linux-kernel - Re: [PATCH v2 1/2] um: Set secure access mode for temporary file

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Date:	Thu, 10 Dec 2015 00:58:28 +0100
From:	Mickaël Salaün <mic@...ikod.net>
To:	Richard Weinberger <richard@....at>,
	Tristan Schmelcher <tschmelcher@...gle.com>
Cc:	linux-kernel@...r.kernel.org, Jeff Dike <jdike@...toit.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	user-mode-linux-devel <user-mode-linux-devel@...ts.sourceforge.net>,
	user-mode-linux-user@...ts.sourceforge.net
Subject: Re: [PATCH v2 1/2] um: Set secure access mode for temporary file

On 08/12/2015 22:45, Richard Weinberger wrote:
> Am 08.12.2015 um 21:37 schrieb Tristan Schmelcher:
>> On 6 December 2015 at 09:43, Mickaël Salaün <mic@...ikod.net> wrote:
>>> Well, I'm concerned to use umask because it is not thread-safe and drivers may use create_mem_file() in a multi-theaded context.
>>
>> You are right. We should perhaps set the umask to 0700 permanently
>> during process start. But I am not sure if this will interfere with
>> other UML code.
> 
> It *should* not hurt. Let's see what explodes. :)

We can't force the kernel process umask without breaking compatibility with current implementation, especially with hostfs (i.e. the host umask prevail the guest one).

>>> I prefer to stick to fchmod and handle the race-condition with O_TMPFILE unsell someone is sure that this will not create bugs :)
>>
>> The fchmod call is basically useless and should probably be removed.
> 
> I agree.

I propose then to simply remove the fchmod call and let the O_TMPFILE flag do the magic :)

Regards,
 Mickaël


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