linux-kernel - Re: Re: WARNING in input_alloc

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Date:   Tue, 07 Aug 2018 07:28:11 -0700
From:   syzbot <syzbot+@...kaller.appspotmail.com>
To:     "'Dmitry Vyukov' via syzkaller-bugs" 
        <syzkaller-bugs@...glegroups.com>
Cc:     dmitry.torokhov@...il.com, linux-input@...r.kernel.org,
        linux-kernel@...r.kernel.org, rydberg@...math.org,
        syzkaller-bugs@...glegroups.com
Subject: Re: Re: WARNING in input_alloc_absinfo

> 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.


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