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 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 02D9CC433EF for ; Thu, 18 Nov 2021 20:59:04 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D6F9660F26 for ; Thu, 18 Nov 2021 20:59:03 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232292AbhKRVCD (ORCPT ); Thu, 18 Nov 2021 16:02:03 -0500 Received: from out01.mta.xmission.com ([166.70.13.231]:41574 "EHLO out01.mta.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232033AbhKRVCC (ORCPT ); Thu, 18 Nov 2021 16:02:02 -0500 Received: from in02.mta.xmission.com ([166.70.13.52]:33074) by out01.mta.xmission.com with esmtps (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.93) (envelope-from ) id 1mnoUm-00DoTt-H5; Thu, 18 Nov 2021 13:59:00 -0700 Received: from ip68-227-160-95.om.om.cox.net ([68.227.160.95]:51282 helo=email.froward.int.ebiederm.org.xmission.com) by in02.mta.xmission.com with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.93) (envelope-from ) id 1mnoUl-00Akvn-Ga; Thu, 18 Nov 2021 13:59:00 -0700 From: ebiederm@xmission.com (Eric W. Biederman) To: Qian Cai Cc: Alexey Gladkov , Yu Zhao , References: <875ysptfgi.fsf@email.froward.int.ebiederm.org> Date: Thu, 18 Nov 2021 14:57:17 -0600 In-Reply-To: (Qian Cai's message of "Thu, 18 Nov 2021 15:32:33 -0500") Message-ID: <87k0h5rxle.fsf@email.froward.int.ebiederm.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-XM-SPF: eid=1mnoUl-00Akvn-Ga;;;mid=<87k0h5rxle.fsf@email.froward.int.ebiederm.org>;;;hst=in02.mta.xmission.com;;;ip=68.227.160.95;;;frm=ebiederm@xmission.com;;;spf=neutral X-XM-AID: U2FsdGVkX1/xFxhvjIdEI4qeidXSmsLguyRERS2BhmM= X-SA-Exim-Connect-IP: 68.227.160.95 X-SA-Exim-Mail-From: ebiederm@xmission.com Subject: Re: BUG: KASAN: use-after-free in dec_rlimit_ucounts X-SA-Exim-Version: 4.2.1 (built Sat, 08 Feb 2020 21:53:50 +0000) X-SA-Exim-Scanned: Yes (on in02.mta.xmission.com) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Qian Cai writes: > On Thu, Nov 18, 2021 at 01:46:05PM -0600, Eric W. Biederman wrote: >> Is it possible? Yes it is possible. That is one place where >> a use-after-free has shown up and I expect would show up in the >> future. >> >> That said it is hard to believe there is still a user-after-free in the >> code. We spent the last kernel development cycle pouring through and >> correcting everything we saw until we ultimately found one very subtle >> use-after-free. >> >> If you have a reliable reproducer that you can share, we can look into >> this and see if we can track down where the reference count is going >> bad. >> >> It tends to take instrumenting the entire life cycle every increment and >> every decrement and then pouring through the logs to track down a >> use-after-free. Which is not something we can really do without a >> reproducer. > > The reproducer is just to run trinity by an unprivileged user on defconfig > with KASAN enabled (On linux-next, you can do "make defconfig debug.conf" > [1], but dont think other debugging options are relevent here.) > > $ trinity -C 31 -N 10000000 > > It is always reproduced on an arm64 server here within 5-minute so far. > Some debugging progress so far. BTW, this could happen on user_shm_unlock() > path as well. Does this only happen on a single architecture? If so I wonder if perhaps some of the architectures atomic primitives are implemented improperly. Unfortunately I don't have any arm64 machines where I can easily test this. The call path you posted from user_shm_unlock is another path where a use-after-free has show up in the past. My blind guess would be that I made an implementation mistake in inc_rlimit_get_ucounts or dec_rlimit_put_ucounts but I can't see it right now. Eric > Call trace: > dec_rlimit_ucounts > user_shm_unlock > (inlined by) user_shm_unlock at mm/mlock.c:854 > shmem_lock > shmctl_do_lock > ksys_shmctl.constprop.0 > __arm64_sys_shmctl > invoke_syscall > el0_svc_common.constprop.0 > do_el0_svc > el0_svc > el0t_64_sync_handler > el0t_64_sync > > I noticed in dec_rlimit_ucounts(), dec == 0 and type == > UCOUNT_RLIMIT_MEMLOCK. > > [1] https://lore.kernel.org/lkml/20211115134754.7334-1-quic_qiancai@quicinc.com/