[ 031/180] usbnet: increase URB reference count before usb_unlink_urb

[Willy Tarreau]

2.6.32-longterm review patch.  If anyone has any objections, please let me know.

------------------

From: tom.leiming@xxxxxxxxx <tom.leiming@xxxxxxxxx>

commit 0956a8c20b23d429e79ff86d4325583fc06f9eb4 upstream.

Commit 4231d47e6fe69f061f96c98c30eaf9fb4c14b96d(net/usbnet: avoid
recursive locking in usbnet_stop()) fixes the recursive locking
problem by releasing the skb queue lock, but it makes usb_unlink_urb
racing with defer_bh, and the URB to being unlinked may be freed before
or during calling usb_unlink_urb, so use-after-free problem may be
triggerd inside usb_unlink_urb.

The patch fixes the use-after-free problem by increasing URB
reference count with skb queue lock held before calling
usb_unlink_urb, so the URB won't be freed until return from
usb_unlink_urb.

Cc: stable@xxxxxxxxxx
Cc: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
Cc: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>
Cc: Oliver Neukum <oliver@xxxxxxxxxx>
Reported-by: Dave Jones <davej@xxxxxxxxxx>
Signed-off-by: Ming Lei <tom.leiming@xxxxxxxxx>
Acked-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Willy Tarreau <w@xxxxxx>
---
 drivers/net/usb/usbnet.c |    9 +++++++++
 1 files changed, 9 insertions(+), 0 deletions(-)

diff --git a/drivers/net/usb/usbnet.c b/drivers/net/usb/usbnet.c
index da33dce..a92a415 100644
--- a/drivers/net/usb/usbnet.c
+++ b/drivers/net/usb/usbnet.c
@@ -584,6 +584,14 @@ static int unlink_urbs (struct usbnet *dev, struct sk_buff_head *q)
 		entry = (struct skb_data *) skb->cb;
 		urb = entry->urb;
 
+		/*
+		 * Get reference count of the URB to avoid it to be
+		 * freed during usb_unlink_urb, which may trigger
+		 * use-after-free problem inside usb_unlink_urb since
+		 * usb_unlink_urb is always racing with .complete
+		 * handler(include defer_bh).
+		 */
+		usb_get_urb(urb);
 		spin_unlock_irqrestore(&q->lock, flags);
 		// during some PM-driven resume scenarios,
 		// these (async) unlinks complete immediately
@@ -592,6 +600,7 @@ static int unlink_urbs (struct usbnet *dev, struct sk_buff_head *q)
 			devdbg (dev, "unlink urb err, %d", retval);
 		else
 			count++;
+		usb_put_urb(urb);
 		spin_lock_irqsave(&q->lock, flags);
 	}
 	spin_unlock_irqrestore (&q->lock, flags);
-- 
1.7.2.1.45.g54fbc



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