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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, "Sven Eckelmann" <sven@narfation.org>,
        "Simon Wunderlich" <sw@simonwunderlich.de>,
        "Maximilian Wilhelm" <max@sdn.clinic>,
        "Matthias Schiffer" <mschiffer@universe-factory.net>
Date:   Thu, 07 Jun 2018 15:05:21 +0100
Message-ID: <lsq.1528380321.39928011@decadent.org.uk>
Subject: [PATCH 3.16 283/410] batman-adv: invalidate checksum on fragment
 reassembly
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 3bf2a09da956b43ecfaa630a2ef9a477f991a46a upstream.

A more sophisticated implementation could try to combine fragment checksums
when all fragments have CHECKSUM_COMPLETE and are split at even offsets.
For now, we just set ip_summed to CHECKSUM_NONE to avoid "hw csum failure"
warnings in the kernel log when fragmented frames are received. In
consequence, skb_pull_rcsum() can be replaced with skb_pull().

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: 610bfc6bc99b ("batman-adv: Receive fragmented packets and merge")
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/fragmentation.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/net/batman-adv/fragmentation.c
+++ b/net/batman-adv/fragmentation.c
@@ -262,7 +262,8 @@ batadv_frag_merge_packets(struct hlist_h
 	/* Move the existing MAC header to just before the payload. (Override
 	 * the fragment header.)
 	 */
-	skb_pull_rcsum(skb_out, hdr_size);
+	skb_pull(skb_out, hdr_size);
+	skb_out->ip_summed = CHECKSUM_NONE;
 	memmove(skb_out->data - ETH_HLEN, skb_mac_header(skb_out), ETH_HLEN);
 	skb_set_mac_header(skb_out, -ETH_HLEN);
 	skb_reset_network_header(skb_out);