[PATCH 4.9 36/66] net: lan78xx: Fix race in tx pending skb size calculation

[Greg Kroah-Hartman]

4.9-stable review patch.  If anyone has any objections, please let me know.

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

From: Stefan Wahren <stefan.wahren@xxxxxxxx>

commit dea39aca1d7aef1e2b95b07edeacf04cc8863a2e upstream.

The skb size calculation in lan78xx_tx_bh is in race with the start_xmit,
which could lead to rare kernel oopses. So protect the whole skb walk with
a spin lock. As a benefit we can unlink the skb directly.

This patch was tested on Raspberry Pi 3B+

Link: https://github.com/raspberrypi/linux/issues/2608
Fixes: 55d7de9de6c3 ("Microchip's LAN7800 family USB 2/3 to 10/100/1000 Ethernet")
Cc: stable <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Floris Bos <bos@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Stefan Wahren <stefan.wahren@xxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 drivers/net/usb/lan78xx.c |    5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

--- a/drivers/net/usb/lan78xx.c
+++ b/drivers/net/usb/lan78xx.c
@@ -2964,6 +2964,7 @@ static void lan78xx_tx_bh(struct lan78xx
 	pkt_cnt = 0;
 	count = 0;
 	length = 0;
+	spin_lock_irqsave(&tqp->lock, flags);
 	for (skb = tqp->next; pkt_cnt < tqp->qlen; skb = skb->next) {
 		if (skb_is_gso(skb)) {
 			if (pkt_cnt) {
@@ -2972,7 +2973,8 @@ static void lan78xx_tx_bh(struct lan78xx
 			}
 			count = 1;
 			length = skb->len - TX_OVERHEAD;
-			skb2 = skb_dequeue(tqp);
+			__skb_unlink(skb, tqp);
+			spin_unlock_irqrestore(&tqp->lock, flags);
 			goto gso_skb;
 		}
 
@@ -2981,6 +2983,7 @@ static void lan78xx_tx_bh(struct lan78xx
 		skb_totallen = skb->len + roundup(skb_totallen, sizeof(u32));
 		pkt_cnt++;
 	}
+	spin_unlock_irqrestore(&tqp->lock, flags);
 
 	/* copy to a single skb */
 	skb = alloc_skb(skb_totallen, GFP_ATOMIC);