linux-kernel - Re: loop subsystem corrupted after mounting multiple btrfs sub-volumes

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Mon, 29 Feb 2016 08:11:34 -0500
From:	"Austin S. Hemmelgarn" <ahferroin7@...il.com>
To:	Al Viro <viro@...IV.linux.org.uk>,
	Stanislav Brabec <sbrabec@...e.cz>
Cc:	linux-kernel@...r.kernel.org, Jens Axboe <axboe@...nel.dk>,
	Btrfs BTRFS <linux-btrfs@...r.kernel.org>,
	David Sterba <dsterba@...e.cz>
Subject: Re: loop subsystem corrupted after mounting multiple btrfs
 sub-volumes

On 2016-02-26 16:45, Al Viro wrote:
> On Fri, Feb 26, 2016 at 10:36:50PM +0100, Stanislav Brabec wrote:
>
>> It should definitely report error whenever trying -oloop on top of
>> anything else than a file. Or at least a warning.
>>
>> Well, even losetup should report a warning.
>
> Keep in mind that with crypto in the game it just might be useful to have
> loop-over-loop - it might be _not_ a no-op (hell, you might have two
> layers of encryption - not the smartest thing to do, but if that's what
> got dumped on your lap, you deal with what you've got).  So such warnings
> shouldn't be hard errors.
>
That and that using a loop device is one of the ways to expose 
partitions on a device the kernel doesn't normally expose them from.  In 
general, I'm pretty certain the preferred method is to use DM based 
mappings, but those aren't always available, and I've had multiple cases 
where I had to use nested loop devices to get to a filesystem.

You can't protect against everything, but you very much should not be 
doing something that is known to cause issues, and the current behavior 
of mount(8) WRT -o loop definitely can cause issues.