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Date: Mon, 1 Jul 2019 13:39:55 +0100 From: Robin Murphy <robin.murphy@....com> To: Joerg Roedel <joro@...tes.org>, Nicolin Chen <nicoleotsuka@...il.com> Cc: iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org Subject: Re: [PATCH] iommu/dma: Fix calculation overflow in __finalise_sg() On 01/07/2019 13:21, Joerg Roedel wrote: > On Fri, Jun 21, 2019 at 09:38:14PM -0700, Nicolin Chen wrote: >> 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@...r.kernel.org >> Signed-off-by: Nicolin Chen <nicoleotsuka@...il.com> > > Looks good to me, but I let Robin take a look too before I apply it, > Robin? I'll need to take a closer look at how exactly an overflow would happen here (just got back off some holiday), but my immediate thought is that if this is a real problem, then what about 32-bit builds where size_t would still overflow? Robin.
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