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authorCyril Strejc <cyril.strejc@skoda.cz>2021-10-24 23:14:25 +0300
committerDavid S. Miller <davem@davemloft.net>2021-10-26 15:09:22 +0300
commit9122a70a6333705c0c35614ddc51c274ed1d3637 (patch)
treea91aa99cda1a19e13e3eb8a0d2d05e1244f14dc7 /net
parent759635760a804b0d8ad0cc677b650f1544cae22f (diff)
downloadlinux-9122a70a6333705c0c35614ddc51c274ed1d3637.tar.xz
net: multicast: calculate csum of looped-back and forwarded packets
During a testing of an user-space application which transmits UDP multicast datagrams and utilizes multicast routing to send the UDP datagrams out of defined network interfaces, I've found a multicast router does not fill-in UDP checksum into locally produced, looped-back and forwarded UDP datagrams, if an original output NIC the datagrams are sent to has UDP TX checksum offload enabled. The datagrams are sent malformed out of the NIC the datagrams have been forwarded to. It is because: 1. If TX checksum offload is enabled on the output NIC, UDP checksum is not calculated by kernel and is not filled into skb data. 2. dev_loopback_xmit(), which is called solely by ip_mc_finish_output(), sets skb->ip_summed = CHECKSUM_UNNECESSARY unconditionally. 3. Since 35fc92a9 ("[NET]: Allow forwarding of ip_summed except CHECKSUM_COMPLETE"), the ip_summed value is preserved during forwarding. 4. If ip_summed != CHECKSUM_PARTIAL, checksum is not calculated during a packet egress. The minimum fix in dev_loopback_xmit(): 1. Preserves skb->ip_summed CHECKSUM_PARTIAL. This is the case when the original output NIC has TX checksum offload enabled. The effects are: a) If the forwarding destination interface supports TX checksum offloading, the NIC driver is responsible to fill-in the checksum. b) If the forwarding destination interface does NOT support TX checksum offloading, checksums are filled-in by kernel before skb is submitted to the NIC driver. c) For local delivery, checksum validation is skipped as in the case of CHECKSUM_UNNECESSARY, thanks to skb_csum_unnecessary(). 2. Translates ip_summed CHECKSUM_NONE to CHECKSUM_UNNECESSARY. It means, for CHECKSUM_NONE, the behavior is unmodified and is there to skip a looped-back packet local delivery checksum validation. Signed-off-by: Cyril Strejc <cyril.strejc@skoda.cz> Reviewed-by: Willem de Bruijn <willemb@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'net')
-rw-r--r--net/core/dev.c3
1 files changed, 2 insertions, 1 deletions
diff --git a/net/core/dev.c b/net/core/dev.c
index ea2366497697..eb3a366bf212 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -3912,7 +3912,8 @@ int dev_loopback_xmit(struct net *net, struct sock *sk, struct sk_buff *skb)
skb_reset_mac_header(skb);
__skb_pull(skb, skb_network_offset(skb));
skb->pkt_type = PACKET_LOOPBACK;
- skb->ip_summed = CHECKSUM_UNNECESSARY;
+ if (skb->ip_summed == CHECKSUM_NONE)
+ skb->ip_summed = CHECKSUM_UNNECESSARY;
WARN_ON(!skb_dst(skb));
skb_dst_force(skb);
netif_rx_ni(skb);