diff mbox series

[bpf-next,V9,7/7] bpf/selftests: tests using bpf_check_mtu BPF-helper

Message ID 160822601093.3481451.9135115478358953965.stgit@firesoul
State Superseded
Headers show
Series bpf: New approach for BPF MTU handling | expand

Commit Message

Jesper Dangaard Brouer Dec. 17, 2020, 5:26 p.m. UTC 
Adding selftest for BPF-helper bpf_check_mtu(). Making sure
it can be used from both XDP and TC.

Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
---
 tools/testing/selftests/bpf/prog_tests/check_mtu.c |  204 ++++++++++++++++++++
 tools/testing/selftests/bpf/progs/test_check_mtu.c |  196 +++++++++++++++++++
 2 files changed, 400 insertions(+)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/check_mtu.c
 create mode 100644 tools/testing/selftests/bpf/progs/test_check_mtu.c

Comments

Jesper Dangaard Brouer Dec. 18, 2020, 10:53 a.m. UTC | #1 
On Thu, 17 Dec 2020 18:26:50 +0100
Jesper Dangaard Brouer <brouer@redhat.com> wrote:

> Adding selftest for BPF-helper bpf_check_mtu(). Making sure
> it can be used from both XDP and TC.
> 
> Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
> ---
>  tools/testing/selftests/bpf/prog_tests/check_mtu.c |  204 ++++++++++++++++++++
>  tools/testing/selftests/bpf/progs/test_check_mtu.c |  196 +++++++++++++++++++
>  2 files changed, 400 insertions(+)
>  create mode 100644 tools/testing/selftests/bpf/prog_tests/check_mtu.c
>  create mode 100644 tools/testing/selftests/bpf/progs/test_check_mtu.c

Will send V10 as I have an error in this selftests

> diff --git a/tools/testing/selftests/bpf/prog_tests/check_mtu.c b/tools/testing/selftests/bpf/prog_tests/check_mtu.c
> new file mode 100644
> index 000000000000..b5d0c3a9abe8
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/prog_tests/check_mtu.c
[...]
> +static void test_check_mtu_run_xdp(struct test_check_mtu *skel,
> +				   struct bpf_program *prog,
> +				   __u32 mtu_expect)
> +{
> +	const char *prog_name = bpf_program__name(prog);
> +	int retval_expect = XDP_PASS;
> +	__u32 mtu_result = 0;
> +	char buf[256];
> +	int err;
> +
> +	struct bpf_prog_test_run_attr tattr = {
> +		.repeat = 1,
> +		.data_in = &pkt_v4,
> +		.data_size_in = sizeof(pkt_v4),
> +		.data_out = buf,
> +		.data_size_out = sizeof(buf),
> +		.prog_fd = bpf_program__fd(prog),
> +	};
> +
> +	memset(buf, 0, sizeof(buf));
> +
> +	err = bpf_prog_test_run_xattr(&tattr);
> +	CHECK_ATTR(err != 0 || errno != 0, "bpf_prog_test_run",
                               ^^^^^^^^^^^
You/I cannot use the check "errno != 0" here, as something else could
have set it earlier.


> +		   "prog_name:%s (err %d errno %d retval %d)\n",
> +		   prog_name, err, errno, tattr.retval);
> +
> +        CHECK(tattr.retval != retval_expect, "retval",
> +	      "progname:%s unexpected retval=%d expected=%d\n",
> +	      prog_name, tattr.retval, retval_expect);
> +
> +	/* Extract MTU that BPF-prog got */
> +	mtu_result = skel->bss->global_bpf_mtu_xdp;
> +	CHECK(mtu_result != mtu_expect, "MTU-compare-user",
> +	      "failed (MTU user:%d bpf:%d)", mtu_expect, mtu_result);
> +}


> +static void test_check_mtu_run_tc(struct test_check_mtu *skel,
> +				  struct bpf_program *prog,
> +				  __u32 mtu_expect)
> +{
[...]
> +	err = bpf_prog_test_run_xattr(&tattr);
> +	CHECK_ATTR(err != 0 || errno != 0, "bpf_prog_test_run",
> +		   "prog_name:%s (err %d errno %d retval %d)\n",
> +		   prog_name, err, errno, tattr.retval);

