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Reply-To: dgilbert@interlog.com
Subject: Re: [PATCH v2] rbtree: fix the red root
To:     Esme <esploit@protonmail.ch>
Cc:     Qian Cai <cai@lca.pw>, David Lechner <david@lechnology.com>,
        Michel Lespinasse <walken@google.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        "jejb@linux.ibm.com" <jejb@linux.ibm.com>,
        "martin.petersen@oracle.com" <martin.petersen@oracle.com>,
        "joeypabalinas@gmail.com" <joeypabalinas@gmail.com>,
        linux-mm <linux-mm@kvack.org>,
        LKML <linux-kernel@vger.kernel.org>
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From:   Douglas Gilbert <dgilbert@interlog.com>
Message-ID: <ad591828-76e8-324b-6ab8-dc87e4390f64@interlog.com>
Date:   Sun, 13 Jan 2019 23:52:06 -0500
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On 2019-01-13 10:59 p.m., Esme wrote:
> ‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐
> On Sunday, January 13, 2019 10:52 PM, Douglas Gilbert <dgilbert@interlog.com> 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