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,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS 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 67401C433E0 for ; Fri, 24 Jul 2020 19:34:48 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3C6DE206F6 for ; Fri, 24 Jul 2020 19:34:48 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=crunchydata-com.20150623.gappssmtp.com header.i=@crunchydata-com.20150623.gappssmtp.com header.b="q9gPeooc" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726381AbgGXTes (ORCPT ); Fri, 24 Jul 2020 15:34:48 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:38610 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726085AbgGXTer (ORCPT ); Fri, 24 Jul 2020 15:34:47 -0400 Received: from mail-lf1-x141.google.com (mail-lf1-x141.google.com [IPv6:2a00:1450:4864:20::141]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 4C191C0619D3 for ; Fri, 24 Jul 2020 12:34:47 -0700 (PDT) Received: by mail-lf1-x141.google.com with SMTP id i19so5777298lfj.8 for ; Fri, 24 Jul 2020 12:34:47 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=crunchydata-com.20150623.gappssmtp.com; s=20150623; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=jgzdS28TdUYp6AbSVTVhIhnNTMyCpjnWrRNxeNwJkTo=; b=q9gPeoocZexnHr8VO+A+FAa+ly2VNNrGRxN7ZFZ9tavk9M4//ZkFGaJnPlUOEroCsJ RHwltftHxT6tG5U0FXrEKQWZ5KVP7YHbCWWrGiiT1mtABvbrhiQfgdVfRTC33sOF+yos shvBz5/AK2+oNLjzSt1h/VtkXCqyIQKQxfg60EH3oqMzkAK7tKW6yxlwQ+t8Sm1DHfL5 N2YWCtZH4N4Sh2qBhGwU1mP5zl+EVBbk/Mjtdl5ILkrJS6AX4QabL7IdhNq27cHQmWWu fcUqBGhov0lb3WqCNYfyfjwA1IueM4JIhuCX7uSJSdLy89Cp2zoZY00Z5+kpuM+ZaMxh HNJA== 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=jgzdS28TdUYp6AbSVTVhIhnNTMyCpjnWrRNxeNwJkTo=; b=pnj32oxB47xpSGXjPXKrmugnxPf+z4I9BePftd2ToGDSZm0iMhEB+lb5hET3G2GYSF 4ueZTFHRKhwlKCLPOJZYpbBRxNHIpta8PmHsFN30M690ghffRCgFn6YTmQmn2ktso18F pyGIF+u3IXL+z+BFy5E4fP54bY1OGptLwiVnPdYEdhxXGyf3EuhAfXD8Eih/lkBpoBJx UZGaE689J7ZDjMrD7j0BCM76qWVX93k8Mk+/m1lRw8h/5GALrNGfPk1JDvQKuzUkxEHE jnt1Boo21SM8ivIqqKn/WQSbHZPkwt0MnswwqF9xJe2KByfMV626LTIfepwtDhMme80d BGuA== X-Gm-Message-State: AOAM530Xpmb5dA5+XF0swbSvX6wTm6NRhj0YDq8+h/Z2myiJAazCVwye w8T9QI0AEB+CyP0TvPrvTxW6yr9JH4t1Zlh8JiAeWw== X-Google-Smtp-Source: ABdhPJwDWq1/O50J63Bg0iTSrRxqhyVyBOq/Z4VXPXRM6OaH5NfTWgcqMuMempW/4LnTm2I4MRTNjlNgOMak4bAgKcA= X-Received: by 2002:a19:848d:: with SMTP id g135mr5800312lfd.1.1595619285638; Fri, 24 Jul 2020 12:34:45 -0700 (PDT) MIME-Version: 1.0 References: <20200724141348.47590-1-mike.palmiotto@crunchydata.com> In-Reply-To: From: Mike Palmiotto Date: Fri, 24 Jul 2020 15:34:33 -0400 Message-ID: Subject: Re: [PATCH v4] libselinux: use kernel status page by default To: Stephen Smalley 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 2:26 PM Stephen Smalley wrote: > > On Fri, Jul 24, 2020 at 12:23 PM Mike Palmiotto > wrote: > > > > On Fri, Jul 24, 2020 at 12:09 PM Stephen Smalley > > wrote: > > > > > > 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. > > > > Perhaps this is misguided, but it seems like avc_init is deprecated > > and along with it the ability to even set a custom thread callback. > > IOTW there does not appear to be a mechanism to set a thread callback > > while using avc_open (only avc_init). Perhaps we can just get rid of > > the default callback for avc_open and allow the (deprecated) avc_init > > to continue using it as it does? > > > > Is this basically what you were proposing for #2? I think I'd be more > > inclined to go with that approach, in case userspace object managers > > are doing other things in their thread callback. > > I think that's the same as #2 if I understood you currently. That's > fine if you prefer it. > So then programs using avc_init() with non-NULL thread callbacks > (hence avc_using_threads == 1) will still create the netlink socket > and start a thread running avc_netlink_loop(). And programs using > avc_netlink_acquire_fd() will create the netlink socket if not already > created and can use it however they want. Everything else will move > to using the status page. What do you think about moving avc_create_thread call (if avc_using_threads is set) into avc_netlink_acquire_fd(). That way, if the caller is using avc_init with a create_thread callback, they can get their netlink socket and create the netlink thread and everything will function as before. In theory, this would also work for the sestatus netlink fallback. -- Mike Palmiotto https://crunchydata.com