Same issue here.
Andrii Nakryiko Dec. 18, 2020, 8:13 p.m. UTC | #2 
On Thu, Dec 17, 2020 at 9:30 AM Jesper Dangaard Brouer
<brouer@redhat.com> wrote:
>
> Adding selftest for BPF-helper bpf_check_mtu(). Making sure
> it can be used from both XDP and TC.
>
> Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
> ---
>  tools/testing/selftests/bpf/prog_tests/check_mtu.c |  204 ++++++++++++++++++++
>  tools/testing/selftests/bpf/progs/test_check_mtu.c |  196 +++++++++++++++++++
>  2 files changed, 400 insertions(+)
>  create mode 100644 tools/testing/selftests/bpf/prog_tests/check_mtu.c
>  create mode 100644 tools/testing/selftests/bpf/progs/test_check_mtu.c
>
> diff --git a/tools/testing/selftests/bpf/prog_tests/check_mtu.c b/tools/testing/selftests/bpf/prog_tests/check_mtu.c
> new file mode 100644
> index 000000000000..b5d0c3a9abe8
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/prog_tests/check_mtu.c
> @@ -0,0 +1,204 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/* Copyright (c) 2020 Jesper Dangaard Brouer */
> +
> +#include <linux/if_link.h> /* before test_progs.h, avoid bpf_util.h redefines */
> +
> +#include <test_progs.h>
> +#include "test_check_mtu.skel.h"
> +#include <network_helpers.h>
> +
> +#include <stdlib.h>
> +#include <inttypes.h>
> +
> +#define IFINDEX_LO 1
> +
> +static __u32 duration; /* Hint: needed for CHECK macro */
> +
> +static int read_mtu_device_lo(void)
> +{
> +       const char *filename = "/sys/devices/virtual/net/lo/mtu";
> +       char buf[11] = {};
> +       int value;
> +       int fd;
> +
> +       fd = open(filename, 0, O_RDONLY);
> +       if (fd == -1)
> +               return -1;
> +
> +       if (read(fd, buf, sizeof(buf)) == -1)

close fd missing here?

> +               return -2;
> +       close(fd);
> +
> +       value = strtoimax(buf, NULL, 10);
> +       if (errno == ERANGE)
> +               return -3;
> +
> +       return value;
> +}
> +
> +static void test_check_mtu_xdp_attach(struct bpf_program *prog)
> +{
> +       int err = 0;
> +       int fd;
> +
> +       fd = bpf_program__fd(prog);
> +       err = bpf_set_link_xdp_fd(IFINDEX_LO, fd, XDP_FLAGS_SKB_MODE);
> +       if (CHECK(err, "XDP-attach", "failed"))
> +               return;
> +
> +       bpf_set_link_xdp_fd(IFINDEX_LO, -1, 0);

can you please use bpf_link-based bpf_program__attach_xdp() which will
provide auto-cleanup in case of crash?

also check that it succeeded?

> +}
> +
> +static void test_check_mtu_run_xdp(struct test_check_mtu *skel,
> +                                  struct bpf_program *prog,
> +                                  __u32 mtu_expect)
> +{
> +       const char *prog_name = bpf_program__name(prog);
> +       int retval_expect = XDP_PASS;
> +       __u32 mtu_result = 0;
> +       char buf[256];
> +       int err;
> +
> +       struct bpf_prog_test_run_attr tattr = {
> +               .repeat = 1,
> +               .data_in = &pkt_v4,
> +               .data_size_in = sizeof(pkt_v4),
> +               .data_out = buf,
> +               .data_size_out = sizeof(buf),
> +               .prog_fd = bpf_program__fd(prog),
> +       };

nit: it's a variable declaration, so keep it all in one block. There
is also opts-based variant, which might be good to use here instead.

> +
> +       memset(buf, 0, sizeof(buf));

char buf[256] = {}; would make this unnecessary


> +
> +       err = bpf_prog_test_run_xattr(&tattr);
> +       CHECK_ATTR(err != 0 || errno != 0, "bpf_prog_test_run",
> +                  "prog_name:%s (err %d errno %d retval %d)\n",
> +                  prog_name, err, errno, tattr.retval);
> +
> +        CHECK(tattr.retval != retval_expect, "retval",

whitespaces are off?

