[PATCH v2] usb: r8a66597: Fix a possible concurrency use-after-free bug in r8a66597_endpoint_disable()

[Jia-Ju Bai]

The function r8a66597_endpoint_disable() and r8a66597_urb_enqueue() may
be concurrently executed.
The two functions both access a possible shared variable "hep->hcpriv".

This shared variable is freed by r8a66597_endpoint_disable() via the
call path:
r8a66597_endpoint_disable
  kfree(hep->hcpriv) (line 1995 in Linux-4.19)

This variable is read by r8a66597_urb_enqueue() via the call path:
r8a66597_urb_enqueue
  spin_lock_irqsave(&r8a66597->lock)
  init_pipe_info
    enable_r8a66597_pipe
      pipe = hep->hcpriv (line 802 in Linux-4.19)

The read operation is protected by a spinlock, but the free operation
is not protected by this spinlock, thus a concurrency use-after-free bug
may occur.

To fix this bug, the spin-lock and spin-unlock function calls in
r8a66597_endpoint_disable() are moved to protect the free operation.

Signed-off-by: Jia-Ju Bai <baijiaju1990@xxxxxxxxx>
---
v2:
* Add __acquires/__releases markings for r8a66597_endpoint_disable().
  Thanks Greg for good advice.
---
 drivers/usb/host/r8a66597-hcd.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/usb/host/r8a66597-hcd.c b/drivers/usb/host/r8a66597-hcd.c
index 984892dd72f5..42668aeca57c 100644
--- a/drivers/usb/host/r8a66597-hcd.c
+++ b/drivers/usb/host/r8a66597-hcd.c
@@ -1979,6 +1979,8 @@ static int r8a66597_urb_dequeue(struct usb_hcd *hcd, struct urb *urb,
 
 static void r8a66597_endpoint_disable(struct usb_hcd *hcd,
 				      struct usb_host_endpoint *hep)
+__acquires(r8a66597->lock)
+__releases(r8a66597->lock)
 {
 	struct r8a66597 *r8a66597 = hcd_to_r8a66597(hcd);
 	struct r8a66597_pipe *pipe = (struct r8a66597_pipe *)hep->hcpriv;
@@ -1991,13 +1993,14 @@ static void r8a66597_endpoint_disable(struct usb_hcd *hcd,
 		return;
 	pipenum = pipe->info.pipenum;
 
+	spin_lock_irqsave(&r8a66597->lock, flags);
 	if (pipenum == 0) {
 		kfree(hep->hcpriv);
 		hep->hcpriv = NULL;
+		spin_unlock_irqrestore(&r8a66597->lock, flags);
 		return;
 	}
 
-	spin_lock_irqsave(&r8a66597->lock, flags);
 	pipe_stop(r8a66597, pipe);
 	pipe_irq_disable(r8a66597, pipenum);
 	disable_irq_empty(r8a66597, pipenum);
-- 
2.17.0