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Date:   Wed, 17 Oct 2018 15:35:15 +0000
From:   Christopher Lameter <cl@linux.com>
To:     Dmitry Torokhov <dmitry.torokhov@gmail.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>
Subject: Re: WARNING: kmalloc bug in input_mt_init_slots
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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. Thus the warning
> > > > and the NULL return.
> > >
> > > The size in this particular case is being derived from a value passed
> > > from userspace. 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.
> > >
> > > For the record: I definitely do not want to pre-sanitize size neither in
> > > uinput nor in input core.
> >
> > Probably should be using kvzalloc then.
>
> No. No sane input device can track so many contacts so we need to use
> kvzalloc(). Failing to allocate memory is proper response here.

What is a "contact" here? Are we talking about SG segments?