> +             "progname:%s unexpected retval=%d expected=%d\n",
> +             prog_name, tattr.retval, retval_expect);
> +
> +       /* Extract MTU that BPF-prog got */
> +       mtu_result = skel->bss->global_bpf_mtu_xdp;
> +       CHECK(mtu_result != mtu_expect, "MTU-compare-user",
> +             "failed (MTU user:%d bpf:%d)", mtu_expect, mtu_result);

There is nicer ASSERT_EQ() macro for such cases:

ASSERT_EQ(mtu_result, mtu_expect, "MTU-compare-user"); it will format
sensible error message automatically

> +}
> +

[...]

> +       char buf[256];
> +       int err;
> +
> +       struct bpf_prog_test_run_attr tattr = {
> +               .repeat = 1,
> +               .data_in = &pkt_v4,
> +               .data_size_in = sizeof(pkt_v4),
> +               .data_out = buf,
> +               .data_size_out = sizeof(buf),
> +               .prog_fd = bpf_program__fd(prog),
> +       };
> +
> +       memset(buf, 0, sizeof(buf));
> +

same as above

> +       err = bpf_prog_test_run_xattr(&tattr);
> +       CHECK_ATTR(err != 0 || errno != 0, "bpf_prog_test_run",
> +                  "prog_name:%s (err %d errno %d retval %d)\n",
> +                  prog_name, err, errno, tattr.retval);
> +
> +        CHECK(tattr.retval != retval_expect, "retval",

same :)

> +             "progname:%s unexpected retval=%d expected=%d\n",
> +             prog_name, tattr.retval, retval_expect);
> +
> +       /* Extract MTU that BPF-prog got */
> +       mtu_result = skel->bss->global_bpf_mtu_tc;
> +       CHECK(mtu_result != mtu_expect, "MTU-compare-user",
> +             "failed (MTU user:%d bpf:%d)", mtu_expect, mtu_result);
> +}
> +
> +

[...]

> +
> +void test_check_mtu(void)
> +{
> +       struct test_check_mtu *skel;
> +       __u32 mtu_lo;
> +
> +       skel = test_check_mtu__open_and_load();
> +       if (CHECK(!skel, "open and load skel", "failed"))
> +               return; /* Exit if e.g. helper unknown to kernel */
> +
> +       if (test__start_subtest("bpf_check_mtu XDP-attach"))
> +               test_check_mtu_xdp_attach(skel->progs.xdp_use_helper_basic);
> +
> +       test_check_mtu__destroy(skel);

here it's not clear why you instantiate skeleton outside of
test_check_mtu_xdp_attach() subtest. Can you please move it in? It
will keep this failure local to that specific subtest, not the entire
test. And is just cleaner, of course.

> +
> +       mtu_lo = read_mtu_device_lo();
> +       if (CHECK(mtu_lo < 0, "reading MTU value", "failed (err:%d)", mtu_lo))

ASSERT_OK() could be used here

> +               return;
> +
> +       if (test__start_subtest("bpf_check_mtu XDP-run"))
> +               test_check_mtu_xdp(mtu_lo, 0);
> +
> +       if (test__start_subtest("bpf_check_mtu XDP-run ifindex-lookup"))
> +               test_check_mtu_xdp(mtu_lo, IFINDEX_LO);
> +
> +       if (test__start_subtest("bpf_check_mtu TC-run"))
> +               test_check_mtu_tc(mtu_lo, 0);
> +
> +       if (test__start_subtest("bpf_check_mtu TC-run ifindex-lookup"))
> +               test_check_mtu_tc(mtu_lo, IFINDEX_LO);
> +}

[...]

> +
> +       global_bpf_mtu_tc = mtu_len;
> +       return retval;
> +}
> +
> +SEC("classifier")

nice use of the same SEC()'tion BPF programs!


