iommu: Don't overwrite domain pointer when there is no default_domain

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.

Cc: stable@vger.kernel.org # v4.4+
Fixes: 1228236de5f9 ('iommu: Move default domain allocation to iommu_group_get_for_dev()')
Signed-off-by: Joerg Roedel <jroedel@suse.de>

1 files changed, 2 insertions, 1 deletions

diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
index bfd4f7c3b1d8..b9df1411c894 100644
--- a/drivers/iommu/iommu.c
+++ b/drivers/iommu/iommu.c
@@ -848,7 +848,8 @@ struct iommu_group *iommu_group_get_for_dev(struct device *dev)
         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);