[maint,v2,1/2] batman-adv: fix packet checksum in receive path
Commit Message
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 nor occur on every
system using batman-adv. I could reproduce this issue by stacking
batman-adv on top of a VXLAN interface.
Signed-off-by: Matthias Schiffer <mschiffer@universe-factory.net>
---
net/batman-adv/soft-interface.c | 8 +-------
1 file changed, 1 insertion(+), 7 deletions(-)
Comments
On Tue, Jan 23, 2018 at 10:59:49AM +0100, Matthias Schiffer wrote:
> 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 nor occur on every
> system using batman-adv. I could reproduce this issue by stacking
> batman-adv on top of a VXLAN interface.
>
> Signed-off-by: Matthias Schiffer <mschiffer@universe-factory.net>
Seems reasonable, this change.
I'm just a little confused though: Two years ago someone had reported
checksumming errors with a Raspberry Pi and batman-adv:
https://www.open-mesh.org/issues/224
And they seemed to be gone in newer kernel versions, while hardware
checksumming was supposedly still enabled.
Are the issues reproduceable without using VXLANs (for instance on
a Pi1 or Pi2)? Are they reproduceable on a recent kernel version?
(I guess you tested with a 4.4 kernel?)
Regards, Linus
On Dienstag, 23. Januar 2018 10:59:49 CET Matthias Schiffer wrote:
> 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 nor occur on every
> system using batman-adv. I could reproduce this issue by stacking
> batman-adv on top of a VXLAN interface.
>
> Signed-off-by: Matthias Schiffer <mschiffer@universe-factory.net>
> ---
Applied both as 798174b15153 [1] and 2c1bce065baa [2]. They are also queued
up in linux-merge [3] but will most likely only forwarded when Simon is back
from his vacation. Tested-by's are still welcome :)
Thanks,
Sven
[1] https://git.open-mesh.org/batman-adv.git/commit/798174b15153afd88268f2f87811602f68b3f2c6
[2] https://git.open-mesh.org/batman-adv.git/commit/2c1bce065baa688bc1eca4116f83ca3b790432a5
[3] https://git.open-mesh.org/linux-merge.git/shortlog/refs/heads/batadv/net
@@ -451,13 +451,7 @@ void batadv_interface_rx(struct net_device *soft_iface,
/* 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,