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

[Jason Gunthorpe]

On Tue, Nov 25, 2025 at 05:11:18PM -0800, Alex Mastro wrote:
> 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@xxxxxx>
> ---
> More color about how I discovered this in [1] for the commit at [2]:
> 
> [1] https://lore.kernel.org/all/aSZHO6otK0Heh+Qj@xxxxxxxxxxxxxxxxxxxxxxxxxxx
> [2] https://lore.kernel.org/all/20251120-dmabuf-vfio-v9-6-d7f71607f371@xxxxxxxxxx
> ---
>  drivers/dma-buf/dma-buf-mapping.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)

Reviewed-by: Jason Gunthorpe <jgg@xxxxxxxxxx>

AlexW, can you pick this up?

Thanks,
Jason