From: Michal Hocko <mhocko@kernel.org>
To: Roman Penyaev <rpenyaev@suse.de>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Andrey Ryabinin <aryabinin@virtuozzo.com>,
Joe Perches <joe@perches.com>,
"Luis R. Rodriguez" <mcgrof@kernel.org>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
stable@vger.kernel.org
Subject: Re: [PATCH 1/3] mm/vmalloc: fix size check for remap_vmalloc_range_partial()
Date: Thu, 3 Jan 2019 20:40:54 +0100 [thread overview]
Message-ID: <20190103194054.GB31793@dhcp22.suse.cz> (raw)
In-Reply-To: <dba7cb2c2882e034c8c99b09a432313a@suse.de>
On Thu 03-01-19 20:27:26, Roman Penyaev wrote:
> On 2019-01-03 16:13, Michal Hocko wrote:
> > On Thu 03-01-19 15:59:52, Roman Penyaev wrote:
> > > area->size can include adjacent guard page but get_vm_area_size()
> > > returns actual size of the area.
> > >
> > > This fixes possible kernel crash when userspace tries to map area
> > > on 1 page bigger: size check passes but the following
> > > vmalloc_to_page()
> > > returns NULL on last guard (non-existing) page.
> >
> > Can this actually happen? I am not really familiar with all the callers
> > of this API but VM_NO_GUARD is not really used wildly in the kernel.
>
> Exactly, by default (VM_NO_GUARD is not set) each area has guard page,
> thus the area->size will be bigger. The bug is not reproduced if
> VM_NO_GUARD is set.
>
> > All I can see is kasan na arm64 which doesn't really seem to use it
> > for vmalloc.
> >
> > So is the problem real or this is a mere cleanup?
>
> This is the real problem, try this hunk for any file descriptor which
> provides
> mapping, or say modify epoll as example:
OK, my response was more confusing than I intended. I meant to say. Is
there any in kernel code that would allow the bug have had in mind?
In other words can userspace trick any existing code?
--
Michal Hocko
SUSE Labs
next prev parent reply other threads:[~2019-01-03 19:40 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20190103145954.16942-1-rpenyaev@suse.de>
2019-01-03 14:59 ` [PATCH 1/3] mm/vmalloc: fix size check for remap_vmalloc_range_partial() Roman Penyaev
2019-01-03 15:13 ` Michal Hocko
2019-01-03 19:27 ` Roman Penyaev
2019-01-03 19:40 ` Michal Hocko [this message]
2019-01-03 20:31 ` Roman Penyaev
2019-01-04 9:38 ` Michal Hocko
2019-01-04 10:21 ` Roman Penyaev
2019-01-04 10:28 ` Michal Hocko
2019-01-03 19:59 ` Michal Hocko
2019-01-04 11:06 ` Roman Penyaev
2019-01-11 19:19 ` Andrey Ryabinin
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