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From: =?utf-8?Q?Dag-Erling_Sm=C3=B8rgrav?= <des@des.no>
To: Konstantin Belousov <kostikbel@gmail.com>
Subject: Re: md(4) (swap-base) disks not cleaned on creation
References: <20121106184658.GA24262@psconsult.nl>
 <20121106192704.GM73505@kib.kiev.ua>
Date: Wed, 07 Nov 2012 13:36:55 +0100
In-Reply-To: <20121106192704.GM73505@kib.kiev.ua> (Konstantin Belousov's
 message of "Tue, 6 Nov 2012 21:27:04 +0200")
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Cc: freebsd-security@freebsd.org, Paul Schenkeveld <freebsd@psconsult.nl>
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Konstantin Belousov <kostikbel@gmail.com> writes:
> It is definitely not a security issue.

I disagree.  There may be legitimate reasons for root to create an md
and give read access to an unprivileged user, under the assumption that
it is zeroed; or to allow root in a jail to create mds.

> That said, the following patch should fix the nit. I am unsure about
> it, because it fixes mostly non-issue by spending CPU time to zero a
> page which would be either zeroed or overwritten right now anyway in
> normal usage.

You can at least partly mitigate this by adding VM_ALLOC_ZERO to the
flags passed to vm_page_grab() on line 666 and then checking the PG_ZERO
bit in m->flags.

DES
--=20
Dag-Erling Sm=C3=B8rgrav - des@des.no