[PATCH v5 4/9] landlock/selftests: Test LANDLOCK_ACCESS_FS_RESOLVE_UNIX

["Günther Noack" <gnoack3000@gmail.com>]

* Extract common helpers from an existing IOCTL test that
  also uses pathname unix(7) sockets.
* These tests use the common scoped domains fixture which is also used
  in other Landlock scoping tests and which was used in Tingmao Wang's
  earlier patch set in [1].

These tests exercise the cross product of the following scenarios:

* Stream connect(), Datagram connect(), Datagram sendmsg() and
  Seqpacket connect().
* Child-to-parent and parent-to-child communication
* The Landlock policy configuration as listed in the scoped_domains
  fixture.
  * In the default variant, Landlock domains are only placed where
    prescribed in the fixture.
  * In the "ALL_DOMAINS" variant, Landlock domains are also placed in
    the places where the fixture says to omit them, but with a
    LANDLOCK_RULE_PATH_BENEATH that allows connection.

Cc: Justin Suess <utilityemal77@gmail.com>
Cc: Tingmao Wang <m@maowtm.org>
Cc: Mickaël Salaün <mic@digikod.net>
Link[1]: https://lore.kernel.org/all/53b9883648225d5a08e82d2636ab0b4fda003bc9.1767115163.git.m@maowtm.org/
Signed-off-by: Günther Noack <gnoack3000@gmail.com>
---
 tools/testing/selftests/landlock/fs_test.c | 384 ++++++++++++++++++++-
 1 file changed, 368 insertions(+), 16 deletions(-)

diff --git a/tools/testing/selftests/landlock/fs_test.c b/tools/testing/selftests/landlock/fs_test.c
index b318627e7561..bdeff2e0e029 100644
--- a/tools/testing/selftests/landlock/fs_test.c
+++ b/tools/testing/selftests/landlock/fs_test.c
@@ -4358,30 +4358,61 @@ TEST_F_FORK(layout1, named_pipe_ioctl)
 	ASSERT_EQ(child_pid, waitpid(child_pid, NULL, 0));
 }
 
+/*
+ * set_up_named_unix_server - Create a pathname unix socket
+ *
+ * If the socket type is not SOCK_DGRAM, also invoke listen(2).
+ *
+ * Return: The listening FD - it is the caller responsibility to close it.
+ */
+static int set_up_named_unix_server(struct __test_metadata *const _metadata,
+				    int type, const char *const path)
+{
+	int fd;
+	struct sockaddr_un addr = {
+		.sun_family = AF_UNIX,
+	};
+
+	fd = socket(AF_UNIX, type, 0);
+	ASSERT_LE(0, fd);
+
+	strncpy(addr.sun_path, path, sizeof(addr.sun_path));
+	ASSERT_EQ(0, bind(fd, (struct sockaddr *)&addr, sizeof(addr)));
+
+	if (type != SOCK_DGRAM)
+		ASSERT_EQ(0, listen(fd, 10 /* qlen */));
+	return fd;
+}
+
+/*
+ * test_connect_named_unix - connect to the given named UNIX socket
+ *
+ * Return: The errno from connect(), or 0
+ */
+static int test_connect_named_unix(int fd, const char *const path)
+{
+	struct sockaddr_un addr = {
+		.sun_family = AF_UNIX,
+	};
+	strncpy(addr.sun_path, path, sizeof(addr.sun_path));
+
+	if (connect(fd, (struct sockaddr *)&addr, sizeof(addr)) == -1)
+		return errno;
+	return 0;
+}
+
 /* For named UNIX domain sockets, no IOCTL restrictions apply. */
 TEST_F_FORK(layout1, named_unix_domain_socket_ioctl)
 {
 	const char *const path = file1_s1d1;
 	int srv_fd, cli_fd, ruleset_fd;
-	struct sockaddr_un srv_un = {
-		.sun_family = AF_UNIX,
-	};
-	struct sockaddr_un cli_un = {
-		.sun_family = AF_UNIX,
-	};
 	const struct landlock_ruleset_attr attr = {
 		.handled_access_fs = LANDLOCK_ACCESS_FS_IOCTL_DEV,
 	};
 
 	/* Sets up a server */
 	ASSERT_EQ(0, unlink(path));
-	srv_fd = socket(AF_UNIX, SOCK_STREAM, 0);
-	ASSERT_LE(0, srv_fd);
-
-	strncpy(srv_un.sun_path, path, sizeof(srv_un.sun_path));
-	ASSERT_EQ(0, bind(srv_fd, (struct sockaddr *)&srv_un, sizeof(srv_un)));
-
-	ASSERT_EQ(0, listen(srv_fd, 10 /* qlen */));
+	srv_fd = set_up_named_unix_server(_metadata, SOCK_STREAM, path);
 
