Re: [PATCH v2] net: ip6: ndisc: fix incorrect forwarding of proxied ns packets

From: Paolo Abeni
Date: Tue Aug 20 2024 - 09:14:00 EST




On 8/15/24 17:18, Nils Fuhler wrote:
When enabling proxy_ndp per interface instead of globally, neighbor
solicitation packets sent to proxied global unicast addresses are
forwarded instead of generating a neighbor advertisement. When
proxy_ndp is enabled globally, these packets generate na responses as
expected.

This patch fixes this behaviour. When an ns packet is sent to a
proxied unicast address, it generates an na response regardless
whether proxy_ndp is enabled per interface or globally.

Signed-off-by: Nils Fuhler <nils@xxxxxxxxxxxxx>

I have mixed feeling WRT this patch. It looks like a fix, but it's changing an established behaviour that is there since a lot of time.

I think it could go via the net-next tree, without fixes
tag to avoid stable backports. As such I guess it deserves a self-test script validating the new behavior.

---
v1 -> v2: ensure that idev is not NULL

net/ipv6/ip6_output.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
index ab504d31f0cd..0356c8189e21 100644
--- a/net/ipv6/ip6_output.c
+++ b/net/ipv6/ip6_output.c
@@ -551,8 +551,8 @@ int ip6_forward(struct sk_buff *skb)
return -ETIMEDOUT;
}
- /* XXX: idev->cnf.proxy_ndp? */
- if (READ_ONCE(net->ipv6.devconf_all->proxy_ndp) &&
+ if ((READ_ONCE(net->ipv6.devconf_all->proxy_ndp) ||
+ (idev && READ_ONCE(idev->cnf.proxy_ndp))) &&
pneigh_lookup(&nd_tbl, net, &hdr->daddr, skb->dev, 0)) {
int proxied = ip6_forward_proxy_check(skb);
if (proxied > 0) {

Note that there is similar chunk in ndisc_recv_na() that also ignores idev->cnf.proxy_ndp, why don't you need to such function, too?

Thanks,

Paolo