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Date:   Thu, 30 Aug 2018 08:40:34 -0700
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Daniel Borkmann <daniel@...earbox.net>
Cc:     Alexander Potapenko <glider@...gle.com>,
        Alexei Starovoitov <ast@...nel.org>,
        netdev <netdev@...r.kernel.org>, Jan Kara <jack@...e.cz>,
        syzbot+45a34334c61a8ecf661d@...kaller.appspotmail.com,
        Jan Kara <jack@...e.com>, linux-ext4@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        "Theodore Ts'o" <tytso@....edu>
Subject: Re: KASAN: stack-out-of-bounds Read in __schedule

On Thu, Aug 30, 2018 at 7:19 AM, Dmitry Vyukov <dvyukov@...gle.com> wrote:
> On Thu, Aug 30, 2018 at 2:52 AM, Daniel Borkmann <daniel@...earbox.net> wrote:
>>>>>> Hello,
>>>>>>
>>>>>> syzbot found the following crash on:
>>>>>>
>>>>>> HEAD commit:    5b394b2ddf03 Linux 4.19-rc1
>>>>>> git tree:       upstream
>>>>>> console output: https://syzkaller.appspot.com/x/log.txt?x=14f4d8e1400000
>>>>>> kernel config:  https://syzkaller.appspot.com/x/.config?x=49927b422dcf0b29
>>>>>> dashboard link: https://syzkaller.appspot.com/bug?extid=45a34334c61a8ecf661d
>>>>>> compiler:       gcc (GCC) 8.0.1 20180413 (experimental)
>>>>>> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=13127e5a400000
>>>>>>
>>>>>> IMPORTANT: if you fix the bug, please add the following tag to the commit:
>>>>>> Reported-by: syzbot+45a34334c61a8ecf661d@...kaller.appspotmail.com
>>>>>>
>>>>>> IPv6: ADDRCONF(NETDEV_UP): veth1: link is not ready
>>>>>> IPv6: ADDRCONF(NETDEV_CHANGE): veth1: link becomes ready
>>>>>> IPv6: ADDRCONF(NETDEV_CHANGE): veth0: link becomes ready
>>>>>> 8021q: adding VLAN 0 to HW filter on device team0
>>>>>> ==================================================================
>>>>>> BUG: KASAN: stack-out-of-bounds in schedule_debug kernel/sched/core.c:3285
>>>>>> [inline]
>>>>>> BUG: KASAN: stack-out-of-bounds in __schedule+0x1977/0x1df0
>>>>>> kernel/sched/core.c:3395
>>>>>> Read of size 8 at addr ffff8801ad090000 by task syz-executor0/4718
>>>>>
>>>>> Weird, can you please help me decipher this? So here KASAN complains about
>>>>> wrong memory access in the scheduler.
>>>
>>> This looks like a result of a previous bad silent memory corruption.
>>>
>>> The KASAN report says there is a stack out-of-bounds in scheduler. And
>>> that if followed by slab corruption report in another task.
>>>
>>> fs/jbd2/transaction.c happens to be the first meaningful file in this
>>> crash, and so that's where it is attributed to.
>>>
>>> Rerunning the reproducer several times can maybe give some better
>>> glues, or maybe not, maybe they all will look equally puzzling.
>>>
>>> This part of the repro looks familiar:
>>>
>>> r1 = bpf$MAP_CREATE(0x0, &(0x7f0000002e40)={0x12, 0x0, 0x4, 0x6e, 0x0,
>>> 0x1}, 0x68)
>>> bpf$MAP_UPDATE_ELEM(0x2, &(0x7f0000000180)={r1, &(0x7f0000000000),
>>> &(0x7f0000000140)}, 0x20)
>>>
>>> We had exactly such consequences of a bug in bpf map very recently,
>>> but that was claimed to be fixed. Maybe not completely?
>>> +bpf maintainers
>>
>> Looks like syzbot found this in Linus tree with HEAD commit 5b394b2ddf03 ("Linux 4.19-rc1")
>> one day later net PR got merged via 050cdc6c9501 ("Merge git://git.kernel.org/pub/...").
>>
>> This PR contained a couple of fixes I did on sockmap code during audit such as:
>>
>>   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=b845c898b2f1ea458d5453f0fa1da6e2dfce3bb4
>>
>> Looking at the reproducer syzkaller found it contains:
>>
>>   r1 = bpf$MAP_CREATE(0x0, &(0x7f0000002e40)={0x12, 0x0, 0x4, 0x6e, 0x0, 0x1}, 0x68)
>>                                                     ^^^
>>
>> So it found the crash with map type of sock hash and key size of 0x0 (which is invalid),
>> where subsequent map update triggered the corruption. I just did a 'syz test' and it
>> wasn't able to trigger the crash anymore.
>>
>> #syz fix: bpf, sockmap: fix sock_hash_alloc and reject zero-sized keys


This crash looks related:
https://groups.google.com/d/msg/syzkaller-bugs/luviyHUQ9N4/dmgK2OmLBAAJ

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