batman-adv: invalidate checksum on fragment reassembly

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>

diff --git a/net/batman-adv/fragmentation.c b/net/batman-adv/fragmentation.c
index 22dde42fd80e63e79faebfdb0d807786f1b9a4b5..5afe641ee4b0daa366ae7c3ce919b26b2802acb1 100644 (file)
--- 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);