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From:   Ben Hutchings <ben@decadent.org.uk>
To:     linux-kernel@vger.kernel.org, stable@vger.kernel.org
CC:     akpm@linux-foundation.org,
        "Simon Wunderlich" <sw@simonwunderlich.de>,
        "Sven Eckelmann" <sven@narfation.org>,
        "Maximilian Wilhelm" <max@sdn.clinic>,
        "Matthias Schiffer" <mschiffer@universe-factory.net>
Date:   Thu, 07 Jun 2018 15:05:21 +0100
Message-ID: <lsq.1528380321.960575087@decadent.org.uk>
Subject: [PATCH 3.16 282/410] batman-adv: fix packet checksum in receive path
In-Reply-To: <lsq.1528380320.647747352@decadent.org.uk>
Sender: linux-kernel-owner@vger.kernel.org
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3.16.57-rc1 review patch.  If anyone has any objections, please let me know.

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

From: Matthias Schiffer <mschiffer@universe-factory.net>

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@sdn.clinic>
Signed-off-by: Matthias Schiffer <mschiffer@universe-factory.net>
Signed-off-by: Sven Eckelmann <sven@narfation.org>
Signed-off-by: Simon Wunderlich <sw@simonwunderlich.de>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
 net/batman-adv/soft-interface.c | 8 +-------
 1 file changed, 1 insertion(+), 7 deletions(-)

--- a/net/batman-adv/soft-interface.c
+++ b/net/batman-adv/soft-interface.c
@@ -401,13 +401,7 @@ void batadv_interface_rx(struct net_devi
 
 	/* 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);
 
 	batadv_inc_counter(bat_priv, BATADV_CNT_RX);
 	batadv_add_counter(bat_priv, BATADV_CNT_RX_BYTES,