bpf, selftests: Test probe_* helpers from SCHED_CLS

Lets test using probe* in SCHED_CLS network programs as well just
to be sure these keep working. Its cheap to add the extra test
and provides a second context to test outside of sk_msg after
we generalized probe* helpers to all networking types.

Signed-off-by: John Fastabend <john.fastabend@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Yonghong Song <yhs@fb.com>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Link: https://lore.kernel.org/bpf/159033911685.12355.15951980509828906214.stgit@john-Precision-5820-Tower
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

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

@@ -0,0 +1,28 @@
+// SPDX-License-Identifier: GPL-2.0-only
+#include "vmlinux.h"
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_endian.h>
+
+#define TEST_COMM_LEN 16
+
+struct {
+	__uint(type, BPF_MAP_TYPE_CGROUP_ARRAY);
+	__uint(max_entries, 1);
+	__type(key, u32);
+	__type(value, u32);
+} cgroup_map SEC(".maps");
+
+char _license[] SEC("license") = "GPL";
+
+SEC("classifier/test_skb_helpers")
+int test_skb_helpers(struct __sk_buff *skb)
+{
+	struct task_struct *task;
+	char comm[TEST_COMM_LEN];
+	__u32 tpid;
+
+	task = (struct task_struct *)bpf_get_current_task();
+	bpf_probe_read_kernel(&tpid , sizeof(tpid), &task->tgid);
+	bpf_probe_read_kernel_str(&comm, sizeof(comm), &task->comm);
+	return 0;
+}