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

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:

quoted

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 <redacted>
Signed-off-by: Matt Porter <redacted>
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.

quoted

 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