can: vxcan: vxcan_xmit: fix use after free bug

After calling netif_rx_ni(skb), dereferencing skb is unsafe.
Especially, the canfd_frame cfd which aliases skb memory is accessed
after the netif_rx_ni().

Fixes: a8f820a380a2 ("can: add Virtual CAN Tunnel driver (vxcan)")
Link: https://lore.kernel.org/r/20210120114137.200019-3-mailhol.vincent@wanadoo.fr
Signed-off-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

diff --git a/drivers/net/can/vxcan.c b/drivers/net/can/vxcan.c
index fa47bab510bb90cb35bcc56fe9d0275dccc57cf4..f9a524c5f6d62710722b920b615154670dfc8992 100644 (file)
--- a/drivers/net/can/vxcan.c
+++ b/drivers/net/can/vxcan.c
@@ -39,6 +39,7 @@ static netdev_tx_t vxcan_xmit(struct sk_buff *skb, struct net_device *dev)
        struct net_device *peer;
        struct canfd_frame *cfd = (struct canfd_frame *)skb->data;
        struct net_device_stats *peerstats, *srcstats = &dev->stats;
+       u8 len;
 
        if (can_dropped_invalid_skb(dev, skb))
                return NETDEV_TX_OK;
@@ -61,12 +62,13 @@ static netdev_tx_t vxcan_xmit(struct sk_buff *skb, struct net_device *dev)
        skb->dev        = peer;
        skb->ip_summed  = CHECKSUM_UNNECESSARY;
 
+       len = cfd->len;
        if (netif_rx_ni(skb) == NET_RX_SUCCESS) {
                srcstats->tx_packets++;
-               srcstats->tx_bytes += cfd->len;
+               srcstats->tx_bytes += len;
                peerstats = &peer->stats;
                peerstats->rx_packets++;
-               peerstats->rx_bytes += cfd->len;
+               peerstats->rx_bytes += len;
        }
 
 out_unlock: