[PATCH] iommu/dma: Fix check for error return from iommu_map_sg_atomic()

[Niklas Schnelle <schnelle@linux.ibm.com>]

In __iommu_dma_alloc_noncontiguous() the value returned by
iommu_map_sg_atomic() is checked for being smaller than size. Before
commit ad8f36e4b6b1 ("iommu: return full error code from
iommu_map_sg[_atomic]()") this simply checked if the requested size was
successfully mapped.

After that commit iommu_map_sg_atomic() may also return a negative
error value. In principle this too would be covered by the existing
check. There is one problem however, as size is of type size_t while the
return type of iommu_map_sg_atomic() is now of type ssize_t the latter gets
converted to size_t and negative error values end up as very large
positive values making the check succeed. Fix this by making the return
type visible with a local variable and add an explicit cast to ssize_t.

Fixes: ad8f36e4b6b1 ("iommu: return full error code from iommu_map_sg[_atomic]()")
Cc: stable@vger.kernel.org
Signed-off-by: Niklas Schnelle <schnelle@linux.ibm.com>
---
 drivers/iommu/dma-iommu.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
index 09f6e1c0f9c0..b4fcf1d92994 100644
--- a/drivers/iommu/dma-iommu.c
+++ b/drivers/iommu/dma-iommu.c
@@ -776,6 +776,7 @@ static struct page **__iommu_dma_alloc_noncontiguous(struct device *dev,
 	unsigned int count, min_size, alloc_sizes = domain->pgsize_bitmap;
 	struct page **pages;
 	dma_addr_t iova;
+	ssize_t mapped;
 
 	if (static_branch_unlikely(&iommu_deferred_attach_enabled) &&
 	    iommu_deferred_attach(dev, domain))
@@ -813,8 +814,8 @@ static struct page **__iommu_dma_alloc_noncontiguous(struct device *dev,
 			arch_dma_prep_coherent(sg_page(sg), sg->length);
 	}
 
-	if (iommu_map_sg_atomic(domain, iova, sgt->sgl, sgt->orig_nents, ioprot)
-			< size)
+	mapped = iommu_map_sg_atomic(domain, iova, sgt->sgl, sgt->orig_nents, ioprot);
+	if (mapped < (ssize_t)size)
 		goto out_free_sg;
 
 	sgt->sgl->dma_address = iova;
-- 
2.32.0