[PATCH 4.4 02/30] USB: dont free bandwidth_mutex too early

Greg Kroah-Hartman
2017-03-24T18:13:08Z

From: Alan Stern <stern@rowland.harvard.edu>

commit ab2a4bf83902c170d29ba130a8abb5f9d90559e1 upstream.

The USB core contains a bug that can show up when a USB-3 host
controller is removed. If the primary (USB-2) hcd structure is
released before the shared (USB-3) hcd, the core will try to do a
double-free of the common bandwidth_mutex.

The problem was described in graphical form by Chung-Geol Kim, who
first reported it:

=================================================
At *remove USB(3.0) Storage
sequence <1> --> <5> ((Problem Case))
=================================================
VOLD
------------------------------------|------------
(uevent)
________|_________
|<1> |
|dwc3_otg_sm_work |
|usb_put_hcd |
|peer_hcd(kref=2)|
|__________________|
________|_________
|<2> |
|New USB BUS #2 |
| |
|peer_hcd(kref=1) |
| |
--(Link)-bandXX_mutex|
| |__________________|
|
___________________ |
|<3> | |
|dwc3_otg_sm_work | |
|usb_put_hcd | |
|primary_hcd(kref=1)| |
|___________________| |
_________|_________ |
|<4> | |
|New USB BUS #1 | |
|hcd_release | |
|primary_hcd(kref=0)| |
| | |
|bandXX_mutex(free) |<-
|___________________|
(( VOLD ))
______|___________
|<5> |
| SCSI |
|usb_put_hcd |
|peer_hcd(kref=0) |
|*hcd_release |
|bandXX_mutex(free*)|<- double free
|__________________|

=================================================

This happens because hcd_release() frees the bandwidth_mutex whenever
it sees a primary hcd being released (which is not a very good idea
in any case), but in the course of releasing the primary hcd, it
changes the pointers in the shared hcd in such a way that the shared
hcd will appear to be primary when it gets released.

This patch fixes the problem by changing hcd_release() so that it
deallocates the bandwidth_mutex only when the _last_ hcd structure
referencing it is released. The patch also removes an unnecessary
test, so that when an hcd is released, both the shared_hcd and
primary_hcd pointers in the hcd's peer will be cleared.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Reported-by: Chung-Geol Kim <chunggeol.kim@samsung.com>
Tested-by: Chung-Geol Kim <chunggeol.kim@samsung.com>
Cc: Sumit Semwal <sumit.semwal@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/usb/core/hcd.c | 17 +++++++----------
1 file changed, 7 insertions(+), 10 deletions(-)

--- a/drivers/usb/core/hcd.c
+++ b/drivers/usb/core/hcd.c
@@ -2573,26 +2573,23 @@ EXPORT_SYMBOL_GPL(usb_create_hcd);
* Don't deallocate the bandwidth_mutex until the last shared usb_hcd is
* deallocated.
*
- * Make sure to only deallocate the bandwidth_mutex when the primary HCD is
- * freed. When hcd_release() is called for either hcd in a peer set
- * invalidate the peer's ->shared_hcd and ->primary_hcd pointers to
- * block new peering attempts
+ * Make sure to deallocate the bandwidth_mutex only when the last HCD is
+ * freed. When hcd_release() is called for either hcd in a peer set,
+ * invalidate the peer's ->shared_hcd and ->primary_hcd pointers.
*/
static void hcd_release(struct kref *kref)
{
struct usb_hcd *hcd = container_of (kref, struct usb_hcd, kref);

mutex_lock(&usb_port_peer_mutex);
- if (usb_hcd_is_primary_hcd(hcd)) {
- kfree(hcd->address0_mutex);
- kfree(hcd->bandwidth_mutex);
- }
if (hcd->shared_hcd) {
struct usb_hcd *peer = hcd->shared_hcd;

peer->shared_hcd = NULL;
- if (peer->primary_hcd == hcd)
- peer->primary_hcd = NULL;
+ peer->primary_hcd = NULL;
+ } else {
+ kfree(hcd->address0_mutex);
+ kfree(hcd->bandwidth_mutex);
}
mutex_unlock(&usb_port_peer_mutex);
kfree(hcd);