[PATCH] selftests/landlock: Add tests for access through disconnected paths

[Tingmao Wang]

On 6/14/25 19:25, Tingmao Wang wrote:
> This adds a test for the edge case discussed in [1], and in addition also
> test rename operations when the operands are through disconnected paths,
> as that go through a separate code path in Landlock.
> [..]

Hi,

Since linkat also uses the separate refer check, and since it's not too
difficult given what we already have, I've made an edit to add tests for
linkat under disconnected paths as well.

Hopefully this helps better confirm that any fix we make does not change
existing user-facing behaviour (unless, of course, if we want to).

Tested with qemu as well as UML. Passes without panic_on_warn.

Signed-off-by: Tingmao Wang <m at maowtm.org>
---
 tools/testing/selftests/landlock/fs_test.c | 118 +++++++++++++++++++++
 1 file changed, 118 insertions(+)

diff --git a/tools/testing/selftests/landlock/fs_test.c b/tools/testing/selftests/landlock/fs_test.c
index 53b167dbd39c..055f6de25d05 100644
--- a/tools/testing/selftests/landlock/fs_test.c
+++ b/tools/testing/selftests/landlock/fs_test.c
@@ -5031,6 +5031,124 @@ TEST_F_FORK(layout1_bind, path_disconnected_rename)
 	ASSERT_EQ(0, test_open(file1_s1d3, O_RDONLY));
 }
 
+/*
+ * Test that linkat with disconnected paths works under Landlock. This
+ * test moves s1d3 to s4d1.
+ */
+TEST_F_FORK(layout1_bind, path_disconnected_link)
+{
+	/* Ruleset to be applied after renaming s1d3 to s4d1 */
+	const struct rule layer1[] = {
+		{
+			.path = dir_s4d1,
+			.access = LANDLOCK_ACCESS_FS_REFER |
+				  LANDLOCK_ACCESS_FS_READ_FILE |
+				  LANDLOCK_ACCESS_FS_MAKE_REG |
+				  LANDLOCK_ACCESS_FS_REMOVE_FILE,
+		},
+		{
+			.path = dir_s2d2,
+			.access = LANDLOCK_ACCESS_FS_REFER |
+				  LANDLOCK_ACCESS_FS_READ_FILE |
+				  LANDLOCK_ACCESS_FS_MAKE_REG |
+				  LANDLOCK_ACCESS_FS_REMOVE_FILE,
+		},
+		{}
+	};
+	int ruleset_fd, bind_s1d3_fd;
+
+	/* Remove unneeded files created by layout1, otherwise we will EEXIST */
+	ASSERT_EQ(0, unlink(file1_s1d2));
+	ASSERT_EQ(0, unlink(file2_s1d3));
+
+	bind_s1d3_fd = open(bind_dir_s1d3, O_PATH | O_CLOEXEC);
+	ASSERT_LE(0, bind_s1d3_fd);
+	ASSERT_EQ(0, test_open_rel(bind_s1d3_fd, file1_name, O_RDONLY));
+
+	/* Make bind_s1d3_fd disconnected */
+	ASSERT_EQ(0, rename(dir_s1d3, dir_s4d1))
+	{
+		TH_LOG("Failed to rename %s to %s: %s", dir_s1d3, dir_s4d1,
+		       strerror(errno));
+	}
+	/* Need this later to test different parent link */
+	ASSERT_EQ(0, mkdir(dir_s4d2, 0755))
+	{
+		TH_LOG("Failed to create %s: %s", dir_s4d2, strerror(errno));
+	}
+
+	ruleset_fd = create_ruleset(_metadata, ACCESS_ALL, layer1);
+	ASSERT_LE(0, ruleset_fd);
+	enforce_ruleset(_metadata, ruleset_fd);
+	ASSERT_EQ(0, close(ruleset_fd));
+
+	/* disconnected to connected */
+	ASSERT_EQ(0, linkat(bind_s1d3_fd, file1_name, AT_FDCWD, file1_s2d2, 0))
+	{
+		TH_LOG("Failed to link %s to %s via disconnected %s: %s",
+		       file1_name, file1_s2d2, bind_dir_s1d3, strerror(errno));
+	}
+	/* Test that we can access via the new link */
+	ASSERT_EQ(0, test_open(file1_s2d2, O_RDONLY))
+	{
+		TH_LOG("Failed to open newly linked %s: %s", file1_s2d2,
+		       strerror(errno));
+	}
+	/* As well as the old one */
+	ASSERT_EQ(0, test_open(file1_s4d1, O_RDONLY))
+	{
+		TH_LOG("Failed to open original %s: %s", file1_s4d1,
+		       strerror(errno));
+	}
+
+	/* connected to disconnected */
+	ASSERT_EQ(0, unlink(file1_s4d1));
+	ASSERT_EQ(0, linkat(AT_FDCWD, file1_s2d2, bind_s1d3_fd, file2_name, 0))
+	{
+		TH_LOG("Failed to link %s to %s via disconnected %s: %s",
+		       file1_s2d2, file2_name, bind_dir_s1d3, strerror(errno));
+	}
+	ASSERT_EQ(0, test_open(file2_s4d1, O_RDONLY));
+	ASSERT_EQ(0, unlink(file1_s2d2));
+
+	/* disconnected to disconnected (same parent) */
+	ASSERT_EQ(0,
+		  linkat(bind_s1d3_fd, file2_name, bind_s1d3_fd, file1_name, 0))
+	{
+		TH_LOG("Failed to link %s to %s within disconnected %s: %s",
+		       file2_name, file1_name, bind_dir_s1d3, strerror(errno));
+	}
+	ASSERT_EQ(0, test_open(file1_s4d1, O_RDONLY))
+	{
+		TH_LOG("Failed to open newly linked %s: %s", file1_s4d1,
+		       strerror(errno));
+	}
+	ASSERT_EQ(0, test_open_rel(bind_s1d3_fd, file1_name, O_RDONLY))
+	{
+		TH_LOG("Failed to open %s through newly created link under disconnected path: %s",
+		       file1_name, strerror(errno));
+	}
+	ASSERT_EQ(0, unlink(file2_s4d1));
+
+	/* disconnected to disconnected (different parent) */
+	ASSERT_EQ(0,
+		  linkat(bind_s1d3_fd, file1_name, bind_s1d3_fd, "s4d2/f1", 0))
+	{
+		TH_LOG("Failed to link %s to %s within disconnected %s: %s",
+		       file1_name, "s4d2/f1", bind_dir_s1d3, strerror(errno));
+	}
+	ASSERT_EQ(0, test_open(file1_s4d2, O_RDONLY))
+	{
+		TH_LOG("Failed to open %s after link: %s", file1_s4d2,
+		       strerror(errno));
+	}
+	ASSERT_EQ(0, test_open_rel(bind_s1d3_fd, "s4d2/f1", O_RDONLY))
+	{
+		TH_LOG("Failed to open %s through disconnected path after link: %s",
+		       "s4d2/f1", strerror(errno));
+	}
+}
+
 #define LOWER_BASE TMP_DIR "/lower"
 #define LOWER_DATA LOWER_BASE "/data"
 static const char lower_fl1[] = LOWER_DATA "/fl1";
-- 
2.49.0