linux-ext4 - Re: [PATCH 5/4] exofs: Handle error from d_splice

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Date:	Tue, 12 Jun 2012 11:04:12 +0200
From:	Jan Kara <jack@...e.cz>
To:	Ted Ts'o <tytso@....edu>
Cc:	Boaz Harrosh <bharrosh@...asas.com>,
	Al Viro <viro@...IV.linux.org.uk>, Jan Kara <jack@...e.cz>,
	linux-ext4@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH 5/4] exofs: Handle error from d_splice_alias()

On Mon 11-06-12 15:01:08, Ted Tso wrote:
> On Mon, Jun 11, 2012 at 06:41:30PM +0300, Boaz Harrosh wrote:
> > 
> > My point being that please any changes made to ext2, in this area please also
> > apply to exofs, since it is just another copy/paste of ext2. I'll ACK any
> > which way you guys decide to properly go with, as part of the VFS changes.
> 
> Well, I already have this quick and dirty fix to address the problem
> in ext4.  See commit 7e936b7372.  If we need to make changes to all of
> the file systems to accomodate some new VFS abstraction, it might be
> worth considering whether it's easier/simpler to just put in a quick
> check like I did for ext4 (just so I could plug the security hole[1]
> quickly).
> 
> [1] It's a denial of service attack for kiosks that do automounts of
> USB sticks; granted, it's not that big a of a security deal, but some
> people care about such things.
> 
> Of course, if the new/changed VFS abstraction solves other problems,
> that's cool, but if not, sometimes a simple brute force check is
> better than something complicated if elegant.  :-)
  I think that fix in ext4 is fine. Just you don't catch the situation when
the directory entry points e.g. to a parent and that's deadlockable
trivially as well. Even if it points to some unrelated directory, you can
easily deadlock rename which tries to lock both directories. So I attempted
for a fix in VFS because that's the only place having enough information to
be able to tell whether you are creating directory hardlink or not.

								Honza
-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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