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

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

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@google.com>

Ack with two minor comments below.

Acked-by: Yonghong Song <yhs@fb.com>


> ---
>   .../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.

On Thu, 2020-11-26 at 23:00 -0800, Yonghong Song wrote:
> On 11/26/20 8:44 AM, Florent Revest wrote:
> > +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.

Good to know!