can: add missing initialisations in CAN related skbuffs

commit 96943901 upstream.

When accessing CAN network interfaces with AF_PACKET sockets e.g. by dhclient
this can lead to a skb_under_panic due to missing skb initialisations.

Add the missing initialisations at the CAN skbuff creation times on driver
level (rx path) and in the network layer (tx path).
Reported-by: Austin Schuh <austin@peloton-tech.com>
Reported-by: Daniel Steer <daniel.steer@mclaren.com>
Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
[bwh: Backported to 3.2:
 - Adjust context
 - Drop changes to alloc_canfd_skb()]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

drivers/net/can/dev.c

@@ -468,6 +468,11 @@ struct sk_buff *alloc_can_skb(struct net_device *dev, struct can_frame **cf)
 	skb->protocol = htons(ETH_P_CAN);
 	skb->pkt_type = PACKET_BROADCAST;
 	skb->ip_summed = CHECKSUM_UNNECESSARY;
+
+	skb_reset_mac_header(skb);
+	skb_reset_network_header(skb);
+	skb_reset_transport_header(skb);
+
 	*cf = (struct can_frame *)skb_put(skb, sizeof(struct can_frame));
 	memset(*cf, 0, sizeof(struct can_frame));
 

net/can/af_can.c

@@ -244,6 +244,9 @@ int can_send(struct sk_buff *skb, int loop)
 	}
 
 	skb->protocol = htons(ETH_P_CAN);
+	skb->ip_summed = CHECKSUM_UNNECESSARY;
+
+	skb_reset_mac_header(skb);
 	skb_reset_network_header(skb);
 	skb_reset_transport_header(skb);