[PATCH] arm: davinci: fix edma dmaengine induced null pointer dereference on da830

[Matt Porter]

On Tue, Mar 05, 2013 at 06:43:41AM +0000, Sekhar Nori wrote:
> Hi Matt,
> 
> I dropped the copy to stable folks since they dont want to be involved
> in patch reviews of this kind.
> 
> On 3/4/2013 10:22 PM, Matt Porter wrote:
> > This adds additional error checking to the private edma api implementation
> > to catch the case where the edma_alloc_slot() has an invalid controller
> > parameter. The edma dmaengine wrapper driver relies on this condition
> > being handled in order to avoid setting up a second edma dmaengine
> > instance on DA830.
> > 
> > Verfied using a DA850 with the second EDMA controller platform instance
> > removed to simulate a DA830 which only has a single EDMA controller.
> > 
> > Reported-by: Tomas Novotny <tomas at novotny.cz>
> > Signed-off-by: Matt Porter <mporter at ti.com>
> > Cc: stable at kernel.org
> 
> This should be stable at vger.kernel.org per
> Documentation/stable_kernel_rules.txt. Also, I think it is better to
> request the back port only from v3.7.x+ since the bug is important only
> after drivers/dma/edma.c was merged. So:
> 
> Cc: stable at vger.kernel.org # v3.7.x+

Agreed. Had the two year old email in my macros. Will update to
reflect 3.7.x+ only.

> >  arch/arm/mach-davinci/dma.c |    2 ++
> >  1 file changed, 2 insertions(+)
> > 
> > diff --git a/arch/arm/mach-davinci/dma.c b/arch/arm/mach-davinci/dma.c
> > index a685e97..f9eb836 100644
> > --- a/arch/arm/mach-davinci/dma.c
> > +++ b/arch/arm/mach-davinci/dma.c
> > @@ -747,6 +747,8 @@ int edma_alloc_slot(unsigned ctlr, int slot)
> >  		slot = EDMA_CHAN_SLOT(slot);
> >  
> >  	if (slot < 0) {
> > +		if (!edma_cc[ctlr])
> > +			return -EINVAL;
> 
> Shouldn't such a check be done outside of the if() since there is an
> 'else if' later which also accesses edma_cc[ctlr]

Yeah, as it turns out I also separately added the correct version
of this in the am33xx dmaengine series as it was an issue there.
I will correct this in v2.

-Matt