On Tue, Aug 25, 2015 at 05:59:11PM -0700, Darrick J. Wong wrote:

On Wed, Aug 26, 2015 at 10:45:02AM +1000, Dave Chinner wrote:

quoted

On Tue, Aug 25, 2015 at 05:32:59PM -0700, Darrick J. Wong wrote:

quoted

Check the v5 fields (uuid, blocknr, owner) of attribute blocks for
obvious errors while scanning xattr blocks.  If the ownership info
is incorrect, kill the block.

Signed-off-by: Darrick J. Wong <redacted>

Why hasn't the buffer verifier done this validation?

Maybe I'm confused here, so here's what I think is going on:

AFAICT most of the verifiers do things like this:

if (crcs_enabled && cksum_verification fails) {
	xfs_buf_ioerror(bp, -EFSBADCRC);
} else if (header_is_insane) {
	xfs_buf_ioerror(bp, -EFSCORRUPTED);
}

The fuzzer corrupts the UUID without updating the CRC.  The verifier first
checks the CRC and it doesn't match, so it sets b_error to -EFSBADCRC and
doesn't get to the header check. 

Ok, that explains it - I didn't consider that case. This would seem
like a general problem for repair when CRC errors are detected? i.e.
we set the repair flag without doing the remaining verifier validity
checks?

As it is, I don't really like duplicating the verifier checks in
repair. ISTR I recently suggested that we need to factor all the
common verifier checks (magic, owner, uuid, blockno) into a single
function that all verifiers called to remove all the code
duplication. If we do this, then repair can also call the function
to verify headers after a CRC failure to determine if repair is
possible....

This is a bit more work, so I'll probably take this specific patch
for 4.2.0, but I'd like to see this all factored out so we aren't
duplicating code unnecessarily.

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com

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