iommu/vt-d: Fix possible use-after-free of private domain

Multiple devices might share a private domain. One real example
is a pci bridge and all devices behind it. When remove a private
domain, make sure that it has been detached from all devices to
avoid use-after-free case.

Cc: Ashok Raj <ashok.raj@intel.com>
Cc: Jacob Pan <jacob.jun.pan@linux.intel.com>
Cc: Kevin Tian <kevin.tian@intel.com>
Cc: Alex Williamson <alex.williamson@redhat.com>
Fixes: 942067f1b6 ("iommu/vt-d: Identify default domains replaced with private")
Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
Tested-by: Alex Williamson <alex.williamson@redhat.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>

drivers/iommu/intel-iommu.c

@@ -4791,7 +4791,8 @@ static void __dmar_remove_one_dev_info(struct device_domain_info *info)
 
 	/* free the private domain */
 	if (domain->flags & DOMAIN_FLAG_LOSE_CHILDREN &&
-	    !(domain->flags & DOMAIN_FLAG_STATIC_IDENTITY))
+	    !(domain->flags & DOMAIN_FLAG_STATIC_IDENTITY) &&
+	    list_empty(&domain->devices))
 		domain_exit(info->domain);
 
 	free_devinfo_mem(info);