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 5B86BC433F5 for ; Tue, 12 Oct 2021 17:31:12 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 45E8560F23 for ; Tue, 12 Oct 2021 17:31:12 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232684AbhJLRdM (ORCPT ); Tue, 12 Oct 2021 13:33:12 -0400 Received: from out02.mta.xmission.com ([166.70.13.232]:55466 "EHLO out02.mta.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232705AbhJLRdK (ORCPT ); Tue, 12 Oct 2021 13:33:10 -0400 Received: from in02.mta.xmission.com ([166.70.13.52]:51984) by out02.mta.xmission.com with esmtps (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.93) (envelope-from ) id 1maLcJ-00Ca0L-CA; Tue, 12 Oct 2021 11:31:07 -0600 Received: from ip68-227-160-95.om.om.cox.net ([68.227.160.95]:60918 helo=email.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 1maLcI-00Gtkd-Gi; Tue, 12 Oct 2021 11:31:06 -0600 From: ebiederm@xmission.com (Eric W. Biederman) To: Rune Kleveland Cc: Yu Zhao , Alexey Gladkov , Jordan Glover , LKML , linux-mm@kvack.org, containers@lists.linux-foundation.org References: <1M9_d6wrcu6rdPe1ON0_k0lOxJMyyot3KAb1gdyuwzDPC777XVUWPHoTCEVmcK3fYfgu7sIo3PSaLe9KulUdm4TWVuqlbKyYGxRAjsf_Cpk=@protonmail.ch> <87ee9pa6xw.fsf@disp2133> <878rzw77i3.fsf@disp2133> <20210929173611.fo5traia77o63gpw@example.org> <20210930130640.wudkpmn3cmah2cjz@example.org> <878rz8wwb6.fsf@disp2133> <87v92cvhbf.fsf@disp2133> Date: Tue, 12 Oct 2021 12:31:00 -0500 In-Reply-To: (Rune Kleveland's message of "Sun, 10 Oct 2021 10:59:10 +0200") Message-ID: <87o87u2lrf.fsf@disp2133> 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=1maLcI-00Gtkd-Gi;;;mid=<87o87u2lrf.fsf@disp2133>;;;hst=in02.mta.xmission.com;;;ip=68.227.160.95;;;frm=ebiederm@xmission.com;;;spf=neutral X-XM-AID: U2FsdGVkX1/mi8WNgfr/F/tuuyDRQWaOtXEfsPIVixM= X-SA-Exim-Connect-IP: 68.227.160.95 X-SA-Exim-Mail-From: ebiederm@xmission.com Subject: Re: linux 5.14.3: free_user_ns causes NULL pointer dereference 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 Rune Kleveland writes: > Hi! > > Just wanted to let you know that I still get these on stock Fedora kernel > 5.14.10 on the IBM blades. But it took 10 hours before the first server > crashed. The other 4 still runs fine since 15 hours ago. So for me it seems more > stable now, but that could just be a coincidence. Alex and I have been working on this and we are still tracking down whatever is going on. While we haven't found the issue yet we have found a trivially correct change that allows us to reproduce the issue faster. Hopefully this will allow us to narrow down on whatever it is soon. diff --git a/kernel/ucount.c b/kernel/ucount.c index bb51849e6375..3b7e176cf7a2 100644 --- a/kernel/ucount.c +++ b/kernel/ucount.c @@ -203,6 +203,7 @@ void put_ucounts(struct ucounts *ucounts) if (atomic_dec_and_lock_irqsave(&ucounts->count, &ucounts_lock, flags)) { hlist_del_init(&ucounts->node); + ucounts->ns = NULL; spin_unlock_irqrestore(&ucounts_lock, flags); kfree(ucounts); } Eric