linux-ext4 - Re: [PATCH] ext3: Avoid false EIO errors

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Message-ID: <49D0E169.7020101@redhat.com>
Date:	Mon, 30 Mar 2009 10:12:41 -0500
From:	Eric Sandeen <sandeen@...hat.com>
To:	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
CC:	Jan Kara <jack@...e.cz>, linux-ext4@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] ext3: Avoid false EIO errors

Aneesh Kumar K.V wrote:
> On Mon, Mar 30, 2009 at 08:53:42AM -0500, Eric Sandeen wrote:
>> Aneesh Kumar K.V wrote:
>>
>>> We do a vmtruncate if we failed to allocate blocks in
>>> ext3_write_begin. That is done after the closing the current
>>> transaction. If we crash in between (ie, after committing the
>>> transaction allocating blocks and before committing the transaction that
>>> is doing truncate) we would only have  some data blocks leaking. But
>>> that would be better than user seeing zero's in the file ?. Also if we
>>> happen to add the inode to the orphan list and crash, the recovery would
>>> truncate it properly. So by doing a vmtruncate I guess the window would be
>>> small and we are already doing that in ext3_write_begin.
>> I don't agree that leaking data blocks is better than exposing zeros...
>> the former is a security flaw, the latter a (significant) annoyance.
>>
> 
> Even when we fail to track few data blocks we do zero them using 
> page_zero_new_buffers. So it should not imply a security flaw. I guess
> if we crash failing to commit the truncate fsck will look at the bitmap
> and find the blocks which are not tracked by any inode and will mark them
> free.

Oh, perhaps I misunderstood.  I thought you meant leaking data in
uninitialized blocks, but you meant losing track of those blocks'
allocation, I guess.  Sorry for the confusion...

-Eric
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