Re: [PATCH] ocfs2: dereference before NULL check in ocfs2_direct_IO_get_blocks()

[Joel Becker <Joel.Becker@oracle.com>]

On Sat, Jun 03, 2006 at 11:15:58PM +0400, Alexey Dobriyan wrote:
> On Sat, Jun 03, 2006 at 11:34:39AM -0400, Florin Malita wrote:
> > 'bh_result' & 'inode' are explicitly checked against NULL so they
> > shouldn't be dereferenced prior to that.
> >
> > Coverity ID: 1273, 1274.
> 
> AFAICS, the patch is BS, as usual with this type of patches.
> 
> Can "inode" and "bh_result" be NULL here? I bet they can't.

	This is a common result of this sort of scan.  The scan merely
provides good information, not a perfect patch.  There are two
possibilities:

	1) The scan is right, and the dereference is dangerous.  The
	   patch is correct.
	2) The dereference is not dangerous ("can't happen"), and the
	   later check for NULL is spurious.  A correct patch would
	   merely remove the check.

	This is clearly a case of (2), but I bet that (1) is seen just
as often.

Joel

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Joel Becker
Principal Software Developer
Oracle
E-mail: joel.becker@oracle.com
Phone: (650) 506-8127