[PATCH] iommu/dma: Fix calculation overflow in __finalise_sg()

[Nicolin Chen <nicoleotsuka@gmail.com>]

The max_len is a u32 type variable so the calculation on the
left hand of the last if-condition will potentially overflow
when a cur_len gets closer to UINT_MAX -- note that there're
drivers setting max_seg_size to UINT_MAX:
  drivers/dma/dw-edma/dw-edma-core.c:745:
    dma_set_max_seg_size(dma->dev, U32_MAX);
  drivers/dma/dma-axi-dmac.c:871:
    dma_set_max_seg_size(&pdev->dev, UINT_MAX);
  drivers/mmc/host/renesas_sdhi_internal_dmac.c:338:
    dma_set_max_seg_size(dev, 0xffffffff);
  drivers/nvme/host/pci.c:2520:
    dma_set_max_seg_size(dev->dev, 0xffffffff);

So this patch just casts the cur_len in the calculation to a
size_t type to fix the overflow issue, as it's not necessary
to change the type of cur_len after all.

Fixes: 809eac54cdd6 ("iommu/dma: Implement scatterlist segment merging")
Cc: stable@vger.kernel.org
Signed-off-by: Nicolin Chen <nicoleotsuka@gmail.com>
---
 drivers/iommu/dma-iommu.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
index a9f13313a22f..676b7ecd451e 100644
--- a/drivers/iommu/dma-iommu.c
+++ b/drivers/iommu/dma-iommu.c
@@ -764,7 +764,7 @@ static int __finalise_sg(struct device *dev, struct scatterlist *sg, int nents,
 		 * - and wouldn't make the resulting output segment too long
 		 */
 		if (cur_len && !s_iova_off && (dma_addr & seg_mask) &&
-		    (cur_len + s_length <= max_len)) {
+		    ((size_t)cur_len + s_length <= max_len)) {
 			/* ...then concatenate it with the previous one */
 			cur_len += s_length;
 		} else {
-- 
2.17.1