selftests/bpf: Check that flow dissector can be re-attached

Make sure a new flow dissector program can be attached to replace the old
one with a single syscall. Also check that attaching the same program twice
is prohibited.
Signed-off-by: Jakub Sitnicki <jakub@cloudflare.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: Stanislav Fomichev <sdf@google.com>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Link: https://lore.kernel.org/bpf/20191011082946.22695-3-jakub@cloudflare.com

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

+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Test that the flow_dissector program can be updated with a single
+ * syscall by attaching a new program that replaces the existing one.
+ *
+ * Corner case - the same program cannot be attached twice.
+ */
+
+#define _GNU_SOURCE
+#include <errno.h>
+#include <fcntl.h>
+#include <sched.h>
+#include <stdbool.h>
+#include <unistd.h>
+
+#include <linux/bpf.h>
+#include <bpf/bpf.h>
+
+#include "test_progs.h"
+
+static bool is_attached(int netns)
+{
+	__u32 cnt;
+	int err;
+
+	err = bpf_prog_query(netns, BPF_FLOW_DISSECTOR, 0, NULL, NULL, &cnt);
+	if (CHECK_FAIL(err)) {
+		perror("bpf_prog_query");
+		return true; /* fail-safe */
+	}
+
+	return cnt > 0;
+}
+
+static int load_prog(void)
+{
+	struct bpf_insn prog[] = {
+		BPF_MOV64_IMM(BPF_REG_0, BPF_OK),
+		BPF_EXIT_INSN(),
+	};
+	int fd;
+
+	fd = bpf_load_program(BPF_PROG_TYPE_FLOW_DISSECTOR, prog,
+			      ARRAY_SIZE(prog), "GPL", 0, NULL, 0);
+	if (CHECK_FAIL(fd < 0))
+		perror("bpf_load_program");
+
+	return fd;
+}
+
+static void do_flow_dissector_reattach(void)
+{
+	int prog_fd[2] = { -1, -1 };
+	int err;
+
+	prog_fd[0] = load_prog();
+	if (prog_fd[0] < 0)
+		return;
+
+	prog_fd[1] = load_prog();
+	if (prog_fd[1] < 0)
+		goto out_close;
+
+	err = bpf_prog_attach(prog_fd[0], 0, BPF_FLOW_DISSECTOR, 0);
+	if (CHECK_FAIL(err)) {
+		perror("bpf_prog_attach-0");
+		goto out_close;
+	}
+
+	/* Expect success when attaching a different program */
+	err = bpf_prog_attach(prog_fd[1], 0, BPF_FLOW_DISSECTOR, 0);
+	if (CHECK_FAIL(err)) {
+		perror("bpf_prog_attach-1");
+		goto out_detach;
+	}
+
+	/* Expect failure when attaching the same program twice */
+	err = bpf_prog_attach(prog_fd[1], 0, BPF_FLOW_DISSECTOR, 0);
+	if (CHECK_FAIL(!err || errno != EINVAL))
+		perror("bpf_prog_attach-2");
+
+out_detach:
+	err = bpf_prog_detach(0, BPF_FLOW_DISSECTOR);
+	if (CHECK_FAIL(err))
+		perror("bpf_prog_detach");
+
+out_close:
+	close(prog_fd[1]);
+	close(prog_fd[0]);
+}
+
+void test_flow_dissector_reattach(void)
+{
+	int init_net, err;
+
+	init_net = open("/proc/1/ns/net", O_RDONLY);
+	if (CHECK_FAIL(init_net < 0)) {
+		perror("open(/proc/1/ns/net)");
+		return;
+	}
+
+	err = setns(init_net, CLONE_NEWNET);
+	if (CHECK_FAIL(err)) {
+		perror("setns(/proc/1/ns/net)");
+		goto out_close;
+	}
+
+	if (is_attached(init_net)) {
+		test__skip();
+		printf("Can't test with flow dissector attached to init_net\n");
+		return;
+	}
+
+	/* First run tests in root network namespace */
+	do_flow_dissector_reattach();
+
+	/* Then repeat tests in a non-root namespace */
+	err = unshare(CLONE_NEWNET);
+	if (CHECK_FAIL(err)) {
+		perror("unshare(CLONE_NEWNET)");
+		goto out_close;
+	}
+	do_flow_dissector_reattach();
+
+out_close:
+	close(init_net);
+}