[PATCH 4.4 116/137] iommu: Dont overwrite domain pointer when there is no default_domain

[Greg Kroah-Hartman]

4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Joerg Roedel <jroedel@xxxxxxx>

commit eebb8034a5be8c2177cbf07ca2ecd2ff8a058958 upstream.

IOMMU drivers that do not support default domains, but make
use of the the group->domain pointer can get that pointer
overwritten with NULL on device add/remove.

Make sure this can't happen by only overwriting the domain
pointer when it is NULL.

Fixes: 1228236de5f9 ('iommu: Move default domain allocation to iommu_group_get_for_dev()')
Signed-off-by: Joerg Roedel <jroedel@xxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 drivers/iommu/iommu.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/drivers/iommu/iommu.c
+++ b/drivers/iommu/iommu.c
@@ -848,7 +848,8 @@ struct iommu_group *iommu_group_get_for_
 	if (!group->default_domain) {
 		group->default_domain = __iommu_domain_alloc(dev->bus,
 							     IOMMU_DOMAIN_DMA);
-		group->domain = group->default_domain;
+		if (!group->domain)
+			group->domain = group->default_domain;
 	}
 
 	ret = iommu_group_add_device(group, dev);