This is a note to let you know that I've just added the patch titled USB: don't free bandwidth_mutex too early to the 4.4-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: usb-don-t-free-bandwidth_mutex-too-early.patch and it can be found in the queue-4.4 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From ab2a4bf83902c170d29ba130a8abb5f9d90559e1 Mon Sep 17 00:00:00 2001 From: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> Date: Mon, 27 Jun 2016 10:23:10 -0400 Subject: USB: don't free bandwidth_mutex too early From: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxxxxxxx> Reported-by: Chung-Geol Kim <chunggeol.kim@xxxxxxxxxxx> Tested-by: Chung-Geol Kim <chunggeol.kim@xxxxxxxxxxx> Cc: Sumit Semwal <sumit.semwal@xxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- 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); Patches currently in stable-queue which might be from stern@xxxxxxxxxxxxxxxxxxx are queue-4.4/usb-don-t-free-bandwidth_mutex-too-early.patch