> +int tc_minus_delta(struct __sk_buff *ctx)
> +{
> +       int retval = BPF_OK; /* Expected retval on successful test */
> +       __u32 ifindex = GLOBAL_USER_IFINDEX;
> +       __u32 skb_len = ctx->len;
> +       __u32 mtu_len = 0;
> +       int delta;
> +
> +       /* Boarderline test case: Minus delta exceeding packet length allowed */
> +       delta = -((skb_len - ETH_HLEN) + 1);
> +
> +       /* Minus length (adjusted via delta) still pass MTU check, other helpers
> +        * are responsible for catching this, when doing actual size adjust
> +        */
> +       if (bpf_check_mtu(ctx, ifindex, &mtu_len, delta, 0))
> +               retval = BPF_DROP;
> +
> +       global_bpf_mtu_xdp = mtu_len;
> +       return retval;
> +}
>
>
diff mbox series

Patch

diff --git a/tools/testing/selftests/bpf/prog_tests/check_mtu.c b/tools/testing/selftests/bpf/prog_tests/check_mtu.c
new file mode 100644
index 000000000000..b5d0c3a9abe8
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/check_mtu.c
@@ -0,0 +1,204 @@ 
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2020 Jesper Dangaard Brouer */
+
+#include <linux/if_link.h> /* before test_progs.h, avoid bpf_util.h redefines */
+
+#include <test_progs.h>
+#include "test_check_mtu.skel.h"
+#include <network_helpers.h>
+
+#include <stdlib.h>
+#include <inttypes.h>
+
+#define IFINDEX_LO 1
+
+static __u32 duration; /* Hint: needed for CHECK macro */
+
+static int read_mtu_device_lo(void)
+{
+	const char *filename = "/sys/devices/virtual/net/lo/mtu";
+	char buf[11] = {};
+	int value;
+	int fd;
+
+	fd = open(filename, 0, O_RDONLY);
+	if (fd == -1)
+		return -1;
+
+	if (read(fd, buf, sizeof(buf)) == -1)
+		return -2;
+	close(fd);
+
+	value = strtoimax(buf, NULL, 10);
+	if (errno == ERANGE)
+		return -3;
+
+	return value;
+}
+
+static void test_check_mtu_xdp_attach(struct bpf_program *prog)
+{
+	int err = 0;
+	int fd;
+
+	fd = bpf_program__fd(prog);
+	err = bpf_set_link_xdp_fd(IFINDEX_LO, fd, XDP_FLAGS_SKB_MODE);
+	if (CHECK(err, "XDP-attach", "failed"))
+		return;
+
+	bpf_set_link_xdp_fd(IFINDEX_LO, -1, 0);
+}
+
+static void test_check_mtu_run_xdp(struct test_check_mtu *skel,
+				   struct bpf_program *prog,
+				   __u32 mtu_expect)
+{
+	const char *prog_name = bpf_program__name(prog);
+	int retval_expect = XDP_PASS;
+	__u32 mtu_result = 0;
+	char buf[256];
+	int err;
+
+	struct bpf_prog_test_run_attr tattr = {
+		.repeat = 1,
+		.data_in = &pkt_v4,
+		.data_size_in = sizeof(pkt_v4),
+		.data_out = buf,
+		.data_size_out = sizeof(buf),
+		.prog_fd = bpf_program__fd(prog),
+	};
+
+	memset(buf, 0, sizeof(buf));
+
+	err = bpf_prog_test_run_xattr(&tattr);
+	CHECK_ATTR(err != 0 || errno != 0, "bpf_prog_test_run",
+		   "prog_name:%s (err %d errno %d retval %d)\n",
+		   prog_name, err, errno, tattr.retval);
+
+        CHECK(tattr.retval != retval_expect, "retval",
+	      "progname:%s unexpected retval=%d expected=%d\n",
+	      prog_name, tattr.retval, retval_expect);
