linux-kernel - Re: Re: WARNING in input_alloc

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Message-ID: <CACT4Y+YAhkymQQAfdMUQnWpQVp6WN=gG1u5Fvgz79eWiw79ZHQ@mail.gmail.com>
Date:   Tue, 7 Aug 2018 16:47:33 +0200
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     syzbot <syzbot+@...kaller.appspotmail.com>,
        syzbot <syzbot+c382812c78d98ecd9fb8@...kaller.appspotmail.com>
Cc:     "'Dmitry Vyukov' via syzkaller-bugs" 
        <syzkaller-bugs@...glegroups.com>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        linux-input@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
        Henrik Rydberg <rydberg@...math.org>
Subject: Re: Re: WARNING in input_alloc_absinfo

On Tue, Aug 7, 2018 at 4:28 PM, syzbot
<syzbot+@...kaller.appspotmail.com> wrote:
>> On Thu, Jul 26, 2018 at 11:40 AM, Dmitry Vyukov <dvyukov@...gle.com>
>> wrote:
>>>
>>> On Mon, Jul 2, 2018 at 11:30 AM, Dmitry Vyukov <dvyukov@...gle.com>
>>> wrote:
>>>>
>>>> On Fri, Jun 29, 2018 at 11:59 PM,  <dmitry.torokhov@...il.com> wrote:
>>>>>
>>>>> On Monday, June 25, 2018 at 5:43:02 AM UTC-7, Dmitry Vyukov wrote:
>
>
>>>>>> On Tue, Jun 19, 2018 at 8:51 PM, Dmitry Torokhov
>>>>>> <dmitry....@...il.com> wrote:
>>>>>> > On Thu, Jun 14, 2018 at 05:47:03AM -0700, syzbot wrote:
>>>>>> >> Hello,
>>>>>> >>
>>>>>> >> syzbot found the following crash on:
>>>>>> >>
>>>>>> >> HEAD commit:    d2d741e5d189 kmsan: add initialization for shmem
>>>>>> >> pages
>>>>>> >> git tree:       https://github.com/google/kmsan.git/master
>>>>>> >> console output:
>>>>>> >> https://syzkaller.appspot.com/x/log.txt?x=1775bae7800000
>>>>>> >> kernel config:
>>>>>> >> https://syzkaller.appspot.com/x/.config?x=48f9de3384bcd0f
>>>>>> >> dashboard link:
>>>>>> >> https://syzkaller.appspot.com/bug?extid=c382812c78d98ecd9fb8
>>>>>> >> compiler:       clang version 7.0.0 (trunk 329391)
>>>>>> >> syzkaller
>>>>>> >> repro:https://syzkaller.appspot.com/x/repro.syz?x=13b31ae7800000
>>>>>> >> C reproducer:
>>>>>> >> https://syzkaller.appspot.com/x/repro.c?x=1733255b800000
>>>>>> >>
>>>>>> >> IMPORTANT: if you fix the bug, please add the following tag to the
>>>>>> >> commit:
>>>>>> >> Reported-by: syzbot+c38281...@...kaller.appspotmail.com
>>>>>> >>
>>>>>> >> RBP: 00000000006cb018 R08: 0000000000000001 R09: 00007ffe93080031
>>>>>> >> R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000004
>>>>>> >> R13: ffffffffffffffff R14: 0000000000000000 R15: 0000000000000000
>>>>>> >> ------------[ cut here ]------------
>>>>>> >> input_alloc_absinfo(): kcalloc() failed?
>>>>>> >> WARNING: CPU: 1 PID: 4498 at drivers/input/input.c:487
>>>>>> >> input_alloc_absinfo+0x183/0x190 drivers/input/input.c:487
>>>>>> >> Kernel panic - not syncing: panic_on_warn set ...
>>>>>> >
>>>>>> > Hmm, so there is not really a problem as far as I am concerned. We
>>>>>> > do
>>>>>> > generate a warning if we can't allocate memory for absinfo,  as this
>>>>>> > is
>>>>>> > really unexpected, but the case is handled properly by the callers
>>>>>> > so
>>>>>> > there is no reason for us to go belly up here.
>
>
>>>>>> Note to myself: ping this bug when "include/asm-generic/bug.h: clarify
>>>>>> valid uses of WARN()" is fully merged.
>
>
>
>>>>> No, this warning will still be there even after the "clarifying" patch
>>>>> is
>>>>> merged. It does not check user inputs, it warns that the system is so
>>>>> low on
>>>>> memory that we could not allocate measly amount needed for absinfo.
>>>>> Treat it
>>>>> as you treat OOM warnings from kmalloc() itself.
>
>
>>>> Hi Dmitry,
>
>
>>>> kmalloc does not produce WARNING on OOM. The rule is not only about
>>>> invalid inputs, it's also about any transient conditions and "WARNING
>>>> only for kernel bugs".
>
>
>>>> To put this in larger context, being able to distinguish kernel bugs
>>>> from non-bugs is a very important and practically useful capability,
>>>> which in particular enables systematic testing, but also makes things
>>>> simpler for all kernel users. There must be a very significant reason
>>>> to abandon this capability. What is that reason in this case?
>
>
>>>> I also don't understand what is so special about this case. If we want
>>>> user message for kmalloc failures, kmalloc is the right place for such
>>>> warning, rather than a random call site out of thousands. Consider,
>>>> the allocation failure can happen on the very next or previous kmalloc
>>>> call, and user won't be warned. The rest of the kernel (including the
>>>> rest of input sybsystem) does not warn on allocation failures, so that
>>>> looks like what we need to do here as well. Or, if there is something
>>>> very special about this particular kmalloc call site, something that
>>>> makes it different from thousands of other call sites, why don't you
>>>> want to replace it with pr_err which would both give the diagnostics
>>>> but also not block systematic testing? Which looks like a win-win to
>>>> me.
>
>
>>>> Thanks
>
>
>
>>> So, Dmitry, do you mind fixing this in the name of unblocking kernel
>>> testing?
>
>
>
>> Let's tell syzbot about the pending fix:
>
>
>> #syz fix: Input: do not use WARN() in input_alloc_absinfo()
>
>
> Can't find the corresponding bug.

Now with syzbot email in CC:

#syz fix: Input: do not use WARN() in input_alloc_absinfo()