[PATCH 5.17 018/772] usb: dwc3: gadget: Move null pinter check to proper place

Greg Kroah-Hartman
2022-06-07T20:18:14Z

From: Albert Wang <albertccwang@google.com>

commit 3c5880745b4439ac64eccdb040e37fc1cc4c5406 upstream.

When dwc3_gadget_ep_cleanup_completed_requests() called to
dwc3_gadget_giveback() where the dwc3 lock is released, other thread is
able to execute. In this situation, usb_ep_disable() gets the chance to
clear endpoint descriptor pointer which leds to the null pointer
dereference problem. So needs to move the null pointer check to a proper
place.

Example call stack:

Thread#1:
dwc3_thread_interrupt()
spin_lock
-> dwc3_process_event_buf()
-> dwc3_process_event_entry()
-> dwc3_endpoint_interrupt()
-> dwc3_gadget_endpoint_trbs_complete()
-> dwc3_gadget_ep_cleanup_completed_requests()
...
-> dwc3_giveback()
spin_unlock
Thread#2 executes

Thread#2:
configfs_composite_disconnect()
-> __composite_disconnect()
-> ffs_func_disable()
-> ffs_func_set_alt()
-> ffs_func_eps_disable()
-> usb_ep_disable()
wait for dwc3 spin_lock
Thread#1 released lock
clear endpoint.desc

Fixes: 26288448120b ("usb: dwc3: gadget: Fix null pointer exception")
Cc: stable <stable@kernel.org>
Signed-off-by: Albert Wang <albertccwang@google.com>
Link: https://lore.kernel.org/r/20220518061315.3359198-1-albertccwang@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/usb/dwc3/gadget.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)

--- a/drivers/usb/dwc3/gadget.c
+++ b/drivers/usb/dwc3/gadget.c
@@ -3335,14 +3335,14 @@ static bool dwc3_gadget_endpoint_trbs_co
struct dwc3 *dwc = dep->dwc;
bool no_started_trb = true;

- if (!dep->endpoint.desc)
- return no_started_trb;
-
dwc3_gadget_ep_cleanup_completed_requests(dep, event, status);

if (dep->flags & DWC3_EP_END_TRANSFER_PENDING)
goto out;

+ if (!dep->endpoint.desc)
+ return no_started_trb;
+
if (usb_endpoint_xfer_isoc(dep->endpoint.desc) &&
list_empty(&dep->started_list) &&
(list_empty(&dep->pending_list) || status == -EXDEV))