+
+	/* Extract MTU that BPF-prog got */
+	mtu_result = skel->bss->global_bpf_mtu_xdp;
+	CHECK(mtu_result != mtu_expect, "MTU-compare-user",
+	      "failed (MTU user:%d bpf:%d)", mtu_expect, mtu_result);
+}
+
+static void test_check_mtu_xdp(__u32 mtu, __u32 ifindex)
+{
+	struct test_check_mtu *skel;
+	int err;
+
+	skel = test_check_mtu__open();
+	if (CHECK(!skel, "skel_open", "failed"))
+		return;
+
+	/* Update "constants" in BPF-prog *BEFORE* libbpf load */
+	skel->rodata->GLOBAL_USER_MTU = mtu;
+	skel->rodata->GLOBAL_USER_IFINDEX = ifindex;
+
+	err = test_check_mtu__load(skel);
+	if (CHECK(err, "skel_load", "failed: %d\n", err))
+		goto cleanup;
+
+	test_check_mtu_run_xdp(skel, skel->progs.xdp_use_helper, mtu);
+	test_check_mtu_run_xdp(skel, skel->progs.xdp_exceed_mtu, mtu);
+	test_check_mtu_run_xdp(skel, skel->progs.xdp_minus_delta, mtu);
+
+cleanup:
+	test_check_mtu__destroy(skel);
+}
+
+static void test_check_mtu_run_tc(struct test_check_mtu *skel,
+				  struct bpf_program *prog,
+				  __u32 mtu_expect)
+{
+	const char *prog_name = bpf_program__name(prog);
+	int retval_expect = BPF_OK;
+	__u32 mtu_result = 0;
+	char buf[256];
+	int err;
+
+	struct bpf_prog_test_run_attr tattr = {
+		.repeat = 1,
+		.data_in = &pkt_v4,
+		.data_size_in = sizeof(pkt_v4),
+		.data_out = buf,
+		.data_size_out = sizeof(buf),
+		.prog_fd = bpf_program__fd(prog),
+	};
+
+	memset(buf, 0, sizeof(buf));
+
+	err = bpf_prog_test_run_xattr(&tattr);
+	CHECK_ATTR(err != 0 || errno != 0, "bpf_prog_test_run",
+		   "prog_name:%s (err %d errno %d retval %d)\n",
+		   prog_name, err, errno, tattr.retval);
+
+        CHECK(tattr.retval != retval_expect, "retval",
+	      "progname:%s unexpected retval=%d expected=%d\n",
+	      prog_name, tattr.retval, retval_expect);
+
+	/* Extract MTU that BPF-prog got */
+	mtu_result = skel->bss->global_bpf_mtu_tc;
+	CHECK(mtu_result != mtu_expect, "MTU-compare-user",
+	      "failed (MTU user:%d bpf:%d)", mtu_expect, mtu_result);
+}
+
+
+static void test_check_mtu_tc(__u32 mtu, __u32 ifindex)
+{
+	struct test_check_mtu *skel;
+	int err;
+
+	skel = test_check_mtu__open();
+	if (CHECK(!skel, "skel_open", "failed"))
+		return;
+
+	/* Update "constants" in BPF-prog *BEFORE* libbpf load */
+	skel->rodata->GLOBAL_USER_MTU = mtu;
+	skel->rodata->GLOBAL_USER_IFINDEX = ifindex;
+
+	err = test_check_mtu__load(skel);
+	if (CHECK(err, "skel_load", "failed: %d\n", err))
+		goto cleanup;
+
+	test_check_mtu_run_tc(skel, skel->progs.tc_use_helper, mtu);
+	test_check_mtu_run_tc(skel, skel->progs.tc_exceed_mtu, mtu);
+	test_check_mtu_run_tc(skel, skel->progs.tc_exceed_mtu_da, mtu);
+	test_check_mtu_run_tc(skel, skel->progs.tc_minus_delta, mtu);
+cleanup:
+	test_check_mtu__destroy(skel);
+}
+
+void test_check_mtu(void)
+{
+	struct test_check_mtu *skel;
+	__u32 mtu_lo;
+
+	skel = test_check_mtu__open_and_load();
+	if (CHECK(!skel, "open and load skel", "failed"))
+		return; /* Exit if e.g. helper unknown to kernel */
