Subject: Re: [RFC PATCH v2 8/9] selftests/landlock: Test changing socket backlog with listen(2)

From: Günther Noack <[email-masked]>
Date: Sat, 5 Oct 2024 18:57:10 +0200

On Wed, Aug 14, 2024 at 11:01:50AM +0800, Mikhail Ivanov wrote:
> listen(2) can be used to change length of the pending connections queue
> of the listening socket. Such scenario shouldn't be restricted by Landlock
> since socket doesn't change its state.

Yes, this behavior makes sense to me as well. 👍 __inet_listen_sk()
only changes sk->sk_max_ack_backlog when listen() gets called a second
time.

> * Implement test that validates this case.
> 
> Signed-off-by: Mikhail Ivanov <[email-masked]>
> ---
>  tools/testing/selftests/landlock/net_test.c | 26 +++++++++++++++++++++
>  1 file changed, 26 insertions(+)
> 
> diff --git a/tools/testing/selftests/landlock/net_test.c b/tools/testing/selftests/landlock/net_test.c
> index 6831d8a2e9aa..dafc433a0068 100644
> --- a/tools/testing/selftests/landlock/net_test.c
> +++ b/tools/testing/selftests/landlock/net_test.c
> @@ -1768,6 +1768,32 @@ TEST_F(ipv4_tcp, with_fs)
>  	EXPECT_EQ(-EACCES, bind_variant(bind_fd, &self->srv1));
>  }
>  
> +TEST_F(ipv4_tcp, double_listen)
> +{
> +	const struct landlock_ruleset_attr ruleset_attr = {
> +		.handled_access_net = LANDLOCK_ACCESS_NET_LISTEN_TCP,
> +	};
> +	int ruleset_fd;
> +	int listen_fd;
> +
> +	listen_fd = socket_variant(&self->srv0);
> +	ASSERT_LE(0, listen_fd);
> +
> +	EXPECT_EQ(0, bind_variant(listen_fd, &self->srv0));
> +	EXPECT_EQ(0, listen_variant(listen_fd, backlog));
> +
> +	ruleset_fd =
> +		landlock_create_ruleset(&ruleset_attr, sizeof(ruleset_attr), 0);
> +	ASSERT_LE(0, ruleset_fd);
> +
> +	/* Denies listen. */
> +	enforce_ruleset(_metadata, ruleset_fd);
> +	EXPECT_EQ(0, close(ruleset_fd));
> +
> +	/* Tries to change backlog value of listening socket. */
> +	EXPECT_EQ(0, listen_variant(listen_fd, backlog + 1));

For test clarity: Without reading the commit message, I believe it
might not be obvious to the reader *why* the second listen() is
supposed to work.  This might be worth a comment.

> +}
> +
>  FIXTURE(port_specific)
>  {
>  	struct service_fixture srv0;
> -- 
> 2.34.1
> 

Reviewed-by: Günther Noack <[email-masked]>