linux-kernel - Re: WARNING: kmalloc bug in xdp_umem

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Message-ID: <CACT4Y+Y6TDof6vvdQYHF_W8aAgHPuW_DS2A9HCudmYx549u0Ag@mail.gmail.com>
Date:   Sun, 10 Jun 2018 14:58:33 +0200
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
Cc:     Björn Töpel <bjorn.topel@...il.com>,
        syzbot+4abadc5d69117b346506@...kaller.appspotmail.com,
        Björn Töpel <bjorn.topel@...el.com>,
        "Karlsson, Magnus" <magnus.karlsson@...el.com>,
        David Miller <davem@...emloft.net>,
        LKML <linux-kernel@...r.kernel.org>,
        Netdev <netdev@...r.kernel.org>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>
Subject: Re: WARNING: kmalloc bug in xdp_umem_create

On Sun, Jun 10, 2018 at 2:53 PM, Tetsuo Handa
<penguin-kernel@...ove.sakura.ne.jp> wrote:
> On 2018/06/10 20:52, Dmitry Vyukov wrote:
>> On Sun, Jun 10, 2018 at 11:31 AM, Björn Töpel <bjorn.topel@...il.com> wrote:
>>> Den sön 10 juni 2018 kl 04:53 skrev Tetsuo Handa
>>> <penguin-kernel@...ove.sakura.ne.jp>:
>>>>
>>>> On 2018/06/10 7:47, syzbot wrote:
>>>>> Hello,
>>>>>
>>>>> syzbot found the following crash on:
>>>>>
>>>>> HEAD commit:    7d3bf613e99a Merge tag 'libnvdimm-for-4.18' of git://git.k..
>>>>> git tree:       upstream
>>>>> console output: https://syzkaller.appspot.com/x/log.txt?x=1073f68f800000
>>>>> kernel config:  https://syzkaller.appspot.com/x/.config?x=f04d8d0a2afb789a
>>>>> dashboard link: https://syzkaller.appspot.com/bug?extid=4abadc5d69117b346506
>>>>> compiler:       gcc (GCC) 8.0.1 20180413 (experimental)
>>>>> syzkaller repro:https://syzkaller.appspot.com/x/repro.syz?x=13c9756f800000
>>>>> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=16366f9f800000
>>>>>
>>>>> IMPORTANT: if you fix the bug, please add the following tag to the commit:
>>>>> Reported-by: syzbot+4abadc5d69117b346506@...kaller.appspotmail.com
>>>>>
>>>>> random: sshd: uninitialized urandom read (32 bytes read)
>>>>> random: sshd: uninitialized urandom read (32 bytes read)
>>>>> random: sshd: uninitialized urandom read (32 bytes read)
>>>>> random: sshd: uninitialized urandom read (32 bytes read)
>>>>> random: sshd: uninitialized urandom read (32 bytes read)
>>>>> WARNING: CPU: 1 PID: 4537 at mm/slab_common.c:996 kmalloc_slab+0x56/0x70 mm/slab_common.c:996
>>>>> Kernel panic - not syncing: panic_on_warn set ...
>>>>
>>>> syzbot gave up upon kmalloc(), but actually error handling path has
>>>> NULL pointer dereference bug.
>>>>
>>>
>>> Thanks Tetsuo! This crash has been fixed by Daniel Borkmann in commit
>>> c09290c56376 ("bpf, xdp: fix crash in xdp_umem_unaccount_pages").
>>
>> Let's tell syzbot about this:
>>
>> #syz fix: bpf, xdp: fix crash in xdp_umem_unaccount_pages
>>
>>
> Excuse me, but that patch fixes NULL pointer dereference which occurs after kmalloc()'s
> "WARNING: CPU: 1 PID: 4537 at mm/slab_common.c:996 kmalloc_slab+0x56/0x70 mm/slab_common.c:996"
> message. That is, "Too large memory allocation" itself is not yet fixed.

You are right! I fixed it up. Thanks