+
+	if (test__start_subtest("bpf_check_mtu XDP-attach"))
+		test_check_mtu_xdp_attach(skel->progs.xdp_use_helper_basic);
+
+	test_check_mtu__destroy(skel);
+
+	mtu_lo = read_mtu_device_lo();
+	if (CHECK(mtu_lo < 0, "reading MTU value", "failed (err:%d)", mtu_lo))
+		return;
+
+	if (test__start_subtest("bpf_check_mtu XDP-run"))
+		test_check_mtu_xdp(mtu_lo, 0);
+
+	if (test__start_subtest("bpf_check_mtu XDP-run ifindex-lookup"))
+		test_check_mtu_xdp(mtu_lo, IFINDEX_LO);
+
+	if (test__start_subtest("bpf_check_mtu TC-run"))
+		test_check_mtu_tc(mtu_lo, 0);
+
+	if (test__start_subtest("bpf_check_mtu TC-run ifindex-lookup"))
+		test_check_mtu_tc(mtu_lo, IFINDEX_LO);
+}
diff --git a/tools/testing/selftests/bpf/progs/test_check_mtu.c b/tools/testing/selftests/bpf/progs/test_check_mtu.c
new file mode 100644
index 000000000000..91a026b8d458
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/test_check_mtu.c
@@ -0,0 +1,196 @@ 
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2020 Jesper Dangaard Brouer */
+
+#include <linux/bpf.h>
+#include <bpf/bpf_helpers.h>
+#include <linux/if_ether.h>
+
+#include <stddef.h>
+#include <stdint.h>
+
+char _license[] SEC("license") = "GPL";
+
+/* Userspace will update with MTU it can see on device */
+static volatile const int GLOBAL_USER_MTU;
+static volatile const __u32 GLOBAL_USER_IFINDEX;
+
+/* BPF-prog will update these with MTU values it can see */
+__u32 global_bpf_mtu_xdp = 0;
+__u32 global_bpf_mtu_tc  = 0;
+
+SEC("xdp")
+int xdp_use_helper_basic(struct xdp_md *ctx)
+{
+	__u32 mtu_len = 0;
+
+	if (bpf_check_mtu(ctx, 0, &mtu_len, 0, 0))
+		return XDP_ABORTED;
+
+	return XDP_PASS;
+}
+
+SEC("xdp")
+int xdp_use_helper(struct xdp_md *ctx)
+{
+	int retval = XDP_PASS; /* Expected retval on successful test */
+	__u32 mtu_len = 0;
+	__u32 ifindex = 0;
+	int delta = 0;
+
+	/* When ifindex is zero, save net_device lookup and use ctx netdev */
+	if (GLOBAL_USER_IFINDEX > 0)
+		ifindex = GLOBAL_USER_IFINDEX;
+
+	if (bpf_check_mtu(ctx, ifindex, &mtu_len, delta, 0)) {
+		/* mtu_len is also valid when check fail */
+		retval = XDP_ABORTED;
+		goto out;
+	}
+
+	if (GLOBAL_USER_MTU != mtu_len)
+		retval = XDP_DROP;
+
+out:
+	global_bpf_mtu_xdp = mtu_len;
+	return retval;
+}
+
+SEC("xdp")
+int xdp_exceed_mtu(struct xdp_md *ctx)
+{
+	void *data_end = (void *)(long)ctx->data_end;
+	void *data = (void *)(long)ctx->data;
+	__u32 ifindex = GLOBAL_USER_IFINDEX;
+	__u32 data_len = data_end - data;
+	int retval = XDP_ABORTED; /* Fail */
+	__u32 mtu_len = 0;
+
+	int delta;
+	int err;
+
+	/* Exceed MTU with 1 via delta adjust */
+	delta = GLOBAL_USER_MTU - (data_len - ETH_HLEN) + 1;
+
+	if ((err = bpf_check_mtu(ctx, ifindex, &mtu_len, delta, 0))) {
+		retval = XDP_PASS; /* Success in exceeding MTU check */
+		if (err != BPF_MTU_CHK_RET_FRAG_NEEDED)
+			retval = XDP_DROP;
+	}
+
+	global_bpf_mtu_xdp = mtu_len;
+	return retval;
+}
+
+SEC("xdp")
+int xdp_minus_delta(struct xdp_md *ctx)
