vfio/pci: Fix potential memory leak in vfio_msi_cap_len

mainline inclusion
from mainline-4.20-rc1
commit 30ea32ab
category: bugfix
bugzilla: 6453
CVE: NA

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

Free allocated vdev->msi_perm in error path.
Signed-off-by: NLi Qiang <liq3ea@gmail.com>
Reviewed-by: NEric Auger <eric.auger@redhat.com>
Signed-off-by: NAlex Williamson <alex.williamson@redhat.com>
Signed-off-by: NZhang Dianfang <zhangdianfang@huawei.com>
Reviewed-by: NHanjun Guo <guohanjun@huawei.com>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>

drivers/vfio/pci/vfio_pci_config.c

@@ -1180,8 +1180,10 @@ static int vfio_msi_cap_len(struct vfio_pci_device *vdev, u8 pos)
 		return -ENOMEM;
 
 	ret = init_pci_cap_msi_perm(vdev->msi_perm, len, flags);
-	if (ret)
+	if (ret) {
+		kfree(vdev->msi_perm);
 		return ret;
+	}
 
 	return len;
 }