 	/* Enables Landlock. */
 	ruleset_fd = landlock_create_ruleset(&attr, sizeof(attr), 0);
@@ -4393,9 +4424,7 @@ TEST_F_FORK(layout1, named_unix_domain_socket_ioctl)
 	cli_fd = socket(AF_UNIX, SOCK_STREAM, 0);
 	ASSERT_LE(0, cli_fd);
 
-	strncpy(cli_un.sun_path, path, sizeof(cli_un.sun_path));
-	ASSERT_EQ(0,
-		  connect(cli_fd, (struct sockaddr *)&cli_un, sizeof(cli_un)));
+	ASSERT_EQ(0, test_connect_named_unix(cli_fd, path));
 
 	/* FIONREAD and other IOCTLs should not be forbidden. */
 	EXPECT_EQ(0, test_fionread_ioctl(cli_fd));
@@ -4570,6 +4599,329 @@ TEST_F_FORK(ioctl, handle_file_access_file)
 	ASSERT_EQ(0, close(file_fd));
 }
 
+/*
+ * test_sendto_named_unix - sendto to the given named UNIX socket
+ *
+ * sendto() is equivalent to sendmsg() in this respect.
+ *
+ * Return: The errno from sendto(), or 0
+ */
+static int test_sendto_named_unix(int fd, const char *const path)
+{
+	static const char buf[] = "dummy";
+	struct sockaddr_un addr = {
+		.sun_family = AF_UNIX,
+	};
+	strncpy(addr.sun_path, path, sizeof(addr.sun_path));
+
+	if (sendto(fd, buf, sizeof(buf), 0, (struct sockaddr *)&addr,
+		   sizeof(addr)) == -1)
+		return errno;
+	return 0;
+}
+
+/* clang-format off */
+FIXTURE(scoped_domains) {};
+/* clang-format on */
+
+#include "scoped_base_variants.h"
+
+FIXTURE_SETUP(scoped_domains)
+{
+	drop_caps(_metadata);
+};
+
+FIXTURE_TEARDOWN(scoped_domains)
+{
+}
+
+static void enforce_fs_resolve_unix(struct __test_metadata *const _metadata,
+				    const struct rule rules[])
+{
+	if (rules) {
+		int fd = create_ruleset(_metadata,
+					LANDLOCK_ACCESS_FS_RESOLVE_UNIX, rules);
+		enforce_ruleset(_metadata, fd);
+		EXPECT_EQ(0, close(fd));
+	} else {
+		drop_access_rights(
+			_metadata,
+			&(struct landlock_ruleset_attr){
+				.handled_access_fs =
+					LANDLOCK_ACCESS_FS_RESOLVE_UNIX,
+			});
+	}
+}
+
+/*
+ * Flags for test_connect_to_parent and test_connect_to_child:
+ *
+ * USE_SENDTO: Use sendto() instead of connect() (for SOCK_DGRAM only)
+ * ENFORCE_ALL: Enforce a Landlock domain even when the variant says
+ *   we shouldn't.  We enforce a domain where the path is allow-listed,
+ *   and expect the behavior to be the same as if none was used.
+ */
+#define USE_SENDTO (1 << 0)
+#define ENFORCE_ALL (1 << 1)
+
+static void test_connect_to_parent(struct __test_metadata *const _metadata,
+				   const FIXTURE_VARIANT(scoped_domains) *
+					   variant,
+				   int sock_type, int flags)
+{
+	const char *const path = "sock";
+	const struct rule rules[] = {
+		{
+			.path = ".",
+			.access = LANDLOCK_ACCESS_FS_RESOLVE_UNIX,
+		},
+		{},
+	};
+	int cli_fd, srv_fd, res, status;
+	pid_t child_pid;
+	int readiness_pipe[2];
+	char buf[1];
+
+	if (variant->domain_both)
+		enforce_fs_resolve_unix(_metadata, NULL);
+	else if (flags & ENFORCE_ALL)
+		enforce_fs_resolve_unix(_metadata, rules);
+
+	unlink(path);
+	ASSERT_EQ(0, pipe2(readiness_pipe, O_CLOEXEC));
+
+	child_pid = fork();
+	ASSERT_LE(0, child_pid);
+
+	if (child_pid == 0) {
+		if (variant->domain_child)
+			enforce_fs_resolve_unix(_metadata, NULL);
+		else if (flags & ENFORCE_ALL)
