linux-kernel - Re: [patch 0/8] mount ownership and unprivileged mount syscall (v4)

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Date:	Tue, 24 Apr 2007 19:04:36 -0600
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Karel Zak <kzak@...hat.com>
Cc:	Miklos Szeredi <miklos@...redi.hu>, akpm@...ux-foundation.org,
	serue@...ibm.com, viro@....linux.org.uk, linuxram@...ibm.com,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	containers@...ts.osdl.org
Subject: Re: [patch 0/8]  mount ownership and unprivileged mount syscall (v4)

Karel Zak <kzak@...hat.com> writes:

> On Fri, Apr 20, 2007 at 12:25:32PM +0200, Miklos Szeredi wrote:
>> The following extra security measures are taken for unprivileged
>> mounts:
>> 
>>  - usermounts are limited by a sysctl tunable
>>  - force "nosuid,nodev" mount options on the created mount
>
>  The original userspace "user=" solution also implies the "noexec"
>  option by default (you can override the default by "exec" option).
>  
>  It means the kernel based solution is not fully compatible ;-(

Why noexec?  Either it was a silly or arbitrary decision, or
our kernel design may be incomplete.

Now I can see not wanting to support executables if you are locking
down a system.  The classic don't execute a program from a CD just because
the CD was stuck in the drive problem.

So I can see how executing code from an untrusted source could prevent
exploitation of other problems, and we certainly don't want to do it
automatically.

Eric
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