RE: [PATCH rc] iommufd: Don't overflow during division for dirty tracking

From: Jason Gunthorpe jgg@nvidia.com Sent: Thursday, October 9, 2025 2:17 AM

If pgshift is 63 then BITS_PER_TYPE(*bitmap->bitmap) * pgsize will overflow to 0 and this triggers divide by 0.

In this case the index should just be 0, so reorganize things to divide by shift and avoid hitting any overflows.

Cc: stable@vger.kernel.org Fixes: 58ccf0190d19 ("vfio: Add an IOVA bitmap support") Reported-by: syzbot+093a8a8b859472e6c257@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=093a8a8b859472e6c257 Signed-off-by: Jason Gunthorpe jgg@nvidia.com

Reviewed-by: Kevin Tian kevin.tian@intel.com