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[71.184.117.43]) by smtp.gmail.com with ESMTPSA id d45sm48658225qtd.56.2019.01.13.18.33.52 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Sun, 13 Jan 2019 18:33:53 -0800 (PST) Subject: Re: [PATCH v2] rbtree: fix the red root To: David Lechner , Michel Lespinasse Cc: 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> <864d6b85-3336-4040-7c95-7d9615873777@lechnology.com> From: Qian Cai Message-ID: Date: Sun, 13 Jan 2019 21:33:51 -0500 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.14; rv:60.0) Gecko/20100101 Thunderbird/60.3.3 MIME-Version: 1.0 In-Reply-To: <864d6b85-3336-4040-7c95-7d9615873777@lechnology.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 1/13/19 9:20 PM, David Lechner wrote: > 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/ > It may be useful for those who could reproduce this issue to turn on those memory corruption debug options to narrow down a bit. CONFIG_DEBUG_PAGEALLOC=y CONFIG_DEBUG_PAGEALLOC_ENABLE_DEFAULT=y CONFIG_KASAN=y CONFIG_KASAN_GENERIC=y CONFIG_SLUB_DEBUG_ON=y