selftests/bpf: Make sure zero-len skbs aren't redirectable

LWT_XMIT to test L3 case, TC to test L2 case.

v2:
- s/veth_ifindex/ipip_ifindex/ in two places (Martin)
- add comment about which condition triggers the rejection (Martin)
Signed-off-by: Stanislav Fomichev <sdf@google.com>
Link: https://lore.kernel.org/r/20221121180340.1983627-2-sdf@google.comSigned-off-by: Martin KaFai Lau <martin.lau@kernel.org>

tools/testing/selftests/bpf/prog_tests/empty_skb.c

+// SPDX-License-Identifier: GPL-2.0
+#include <test_progs.h>
+#include <network_helpers.h>
+#include <net/if.h>
+#include "empty_skb.skel.h"
+
+#define SYS(cmd) ({ \
+	if (!ASSERT_OK(system(cmd), (cmd))) \
+		goto out; \
+})
+
+void test_empty_skb(void)
+{
+	LIBBPF_OPTS(bpf_test_run_opts, tattr);
+	struct empty_skb *bpf_obj = NULL;
+	struct nstoken *tok = NULL;
+	struct bpf_program *prog;
+	char eth_hlen_pp[15];
+	char eth_hlen[14];
+	int veth_ifindex;
+	int ipip_ifindex;
+	int err;
+	int i;
+
+	struct {
+		const char *msg;
+		const void *data_in;
+		__u32 data_size_in;
+		int *ifindex;
+		int err;
+		int ret;
+		bool success_on_tc;
+	} tests[] = {
+		/* Empty packets are always rejected. */
+
+		{
+			/* BPF_PROG_RUN ETH_HLEN size check */
+			.msg = "veth empty ingress packet",
+			.data_in = NULL,
+			.data_size_in = 0,
+			.ifindex = &veth_ifindex,
+			.err = -EINVAL,
+		},
+		{
+			/* BPF_PROG_RUN ETH_HLEN size check */
+			.msg = "ipip empty ingress packet",
+			.data_in = NULL,
+			.data_size_in = 0,
+			.ifindex = &ipip_ifindex,
+			.err = -EINVAL,
+		},
+
+		/* ETH_HLEN-sized packets:
+		 * - can not be redirected at LWT_XMIT
+		 * - can be redirected at TC to non-tunneling dest
+		 */
+
+		{
+			/* __bpf_redirect_common */
+			.msg = "veth ETH_HLEN packet ingress",
+			.data_in = eth_hlen,
+			.data_size_in = sizeof(eth_hlen),
+			.ifindex = &veth_ifindex,
+			.ret = -ERANGE,
+			.success_on_tc = true,
+		},
+		{
+			/* __bpf_redirect_no_mac
+			 *
+			 * lwt: skb->len=0 <= skb_network_offset=0
+			 * tc: skb->len=14 <= skb_network_offset=14
+			 */
+			.msg = "ipip ETH_HLEN packet ingress",
+			.data_in = eth_hlen,
+			.data_size_in = sizeof(eth_hlen),
+			.ifindex = &ipip_ifindex,
+			.ret = -ERANGE,
+		},
+
+		/* ETH_HLEN+1-sized packet should be redirected. */
+
+		{
+			.msg = "veth ETH_HLEN+1 packet ingress",
+			.data_in = eth_hlen_pp,
+			.data_size_in = sizeof(eth_hlen_pp),
+			.ifindex = &veth_ifindex,
+		},
+		{
+			.msg = "ipip ETH_HLEN+1 packet ingress",
+			.data_in = eth_hlen_pp,
+			.data_size_in = sizeof(eth_hlen_pp),
+			.ifindex = &ipip_ifindex,
+		},
+	};
+
+	SYS("ip netns add empty_skb");
+	tok = open_netns("empty_skb");
+	SYS("ip link add veth0 type veth peer veth1");
+	SYS("ip link set dev veth0 up");
+	SYS("ip link set dev veth1 up");
+	SYS("ip addr add 10.0.0.1/8 dev veth0");
+	SYS("ip addr add 10.0.0.2/8 dev veth1");
+	veth_ifindex = if_nametoindex("veth0");
+
+	SYS("ip link add ipip0 type ipip local 10.0.0.1 remote 10.0.0.2");
+	SYS("ip link set ipip0 up");
+	SYS("ip addr add 192.168.1.1/16 dev ipip0");
+	ipip_ifindex = if_nametoindex("ipip0");
+
+	bpf_obj = empty_skb__open_and_load();
+	if (!ASSERT_OK_PTR(bpf_obj, "open skeleton"))
+		goto out;
+
+	for (i = 0; i < ARRAY_SIZE(tests); i++) {
+		bpf_object__for_each_program(prog, bpf_obj->obj) {
+			char buf[128];
+			bool at_tc = !strncmp(bpf_program__section_name(prog), "tc", 2);
+
+			tattr.data_in = tests[i].data_in;
+			tattr.data_size_in = tests[i].data_size_in;
+
+			tattr.data_size_out = 0;
+			bpf_obj->bss->ifindex = *tests[i].ifindex;
+			bpf_obj->bss->ret = 0;
+			err = bpf_prog_test_run_opts(bpf_program__fd(prog), &tattr);
+			sprintf(buf, "err: %s [%s]", tests[i].msg, bpf_program__name(prog));
+
+			if (at_tc && tests[i].success_on_tc)
+				ASSERT_GE(err, 0, buf);
+			else
+				ASSERT_EQ(err, tests[i].err, buf);
+			sprintf(buf, "ret: %s [%s]", tests[i].msg, bpf_program__name(prog));
+			if (at_tc && tests[i].success_on_tc)
+				ASSERT_GE(bpf_obj->bss->ret, 0, buf);
+			else
+				ASSERT_EQ(bpf_obj->bss->ret, tests[i].ret, buf);
+		}
+	}
+
+out:
+	if (bpf_obj)
+		empty_skb__destroy(bpf_obj);
+	if (tok)
+		close_netns(tok);
+	system("ip netns del empty_skb");
+}

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

+// SPDX-License-Identifier: GPL-2.0 OR BSD-3-Clause
+#include <linux/bpf.h>
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_endian.h>
+
+char _license[] SEC("license") = "GPL";
+
+int ifindex;
+int ret;
+
+SEC("lwt_xmit")
+int redirect_ingress(struct __sk_buff *skb)
+{
+	ret = bpf_clone_redirect(skb, ifindex, BPF_F_INGRESS);
+	return 0;
+}
+
+SEC("lwt_xmit")
+int redirect_egress(struct __sk_buff *skb)
+{
+	ret = bpf_clone_redirect(skb, ifindex, 0);
+	return 0;
+}
+
+SEC("tc")
+int tc_redirect_ingress(struct __sk_buff *skb)
+{
+	ret = bpf_clone_redirect(skb, ifindex, BPF_F_INGRESS);
+	return 0;
+}
+
+SEC("tc")
+int tc_redirect_egress(struct __sk_buff *skb)
+{
+	ret = bpf_clone_redirect(skb, ifindex, 0);
+	return 0;
+}