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Date: Sat, 12 Mar 2016 02:19:45 -0500
From: "Theodore Ts'o" <tytso@mit.edu>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Dave Chinner <david@fromorbit.com>, Andy Lutomirski <luto@amacapital.net>,
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Subject: Re: [PATCH 2/2] block: create ioctl to discard-or-zeroout a range of
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On Fri, Mar 11, 2016 at 04:44:16PM -0800, Linus Torvalds wrote:
> On Fri, Mar 11, 2016 at 4:35 PM, Theodore Ts'o <tytso@mit.edu> wrote:
> >
> > At the end of the day it's about whether you trust the userspace
> > program or not.
> 
> There's a big difference between "give the user rope", and "tie the
> rope in a noose and put a banana peel so that the user might stumble
> into the rope and hang himself", though.

So let's see.  The user application has to explicitly request
NO_HIDE_STALE via an fallocate flag --- so it requires changing the
source code and recompiling the application.  And then, the system
administrator has to pass in a mount option specifying a group that
the application has to run under.  And then the application has to run
setgid with that group's privileges.

I hardly think that can be considered handing the user a pre-tied
noose.

Sure, the application can do something stupid --- but I'd arguing
giving root to some junior sysadmin is far more likely to cause
problems.

Cheers,

						- Ted