMh0S7Y0WlWaLzfM/58bqg2aG o0XnwDvGIzdpT9Kzy5HoWIN/8ZJVrevxB2k3u0w6LGBOR46gYl+JBSzNJgMBcXbzRVxq ydpg== X-Gm-Message-State: AOAM530VC1PGtj1HE1lHQZolKNNTCDSS5MoXHAa8gdwYOzbbaOZcm6P8 he6Yn5H6KqRxwcfEwaZlhlO/uD2vTQj0olAkKpPsQg== X-Google-Smtp-Source: ABdhPJzRTkZECU5UwmdUKVOhoZsiJCsl1mjOtJIioln/bzxFo5jfZPMU/ZjUw1EAYvUqc1iCjdTvykKjgV1e39k9a+Y= X-Received: by 2002:a4a:b006:: with SMTP id f6mr10216699oon.13.1595606984185; Fri, 24 Jul 2020 09:09:44 -0700 (PDT) MIME-Version: 1.0 References: <20200724141348.47590-1-mike.palmiotto@crunchydata.com> In-Reply-To: From: Stephen Smalley Date: Fri, 24 Jul 2020 12:09:33 -0400 Message-ID: Subject: Re: [PATCH v4] libselinux: use kernel status page by default To: Mike Palmiotto Cc: SElinux list Content-Type: text/plain; charset="UTF-8" Sender: selinux-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: selinux@vger.kernel.org On Fri, Jul 24, 2020 at 11:48 AM Stephen Smalley wrote: > > On Fri, Jul 24, 2020 at 11:34 AM Stephen Smalley > wrote: > > > > On Fri, Jul 24, 2020 at 10:14 AM Mike Palmiotto > > wrote: > > > > > > Commit bc2a8f418e3b ("libselinux: add selinux_status_* interfaces for > > > /selinux/status") introduced the sestatus mechanism, which allows for > > > mmap()'ing of the kernel status page as a replacement for avc_netlink. > > > > > > The mechanism was initially intended for use by userspace object > > > managers which were calculating access decisions within their > > > application and did not rely on the libselinux AVC implementation. In > > > order to properly make use of sestatus within avc_has_perm(), the status > > > mechanism needs to properly set avc internals during status events; > > > else, avc_enforcing is never updated upon sestatus changes. > > > > > > This commit introduces a new selinux_status_loop() function, which > > > replaces the default netlink-equivalent, avc_netlink_loop(). The > > > function watches the kernel status page until an error occurs, at which > > > point it will exit the thread. In the event that the status page cannot > > > be opened (on avc_open), the thread will continue to function as before > > > by using a fallback netlink socket. > > > > > > This allows us to replace the call to avc_netlink_open() in > > > avc_init_internal() with a call to selinux_status_open() and remove the > > > avc_netlink_check_nb() call from the critical code path in > > > avc_has_perm_noaudit(), as well as selinux_check_access(). > > > > > > Userspace object managers that still need a netlink socket can call > > > avc_netlink_acquire_fd() to open open and/or obtain one. > > > > > > Update the manpage to reflect the new avc_netlink_acquire_fd() > > > functionality. > > > > > > Signed-off-by: Mike Palmiotto > > > --- > > > Testing: > > > - dbus-daemon v1.12.8 on RHEL8.2 > > > - dbus-broker v22 on F32 > > > > This looks good to me as far as the code is concerned. However, > > installing the patched libselinux and rebooting, I notice that > > afterward I have dbus-daemon running on a Fedora rawhide instance and > > consuming nearly 100% CPU constantly. I'm guessing it is sitting in > > the status loop. Not sure why there is a dbus-daemon instance running > > at all since dbus-broker seems to be the default in Fedora and > > systemctl shows dbus-daemon as disabled. But if I revert to the stock > > libselinux, it stops hogging CPU. Thoughts? > > Used gdb to attach to the separate thread and got a traceback before > and after the libselinux patch. > Sure enough, before it is performing a blocking poll() operation and > hence sleeping. After it is spinning in > the status loop. So, options would appear to be: 1) Drop the usage of avc_using_threads altogether, i.e. even if the caller provided a thread callback, don't create another thread and just call selinux_status_updated() on every avc_has_perm_noaudit() unless avc_app_main_loop is set. Rationale: dbus-daemon was only using threads to avoid the overhead of avc_netlink_check_nb() on every avc_has_perm_noaudit() call, and we've eliminated that via use of sestatus, hence we don't need to create a separate thread at all. -or- 2) If using threads, then create the netlink socket during avc_init and keep using the netlink loop for the thread. This preserves the blocking behavior. #1 seems more optimal to me and gets rid of threading for dbus-daemon, which was something they didn't like anyway.