selftests: netfilter: add phony nft_offload test

... "phony", because its not testing offloads, it tests the control
plane code.  Also test error unwind via fault injection framework.

For a proper test, real hardware would be required given we'd have
check if 'previously handed off to hardware' offload commands are
properly removed again on failure or rule flush.

Signed-off-by: Florian Westphal <fw@strlen.de>
Link: https://patch.msgid.link/20260612092209.11966-3-fw@strlen.de
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

tools/testing/selftests/net/netfilter/Makefile

@@ -32,6 +32,7 @@ TEST_PROGS := \
 	nft_meta.sh \
 	nft_nat.sh \
 	nft_nat_zones.sh \
+	nft_offload.sh \
 	nft_queue.sh \
 	nft_synproxy.sh \
 	nft_tproxy_tcp.sh \

tools/testing/selftests/net/netfilter/config

@@ -11,7 +11,12 @@ CONFIG_BRIDGE_NF_EBTABLES_LEGACY=m
 CONFIG_BRIDGE_VLAN_FILTERING=y
 CONFIG_CGROUP_BPF=y
 CONFIG_CRYPTO_SHA1=m
+CONFIG_DEBUG_FS=y
 CONFIG_DUMMY=m
+CONFIG_FAIL_FUNCTION=y
+CONFIG_FAULT_INJECTION=y
+CONFIG_FAULT_INJECTION_DEBUG_FS=y
+CONFIG_FUNCTION_ERROR_INJECTION=y
 CONFIG_INET_DIAG=m
 CONFIG_INET_ESP=m
 CONFIG_INET_SCTP_DIAG=m
@@ -36,6 +41,7 @@ CONFIG_IP_VS_RR=m
 CONFIG_MACVLAN=m
 CONFIG_NAMESPACES=y
 CONFIG_NET_CLS_U32=m
+CONFIG_NETDEVSIM=m
 CONFIG_NETFILTER=y
 CONFIG_NETFILTER_ADVANCED=y
 CONFIG_NETFILTER_NETLINK=m

tools/testing/selftests/net/netfilter/nft_offload.sh

@@ -0,0 +1,132 @@
+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0
+
+source lib.sh
+
+checktool "nft --version" "run test without nft tool"
+modprobe -q netdevsim
+
+sysfs="/sys/kernel/debug/fail_function"
+failname="/proc/self/make-it-fail"
+duration=30
+fault=0
+ret=0
+file_ft=""
+file_rs=""
+id=$((RANDOM%65536))
+
+read -r t < /proc/sys/kernel/tainted
+if [ "$t" -ne 0 ];then
+	echo SKIP: kernel is tainted
+	exit $ksft_skip
+fi
+
+cleanup() {
+    cleanup_netdevsim "$id" "$NS"
+    cleanup_ns "$NS"
+    [ "$fault" -eq 1 ] && echo '!nsim_setup_tc' > "$sysfs/inject"
+    rm -f "$file_ft" "$file_rs"
+}
+trap cleanup EXIT
+
+skip() {
+	echo "SKIP: $*"
+	[ $ret -eq 0 ] && exit 4
+
+	exit $ret
+}
+
+set -e
+setup_ns NS
+
+create_netdevsim "$id" "$NS" >/dev/null
+nsim_port=$(create_netdevsim_port "$id" "$NS" 2)
+
+file_ft=$(mktemp)
+cat > "$file_ft" <<EOF
+flush ruleset
+table inet t {
+	flowtable f {
+		flags offload
+		hook ingress priority filter + 10
+		devices = { "$nsim_port", "dummyf1" }
+	}
+
+	chain cf {
+		type filter hook forward priority 0; policy accept;
+		ct state new meta l4proto tcp flow add @f
+	}
+}
+EOF
+
+if ip netns exec "$NS" nft -f "$file_ft"; then
+	echo "PASS: flowtable offload"
+else
+	echo "FAIL: flowtable offload"
+	ret=1
+fi
+
+file_rs=$(mktemp)
+cat > "$file_rs" <<EOF
+table netdev t {
+	chain c {
+		type filter hook ingress device $nsim_port priority 1
+		flags offload
+		ip saddr 10.2.1.1 ip daddr 10.2.1.2 ip protocol icmp accept
+		ip saddr 10.2.1.1 ip daddr 10.2.1.3 ip protocol icmp drop
+		ip saddr 10.2.1.0/24 ip daddr 10.2.1.0/24 ip protocol icmp accept
+		ip6 saddr dead:beef::1 ip6 daddr dead:beef::2 meta l4proto ipv6-icmp accept
+		ip6 saddr dead:beef::1 ip6 daddr dead:beef::3 meta l4proto ipv6-icmp drop
+		ip6 saddr dead:beef::/64 ip6 daddr dead:beef::/64 meta l4proto ipv6-icmp accept
+	}
+}
+EOF
+if ip netns exec "$NS" nft -f "$file_rs"; then
+	echo "PASS: ruleset offload"
+else
+	echo "FAIL: ruleset offload"
+	ret=1
+fi
+
+test -d "$sysfs" || skip "$sysfs not present"
+grep -q nsim_setup_tc "$sysfs/injectable" || skip "nsim_setup_tc fault injection not available"
+
+echo Y > "$sysfs/task-filter"
+echo 0 > "$sysfs/verbose"
+echo "nsim_setup_tc" > "$sysfs/inject"
+fault=1
+
+p=$(((RANDOM%90) + 10))
+echo $p > "$sysfs/probability"
+echo -1 > "$sysfs/times"
+
+count=0
+ok=0
+
+now=$(date +%s)
+stop=$((now+duration))
+
+# fault-injection enabled rule loads are expected to fail.
+set +e
+while [ "$now" -le "$stop" ]; do
+	for f in "$file_ft" "$file_rs"; do
+		if ip netns exec "$NS" bash -c "echo 1 > $failname ; ip netns exec \"$NS\" nft -f $f" 2> /dev/null;then
+			ok=$((ok+1))
+		fi
+		count=$((count+1))
+	done
+	now=$(date +%s)
+done
+
+sleep 5
+
+read -r t < /proc/sys/kernel/tainted
+if [ "$t" -eq 0 ];then
+	echo "PASS: Not tainted. $count rounds, $ok successful ruleset loads with P $p."
+else
+	echo "ERROR: Tainted. $count rounds, $ok successful ruleset loads with P $p."
+	dmesg
+	ret=1
+fi
+
+exit $ret