From: Eric Auger <eric.auger@redhat.com>
Date: Fri, 11 Aug 2017 13:16:06 +0000 (+0200)
Subject: vfio: fix noiommu vfio_iommu_group_get reference count
X-Git-Url: https://git.stricted.de/?a=commitdiff_plain;h=d935ad91f07d20268fca97b1ddc56a816ac71826;p=GitHub%2Fmoto-9609%2Fandroid_kernel_motorola_exynos9610.git

vfio: fix noiommu vfio_iommu_group_get reference count

In vfio_iommu_group_get() we want to increase the reference
count of the iommu group.

In noiommu case, the group does not exist and is allocated.
iommu_group_add_device() increases the group ref count. However we
then call iommu_group_put() which decrements it.

This leads to a "refcount_t: underflow WARN_ON".

Only decrement the ref count in case of iommu_group_add_device
failure.

Signed-off-by: Eric Auger <eric.auger@redhat.com>
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
---

diff --git a/drivers/vfio/vfio.c b/drivers/vfio/vfio.c
index 330d50582f40..4ee4f361fe9f 100644
--- a/drivers/vfio/vfio.c
+++ b/drivers/vfio/vfio.c
@@ -138,9 +138,10 @@ struct iommu_group *vfio_iommu_group_get(struct device *dev)
 	iommu_group_set_name(group, "vfio-noiommu");
 	iommu_group_set_iommudata(group, &noiommu, NULL);
 	ret = iommu_group_add_device(group, dev);
-	iommu_group_put(group);
-	if (ret)
+	if (ret) {
+		iommu_group_put(group);
 		return NULL;
+	}
 
 	/*
 	 * Where to taint?  At this point we've added an IOMMU group for a