fix: use iifname for input interface name matches

[jack4it]

What type of PR is this?

/kind bug

What this PR does / why we need it:

This PR fixes a bug in the nftables support of kube-proxy. An example error without this fix. Notice that iif was mistakenly used instead of iifname in that.

I0911 16:35:49.542259       1 proxier.go:1840] "Reloading service nftables data" ipFamily="IPv4" numServices=5 numEndpoints=8
E0911 16:35:49.547707       1 proxier.go:1851] "nftables sync failed" err=<
	/dev/stdin:72:109-112: Error: Interface does not exist
	add rule ip kube-proxy service-2QRHZV4L-default/kubernetes/tcp/https ip daddr 10.0.0.1 tcp dport 443 iif != azv* jump mark-for-masquerade
	                                                                                                            ^^^^
	/dev/stdin:84:109-112: Error: Interface does not exist
	add rule ip kube-proxy service-FY5PMXPG-kube-system/kube-dns/udp/dns ip daddr 10.0.0.10 udp dport 53 iif != azv* jump mark-for-masquerade
	                                                                                                            ^^^^
	/dev/stdin:97:113-116: Error: Interface does not exist
	add rule ip kube-proxy service-NWBZK7IH-kube-system/kube-dns/tcp/dns-tcp ip daddr 10.0.0.10 tcp dport 53 iif != azv* jump mark-for-masquerade
	                                                                                                                ^^^^
	/dev/stdin:111:129-132: Error: Interface does not exist
	add rule ip kube-proxy service-EZ4UY2LR-calico-system/calico-typha/tcp/calico-typha ip daddr 10.0.172.152 tcp dport 5473 iif != azv* jump mark-for-masquerade
	                                                                                                                                ^^^^
 > ipFamily="IPv4"
I0911 16:35:49.547728       1 proxier.go:1204] "Sync failed" ipFamily="IPv4" retryingTime="30s"

Which issue(s) this PR is related to:

KEP: https://github.com/kubernetes/enhancements/blob/master/keps/sig-network/3866-nftables-proxy/README.md

Special notes for your reviewer:

Does this PR introduce a user-facing change?

Fixed a bug in kube-proxy nftables mode (GA as of 1.33) that fails to determine if traffic originates from a local source on the node. The issue was caused by using the wrong meta `iif` instead of `iifname` for name based matches.

Additional documentation e.g., KEPs (Kubernetes Enhancement Proposals), usage docs, etc.:

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: jack4it / name: Jack Ma (b81e87c)

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[aojea]

/assign @danwinship @aroradaman

based on https://wiki.nftables.org/wiki-nftables/index.php/Matching_packet_metainformation it looks correct, iif is the index and iifname is the name

/ok-to-test
/lgtm
/kind bug

[jack4it]

/retest-required

[adrianmoisey]

/lgtm

[k8s-ci-robot]

LGTM label has been added.

Details

Git tree hash: 84ba230a77262661c9c66504219dad03c576b6d2

[aojea]

@jack4it one final request sorry, do you mind to squash the commits? so we backport the fix and the unit test altogether in one commit

[jack4it]

@jack4it one final request sorry, do you mind to squash the commits? so we backport the fix and the unit test altogether in one commit

absolutely, squashed. thx @aojea for the review

[aojea]

/lgtm
/approve

Thanks, @jack4it since we do not seem to have CI on this mode and you find it, I assume you already validated this works fine, right?

[jack4it]

/lgtm /approve

Thanks, @jack4it since we do not seem to have CI on this mode and you find it, I assume you already validated this works fine, right?

before i merge, i'll make sure it's verified in my setup. thx @aojea. will circle back

[aojea]

before i merge, i'll make sure it's verified in my setup. thx @aojea. will circle back

ok, then I put it on hold and you just do /hold cancel once you validated it

/hold

the PR is already approved and it will marge if no changes are done

[aroradaman]

/lgtm

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: aojea, aroradaman, jack4it

The full list of commands accepted by this bot can be found here.

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Details

Needs approval from an approver in each of these files:

• pkg/proxy/OWNERS [aojea]

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

[aroradaman]

Once verified we should back port this to v1.33 as well.

[aojea]

kindly ping @jack4it 😄

[jack4it]

circling back. had a successful integration test

│     Command:                                                                                                                                                                                                                                 │
│       kube-proxy                                                                                                                                                                                                                             │
│       --conntrack-max-per-core=0                                                                                                                                                                                                             │
│       --metrics-bind-address=0.0.0.0:10249                                                                                                                                                                                                   │
│       --cluster-cidr=10.244.0.0/16                                                                                                                                                                                                           │
│       --detect-local-mode=InterfaceNamePrefix                                                                                                                                                                                                │
│       --pod-interface-name-prefix=azv                                                                                                                                                                                                        │
│       --v=3                                                                                                                                                                                                                                  │
│       --proxy-mode=nftables                                                                                                                                                                                                                  │
│     State:          Running                                                                                                                                                                                                                  │
│       Started:      Tue, 16 Sep 2025 13:39:12 -0700                                                                                                                                                                                          │
│     Ready:          True                                                                                                                                                                                                                     │

│ I0916 20:41:08.768503       1 proxier.go:1199] "Syncing nftables rules" ipFamily="IPv4" fullSync=false                                                                                                                                       │
│ I0916 20:41:08.780704       1 proxier.go:1840] "Reloading service nftables data" ipFamily="IPv4" numServices=5 numEndpoints=9                                                                                                                │
│ I0916 20:41:08.808435       1 proxier.go:1193] "SyncProxyRules complete" ipFamily="IPv4" elapsed="40.038299ms"                                                                                                                               │
│ I0916 20:41:08.808464       1 bounded_frequency_runner.go:296] sync-runner: ran, next possible in 1s, periodic in 1h0m0s                                                                                                                     │

@aojea

/hold cancel