From 0956a8c20b23d429e79ff86d4325583fc06f9eb4 Mon Sep 17 00:00:00 2001 From: "tom.leiming@gmail.com" Date: Thu, 22 Mar 2012 03:22:18 +0000 Subject: [PATCH] usbnet: increase URB reference count before usb_unlink_urb 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@kernel.org Cc: Sebastian Andrzej Siewior Cc: Alan Stern Cc: Oliver Neukum Reported-by: Dave Jones Signed-off-by: Ming Lei Acked-by: Greg Kroah-Hartman Signed-off-by: David S. Miller --- drivers/net/usb/usbnet.c | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/drivers/net/usb/usbnet.c b/drivers/net/usb/usbnet.c index 4b8b52ca09d8..febfdceeb9e5 100644 --- a/drivers/net/usb/usbnet.c +++ b/drivers/net/usb/usbnet.c @@ -589,6 +589,14 @@ 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 @@ -597,6 +605,7 @@ static int unlink_urbs (struct usbnet *dev, struct sk_buff_head *q) netdev_dbg(dev->net, "unlink urb err, %d\n", retval); else count++; + usb_put_urb(urb); spin_lock_irqsave(&q->lock, flags); } spin_unlock_irqrestore (&q->lock, flags); -- 2.20.1