From: David Rientjes <rientjes@google.com>
To: Dmitry Vyukov <dvyukov@google.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Jiri Slaby <jslaby@suse.com>,
Peter Hurley <peter@hurleysoftware.com>,
One Thousand Gnomes <gnomes@lxorguk.ukuu.org.uk>,
LKML <linux-kernel@vger.kernel.org>,
syzkaller <syzkaller@googlegroups.com>,
Kostya Serebryany <kcc@google.com>,
Alexander Potapenko <glider@google.com>
Subject: Re: [PATCH] tty: use __GFP_NOWARN for user-controlled kmalloc
Date: Fri, 5 Feb 2016 02:32:00 -0800 (PST) [thread overview]
Message-ID: <alpine.DEB.2.10.1602050227580.10138@chino.kir.corp.google.com> (raw)
In-Reply-To: <CACT4Y+Zj29ZmsUZCR7FhkxMz_kdV51qhp3SwJ31Sj40y=A7W0w@mail.gmail.com>
On Fri, 5 Feb 2016, Dmitry Vyukov wrote:
> On Thu, Feb 4, 2016 at 11:11 PM, David Rientjes <rientjes@google.com> wrote:
> > On Thu, 4 Feb 2016, Dmitry Vyukov wrote:
> >
> >> Size of kmalloc() in vc_do_resize() is controlled by user.
> >> Too large kmalloc() size triggers WARNING message on console.
> >>
> >> Use __GFP_NOWARN for this kmalloc() to not scare admins.
> >>
> >
> > Hmm, this is hitting the WARN_ON_ONCE(!(gfp_mask & __GFP_NOWARN)) for
> > order >= MAX_ORDER.
> >
> > vc_do_resize() has
> >
> > if (cols > VC_RESIZE_MAXCOL || lines > VC_RESIZE_MAXROW)
> > return -EINVAL;
> >
> > so the appropriate fix would seem to be to reject sizes that would exceed
> > the page allocator's ability to return contiguous memory (MAX_ORDER)
> > rather than ever trying the allocation in the first place.
>
> Hi David,
>
> Please see Alan response to original report here:
> https://groups.google.com/d/msg/syzkaller/ufjvr5j0URo/lTlpYP0DBQAJ
> I can't say that I fully understand it.
>
vc_do_resize() might not know a stricter limit, but we know the limit that
the page allocator can provide, and that's MAX_ORDER-1. kmalloc() with a
size >= (1 << (PAGE_SHIFT + MAX_ORDER)) will always fail, so if that is
really the upper limit, then so be it. We should return -EINVAL
appropriately and not -ENOMEM.
I'm thinking that the actual limit would actually be
(1 << (PAGE_SHIFT + pageblock_order)) since even memory compaction isn't
going to be able to defragment more than that, but the absolute max would
always be MAX_ORDER-1.
next prev parent reply other threads:[~2016-02-05 10:32 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-02-04 15:55 [PATCH] tty: use __GFP_NOWARN for user-controlled kmalloc() Dmitry Vyukov
2016-02-04 17:49 ` Peter Hurley
2016-02-04 18:28 ` [PATCH] tty: use __GFP_NOWARN for user-controlled kmalloc Dmitry Vyukov
2016-02-04 22:11 ` David Rientjes
2016-02-05 7:06 ` Dmitry Vyukov
2016-02-05 10:32 ` David Rientjes [this message]
2016-02-05 10:35 ` One Thousand Gnomes
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