[PATCH] dma-buf: fix integer overflow in fill_sg_entry() for buffers >= 8GiB

[Alex Mastro <amastro@fb.com>]

fill_sg_entry() splits large DMA buffers into multiple scatter-gather
entries, each holding up to UINT_MAX bytes. When calculating the DMA
address for entries beyond the second one, the expression (i * UINT_MAX)
causes integer overflow due to 32-bit arithmetic.

This manifests when the input arg length >= 8 GiB results in looping for
i >= 2.

Fix by casting i to dma_addr_t before multiplication.

Fixes: 3aa31a8bb11e ("dma-buf: provide phys_vec to scatter-gather mapping routine")
Signed-off-by: Alex Mastro <amastro@fb.com>
---
More color about how I discovered this in [1] for the commit at [2]:

[1] https://lore.kernel.org/all/aSZHO6otK0Heh+Qj@devgpu015.cco6.facebook.com
[2] https://lore.kernel.org/all/20251120-dmabuf-vfio-v9-6-d7f71607f371@nvidia.com
---
 drivers/dma-buf/dma-buf-mapping.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/dma-buf/dma-buf-mapping.c b/drivers/dma-buf/dma-buf-mapping.c
index b4819811a64a..b7352e609fbd 100644
--- a/drivers/dma-buf/dma-buf-mapping.c
+++ b/drivers/dma-buf/dma-buf-mapping.c
@@ -24,7 +24,7 @@ static struct scatterlist *fill_sg_entry(struct scatterlist *sgl, size_t length,
 		 * does not require the CPU list for mapping or unmapping.
 		 */
 		sg_set_page(sgl, NULL, 0, 0);
-		sg_dma_address(sgl) = addr + i * UINT_MAX;
+		sg_dma_address(sgl) = addr + (dma_addr_t)i * UINT_MAX;
 		sg_dma_len(sgl) = len;
 		sgl = sg_next(sgl);
 	}

---
base-commit: 5415d887db0e059920cb5673a32cc4d66daa280f
change-id: 20251125-dma-buf-overflow-e3253f108e36

Best regards,
-- 
Alex Mastro <amastro@fb.com>