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Date:   Wed, 17 Oct 2018 08:43:30 -0700
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Subject: Re: WARNING: kmalloc bug in input_mt_init_slots
To:     Christopher Lameter <cl@linux.com>
CC:     Matthew Wilcox <willy@infradead.org>,
        Dmitry Vyukov <dvyukov@google.com>,
        syzbot+87829a10073277282ad1@syzkaller.appspotmail.com,
        Pekka Enberg <penberg@kernel.org>,
        "linux-input@vger.kernel.org" <linux-input@vger.kernel.org>,
        lkml <linux-kernel@vger.kernel.org>,
        Henrik Rydberg <rydberg@bitmath.org>,
        syzkaller-bugs <syzkaller-bugs@googlegroups.com>,
        Linux-MM <linux-mm@kvack.org>
From:   Dmitry Torokhov <dmitry.torokhov@gmail.com>
Message-ID: <CE3D3608-F320-4DAB-8BEB-3EFDDB54F97E@gmail.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On October 17, 2018 8:35:15 AM PDT, Christopher Lameter <cl@linux=2Ecom> wr=
ote:
>On Tue, 16 Oct 2018, Dmitry Torokhov wrote:
>
>> On Thu, Sep 27, 2018 at 07:35:37AM -0700, Matthew Wilcox wrote:
>> > On Mon, Sep 24, 2018 at 11:41:58AM -0700, Dmitry Torokhov wrote:
>> > > > How large is the allocation? AFACIT nRequests larger than
>KMALLOC_MAX_SIZE
>> > > > are larger than the maximum allowed by the page allocator=2E Thus
>the warning
>> > > > and the NULL return=2E
>> > >
>> > > The size in this particular case is being derived from a value
>passed
>> > > from userspace=2E Input core does not care about any limits on size
>of
>> > > memory kmalloc() can support and is perfectly happy with getting
>NULL
>> > > and telling userspace to go away with their silly requests by
>returning
>> > > -ENOMEM=2E
>> > >
>> > > For the record: I definitely do not want to pre-sanitize size
>neither in
>> > > uinput nor in input core=2E
>> >
>> > Probably should be using kvzalloc then=2E
>>
>> No=2E No sane input device can track so many contacts so we need to use
>> kvzalloc()=2E Failing to allocate memory is proper response here=2E
>
>What is a "contact" here? Are we talking about SG segments?

No, we are talking about maximum number of fingers a person can have=2E De=
vices don't usually track more than 10 distinct contacts on the touch surfa=
ce at a time=2E


Thanks=2E

--=20
Dmitry