[PATCH 3.2 107/153] batman-adv: fix packet checksum in receive path

[Ben Hutchings]

3.2.102-rc1 review patch.  If anyone has any objections, please let me know.

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

From: Matthias Schiffer <mschiffer@xxxxxxxxxxxxxxxxxxxx>

commit abd6360591d3f8259f41c34e31ac4826dfe621b8 upstream.

eth_type_trans() internally calls skb_pull(), which does not adjust the
skb checksum; skb_postpull_rcsum() is necessary to avoid log spam of the
form "bat0: hw csum failure" when packets with CHECKSUM_COMPLETE are
received.

Note that in usual setups, packets don't reach batman-adv with
CHECKSUM_COMPLETE (I assume NICs bail out of checksumming when they see
batadv's ethtype?), which is why the log messages do not occur on every
system using batman-adv. I could reproduce this issue by stacking
batman-adv on top of a VXLAN interface.

Fixes: c6c8fea29769 ("net: Add batman-adv meshing protocol")
Tested-by: Maximilian Wilhelm <max@xxxxxxxxxx>
Signed-off-by: Matthias Schiffer <mschiffer@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Sven Eckelmann <sven@xxxxxxxxxxxxx>
Signed-off-by: Simon Wunderlich <sw@xxxxxxxxxxxxxxxxxx>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
--- a/net/batman-adv/soft-interface.c
+++ b/net/batman-adv/soft-interface.c
@@ -733,12 +733,7 @@ void interface_rx(struct net_device *sof
 
 	/* skb->dev & skb->pkt_type are set here */
 	skb->protocol = eth_type_trans(skb, soft_iface);
-
-	/* should not be necessary anymore as we use skb_pull_rcsum()
-	 * TODO: please verify this and remove this TODO
-	 * -- Dec 21st 2009, Simon Wunderlich */
-
-/*	skb->ip_summed = CHECKSUM_UNNECESSARY;*/
+	skb_postpull_rcsum(skb, eth_hdr(skb), ETH_HLEN);
 
 	bat_priv->stats.rx_packets++;
 	bat_priv->stats.rx_bytes += skb->len + sizeof(struct ethhdr);