net: netpoll: Initialize UDP checksum field before checksumming

commit f1fce08e63fe ("netpoll: Eliminate redundant assignment") removed
the initialization of the UDP checksum, which was wrong and broke
netpoll IPv6 transmission due to bad checksumming.

udph->check needs to be set before calling csum_ipv6_magic().

Fixes: f1fce08e63fe ("netpoll: Eliminate redundant assignment")
Signed-off-by: Breno Leitao <leitao@debian.org>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20250620-netpoll_fix-v1-1-f9f0b82bc059@debian.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/net/core/netpoll.c b/net/core/netpoll.c
index 4ddb7490df4b88bee03673edd540c2694ae57920..6ad84d4a2b464b252b3823f912aef1a661424ca5 100644 (file)
--- a/net/core/netpoll.c
+++ b/net/core/netpoll.c
@@ -432,6 +432,7 @@ int netpoll_send_udp(struct netpoll *np, const char *msg, int len)
        udph->dest = htons(np->remote_port);
        udph->len = htons(udp_len);
 
+       udph->check = 0;
        if (np->ipv6) {
                udph->check = csum_ipv6_magic(&np->local_ip.in6,
                                              &np->remote_ip.in6,
@@ -460,7 +461,6 @@ int netpoll_send_udp(struct netpoll *np, const char *msg, int len)
                skb_reset_mac_header(skb);
                skb->protocol = eth->h_proto = htons(ETH_P_IPV6);
        } else {
-               udph->check = 0;
                udph->check = csum_tcpudp_magic(np->local_ip.ip,
                                                np->remote_ip.ip,
                                                udp_len, IPPROTO_UDP,