From: William Lee Irwin III <wli@holomorphy.com>
To: Oleg Nesterov <oleg@tv-sign.ru>
Cc: linux-kernel@vger.kernel.org, Andrew Morton <akpm@osdl.org>,
David Gibson <david@gibson.dropbear.id.au>
Subject: Re: [PATCH] hugetlbfs private mappings.
Date: Sun, 11 Jul 2004 17:15:02 -0700 [thread overview]
Message-ID: <20040712001502.GS21066@holomorphy.com> (raw)
In-Reply-To: <40F139BA.F1F10B22@tv-sign.ru>
On Sun, Jul 11, 2004 at 04:59:38PM +0400, Oleg Nesterov wrote:
> Hugetlbfs silently coerce private mappings of hugetlb files
> into shared ones. So private writable mapping has MAP_SHARED
> semantics. I think, such mappings should be disallowed.
> First, such behavior allows open hugetlbfs file O_RDONLY, and
> overwrite it via mmap(PROT_READ|PROT_WRITE, MAP_PRIVATE), so
> it is security bug.
> Second, private writable mmap() should fail just because kernel
> does not support this.
> I beleive, it is ok to allow private readonly hugetlb mappings,
> sys_mprotect() does not work with hugetlb vmas.
> There is another problem. Hugetlb mapping is always prefaulted,
> pages allocated at mmap() time. So even readonly mapping allows
> to enlarge the size of the hugetlbfs file, and steal huge pages
> without appropriative permissions.
> Patch on top of vm_pgoff fixes, see
> http://marc.theaimsgroup.com/?l=linux-kernel&m=108938233708584
This probably doesn't break anything worth caring about, but it may
make people happier to just force MAP_SHARED on.
-- wli
next prev parent reply other threads:[~2004-07-12 0:15 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2004-07-11 12:59 [PATCH] hugetlbfs private mappings Oleg Nesterov
2004-07-12 0:15 ` William Lee Irwin III [this message]
2004-07-12 12:11 ` Oleg Nesterov
2004-07-12 19:35 ` William Lee Irwin III
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