vfio: Limit group opens

vfio_group_fops_open attempts to limit concurrent sessions by
disallowing opens once group->container is set.  This really doesn't
do what we want and allow for inconsistent behavior, for instance a
group can be opened twice, then a container set giving the user two
file descriptors to the group.  But then it won't allow more to be
opened.  There's not much reason to have the group opened multiple
times since most access is through devices or the container, so
complete what the original code intended and only allow a single
instance.

Signed-off-by: Alex Williamson <alex.williamson@redhat.com>

1 files changed, 14 insertions, 0 deletions

diff --git a/drivers/vfio/vfio.c b/drivers/vfio/vfio.c
index 6d78736563de..d30f44da8762 100644
--- a/drivers/vfio/vfio.c
+++ b/drivers/vfio/vfio.c
@@ -76,6 +76,7 @@ struct vfio_group {
         struct notifier_block           nb;
         struct list_head                vfio_next;
         struct list_head                container_next;
+        atomic_t                        opened;
 };
 
 struct vfio_device {
@@ -206,6 +207,7 @@ static struct vfio_group *vfio_create_group(struct iommu_group *iommu_group)
         INIT_LIST_HEAD(&group->device_list);
         mutex_init(&group->device_lock);
         atomic_set(&group->container_users, 0);
+        atomic_set(&group->opened, 0);
         group->iommu_group = iommu_group;
 
         group->nb.notifier_call = vfio_iommu_group_notifier;
@@ -1236,12 +1238,22 @@ static long vfio_group_fops_compat_ioctl(struct file *filep,
 static int vfio_group_fops_open(struct inode *inode, struct file *filep)
 {
         struct vfio_group *group;
+        int opened;
 
         group = vfio_group_get_from_minor(iminor(inode));
         if (!group)
                 return -ENODEV;
 
+        /* Do we need multiple instances of the group open?  Seems not. */
+        opened = atomic_cmpxchg(&group->opened, 0, 1);
+        if (opened) {
+                vfio_group_put(group);
+                return -EBUSY;
+        }
+
+        /* Is something still in use from a previous open? */
         if (group->container) {
+                atomic_dec(&group->opened);
                 vfio_group_put(group);
                 return -EBUSY;
         }
@@ -1259,6 +1271,8 @@ static int vfio_group_fops_release(struct inode *inode, struct file *filep)
 
         vfio_group_try_dissolve_container(group);
 
+        atomic_dec(&group->opened);
+
         vfio_group_put(group);
 
         return 0;