[PATCH 3/4] iommufd: Reject a zero-length dirty bitmap request

[Andrea Parri <parri.andrea@gmail.com>]

iommufd_check_iova_range() subtracts one from bitmap->length before it
checks the length, so a zero-length request wraps to SIZE_MAX.  With
iova = 0 the wrapped value passes the overflow and alignment checks, and
the request reaches iova_bitmap_alloc() with length 0.

iova_bitmap_alloc() then sizes the bitmap from a length - 1 of SIZE_MAX,
so mapped_total_index is effectively unbounded.  The scan uses
last_iova = ULONG_MAX, which spans the whole IOAS when an area is mapped
at IOVA 0.  Reject a zero length before the subtraction.

Fixes: b9a60d6f850e ("iommufd: Add IOMMU_HWPT_GET_DIRTY_BITMAP")
Cc: stable@vger.kernel.org
Assisted-by: LLM
Signed-off-by: Andrea Parri <parri.andrea@gmail.com>
---
 drivers/iommu/iommufd/io_pagetable.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/iommu/iommufd/io_pagetable.c b/drivers/iommu/iommufd/io_pagetable.c
index 4e447ce74cf6c..283ab372e8da8 100644
--- a/drivers/iommu/iommufd/io_pagetable.c
+++ b/drivers/iommu/iommufd/io_pagetable.c
@@ -605,6 +605,9 @@ int iommufd_check_iova_range(struct io_pagetable *iopt,
 	size_t iommu_pgsize = iopt->iova_alignment;
 	u64 last_iova;
 
+	if (!bitmap->length)
+		return -EINVAL;
+
 	if (check_add_overflow(bitmap->iova, bitmap->length - 1, &last_iova))
 		return -EOVERFLOW;
 
-- 
2.53.0