Re: [PATCH 3.2 108/221] spi: dw-mid: avoid potential NULL dereference

[Ben Hutchings]

On Wed, 2015-05-06 at 11:25 +0100, Luis Henriques wrote:
> On Tue, May 05, 2015 at 02:16:39AM +0100, Ben Hutchings wrote:
> > 3.2.69-rc1 review patch.  If anyone has any objections, please let me know.
> > 
> > ------------------
> > 
> > From: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
> > 
> > commit c9dafb27c84412fe4b17c3b94cc4ffeef5df1833 upstream.
> > 
> > When DMA descriptor allocation fails we should not try to assign any fields in
> > the bad descriptor. The patch adds the necessary checks for that.
> > 
> > Fixes: 7063c0d942a1 (spi/dw_spi: add DMA support)
> > Signed-off-by: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
> > Signed-off-by: Mark Brown <broonie@xxxxxxxxxx>
> > [bwh: Backported to 3.2: adjust context]
> > Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
> > ---
> >  drivers/spi/spi-dw-mid.c | 6 ++++++
> >  1 file changed, 6 insertions(+)
> > 
> > --- a/drivers/spi/spi-dw-mid.c
> > +++ b/drivers/spi/spi-dw-mid.c
> > @@ -155,6 +155,9 @@ static int mid_spi_dma_transfer(struct d
> >  				1,
> >  				DMA_TO_DEVICE,
> >  				DMA_PREP_INTERRUPT | DMA_COMPL_SKIP_DEST_UNMAP);
> > +	if (!txdesc)
> > +		return NULL;
> > +
> 
> This backport doesn't look right to me as the function returns an int,
> not a pointer.  OTOH, it seems like this return value is not checked
> anywhere, which is why I dropped this patch in the 3.16 kernel.

In mainline the DMA descriptor setup is split out into the
dw_spi_dma_prepare_tx() and dw_spi_dma_prepare_rx() functions.  If they
return NULL then mid_spi_dma_transfer() doesn't attempt to submit
adescriptor to the respective channel, but it still returns 0.

So not only is this backport pretty useless, but so is the upstream
'fix'.

Ben.

> Cheers,
> --
> LuÃs
> 
> >  	txdesc->callback = dw_spi_dma_done;
> >  	txdesc->callback_param = dws;
> >  
> > @@ -177,6 +180,9 @@ static int mid_spi_dma_transfer(struct d
> >  				1,
> >  				DMA_FROM_DEVICE,
> >  				DMA_PREP_INTERRUPT | DMA_COMPL_SKIP_DEST_UNMAP);
> > +	if (!rxdesc)
> > +		return NULL;
> > +
> >  	rxdesc->callback = dw_spi_dma_done;
> >  	rxdesc->callback_param = dws;
> >  
> > 
> > --
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-- 
Ben Hutchings
If at first you don't succeed, you're doing about average.

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