linux-ext4 - Re: [PATCH 05/39] libext2fs: don't memcpy identical pointers when writing a cache block

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Date:	Tue, 4 Nov 2014 11:48:52 -0500
From:	Theodore Ts'o <tytso@....edu>
To:	"Darrick J. Wong" <darrick.wong@...cle.com>
Cc:	Sami Liedes <sami.liedes@....fi>, linux-ext4@...r.kernel.org
Subject: Re: [PATCH 05/39] libext2fs: don't memcpy identical pointers when
 writing a cache block

On Sat, Oct 25, 2014 at 01:56:55PM -0700, Darrick J. Wong wrote:
> Sami Liedes found a scenario where we could memcpy incorrectly:
> 
> If a block read fails during an e2fsck run, the UNIX IO manager will
> call the io->read_error routine with a pointer to the internal block
> cache.  The e2fsck read error handler immediately tries to write the
> buffer back out to disk(!), at which point the block write code will
> try to copy the buffer contents back into the block cache.  Normally
> this is fine, but not when the write buffer is the cache itself!
> 
> So, plumb in a trivial check for this condition.  A more thorough
> solution would pass a duplicated buffer to the IO error handlers, but
> I don't know if that happens frequently enough to be worth the extra
> point of failure.
> 
> Signed-off-by: Darrick J. Wong <darrick.wong@...cle.com>
> Reported-by: Sami Liedes <sami.liedes@....fi>

Applied, thanks.

	 				- Ted
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