linux-kernel - Re: [PATCH] dma-buf: fix integer overflow in fill_sg

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Message-ID: <20251126115509.27d420b9.alex@shazbot.org>
Date: Wed, 26 Nov 2025 11:55:09 -0700
From: Alex Williamson <alex@...zbot.org>
To: Jason Gunthorpe <jgg@...pe.ca>
Cc: Alex Mastro <amastro@...com>, Sumit Semwal <sumit.semwal@...aro.org>,
 Christian König <christian.koenig@....com>, Leon Romanovsky
 <leon@...nel.org>, Kevin Tian <kevin.tian@...el.com>, Nicolin Chen
 <nicolinc@...dia.com>, linux-media@...r.kernel.org,
 dri-devel@...ts.freedesktop.org, linaro-mm-sig@...ts.linaro.org,
 linux-kernel@...r.kernel.org, kvm@...r.kernel.org, Ankit Agrawal
 <ankita@...dia.com>
Subject: Re: [PATCH] dma-buf: fix integer overflow in fill_sg_entry() for
 buffers >= 8GiB

On Wed, 26 Nov 2025 14:01:07 -0400
Jason Gunthorpe <jgg@...pe.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@...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@...dia.com>
> 
> AlexW, can you pick this up?

Yes, I'm planning to.  Thanks,

Alex