iommu: Don't take group reference in iommu_alloc_default_domain()

The iommu_alloc_default_domain() function takes a reference to an IOMMU
group without releasing it. This causes the group to never be released,
with undefined side effects.

The function has only one call-site, which takes a group reference on
its own, so to fix this leak, do not take another reference in
iommu_alloc_default_domain() and pass the group as a function parameter
instead.

Fixes: 6e1aa204 ("iommu: Move default domain allocation to iommu_probe_device()")
Reported-by: Sai Prakash Ranjan <saiprakash.ranjan@codeaurora.org>
Signed-off-by: Joerg Roedel <jroedel@suse.de>
Tested-by: Sai Prakash Ranjan <saiprakash.ranjan@codeaurora.org>
Cc: Sai Prakash Ranjan <saiprakash.ranjan@codeaurora.org>
Link: https://lore.kernel.org/r/20200525130122.380-1-joro@8bytes.org
Reference: https://lore.kernel.org/lkml/20200522130145.30067-1-saiprakash.ranjan@codeaurora.org/

drivers/iommu/iommu.c

@@ -80,7 +80,8 @@ static bool iommu_cmd_line_dma_api(void)
 	return !!(iommu_cmd_line & IOMMU_CMD_LINE_DMA_API);
 }
 
-static int iommu_alloc_default_domain(struct device *dev);
+static int iommu_alloc_default_domain(struct iommu_group *group,
+				      struct device *dev);
 static struct iommu_domain *__iommu_domain_alloc(struct bus_type *bus,
 						 unsigned type);
 static int __iommu_attach_device(struct iommu_domain *domain,
@@ -251,17 +252,17 @@ int iommu_probe_device(struct device *dev)
 	if (ret)
 		goto err_out;
 
+	group = iommu_group_get(dev);
+	if (!group)
+		goto err_release;
+
 	/*
 	 * Try to allocate a default domain - needs support from the
 	 * IOMMU driver. There are still some drivers which don't
 	 * support default domains, so the return value is not yet
 	 * checked.
 	 */
-	iommu_alloc_default_domain(dev);
-
-	group = iommu_group_get(dev);
-	if (!group)
-		goto err_release;
+	iommu_alloc_default_domain(group, dev);
 
 	if (group->default_domain)
 		ret = __iommu_attach_device(group->default_domain, dev);
@@ -1478,15 +1479,11 @@ static int iommu_group_alloc_default_domain(struct bus_type *bus,
 	return 0;
 }
 
-static int iommu_alloc_default_domain(struct device *dev)
+static int iommu_alloc_default_domain(struct iommu_group *group,
+				      struct device *dev)
 {
-	struct iommu_group *group;
 	unsigned int type;
 
-	group = iommu_group_get(dev);
-	if (!group)
-		return -ENODEV;
-
 	if (group->default_domain)
 		return 0;