HID: hiddev: fix race between hiddev_disconnect and hiddev_release

When hiddev_disconnect() runs with chardev open, it will proceed with
usbhid_close(). When userspace in parallel runs the hiddev_release(),
it sees !hiddev->exists (as it has been already set so by
hiddev_disconnect()) and kfrees hiddev while hiddev_disconnect() hasn't
finished yet.

Serialize the access to hiddev->exists and hiddev->open by existancelock.

Reported-by: mike-@cinci.rr.com
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

1 files changed, 8 insertions, 2 deletions

diff --git a/drivers/hid/usbhid/hiddev.c b/drivers/hid/usbhid/hiddev.c
index 2baa71e6cc29..f4c67a5021c7 100644
--- a/drivers/hid/usbhid/hiddev.c
+++ b/drivers/hid/usbhid/hiddev.c
@@ -242,6 +242,7 @@ static int hiddev_release(struct inode * inode, struct file * file)
         list_del(&list->node);
         spin_unlock_irqrestore(&list->hiddev->list_lock, flags);
 
+        mutex_lock(&list->hiddev->existancelock);
         if (!--list->hiddev->open) {
                 if (list->hiddev->exist) {
                         usbhid_close(list->hiddev->hid);
@@ -252,6 +253,7 @@ static int hiddev_release(struct inode * inode, struct file * file)
         }
 
         kfree(list);
+        mutex_unlock(&list->hiddev->existancelock);
 
         return 0;
 }
@@ -300,17 +302,21 @@ static int hiddev_open(struct inode *inode, struct file *file)
         list_add_tail(&list->node, &hiddev->list);
         spin_unlock_irq(&list->hiddev->list_lock);
 
+        mutex_lock(&hiddev->existancelock);
         if (!list->hiddev->open++)
                 if (list->hiddev->exist) {
                         struct hid_device *hid = hiddev->hid;
                         res = usbhid_get_power(hid);
                         if (res < 0) {
                                 res = -EIO;
-                                goto bail;
+                                goto bail_unlock;
                         }
                         usbhid_open(hid);
                 }
+        mutex_unlock(&hiddev->existancelock);
         return 0;
+bail_unlock:
+        mutex_unlock(&hiddev->existancelock);
 bail:
         file->private_data = NULL;
         kfree(list);
@@ -911,7 +917,6 @@ void hiddev_disconnect(struct hid_device *hid)
 
         mutex_lock(&hiddev->existancelock);
         hiddev->exist = 0;
-        mutex_unlock(&hiddev->existancelock);
 
         usb_deregister_dev(usbhid->intf, &hiddev_class);
 
@@ -921,4 +926,5 @@ void hiddev_disconnect(struct hid_device *hid)
         } else {
                 kfree(hiddev);
         }
+        mutex_unlock(&hiddev->existancelock);
 }