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=-10.0 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 54DD9C433E1 for ; Sat, 25 Jul 2020 03:25:23 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3B972206C1 for ; Sat, 25 Jul 2020 03:25:23 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726592AbgGYDZW (ORCPT ); Fri, 24 Jul 2020 23:25:22 -0400 Received: from mga04.intel.com ([192.55.52.120]:10202 "EHLO mga04.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726572AbgGYDZW (ORCPT ); Fri, 24 Jul 2020 23:25:22 -0400 IronPort-SDR: o9RvZeBGp7YEphIY6umZ+RWxEQzbk+q1PBhyJFp4EgJ+gNZ1reYjjrGVopff1x0qF8xKs9CIpg XRXMGqAUr7ow== X-IronPort-AV: E=McAfee;i="6000,8403,9692"; a="148297666" X-IronPort-AV: E=Sophos;i="5.75,392,1589266800"; d="scan'208";a="148297666" X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga006.jf.intel.com ([10.7.209.51]) by fmsmga104.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 24 Jul 2020 20:25:21 -0700 IronPort-SDR: eOIC+S4SulEMj5oJcjW9Qdy4I/m4tVpBq2wf0qTX16TbvS5WituY8v9vhrcYi+Sw5+PB1sWWu/ Ta50tujzkKYw== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.75,392,1589266800"; d="scan'208";a="289178631" Received: from jcrametz-mobl.ger.corp.intel.com (HELO localhost) ([10.252.58.73]) by orsmga006.jf.intel.com with ESMTP; 24 Jul 2020 20:25:18 -0700 Date: Sat, 25 Jul 2020 06:25:16 +0300 From: Jarkko Sakkinen To: David Howells Cc: torvalds@linux-foundation.org, keyrings@vger.kernel.org, linux-security-module@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] watch_queue: Limit the number of watches a user can hold Message-ID: <20200725032516.GA78242@linux.intel.com> References: <159562904644.2287160.13294507067766261970.stgit@warthog.procyon.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <159562904644.2287160.13294507067766261970.stgit@warthog.procyon.org.uk> Organization: Intel Finland Oy - BIC 0357606-4 - Westendinkatu 7, 02160 Espoo Sender: owner-linux-security-module@vger.kernel.org Precedence: bulk List-ID: On Fri, Jul 24, 2020 at 11:17:26PM +0100, David Howells wrote: > Impose a limit on the number of watches that a user can hold so that they > can't use this mechanism to fill up all the available memory. > > This is done by putting a counter in user_struct that's incremented when a > watch is allocated and decreased when it is released. If the number > exceeds the RLIMIT_NOFILE limit, the watch is rejected with EAGAIN. > > This can be tested by the following means: > > (1) Create a watch queue and attach it to fd 5 in the program given - in > this case, bash: > > keyctl watch_session /tmp/nlog /tmp/gclog 5 bash > > (2) In the shell, set the maximum number of files to, say, 99: > > ulimit -n 99 > > (3) Add 200 keyrings: > > for ((i=0; i<200; i++)); do keyctl newring a$i @s || break; done > > (4) Try to watch all of the keyrings: > > for ((i=0; i<200; i++)); do echo $i; keyctl watch_add 5 %:a$i || break; done > > This should fail when the number of watches belonging to the user hits > 99. > > (5) Remove all the keyrings and all of those watches should go away: > > for ((i=0; i<200; i++)); do keyctl unlink %:a$i; done > > (6) Kill off the watch queue by exiting the shell spawned by > watch_session. > > Fixes: c73be61cede5 ("pipe: Add general notification queue support") > Reported-by: Linus Torvalds > Signed-off-by: David Howells > --- > > include/linux/sched/user.h | 3 +++ > kernel/watch_queue.c | 8 ++++++++ > 2 files changed, 11 insertions(+) > > diff --git a/include/linux/sched/user.h b/include/linux/sched/user.h > index 917d88edb7b9..a8ec3b6093fc 100644 > --- a/include/linux/sched/user.h > +++ b/include/linux/sched/user.h > @@ -36,6 +36,9 @@ struct user_struct { > defined(CONFIG_NET) || defined(CONFIG_IO_URING) > atomic_long_t locked_vm; > #endif > +#ifdef CONFIG_WATCH_QUEUE > + atomic_t nr_watches; /* The number of watches this user currently has */ > +#endif > > /* Miscellaneous per-user rate limit */ > struct ratelimit_state ratelimit; > diff --git a/kernel/watch_queue.c b/kernel/watch_queue.c > index f74020f6bd9d..0ef8f65bd2d7 100644 > --- a/kernel/watch_queue.c > +++ b/kernel/watch_queue.c > @@ -393,6 +393,7 @@ static void free_watch(struct rcu_head *rcu) > struct watch *watch = container_of(rcu, struct watch, rcu); > > put_watch_queue(rcu_access_pointer(watch->queue)); > + atomic_dec(&watch->cred->user->nr_watches); > put_cred(watch->cred); > } > > @@ -452,6 +453,13 @@ int add_watch_to_object(struct watch *watch, struct watch_list *wlist) > watch->cred = get_current_cred(); > rcu_assign_pointer(watch->watch_list, wlist); > > + if (atomic_inc_return(&watch->cred->user->nr_watches) > > + task_rlimit(current, RLIMIT_NOFILE)) { > + atomic_dec(&watch->cred->user->nr_watches); > + put_cred(watch->cred); > + return -EAGAIN; > + } > + > spin_lock_bh(&wqueue->lock); > kref_get(&wqueue->usage); > kref_get(&watch->usage); > > Reviewed-by: Jarkko Sakkinen David, BTW, would it be possible to push keyrings to lore.kernel.org? I don't have an archive for keyrings, which means that I cannot push this forward. /Jarkko