linux-kernel - Re: [PATCH] utimensat() non-conformances and fixes [v3]

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Message-ID: <cfd18e0f0806030439n5a11fa4aocd6251ffab66b6dd@mail.gmail.com>
Date:	Tue, 3 Jun 2008 13:39:07 +0200
From:	"Michael Kerrisk" <mtk.manpages@...glemail.com>
To:	"Jamie Lokier" <jamie@...reable.org>
Cc:	"Al Viro" <viro@...iv.linux.org.uk>,
	"Miklos Szeredi" <miklos@...redi.hu>, drepper@...hat.com,
	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	linux-man@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH] utimensat() non-conformances and fixes [v3]

On Tue, Jun 3, 2008 at 1:30 PM, Jamie Lokier <jamie@...reable.org> wrote:
> Michael Kerrisk wrote:
>> > FWIW, I very much doubt that you are right wrt required
>> > permissions, though.  AFAICS, intent here is "if you can write to
>> > file, you can touch the timestamps anyway" and having descriptor
>> > opened for write gives that, current permissions be damned.
>>
>> The standard is pretty clear on this point:
>>
>> [[
>> Only a process with the effective user ID equal to the user ID of the
>> file, or with write access to the file, or with appropriate privileges
>> may use futimens( ) or utimensat( ) with a null pointer as the times
>> argument or with both tv_nsec fields set to the special value
>> UTIME_NOW.
>> ]]
>>
>> The crucial words here are "a process ... with write access to the
>> file" -- in other words, the permissions are determined by the
>> process's credentials, not by the access mode of the file descriptor.
>> I was not 100% sure on that to start with, so I did check it out with
>> one of the folk at The Open Group, to make sure of my understanding.
>
> Is there anything else where the file descriptor's access mode allows
> doing things on Linux, but the standard requires a permissions check
> each time?

Jamie,

I can't think of examples offhand -- but I'm also not quite sure what
your question is about.  Could you say a little more?

Cheers,

Michael


-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Found a bug? http://www.kernel.org/doc/man-pages/reporting_bugs.html
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