+{
+	int retval = XDP_PASS; /* Expected retval on successful test */
+	void *data_end = (void *)(long)ctx->data_end;
+	void *data = (void *)(long)ctx->data;
+	__u32 ifindex = GLOBAL_USER_IFINDEX;
+	__u32 data_len = data_end - data;
+	__u32 mtu_len = 0;
+	int delta;
+
+	/* Boarderline test case: Minus delta exceeding packet length allowed */
+	delta = -((data_len - ETH_HLEN) + 1);
+
+	/* Minus length (adjusted via delta) still pass MTU check, other helpers
+	 * are responsible for catching this, when doing actual size adjust
+	 */
+	if (bpf_check_mtu(ctx, ifindex, &mtu_len, delta, 0))
+		retval = XDP_ABORTED;
+
+	global_bpf_mtu_xdp = mtu_len;
+	return retval;
+}
+
+SEC("classifier")
+int tc_use_helper(struct __sk_buff *ctx)
+{
+	int retval = BPF_OK; /* Expected retval on successful test */
+	__u32 mtu_len = 0;
+	int delta = 0;
+
+	if (bpf_check_mtu(ctx, 0, &mtu_len, delta, 0)) {
+		retval = BPF_DROP;
+		goto out;
+	}
+
+	if (GLOBAL_USER_MTU != mtu_len)
+		retval = BPF_REDIRECT;
+out:
+	global_bpf_mtu_tc = mtu_len;
+	return retval;
+}
+
+SEC("classifier")
+int tc_exceed_mtu(struct __sk_buff *ctx)
+{
+	__u32 ifindex = GLOBAL_USER_IFINDEX;
+	int retval = BPF_DROP; /* Fail */
+	__u32 skb_len = ctx->len;
+	__u32 mtu_len = 0;
+	int delta;
+	int err;
+
+	/* Exceed MTU with 1 via delta adjust */
+	delta = GLOBAL_USER_MTU - (skb_len - ETH_HLEN) + 1;
+
+	if ((err = bpf_check_mtu(ctx, ifindex, &mtu_len, delta, 0))) {
+		retval = BPF_OK; /* Success in exceeding MTU check */
+		if (err != BPF_MTU_CHK_RET_FRAG_NEEDED)
+			retval = BPF_DROP;
+	}
+
+	global_bpf_mtu_tc = mtu_len;
+	return retval;
+}
+
+SEC("classifier")
+int tc_exceed_mtu_da(struct __sk_buff *ctx)
+{
+	/* SKB Direct-Access variant */
+	void *data_end = (void *)(long)ctx->data_end;
+	void *data = (void *)(long)ctx->data;
+	__u32 ifindex = GLOBAL_USER_IFINDEX;
+	__u32 data_len = data_end - data;
+	int retval = BPF_DROP; /* Fail */
+	__u32 mtu_len = 0;
+	int delta;
+	int err;
+
+	/* Exceed MTU with 1 via delta adjust */
+	delta = GLOBAL_USER_MTU - (data_len - ETH_HLEN) + 1;
+
+	if ((err = bpf_check_mtu(ctx, ifindex, &mtu_len, delta, 0))) {
+		retval = BPF_OK; /* Success in exceeding MTU check */
+		if (err != BPF_MTU_CHK_RET_FRAG_NEEDED)
+			retval = BPF_DROP;
+	}
+
+	global_bpf_mtu_tc = mtu_len;
+	return retval;
+}
+
+SEC("classifier")
+int tc_minus_delta(struct __sk_buff *ctx)
+{
+	int retval = BPF_OK; /* Expected retval on successful test */
+	__u32 ifindex = GLOBAL_USER_IFINDEX;
+	__u32 skb_len = ctx->len;
+	__u32 mtu_len = 0;
+	int delta;
+
+	/* Boarderline test case: Minus delta exceeding packet length allowed */
+	delta = -((skb_len - ETH_HLEN) + 1);
+
+	/* Minus length (adjusted via delta) still pass MTU check, other helpers
+	 * are responsible for catching this, when doing actual size adjust
+	 */
+	if (bpf_check_mtu(ctx, ifindex, &mtu_len, delta, 0))
+		retval = BPF_DROP;
+
+	global_bpf_mtu_xdp = mtu_len;
+	return retval;
+}