From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-lj1-f199.google.com (mail-lj1-f199.google.com [209.85.208.199]) by kanga.kvack.org (Postfix) with ESMTP id 55F848E0002 for ; Sun, 13 Jan 2019 23:52:20 -0500 (EST) Received: by mail-lj1-f199.google.com with SMTP id e12-v6so5037830ljb.18 for ; Sun, 13 Jan 2019 20:52:20 -0800 (PST) Received: from smtp.infotech.no (smtp.infotech.no. [82.134.31.41]) by mx.google.com with ESMTP id y127si59516925lfc.121.2019.01.13.20.52.17 for ; Sun, 13 Jan 2019 20:52:17 -0800 (PST) Reply-To: dgilbert@interlog.com Subject: Re: [PATCH v2] rbtree: fix the red root References: <20190111181600.GJ6310@bombadil.infradead.org> <20190111205843.25761-1-cai@lca.pw> <864d6b85-3336-4040-7c95-7d9615873777@lechnology.com> <8v11ZOLyufY7NLAHDFApGwXOO_wGjVHtsbw1eiZ__YvI9EZCDe_4FNmlp0E-39lnzGQHhHAczQ6Q6lQPzVU2V6krtkblM8IFwIXPHZCuqGE=@protonmail.ch> From: Douglas Gilbert Message-ID: Date: Sun, 13 Jan 2019 23:52:06 -0500 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-CA Content-Transfer-Encoding: 8bit Sender: owner-linux-mm@kvack.org List-ID: To: Esme Cc: Qian Cai , David Lechner , Michel Lespinasse , Andrew Morton , "jejb@linux.ibm.com" , "martin.petersen@oracle.com" , "joeypabalinas@gmail.com" , linux-mm , LKML On 2019-01-13 10:59 p.m., Esme wrote: > ‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐ > On Sunday, January 13, 2019 10:52 PM, Douglas Gilbert wrote: > >> On 2019-01-13 10:07 p.m., Esme wrote: >> >>> ‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐ >>> On Sunday, January 13, 2019 9:33 PM, Qian Cai cai@lca.pw wrote: >>> >>>> 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 david@lechnology.com 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 esploit@protonmail.ch >>>>>>>> Tested-by: Joey Pabalinas joeypabalinas@gmail.com >>>>>>>> Signed-off-by: Qian Cai cai@lca.pw >>>>>>> >>>>>>> Tested-by: David Lechner david@lechnology.com >>>>>>> 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 >>> >>> I have been on SLAB, I configured SLAB DEBUG with a fresh pull from github. Linux syzkaller 5.0.0-rc2 #9 SMP Sun Jan 13 21:57:40 EST 2019 x86_64 >>> ... >>> In an effort to get a different stack into the kernel, I felt that nothing works better than fork bomb? :) >>> Let me know if that helps. >>> root@syzkaller:~# gcc -o test3 test3.c >>> root@syzkaller:~# while : ; do ./test3 & done >> >> And is test3 the same multi-threaded program that enters the kernel via >> /dev/sg0 and then calls SCSI_IOCTL_SEND_COMMAND which goes to the SCSI >> mid-level and thence to the block layer? >> >> And please remind me, does it also fail on lk 4.20.2 ? >> >> Doug Gilbert > > Yes, the same C repro from the earlier thread. It was a 4.20.0 kernel where it was first detected. I can move to 4.20.2 and see if that changes anything. Hi, I don't think there is any need to check lk 4.20.2 (as it would be very surprising if it didn't also have this "feature"). More interesting might be: has "test3" been run on lk 4.19 or any earlier kernel? Doug Gilbert