[PATCH v1 5/5] selftests/landlock: Add tests for pseudo filesystems

[Mickaël Salaün]

Add generic and read-only tests for 7 pseudo filesystems to make sure
they have a consistent inode management, which is required for
Landlock's file hierarchy identification:
- ramfs
- tmpfs
- cgroup
- cgroup2
- proc
- sysfs
- hostfs

Update related kernel configuration to support these new filesystems,
and sort all entries.  If these filesystems are not supported by the
kernel running tests, the related tests are skipped.

Expanding variants, this adds 35 new tests for layout3_fs:
- tag_inode_dir_parent
- tag_inode_dir_mnt
- tag_inode_dir_child
- tag_inode_dir_file
- release_inodes

The hostfs filesystem, only available for an User-Mode Linux kernel, is
special because we cannot explicitly mount it.  The layout3_fs.hostfs
variant tests are skipped if the current test directory is not backed by
this filesystem.

The layout3_fs.hostfs.tag_inode_dir_child and
layout3_fs.hostfs.tag_inode_file tests pass thanks to a previous
commit fixing hostfs inode management.  Without this fix, the
deny-by-default policy would apply and all access requests would be
denied.

Cc: <stable@xxxxxxxxxxxxxxx> # 5.15.x: 63e6b2a42342: selftests/harness: Run TEARDOWN for ASSERT failures
Cc: <stable@xxxxxxxxxxxxxxx> # 5.15.x: 79ee8aa31d51: selftests/harness: Pass variant to teardown
Cc: <stable@xxxxxxxxxxxxxxx> # 5.15+
Signed-off-by: Mickaël Salaün <mic@xxxxxxxxxxx>
Link: https://lore.kernel.org/r/20230309165455.175131-6-mic@xxxxxxxxxxx
---
 tools/testing/selftests/landlock/config    |   8 +-
 tools/testing/selftests/landlock/fs_test.c | 285 +++++++++++++++++++++
 2 files changed, 291 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/landlock/config b/tools/testing/selftests/landlock/config
index 0f0a65287bac..5501108d00b7 100644
--- a/tools/testing/selftests/landlock/config
+++ b/tools/testing/selftests/landlock/config
@@ -1,7 +1,11 @@
+CONFIG_CGROUPS=y
+CONFIG_CGROUP_SCHED=y
 CONFIG_OVERLAY_FS=y
+CONFIG_PROC_FS=y
+CONFIG_SECURITY=y
 CONFIG_SECURITY_LANDLOCK=y
 CONFIG_SECURITY_PATH=y
-CONFIG_SECURITY=y
 CONFIG_SHMEM=y
-CONFIG_TMPFS_XATTR=y
+CONFIG_SYSFS=y
 CONFIG_TMPFS=y
+CONFIG_TMPFS_XATTR=y
diff --git a/tools/testing/selftests/landlock/fs_test.c b/tools/testing/selftests/landlock/fs_test.c
index de29c8c9e194..f6a80ad738e1 100644
--- a/tools/testing/selftests/landlock/fs_test.c
+++ b/tools/testing/selftests/landlock/fs_test.c
@@ -10,6 +10,7 @@
 #define _GNU_SOURCE
 #include <fcntl.h>
 #include <linux/landlock.h>
+#include <linux/magic.h>
 #include <sched.h>
 #include <stdio.h>
 #include <string.h>
@@ -19,6 +20,7 @@
 #include <sys/sendfile.h>
 #include <sys/stat.h>
 #include <sys/sysmacros.h>
+#include <sys/vfs.h>
 #include <unistd.h>
 
 #include "common.h"
@@ -121,6 +123,10 @@ static bool supports_filesystem(const char *const filesystem)
 	if (!inf)
 		return true;
 
+	/* filesystem can be null for bind mounts. */
+	if (!filesystem)
+		return true;
+
 	len = snprintf(str, sizeof(str), "nodev\t%s\n", filesystem);
 	if (len >= sizeof(str))
 		/* Ignores too-long filesystem names. */
@@ -131,6 +137,19 @@ static bool supports_filesystem(const char *const filesystem)
 	return res;
 }
 
+static bool cwd_matches_fs(unsigned int fs_magic)
+{
+	struct statfs statfs_buf;
+
+	if (!fs_magic)
+		return true;
+
+	if (statfs(".", &statfs_buf))
+		return true;
+
+	return statfs_buf.f_type == fs_magic;
+}
+
 static void mkdir_parents(struct __test_metadata *const _metadata,
 			  const char *const path)
 {
@@ -307,11 +326,13 @@ static void remove_layout1(struct __test_metadata *const _metadata)
 	EXPECT_EQ(0, remove_path(file1_s1d3));
 	EXPECT_EQ(0, remove_path(file1_s1d2));
 	EXPECT_EQ(0, remove_path(file1_s1d1));
+	EXPECT_EQ(0, remove_path(dir_s1d3));
 
 	EXPECT_EQ(0, remove_path(file2_s2d3));
 	EXPECT_EQ(0, remove_path(file1_s2d3));
 	EXPECT_EQ(0, remove_path(file1_s2d2));
 	EXPECT_EQ(0, remove_path(file1_s2d1));
+	EXPECT_EQ(0, remove_path(dir_s2d2));
 
 	EXPECT_EQ(0, remove_path(file1_s3d1));
 	EXPECT_EQ(0, remove_path(dir_s3d3));
@@ -4471,4 +4492,268 @@ TEST_F_FORK(layout2_overlay, same_content_different_file)
 	}
 }
 
