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>

1 files changed, 4 insertions, 1 deletions

diff --git a/drivers/net/usb/lan78xx.c b/drivers/net/usb/lan78xx.c
index 2e4130746c40..ed10d49eb5e0 100644
--- 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);