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Date: Fri, 30 Aug 2013 12:03:41 -0600
From: Jamie Gritton <jamie@FreeBSD.org>
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To: Jase Thew <jase@FreeBSD.org>
Subject: Re: svn commit: r252841 - in head/sys: dev/mem kern sys
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On 08/30/13 11:13, Jase Thew wrote:
> On 05/07/2013 22:31, Jamie Gritton wrote:
>> Author: jamie
>> Date: Fri Jul  5 21:31:16 2013
>> New Revision: 252841
>> URL: http://svnweb.freebsd.org/changeset/base/252841
>>
>> Log:
>>    Add new privileges, PRIV_KMEM_READ and PRIV_KMEM_WRITE, used in
>> opening
>>    /dev/kmem and /dev/mem (in addition to traditional file permission
>> checks).
>>    PRIV_KMEM_READ is different from other PRIV_* checks in that it's
>> allowed
>>    by default.
>>
>>    Reviewed by:    kib, mckusick
>>
> 
> Hi Jamie,
> 
> As a result of this commit (and r252845), it is no longer possible to
> access /dev/mem and /dev/kmem inside of a jail - is this behaviour
> intentional?
> 
> # dd if=/dev/mem bs=64 count=1
> dd: /dev/mem: Operation not permitted

It's intentional, but it's not intended to be the full solution. I also
need to add a permission flag to jails to allow kmem access. However I
didn't intend to disrupt read permission, though clearly it does since
it now passes through prison_priv_check. So I ought to add some code in
prison_priv_check that mirrors the code in priv_check_cred to allow
PRIV_KMEM_READ by default.

- Jamie