Re: [PATCHv3 1/2] arm64: Check for NULL device before getting the coherent_dma_mask

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On 12/11/2013 2:42 AM, Will Deacon wrote:
On Tue, Dec 10, 2013 at 09:43:35PM +0000, Laura Abbott wrote:
The device passed in to dma_alloc may be NULL. Check for this before
trying to get the coherent_dma_mask.

Cc: Will Deacon <will.deacon@xxxxxxx>
Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
Cc: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx>
Signed-off-by: Laura Abbott <lauraa@xxxxxxxxxxxxxx>
---
  arch/arm64/mm/dma-mapping.c |    2 +-
  1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/arch/arm64/mm/dma-mapping.c b/arch/arm64/mm/dma-mapping.c
index 4bd7579..4134212 100644
--- a/arch/arm64/mm/dma-mapping.c
+++ b/arch/arm64/mm/dma-mapping.c
@@ -33,7 +33,7 @@ static void *arm64_swiotlb_alloc_coherent(struct device *dev, size_t size,
  					  dma_addr_t *dma_handle, gfp_t flags,
  					  struct dma_attrs *attrs)
  {
-	if (IS_ENABLED(CONFIG_ZONE_DMA32) &&
+	if (dev && IS_ENABLED(CONFIG_ZONE_DMA32) &&
  	    dev->coherent_dma_mask <= DMA_BIT_MASK(32))
  		flags |= GFP_DMA32;
  	return swiotlb_alloc_coherent(dev, size, dma_handle, flags);

Unless I'm misreading the code, it looks like there are paths through
swiotlb_alloc_coherent that will dereference the dev parameter without a
NULL check. Are you sure we should allow for NULL devices here?


The current ARM code allows for NULL devices so that would be a difference in behavior between arm and arm64. We're also relying on this behavior in some code. Where exactly in swiotlb_alloc_coherent does this dereference happen? The only one I see is checked with 'if (hwdev && hwdev->coherent_dma_mask)'

Will


Thanks,
Laura
--
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