[PATCH] iommu: Fix refcount leak in iommu_device_claim_dma_owner

[Miaoqian Lin <linmq006@gmail.com>]

iommu_group_get() returns the group with the reference incremented.
Also an empty @owner is a more serious problem than refcount leak.
Move iommu_group_get() after owner check to fix the refcount leak.

Fixes: 89395ccedbc1 ("iommu: Add device-centric DMA ownership interfaces")
Signed-off-by: Miaoqian Lin <linmq006@gmail.com>
---
changes in v2:
- Remove set NULL to group as suggested by Baolu Lu.
- Update commit message according to Lu's explanation.
---
 drivers/iommu/iommu.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
index de91dd88705b..5f6a85aea501 100644
--- a/drivers/iommu/iommu.c
+++ b/drivers/iommu/iommu.c
@@ -3185,14 +3185,16 @@ EXPORT_SYMBOL_GPL(iommu_group_claim_dma_owner);
  */
 int iommu_device_claim_dma_owner(struct device *dev, void *owner)
 {
-	struct iommu_group *group = iommu_group_get(dev);
+	struct iommu_group *group;
 	int ret = 0;
 
-	if (!group)
-		return -ENODEV;
 	if (WARN_ON(!owner))
 		return -EINVAL;
 
+	group = iommu_group_get(dev);
+	if (!group)
+		return -ENODEV;
+
 	mutex_lock(&group->mutex);
 	if (group->owner_cnt) {
 		if (group->owner != owner) {
-- 
2.25.1