[B.A.T.M.A.N.] [PATCH maint v2 1/2] batman-adv: fix packet checksum in receive path

[B.A.T.M.A.N.] [PATCH maint v2 1/2] batman-adv: fix packet checksum in receive path

[Matthias Schiffer]

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(-)

diff --git a/net/batman-adv/soft-interface.c b/net/batman-adv/soft-interface.c
index 9f673cdf..6f7ce7a6 100644
--- a/net/batman-adv/soft-interface.c
+++ b/net/batman-adv/soft-interface.c
@@ -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,
-- 
2.16.1

[B.A.T.M.A.N.] [PATCH maint v2 2/2] batman-adv: invalidate checksum on fragment reassembly

[Matthias Schiffer]

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 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/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 ebe6e389..1bb2b43f 100644
--- a/net/batman-adv/fragmentation.c
+++ b/net/batman-adv/fragmentation.c
@@ -287,7 +287,8 @@ 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);
-- 
2.16.1

Re: [B.A.T.M.A.N.] [PATCH maint v2 1/2] batman-adv: fix packet checksum in receive path

[Linus Lüssing]

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

Re: [B.A.T.M.A.N.] [PATCH maint v2 1/2] batman-adv: fix packet checksum in receive path

[Sven Eckelmann]

[-- Attachment #1: Type: text/plain, Size: 1213 bytes --]

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

[-- Attachment #2: This is a digitally signed message part. --]
[-- Type: application/pgp-signature, Size: 833 bytes --]