Subject: Re: [RFC PATCH v3 16/19] selftests/landlock: Test that accept(2) is not restricted

From: "Günther Noack" <[email-masked]>
Date: Fri, 27 Sep 2024 16:53:51 +0200

On Wed, Sep 04, 2024 at 06:48:21PM +0800, Mikhail Ivanov wrote:
> Add test validating that socket creation with accept(2) is not restricted
> by Landlock.
> 
> Signed-off-by: Mikhail Ivanov <[email-masked]>
> ---
>  .../testing/selftests/landlock/socket_test.c  | 71 +++++++++++++++++++
>  1 file changed, 71 insertions(+)
> 
> diff --git a/tools/testing/selftests/landlock/socket_test.c b/tools/testing/selftests/landlock/socket_test.c
> index 2ab27196fa3d..052dbe0d1227 100644
> --- a/tools/testing/selftests/landlock/socket_test.c
> +++ b/tools/testing/selftests/landlock/socket_test.c
> @@ -939,4 +939,75 @@ TEST_F(socket_creation, sctp_peeloff)
>  	ASSERT_EQ(0, close(server_fd));
>  }
>  
> +TEST_F(socket_creation, accept)
> +{
> +	int status;
> +	pid_t child;
> +	struct sockaddr_in addr;
> +	int server_fd, client_fd;
> +	char buf;
> +	const struct landlock_ruleset_attr ruleset_attr = {
> +		.handled_access_socket = LANDLOCK_ACCESS_SOCKET_CREATE,
> +	};
> +	struct landlock_socket_attr tcp_socket_create = {
        ^^^^^^

Could be const as well, just like the ruleset_attr?

(I probably overlooked this as well in some of the other tests.)

> +		.allowed_access = LANDLOCK_ACCESS_SOCKET_CREATE,
> +		.family = AF_INET,
> +		.type = SOCK_STREAM,
> +	};
> +
> +	server_fd = socket(AF_INET, SOCK_STREAM | SOCK_CLOEXEC, 0);
> +	ASSERT_LE(0, server_fd);
> +
> +	addr.sin_family = AF_INET;
> +	addr.sin_port = htons(loopback_port);
> +	addr.sin_addr.s_addr = inet_addr(loopback_ipv4);
> +
> +	ASSERT_EQ(0, bind(server_fd, &addr, sizeof(addr)));
> +	ASSERT_EQ(0, listen(server_fd, backlog));
> +
> +	child = fork();
> +	ASSERT_LE(0, child);
> +	if (child == 0) {

Nit:
I feel like the child code would benefit from a higher level comment,
like "Connects to the server once and exits." or such.

> +		/* Closes listening socket for the child. */
> +		ASSERT_EQ(0, close(server_fd));
> +
> +		client_fd = socket(AF_INET, SOCK_STREAM | SOCK_CLOEXEC, 0);
> +		ASSERT_LE(0, client_fd);
> +
> +		ASSERT_EQ(0, connect(client_fd, &addr, sizeof(addr)));
> +		EXPECT_EQ(1, write(client_fd, ".", 1));
> +
> +		ASSERT_EQ(0, close(client_fd));
> +		_exit(_metadata->exit_code);
> +		return;
> +	}
> +
> +	if (self->sandboxed) {
> +		int ruleset_fd = landlock_create_ruleset(
> +			&ruleset_attr, sizeof(ruleset_attr), 0);
> +		ASSERT_LE(0, ruleset_fd);
> +		if (self->allowed) {
> +			ASSERT_EQ(0, landlock_add_rule(ruleset_fd,
> +						       LANDLOCK_RULE_SOCKET,
> +						       &tcp_socket_create, 0));
> +		}
> +		enforce_ruleset(_metadata, ruleset_fd);
> +		ASSERT_EQ(0, close(ruleset_fd));
> +	}
> +
> +	client_fd = accept(server_fd, NULL, 0);
> +
> +	/* accept(2) should not be restricted by Landlock. */
> +	EXPECT_LE(0, client_fd);

Should be an ASSERT, IMHO.
If this fails, client_fd will be -1,
and a lot of the stuff afterwards will fail as well.

> +
> +	EXPECT_EQ(1, read(client_fd, &buf, 1));
> +	EXPECT_EQ('.', buf);

I'm torn on whether the "." write and the check for it is very useful in this test.
It muddies the test's purpose a bit, and makes it harder to recognize the main use case.
Might make the test a bit simpler to drop it.

> +
> +	ASSERT_EQ(child, waitpid(child, &status, 0));
> +	ASSERT_EQ(1, WIFEXITED(status));
> +	ASSERT_EQ(EXIT_SUCCESS, WEXITSTATUS(status));
> +
> +	ASSERT_EQ(0, close(server_fd));

You are missing to close client_fd.

> +}
> +
>  TEST_HARNESS_MAIN
> -- 
> 2.34.1