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

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

[Alex Mastro]

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>

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

[Leon Romanovsky]

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@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(-)
> 

Thanks,
Reviewed-by: Leon Romanovsky <leon@kernel.org>

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@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(-)

Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>

AlexW, can you pick this up?

Thanks,
Jason

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

[Alex Williamson]

On Wed, 26 Nov 2025 14:01:07 -0400
Jason Gunthorpe <jgg@ziepe.ca> wrote:

> 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@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(-)  
> 
> Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
> 
> AlexW, can you pick this up?

Yes, I'm planning to.  Thanks,

Alex

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

[Alex Williamson]

On Tue, 25 Nov 2025 17:11:18 -0800
Alex Mastro <amastro@fb.com> 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@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);
>  	}
> 

Applied to vfio next branch for v6.19.  Thanks,

Alex