From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-vs1-f72.google.com (mail-vs1-f72.google.com [209.85.217.72]) by kanga.kvack.org (Postfix) with ESMTP id 1E8448E0002 for ; Sun, 13 Jan 2019 21:20:17 -0500 (EST) Received: by mail-vs1-f72.google.com with SMTP id x1so10330669vsc.0 for ; Sun, 13 Jan 2019 18:20:17 -0800 (PST) Received: from vern.gendns.com (vern.gendns.com. [98.142.107.122]) by mx.google.com with ESMTPS id w20si19451407vse.127.2019.01.13.18.20.16 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Sun, 13 Jan 2019 18:20:16 -0800 (PST) Subject: Re: [PATCH v2] rbtree: fix the red root 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 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: 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 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... >