linux-kernel - Re: For review: user

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Date:	Tue, 09 Sep 2014 11:51:49 -0400
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	"Michael Kerrisk \(man-pages\)" <mtk.manpages@...il.com>
Cc:	lkml <linux-kernel@...r.kernel.org>,
	"linux-man\@vger.kernel.org" <linux-man@...r.kernel.org>,
	containers@...ts.linux-foundation.org,
	Andy Lutomirski <luto@...capital.net>,
	richard.weinberger@...il.com, "Serge E. Hallyn" <serge@...lyn.com>
Subject: Re: For review: user_namespace(7) man page

"Michael Kerrisk (man-pages)" <mtk.manpages@...il.com> writes:

> On 08/30/2014 02:53 PM, Eric W. Biederman wrote:
>> "Michael Kerrisk (man-pages)" <mtk.manpages@...il.com> writes:
> [...]
>
>
>>>        The initial user namespace has no parent namespace, but, for con‐
>>>        sistency, the kernel provides dummy user  and  group  ID  mapping
>>>        files  for  this namespace.  Looking at the uid_map file (gid_map
>>>        is the same) from a shell in the initial namespace shows:
>>>
>>>            $ cat /proc/$$/uid_map
>>>                     0          0 4294967295
>>>
>>>        This mapping tells us that the range starting at  user  ID  0  in
>>>        this namespace maps to a range starting at 0 in the (nonexistent)
>>>        parent namespace, and the length of  the  range  is  the  largest
>>>        32-bit unsigned integer.
>> 
>> Which deliberately leaves 4294967295 32bit (-1) unmapped.  (uid_t)-1 is
>> used in several interfaces (like setreuid) as a way to specify no uid
>> leaving it unmapped and unusuable guarantees that there will be no
>> confusion when using those kernel methods.
>
> So, I worked that piece into the text to give:
>
>        This  mapping  tells us that the range starting at user ID 0 in
>        this namespace maps to a range starting at 0 in  the  (nonexis‐
>        tent)  parent  namespace,  and  the  length of the range is the
>        largest 32-bit unsigned  integer.   (This  deliberately  leaves
>        4294967295  (the  32-bit  signed  -1  value) unmapped.  This is
>        deliberate: (uid_t) -1 is used  in  several  interfaces  (e.g.,
>        setreuid(2))  as  a  way  to  specify  "no  user  ID".  Leaving
>        setreuid(2)) unmapped and unusuable guarantees that there  will
         ^^^^ (uid_t) -1 (not setreuid(2)
>        be no confusion when using these interfaces.
>
> Okay?

Other than the typo fix above this looks good.

Eric
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