[PATCH 2/7] batman-adv: invalidate checksum on fragment reassembly

From: Matthias Schiffer <mschiffer-Nyw9WiXk/RKXhJHkyCwd5uTW4wlIGRCZ@public.gmane.org>

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-V58sJan5vl79KIQWOO/q1A@public.gmane.org>
Signed-off-by: Matthias Schiffer <mschiffer-Nyw9WiXk/RKXhJHkyCwd5uTW4wlIGRCZ@public.gmane.org>
Signed-off-by: Sven Eckelmann <redacted>
Signed-off-by: Simon Wunderlich <redacted>
---
 net/batman-adv/fragmentation.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/batman-adv/fragmentation.c b/net/batman-adv/fragmentation.c
index 22dde42fd80e..5afe641ee4b0 100644
--- a/net/batman-adv/fragmentation.c
+++ b/net/batman-adv/fragmentation.c

@@ -288,7 +288,8 @@ batadv_frag_merge_packets(struct hlist_head *chain)
 	/* 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);

-- 
2.11.0