+			enforce_fs_resolve_unix(_metadata, rules);
+
+		/* Wait for server to be available. */
+		EXPECT_EQ(0, close(readiness_pipe[1]));
+		EXPECT_EQ(1, read(readiness_pipe[0], &buf, 1));
+		EXPECT_EQ(0, close(readiness_pipe[0]));
+
+		/* Talk to server. */
+		cli_fd = socket(AF_UNIX, sock_type, 0);
+		ASSERT_LE(0, cli_fd);
+
+		if (flags & USE_SENDTO)
+			res = test_sendto_named_unix(cli_fd, path);
+		else
+			res = test_connect_named_unix(cli_fd, path);
+
+		EXPECT_EQ(variant->domain_child ? EACCES : 0, res);
+
+		/* Clean up. */
+		EXPECT_EQ(0, close(cli_fd));
+
+		_exit(_metadata->exit_code);
+		return;
+	}
+
+	if (variant->domain_parent)
+		enforce_fs_resolve_unix(_metadata, NULL);
+	else if (flags & ENFORCE_ALL)
+		enforce_fs_resolve_unix(_metadata, rules);
+
+	srv_fd = set_up_named_unix_server(_metadata, sock_type, path);
+
+	/* Tell the child that it can connect. */
+	EXPECT_EQ(0, close(readiness_pipe[0]));
+	EXPECT_EQ(sizeof(buf), write(readiness_pipe[1], buf, sizeof(buf)));
+	EXPECT_EQ(0, close(readiness_pipe[1]));
+
+	/* Wait for child. */
+	ASSERT_EQ(child_pid, waitpid(child_pid, &status, 0));
+	EXPECT_EQ(1, WIFEXITED(status));
+	EXPECT_EQ(EXIT_SUCCESS, WEXITSTATUS(status));
+
+	/* Clean up. */
+	EXPECT_EQ(0, close(srv_fd));
+	EXPECT_EQ(0, unlink(path));
+}
+
+static void test_connect_to_child(struct __test_metadata *const _metadata,
+				  const FIXTURE_VARIANT(scoped_domains) *
+					  variant,
+				  int sock_type, int flags)
+{
+	const char *const path = "sock";
+	const struct rule rules[] = {
+		{
+			.path = ".",
+			.access = LANDLOCK_ACCESS_FS_RESOLVE_UNIX,
+		},
+		{},
+	};
+	int readiness_pipe[2];
+	int shutdown_pipe[2];
+	int cli_fd, srv_fd, res, status;
+	pid_t child_pid;
+	char buf[1];
+
+	if (variant->domain_both)
+		enforce_fs_resolve_unix(_metadata, NULL);
+	else if (flags & ENFORCE_ALL)
+		enforce_fs_resolve_unix(_metadata, rules);
+
+	unlink(path);
+	ASSERT_EQ(0, pipe2(readiness_pipe, O_CLOEXEC));
+	ASSERT_EQ(0, pipe2(shutdown_pipe, O_CLOEXEC));
+
+	child_pid = fork();
+	ASSERT_LE(0, child_pid);
+
+	if (child_pid == 0) {
+		if (variant->domain_child)
+			enforce_fs_resolve_unix(_metadata, NULL);
+		else if (flags & ENFORCE_ALL)
+			enforce_fs_resolve_unix(_metadata, rules);
+
+		srv_fd = set_up_named_unix_server(_metadata, sock_type, path);
+
+		/* Tell the parent that it can connect. */
+		EXPECT_EQ(0, close(readiness_pipe[0]));
+		EXPECT_EQ(sizeof(buf),
+			  write(readiness_pipe[1], buf, sizeof(buf)));
+		EXPECT_EQ(0, close(readiness_pipe[1]));
+
+		/* Wait until it is time to shut down. */
+		EXPECT_EQ(0, close(shutdown_pipe[1]));
+		EXPECT_EQ(1, read(shutdown_pipe[0], &buf, 1));
+		EXPECT_EQ(0, close(shutdown_pipe[0]));
+
+		/* Cleanup */
+		EXPECT_EQ(0, close(srv_fd));
+		EXPECT_EQ(0, unlink(path));
+
+		_exit(_metadata->exit_code);
+		return;
+	}
+
+	if (variant->domain_parent)
+		enforce_fs_resolve_unix(_metadata, NULL);
+	else if (flags & ENFORCE_ALL)
+		enforce_fs_resolve_unix(_metadata, rules);
+
+	/* Wait for server to be available. */
+	EXPECT_EQ(0, close(readiness_pipe[1]));
