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

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Date:	Sun, 6 Dec 2015 12:32:58 +0100
From:	Mickaël Salaün <mic@...ikod.net>
To:	Tristan Schmelcher <tschmelcher@...gle.com>
Cc:	linux-kernel@...r.kernel.org, Jeff Dike <jdike@...toit.com>,
	Richard Weinberger <richard@....at>,
	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 04/12/2015 18:13, Tristan Schmelcher wrote:
> File permissions are checked at time of open, so I think this fchmod
> call has never had any effect.

Indeed, mmap doesn't require the file to be executable, only readable and writable. The fchmod seems to be a guarantee for this permissions but I don't see why a file newly created could not be writable.

> 
> If there is a concern that the mkstemp implementation may be insecure,
> why not set and restore the umask?
> 

I will add this safeguard.

 Mickaël


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