[PATCH] usb: dwc3: gadget: Fix list_del corruption in dwc3_ep_dequeue

[PATCH] usb: dwc3: gadget: Fix list_del corruption in dwc3_ep_dequeue

[Jack Pham]

From: Mayank Rana <mrana@codeaurora.org>

dwc3_ep_dequeue() waits for completion of End Transfer command
using wait_event_lock_irq(), which will release the dwc3->lock
while waiting and reacquire after completion. This allows a
potential race condition with ep_disable() which also removes
all requests from started_list and pending_list. The check for
NULL r->trb should catch this but currently it exits to the
wrong 'out1' label which calls dwc3_gadget_giveback(). Since
its list entry was already removed, if CONFIG_DEBUG_LIST is
enabled a 'list_del corruption' bug is thrown since its
next/prev pointers are already LIST_POISON1/2. If r->trb is
NULL it should simply exit to 'out0'.

Fixes: cf3113d893d4 ("usb: dwc3: gadget: properly increment dequeue pointer on ep_dequeue")
Cc: stable@vger.kernel.org
Signed-off-by: Mayank Rana <mrana@codeaurora.org>
Signed-off-by: Jack Pham <jackp@codeaurora.org>
---
 drivers/usb/dwc3/gadget.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/usb/dwc3/gadget.c b/drivers/usb/dwc3/gadget.c
index 2bda4eb..1238a97 100644
--- a/drivers/usb/dwc3/gadget.c
+++ b/drivers/usb/dwc3/gadget.c
@@ -1417,7 +1417,7 @@ static int dwc3_gadget_ep_dequeue(struct usb_ep *ep,
 					dwc->lock);
 
 			if (!r->trb)
-				goto out1;
+				goto out0;
 
 			if (r->num_pending_sgs) {
 				struct dwc3_trb *trb;
-- 
2.9.1.200.gb1ec08f

Re: [PATCH] usb: dwc3: gadget: Fix list_del corruption in dwc3_ep_dequeue

[Jack Pham]

Hi Felipe,

On Fri, Mar 23, 2018 at 10:05:33AM -0700, Jack Pham wrote:
> dwc3_ep_dequeue() waits for completion of End Transfer command
> using wait_event_lock_irq(), which will release the dwc3->lock
> while waiting and reacquire after completion. This allows a
> potential race condition with ep_disable() which also removes
> all requests from started_list and pending_list. The check for
> NULL r->trb should catch this but currently it exits to the
> wrong 'out1' label which calls dwc3_gadget_giveback(). Since
> its list entry was already removed, if CONFIG_DEBUG_LIST is
> enabled a 'list_del corruption' bug is thrown since its
> next/prev pointers are already LIST_POISON1/2. If r->trb is
> NULL it should simply exit to 'out0'.
> 
> Fixes: cf3113d893d4 ("usb: dwc3: gadget: properly increment dequeue pointer on ep_dequeue")

Upon taking a second look at this patch, and noting the subject of the
Fixes tag here, one side effect of this fix is that dep->queued_requests
won't get decremented. I see this is a counter for tracing purposes so
probably doesn't affect function. But it begs the question of whether
dwc3_remove_requests() as called from __dwc3_gadget_ep_disable() should
have decremented this counter or even zeroed it out completely?

>  			if (!r->trb)
> -				goto out1;
> +				goto out0;
>  

Thanks,
Jack
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