linux-kernel - Re: [patch 7/8] allow unprivileged mounts

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Date:	Sat, 21 Apr 2007 10:57:10 -0600
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Jan Engelhardt <jengelh@...ux01.gwdg.de>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Miklos Szeredi <miklos@...redi.hu>, 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 7/8] allow unprivileged mounts

Jan Engelhardt <jengelh@...ux01.gwdg.de> writes:

> On Apr 21 2007 08:10, Eric W. Biederman wrote:
>>>
>>>> Define a new fs flag FS_SAFE, which denotes, that unprivileged
>>>> mounting of this filesystem may not constitute a security problem.
>>>> 
>>>> Since most filesystems haven't been designed with unprivileged
>>>> mounting in mind, a thorough audit is needed before setting this flag.
>>>
>>> Practically speaking, is there any realistic likelihood that any filesystem
>>> apart from FUSE will ever use this?
>>
>>Also potentially some of the kernel virtual filesystems.  /proc should
>>be safe already.  If you don't have any kind of backing store this problem
>>gets easier.
>
> tmpfs!

tmpfs is a possible problem because it can consume lots of ram/swap.  Which
is why it has limits on the amount of space it can consume.  Those are set as
mount options as I recall.  Which means that we would need to do something
different with respect to limits before tmpfs could become safe for
an untrusted user to mount.

Still it's close.


Eric
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