linux-kernel - [PATCH] r8a66597: Fix a possible concurrency use-after-free bug in r8a66597_endpoint

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Date:   Tue, 18 Dec 2018 18:00:20 +0800
From:   Jia-Ju Bai <baijiaju1990@...il.com>
To:     gregkh@...uxfoundation.org
Cc:     linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        Jia-Ju Bai <baijiaju1990@...il.com>
Subject: [PATCH] r8a66597: Fix a possible concurrency use-after-free bug in r8a66597_endpoint_disable()

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@...il.com>
---
 drivers/usb/host/r8a66597-hcd.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/usb/host/r8a66597-hcd.c b/drivers/usb/host/r8a66597-hcd.c
index 984892dd72f5..1495ce14ad22 100644
--- a/drivers/usb/host/r8a66597-hcd.c
+++ b/drivers/usb/host/r8a66597-hcd.c
@@ -1991,13 +1991,14 @@ 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