Re: [PATCH bpf-next v3 5/6] bpf: Add an iterator selftest for bpf_sk_storage_get

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On 11/26/20 8:44 AM, Florent Revest wrote:
The eBPF program iterates over all files and tasks. For all socket
files, it stores the tgid of the last task it encountered with a handle
to that socket. This is a heuristic for finding the "owner" of a socket
similar to what's done by lsof, ss, netstat or fuser. Potentially, this
information could be used from a cgroup_skb/*gress hook to try to
associate network traffic with processes.

The test makes sure that a socket it created is tagged with prog_tests's
pid.

Signed-off-by: Florent Revest <revest@xxxxxxxxxx>

Ack with two minor comments below.

Acked-by: Yonghong Song <yhs@xxxxxx>


---
  .../selftests/bpf/prog_tests/bpf_iter.c       | 40 +++++++++++++++++++
  .../progs/bpf_iter_bpf_sk_storage_helpers.c   | 25 ++++++++++++
  2 files changed, 65 insertions(+)

diff --git a/tools/testing/selftests/bpf/prog_tests/bpf_iter.c b/tools/testing/selftests/bpf/prog_tests/bpf_iter.c
index bb4a638f2e6f..9336d0f18331 100644
--- a/tools/testing/selftests/bpf/prog_tests/bpf_iter.c
+++ b/tools/testing/selftests/bpf/prog_tests/bpf_iter.c
@@ -975,6 +975,44 @@ static void test_bpf_sk_storage_delete(void)
  	bpf_iter_bpf_sk_storage_helpers__destroy(skel);
  }
+/* This creates a socket and its local storage. It then runs a task_iter BPF
+ * program that replaces the existing socket local storage with the tgid of the
+ * only task owning a file descriptor to this socket, this process, prog_tests.
+ */
+static void test_bpf_sk_storage_get(void)
+{
+	struct bpf_iter_bpf_sk_storage_helpers *skel;
+	int err, map_fd, val = -1;
+	int sock_fd = -1;
+
+	skel = bpf_iter_bpf_sk_storage_helpers__open_and_load();
+	if (CHECK(!skel, "bpf_iter_bpf_sk_storage_helpers__open_and_load",
+		  "skeleton open_and_load failed\n"))
+		return;
+
+	sock_fd = socket(AF_INET6, SOCK_STREAM, 0);
+	if (CHECK(sock_fd < 0, "socket", "errno: %d\n", errno))
+		goto out;
+
+	map_fd = bpf_map__fd(skel->maps.sk_stg_map);
+
+	err = bpf_map_update_elem(map_fd, &sock_fd, &val, BPF_NOEXIST);
+	if (CHECK(err, "bpf_map_update_elem", "map_update_failed\n"))
+		goto close_socket;
+
+	do_dummy_read(skel->progs.fill_socket_owner);
+
+	err = bpf_map_lookup_elem(map_fd, &sock_fd, &val);
+	CHECK(err || val != getpid(), "bpf_map_lookup_elem",
+	      "map value wasn't set correctly (expected %d, got %d, err=%d)\n",
+	      getpid(), val, err);
+
+close_socket:
+	close(sock_fd);
+out:
+	bpf_iter_bpf_sk_storage_helpers__destroy(skel);
+}
+
  static void test_bpf_sk_storage_map(void)
  {
  	DECLARE_LIBBPF_OPTS(bpf_iter_attach_opts, opts);
@@ -1131,6 +1169,8 @@ void test_bpf_iter(void)
  		test_bpf_sk_storage_map();
  	if (test__start_subtest("bpf_sk_storage_delete"))
  		test_bpf_sk_storage_delete();
+	if (test__start_subtest("bpf_sk_storage_get"))
+		test_bpf_sk_storage_get();
  	if (test__start_subtest("rdonly-buf-out-of-bound"))
  		test_rdonly_buf_out_of_bound();
  	if (test__start_subtest("buf-neg-offset"))
diff --git a/tools/testing/selftests/bpf/progs/bpf_iter_bpf_sk_storage_helpers.c b/tools/testing/selftests/bpf/progs/bpf_iter_bpf_sk_storage_helpers.c
index 01ff3235e413..d7a7a802d172 100644
--- a/tools/testing/selftests/bpf/progs/bpf_iter_bpf_sk_storage_helpers.c
+++ b/tools/testing/selftests/bpf/progs/bpf_iter_bpf_sk_storage_helpers.c
@@ -21,3 +21,28 @@ int delete_bpf_sk_storage_map(struct bpf_iter__bpf_sk_storage_map *ctx)
return 0;
  }
+
+SEC("iter/task_file")
+int fill_socket_owner(struct bpf_iter__task_file *ctx)
+{
+	struct task_struct *task = ctx->task;
+	struct file *file = ctx->file;
+	struct socket *sock;
+	int *sock_tgid;
+
+	if (!task || !file || task->tgid != task->pid)

task->tgid != task->pid is not needed here.
The task_file iterator already tries to skip task with task->pid
if its file table is the same as task->tgid.

+		return 0;
+
+	sock = bpf_sock_from_file(file);
+	if (!sock)
+		return 0;
+
+	sock_tgid = bpf_sk_storage_get(&sk_stg_map, sock->sk, 0, 0);
+	if (!sock_tgid)
+		return 0;
+
+	*sock_tgid = task->tgid;
+
+	return 0;
+}
+

Extra empty line.



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