+	EXPECT_EQ(1, read(readiness_pipe[0], &buf, 1));
+	EXPECT_EQ(0, close(readiness_pipe[0]));
+
+	/* Talk to server. */
+	cli_fd = socket(AF_UNIX, sock_type, 0);
+	ASSERT_LE(0, cli_fd);
+
+	if (flags & USE_SENDTO)
+		res = test_sendto_named_unix(cli_fd, path);
+	else
+		res = test_connect_named_unix(cli_fd, path);
+
+	EXPECT_EQ(variant->domain_parent ? EACCES : 0, res);
+
+	/* Clean up. */
+	EXPECT_EQ(0, close(cli_fd));
+
+	/* Tell the server to shut down. */
+	EXPECT_EQ(0, close(shutdown_pipe[0]));
+	EXPECT_EQ(sizeof(buf), write(shutdown_pipe[1], buf, sizeof(buf)));
+	EXPECT_EQ(0, close(shutdown_pipe[1]));
+
+	/* Wait for child. */
+	ASSERT_EQ(child_pid, waitpid(child_pid, &status, 0));
+	EXPECT_EQ(1, WIFEXITED(status));
+	EXPECT_EQ(EXIT_SUCCESS, WEXITSTATUS(status));
+}
+
+TEST_F(scoped_domains, unix_stream_connect_to_parent)
+{
+	test_connect_to_parent(_metadata, variant, SOCK_STREAM, 0);
+}
+
+TEST_F(scoped_domains, unix_dgram_connect_to_parent)
+{
+	test_connect_to_parent(_metadata, variant, SOCK_DGRAM, 0);
+}
+
+TEST_F(scoped_domains, unix_dgram_sendmsg_to_parent)
+{
+	test_connect_to_parent(_metadata, variant, SOCK_DGRAM, USE_SENDTO);
+}
+
+TEST_F(scoped_domains, unix_seqpacket_connect_to_parent)
+{
+	test_connect_to_parent(_metadata, variant, SOCK_SEQPACKET, 0);
+}
+
+TEST_F(scoped_domains, unix_stream_connect_to_parent_full)
+{
+	test_connect_to_parent(_metadata, variant, SOCK_STREAM, ENFORCE_ALL);
+}
+
+TEST_F(scoped_domains, unix_dgram_connect_to_parent_full)
+{
+	test_connect_to_parent(_metadata, variant, SOCK_DGRAM, ENFORCE_ALL);
+}
+
+TEST_F(scoped_domains, unix_dgram_sendmsg_to_parent_full)
+{
+	test_connect_to_parent(_metadata, variant, SOCK_DGRAM,
+			       USE_SENDTO | ENFORCE_ALL);
+}
+
+TEST_F(scoped_domains, unix_seqpacket_connect_to_parent_full)
+{
+	test_connect_to_parent(_metadata, variant, SOCK_SEQPACKET, ENFORCE_ALL);
+}
+
+TEST_F(scoped_domains, unix_stream_connect_to_child)
+{
+	test_connect_to_child(_metadata, variant, SOCK_STREAM, 0);
+}
+
+TEST_F(scoped_domains, unix_dgram_connect_to_child)
+{
+	test_connect_to_child(_metadata, variant, SOCK_DGRAM, 0);
+}
+
+TEST_F(scoped_domains, unix_dgram_sendmsg_to_child)
+{
+	test_connect_to_child(_metadata, variant, SOCK_DGRAM, USE_SENDTO);
+}
+
+TEST_F(scoped_domains, unix_seqpacket_connect_to_child)
+{
+	test_connect_to_child(_metadata, variant, SOCK_SEQPACKET, 0);
+}
+
+TEST_F(scoped_domains, unix_stream_connect_to_child_full)
+{
+	test_connect_to_child(_metadata, variant, SOCK_STREAM, ENFORCE_ALL);
+}
+
+TEST_F(scoped_domains, unix_dgram_connect_to_child_full)
+{
+	test_connect_to_child(_metadata, variant, SOCK_DGRAM, ENFORCE_ALL);
+}
+
+TEST_F(scoped_domains, unix_dgram_sendmsg_to_child_full)
+{
+	test_connect_to_child(_metadata, variant, SOCK_DGRAM,
+			      USE_SENDTO | ENFORCE_ALL);
+}
+
+TEST_F(scoped_domains, unix_seqpacket_connect_to_child_full)
+{
+	test_connect_to_child(_metadata, variant, SOCK_SEQPACKET, ENFORCE_ALL);
+}
+
+#undef USE_SENDTO
+#undef ENFORCE_ALL
+
 /* clang-format off */
 FIXTURE(layout1_bind) {};
 /* clang-format on */
-- 
2.52.0