net: lan78xx: Fix race in tx pending skb size calculation

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@vger.kernel.org>
Signed-off-by: Floris Bos <bos@je-eigen-domein.nl>
Signed-off-by: Stefan Wahren <stefan.wahren@i2se.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/drivers/net/usb/lan78xx.c b/drivers/net/usb/lan78xx.c
index 2e41307..ed10d49 100644 (file)
--- a/drivers/net/usb/lan78xx.c
+++ b/drivers/net/usb/lan78xx.c
@@ -3344,6 +3344,7 @@ static void lan78xx_tx_bh(struct lan78xx_net *dev)
        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) {
@@ -3352,7 +3353,8 @@ static void lan78xx_tx_bh(struct lan78xx_net *dev)
                        }
                        count = 1;
                        length = skb->len - TX_OVERHEAD;
-                       skb2 = skb_dequeue(tqp);
+                       __skb_unlink(skb, tqp);
+                       spin_unlock_irqrestore(&tqp->lock, flags);
                        goto gso_skb;
                }
 
@@ -3361,6 +3363,7 @@ static void lan78xx_tx_bh(struct lan78xx_net *dev)
                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);