linux-kernel - Re: Bad ext3/nfs DoS bug

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Message-ID: <20060719155502.GD3270@atrey.karlin.mff.cuni.cz>
Date:	Wed, 19 Jul 2006 17:55:02 +0200
From:	Jan Kara <jack@...e.cz>
To:	James <20@...ingley.org>
Cc:	Marcel Holtmann <marcel@...tmann.org>,
	linux-kernel@...r.kernel.org, akpm@...l.org, sct@...hat.com
Subject: Re: Bad ext3/nfs DoS bug

> So what happens next? Is the ext3 maintainer on sabatical,
> or am I expected to submit a patch to fix this?
  I guess people are mostly busy with OLS and such so maybe they missed
the discussion.. Giving CC to relevant people to catch their attention
:)
  Andrew, Stephen: James has come across a nasty bug (potentially remote
DoS). NFS extracts inode number from a filehandle and the inode number
eventually ends in ext3_read_inode(). Now if the inode number is bogus,
ext3_get_inode_block() calls ext3_error() and filesystem is remounted
RO or whatever else is configured. That is quite undesirable in this
case.
  Now the easy "fix" is to change ext3_error() to ext3_warning() but an
attacker flooding your logs with warnings is probably not good either
and in case the inode number comes from ext3 itself we should really do
ext3_error() as there is some corruption in the fs.
  Better fix would be to add a flag to read_inode() saying that the inode
number is from untrusted source (but that means changing a prototype of a
function every fs uses) and change export_iget() to pass this flag. Yet
another solution would be to make ext3 implement its own get_dentry() export
function and pass the flag internally...
  What do you think is the best solution?

								Honza

-- 
Jan Kara <jack@...e.cz>
SuSE CR Labs
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