[PATCH net 2/2] wireguard: selftests: add metadata_dst xmit selftest

[Nikolay Aleksandrov <razor@blackwall.org>]

Add a selftest for transmitting skb with md_dst attached. It is done via
a bpf program which uses bpf_skb_set_tunnel_key on wireguard's egress
path. It requires clang and tc to be installed. If the test finishes
without a crash it is considered successful.

CC: wireguard@lists.zx2c4.com
CC: Jason A. Donenfeld <Jason@zx2c4.com>
CC: Daniel Borkmann <daniel@iogearbox.net>
CC: Martynas Pumputis <m@lambda.lt>
Signed-off-by: Nikolay Aleksandrov <razor@blackwall.org>
---
Executed the prep compilation commands with n1 to make them visible.

 tools/testing/selftests/wireguard/netns.sh | 63 ++++++++++++++++++++++
 1 file changed, 63 insertions(+)

diff --git a/tools/testing/selftests/wireguard/netns.sh b/tools/testing/selftests/wireguard/netns.sh
index 8a9461aa0878..b492dbb94245 100755
--- a/tools/testing/selftests/wireguard/netns.sh
+++ b/tools/testing/selftests/wireguard/netns.sh
@@ -156,6 +156,67 @@ tests() {
 	done
 }
 
+md_dst_test_cleanup() {
+	rm -rf /tmp/test_wg_tun.c /tmp/test_wg_tun.ll /tmp/test_wg_tun.o
+	n1 tc qdisc del dev wg0 clsact
+}
+
+# test for md dst on wireguard's egress path
+md_dst_test() {
+	# clang is required for the test
+	if [[ ! -x "$(command -v "clang")" ]]; then
+		return
+	fi
+
+	# attach md dst to the skb on egress using bpf_skb_set_tunnel_key
+	n1 cat > /tmp/test_wg_tun.c <<EOF
+#include <linux/bpf.h>
+
+#ifndef TC_ACT_OK
+# define TC_ACT_OK 0
+#endif
+
+static long (*bpf_skb_set_tunnel_key)(struct __sk_buff *skb, struct bpf_tunnel_key *key, __u32 size, __u64 flags) = (void *) 21;
+
+__attribute__((section("egress"), used))
+int tc_egress(struct __sk_buff *skb)
+{
+	struct bpf_tunnel_key key = {};
+
+        bpf_skb_set_tunnel_key(skb, &key, sizeof(key), 0);
+
+	return TC_ACT_OK;
+}
+
+char __license[] __attribute__((section("license"), used)) = "GPL";
+EOF
+
+	n1 clang -O2 -emit-llvm -c /tmp/test_wg_tun.c -o /tmp/test_wg_tun.ll
+	if [[ ! -f "/tmp/test_wg_tun.ll" ]]; then
+		md_dst_test_cleanup
+		return
+	fi
+	n1 llc -march=bpf -filetype=obj -o /tmp/test_wg_tun.o /tmp/test_wg_tun.ll
+	if [[ ! -f "/tmp/test_wg_tun.o" ]]; then
+		md_dst_test_cleanup
+		return
+	fi
+
+	n1 tc qdisc add dev wg0 clsact
+	if [[ $? -ne 0 ]]; then
+		md_dst_test_cleanup
+		return
+	fi
+	n1 tc filter add dev wg0 egress basic action bpf obj /tmp/test_wg_tun.o sec egress
+	if [[ $? -ne 0 ]]; then
+		md_dst_test_cleanup
+		return
+	fi
+	n1 ping -c 2 -f -W 1 192.168.241.2
+	# if we reach here without a crash the test passed
+	md_dst_test_cleanup
+}
+
 [[ $(ip1 link show dev wg0) =~ mtu\ ([0-9]+) ]] && orig_mtu="${BASH_REMATCH[1]}"
 big_mtu=$(( 34816 - 1500 + $orig_mtu ))
 
@@ -175,6 +236,8 @@ read _ rx_bytes tx_bytes < <(n1 wg show wg0 transfer)
 read _ timestamp < <(n1 wg show wg0 latest-handshakes)
 (( timestamp != 0 ))
 
+md_dst_test
+
 tests
 ip1 link set wg0 mtu $big_mtu
 ip2 link set wg0 mtu $big_mtu
-- 
2.35.1