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=-3.8 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS autolearn=ham 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 5A73EC43387 for ; Mon, 14 Jan 2019 02:29:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 1CC7120657 for ; Mon, 14 Jan 2019 02:29:09 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=lechnology.com header.i=@lechnology.com header.b="rMohatD8" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726696AbfANCUR (ORCPT ); Sun, 13 Jan 2019 21:20:17 -0500 Received: from vern.gendns.com ([98.142.107.122]:51826 "EHLO vern.gendns.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726631AbfANCUR (ORCPT ); Sun, 13 Jan 2019 21:20:17 -0500 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lechnology.com; s=default; h=Content-Transfer-Encoding:Content-Type: In-Reply-To:MIME-Version:Date:Message-ID:From:References:Cc:To:Subject:Sender :Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id:List-Help: List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=LSCJrilXSGYqK3aJwSPv20MWlxip3Z4F3ABQ1V09Cvk=; b=rMohatD8mOLHnIjhUGgvsCl7Ov I+mP1FpSMJ90fwzkulggkYV6WSA5q7DSXOaWUR80lqu0keTno91m6lYkiZInR5ybxZzn4zSrqwmcU ishjO83lxuzAYotDa1OEzus3N4bS4I9fK2vHM66XisDYjE0q1QwHJ8gIQjjc/6OSDs4JmyZ87rGsn 6+CzBWvDkBwZIODBu5VRbcZGrglPjUv4y8STJW7uOYu9xR6McbyQFLp9lrX8zLS0VSx6KnVkLNqm9 xjtucofrCBtyVq8hNKWeJPZ8KuaFUSaWMR1SrAbk0YUjiUWbBpUTVR0pMfuIQelqn/8CWji4kXeSO bOcxpshw==; Received: from 108-198-5-147.lightspeed.okcbok.sbcglobal.net ([108.198.5.147]:58330 helo=[192.168.0.134]) by vern.gendns.com with esmtpsa (TLSv1.2:ECDHE-RSA-AES128-GCM-SHA256:128) (Exim 4.91) (envelope-from ) id 1girog-0004Cz-F4; Sun, 13 Jan 2019 21:17:30 -0500 Subject: Re: [PATCH v2] rbtree: fix the red root To: Michel Lespinasse Cc: Qian Cai , Andrew Morton , esploit@protonmail.ch, jejb@linux.ibm.com, dgilbert@interlog.com, martin.petersen@oracle.com, joeypabalinas@gmail.com, linux-mm , LKML References: <20190111181600.GJ6310@bombadil.infradead.org> <20190111205843.25761-1-cai@lca.pw> From: David Lechner Message-ID: <864d6b85-3336-4040-7c95-7d9615873777@lechnology.com> Date: Sun, 13 Jan 2019 20:20:12 -0600 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.2.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-AntiAbuse: This header was added to track abuse, please include it with any abuse report X-AntiAbuse: Primary Hostname - vern.gendns.com X-AntiAbuse: Original Domain - vger.kernel.org X-AntiAbuse: Originator/Caller UID/GID - [47 12] / [47 12] X-AntiAbuse: Sender Address Domain - lechnology.com X-Get-Message-Sender-Via: vern.gendns.com: authenticated_id: davidmain+lechnology.com/only user confirmed/virtual account not confirmed X-Authenticated-Sender: vern.gendns.com: davidmain@lechnology.com X-Source: X-Source-Args: X-Source-Dir: Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 1/11/19 8:58 PM, Michel Lespinasse wrote: > On Fri, Jan 11, 2019 at 3:47 PM David Lechner wrote: >> >> On 1/11/19 2:58 PM, Qian Cai wrote: >>> A GPF was reported, >>> >>> kasan: CONFIG_KASAN_INLINE enabled >>> kasan: GPF could be caused by NULL-ptr deref or user memory access >>> general protection fault: 0000 [#1] SMP KASAN >>> kasan_die_handler.cold.22+0x11/0x31 >>> notifier_call_chain+0x17b/0x390 >>> atomic_notifier_call_chain+0xa7/0x1b0 >>> notify_die+0x1be/0x2e0 >>> do_general_protection+0x13e/0x330 >>> general_protection+0x1e/0x30 >>> rb_insert_color+0x189/0x1480 >>> create_object+0x785/0xca0 >>> kmemleak_alloc+0x2f/0x50 >>> kmem_cache_alloc+0x1b9/0x3c0 >>> getname_flags+0xdb/0x5d0 >>> getname+0x1e/0x20 >>> do_sys_open+0x3a1/0x7d0 >>> __x64_sys_open+0x7e/0xc0 >>> do_syscall_64+0x1b3/0x820 >>> entry_SYSCALL_64_after_hwframe+0x49/0xbe >>> >>> It turned out, >>> >>> gparent = rb_red_parent(parent); >>> tmp = gparent->rb_right; <-- GPF was triggered here. >>> >>> Apparently, "gparent" is NULL which indicates "parent" is rbtree's root >>> which is red. Otherwise, it will be treated properly a few lines above. >>> >>> /* >>> * If there is a black parent, we are done. >>> * Otherwise, take some corrective action as, >>> * per 4), we don't want a red root or two >>> * consecutive red nodes. >>> */ >>> if(rb_is_black(parent)) >>> break; >>> >>> Hence, it violates the rule #1 (the root can't be red) and need a fix >>> up, and also add a regression test for it. This looks like was >>> introduced by 6d58452dc06 where it no longer always paint the root as >>> black. >>> >>> Fixes: 6d58452dc06 (rbtree: adjust root color in rb_insert_color() only >>> when necessary) >>> Reported-by: Esme >>> Tested-by: Joey Pabalinas >>> Signed-off-by: Qian Cai >>> --- >> >> Tested-by: David Lechner >> FWIW, this fixed the following crash for me: >> >> Unable to handle kernel NULL pointer dereference at virtual address 00000004 > > Just to clarify, do you have a way to reproduce this crash without the fix ? I am starting to suspect that my crash was caused by some new code in the drm-misc-next tree that might be causing a memory corruption. It threw me off that the stack trace didn't contain anything related to drm. See: https://patchwork.freedesktop.org/patch/276719/ > > I don't think the fix is correct, because it just silently ignores a > corrupted rbtree (red root node). But the code that creates this > situation certainly needs to be fixed - having a reproduceable test > case would certainly help here. > > Regarding 6d58452dc06, the reasoning was that this code expects to be > called after inserting a new (red) leaf into an rbtree that had all of > its data structure invariants satisfied. So in this context, it should > not be necessary to always reset the root to black, as this should > already be the case... >