selftests/bpf: Add BPF_F_NO_TUNNEL_KEY test

This patch adds a selftest simulating a GRE sender and receiver using
tunnel headers without tunnel keys. It validates if packets encapsulated
using BPF_F_NO_TUNNEL_KEY are decapsulated by a GRE receiver not
configured with tunnel keys.
Signed-off-by: Christian Ehrig <cehrig@cloudflare.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: Jakub Sitnicki <jakub@cloudflare.com>
Acked-by: Stanislav Fomichev <sdf@google.com>
Link: https://lore.kernel.org/bpf/20221218051734.31411-2-cehrig@cloudflare.com

tools/testing/selftests/bpf/progs/test_tunnel_kern.c

@@ -81,6 +81,27 @@ int gre_set_tunnel(struct __sk_buff *skb)
 	return TC_ACT_OK;
 }
 
+SEC("tc")
+int gre_set_tunnel_no_key(struct __sk_buff *skb)
+{
+	int ret;
+	struct bpf_tunnel_key key;
+
+	__builtin_memset(&key, 0x0, sizeof(key));
+	key.remote_ipv4 = 0xac100164; /* 172.16.1.100 */
+	key.tunnel_ttl = 64;
+
+	ret = bpf_skb_set_tunnel_key(skb, &key, sizeof(key),
+				     BPF_F_ZERO_CSUM_TX | BPF_F_SEQ_NUMBER |
+				     BPF_F_NO_TUNNEL_KEY);
+	if (ret < 0) {
+		log_err(ret);
+		return TC_ACT_SHOT;
+	}
+
+	return TC_ACT_OK;
+}
+
 SEC("tc")
 int gre_get_tunnel(struct __sk_buff *skb)
 {

tools/testing/selftests/bpf/test_tunnel.sh

@@ -66,15 +66,20 @@ config_device()
 
 add_gre_tunnel()
 {
+	tun_key=
+	if [ -n "$1" ]; then
+		tun_key="key $1"
+	fi
+
 	# at_ns0 namespace
 	ip netns exec at_ns0 \
-        ip link add dev $DEV_NS type $TYPE seq key 2 \
+        ip link add dev $DEV_NS type $TYPE seq $tun_key \
 		local 172.16.1.100 remote 172.16.1.200
 	ip netns exec at_ns0 ip link set dev $DEV_NS up
 	ip netns exec at_ns0 ip addr add dev $DEV_NS 10.1.1.100/24
 
 	# root namespace
-	ip link add dev $DEV type $TYPE key 2 external
+	ip link add dev $DEV type $TYPE $tun_key external
 	ip link set dev $DEV up
 	ip addr add dev $DEV 10.1.1.200/24
 }
@@ -238,7 +243,7 @@ test_gre()
 
 	check $TYPE
 	config_device
-	add_gre_tunnel
+	add_gre_tunnel 2
 	attach_bpf $DEV gre_set_tunnel gre_get_tunnel
 	ping $PING_ARG 10.1.1.100
 	check_err $?
@@ -253,6 +258,30 @@ test_gre()
         echo -e ${GREEN}"PASS: $TYPE"${NC}
 }
 
+test_gre_no_tunnel_key()
+{
+	TYPE=gre
+	DEV_NS=gre00
+	DEV=gre11
+	ret=0
+
+	check $TYPE
+	config_device
+	add_gre_tunnel
+	attach_bpf $DEV gre_set_tunnel_no_key gre_get_tunnel
+	ping $PING_ARG 10.1.1.100
+	check_err $?
+	ip netns exec at_ns0 ping $PING_ARG 10.1.1.200
+	check_err $?
+	cleanup
+
+        if [ $ret -ne 0 ]; then
+                echo -e ${RED}"FAIL: $TYPE"${NC}
+                return 1
+        fi
+        echo -e ${GREEN}"PASS: $TYPE"${NC}
+}
+
 test_ip6gre()
 {
 	TYPE=ip6gre
@@ -589,6 +618,7 @@ cleanup()
 	ip link del ipip6tnl11 2> /dev/null
 	ip link del ip6ip6tnl11 2> /dev/null
 	ip link del gretap11 2> /dev/null
+	ip link del gre11 2> /dev/null
 	ip link del ip6gre11 2> /dev/null
 	ip link del ip6gretap11 2> /dev/null
 	ip link del geneve11 2> /dev/null
@@ -641,6 +671,10 @@ bpf_tunnel_test()
 	test_gre
 	errors=$(( $errors + $? ))
 
+	echo "Testing GRE tunnel (without tunnel keys)..."
+	test_gre_no_tunnel_key
+	errors=$(( $errors + $? ))
+
 	echo "Testing IP6GRE tunnel..."
 	test_ip6gre
 	errors=$(( $errors + $? ))