+FIXTURE(layout3_fs)
+{
+	bool has_created_dir;
+	bool has_created_file;
+	char *dir_path;
+	bool skip_test;
+};
+
+FIXTURE_VARIANT(layout3_fs)
+{
+	const struct mnt_opt mnt;
+	const char *const file_path;
+	unsigned int cwd_fs_magic;
+};
+
+/* clang-format off */
+FIXTURE_VARIANT_ADD(layout3_fs, tmpfs) {
+	/* clang-format on */
+	.mnt = mnt_tmp,
+	.file_path = file1_s1d1,
+};
+
+FIXTURE_VARIANT_ADD(layout3_fs, ramfs) {
+	.mnt = {
+		.type = "ramfs",
+		.data = "mode=700",
+	},
+	.file_path = TMP_DIR "/dir/file",
+};
+
+FIXTURE_VARIANT_ADD(layout3_fs, cgroup) {
+	.mnt = {
+		.type = "cgroup",
+	},
+	.file_path = TMP_DIR "/test/tasks",
+};
+
+FIXTURE_VARIANT_ADD(layout3_fs, cgroup2) {
+	.mnt = {
+		.type = "cgroup2",
+	},
+	.file_path = TMP_DIR "/test/cgroup.procs",
+};
+
+FIXTURE_VARIANT_ADD(layout3_fs, proc) {
+	.mnt = {
+		.type = "proc",
+	},
+	.file_path = TMP_DIR "/self/status",
+};
+
+FIXTURE_VARIANT_ADD(layout3_fs, sysfs) {
+	.mnt = {
+		.type = "sysfs",
+	},
+	.file_path = TMP_DIR "/kernel/notes",
+};
+
+FIXTURE_VARIANT_ADD(layout3_fs, hostfs) {
+	.mnt = {
+		.source = TMP_DIR,
+		.flags = MS_BIND,
+	},
+	.file_path = TMP_DIR "/dir/file",
+	.cwd_fs_magic = HOSTFS_SUPER_MAGIC,
+};
+
+FIXTURE_SETUP(layout3_fs)
+{
+	struct stat statbuf;
+	const char *slash;
+	size_t dir_len;
+
+	if (!supports_filesystem(variant->mnt.type) ||
+	    !cwd_matches_fs(variant->cwd_fs_magic)) {
+		self->skip_test = true;
+		SKIP(return, "this filesystem is not supported (setup)");
+	}
+
+	slash = strrchr(variant->file_path, '/');
+	ASSERT_NE(slash, NULL);
+	dir_len = (size_t)slash - (size_t)variant->file_path;
+	ASSERT_LT(0, dir_len);
+	self->dir_path = malloc(dir_len + 1);
+	self->dir_path[dir_len] = '\0';
+	strncpy(self->dir_path, variant->file_path, dir_len);
+
+	prepare_layout_opt(_metadata, &variant->mnt);
+
+	/* Creates directory when required. */
+	if (stat(self->dir_path, &statbuf)) {
+		set_cap(_metadata, CAP_DAC_OVERRIDE);
+		EXPECT_EQ(0, mkdir(self->dir_path, 0700))
+		{
+			TH_LOG("Failed to create directory \"%s\": %d %s",
+			       self->dir_path, errno, strerror(errno));
+			free(self->dir_path);
+			self->dir_path = NULL;
+		}
+		self->has_created_dir = true;
+		clear_cap(_metadata, CAP_DAC_OVERRIDE);
+	}
+
+	/* Creates file when required. */
+	if (stat(variant->file_path, &statbuf)) {
+		int fd;
+
+		set_cap(_metadata, CAP_DAC_OVERRIDE);
+		fd = creat(variant->file_path, 0600);
+		EXPECT_LE(0, fd)
+		{
+			TH_LOG("Failed to create file \"%s\": %d %s",
+			       variant->file_path, errno, strerror(errno));
+		}
+		EXPECT_EQ(0, close(fd));
+		self->has_created_file = true;
+		clear_cap(_metadata, CAP_DAC_OVERRIDE);
+	}
+}
+
+FIXTURE_TEARDOWN(layout3_fs)
+{
+	if (self->skip_test)
+		SKIP(return, "this filesystem is not supported (teardown)");
+
+	if (self->has_created_file) {
+		set_cap(_metadata, CAP_DAC_OVERRIDE);
+		/*
+		 * Don't check for error because the file might already
+		 * have been removed (cf. release_inode test).
+		 */
+		unlink(variant->file_path);
+		clear_cap(_metadata, CAP_DAC_OVERRIDE);
+	}
+
+	if (self->has_created_dir) {
+		set_cap(_metadata, CAP_DAC_OVERRIDE);
+		/*
+		 * Don't check for error because the directory might already
+		 * have been removed (cf. release_inode test).
+		 */
+		rmdir(self->dir_path);
+		clear_cap(_metadata, CAP_DAC_OVERRIDE);
+	}
+	free(self->dir_path);
+	self->dir_path = NULL;
+
+	cleanup_layout(_metadata);
+}
+
+static void layer3_fs_tag_inode(struct __test_metadata *const _metadata,
+				FIXTURE_DATA(layout3_fs) * self,
+				const FIXTURE_VARIANT(layout3_fs) * variant,
+				const char *const rule_path)
+{
+	const struct rule layer1_allow_read_file[] = {
+		{
+			.path = rule_path,
+			.access = LANDLOCK_ACCESS_FS_READ_FILE,
+		},
+		{},
+	};
+	const struct landlock_ruleset_attr layer2_deny_everything_attr = {
+		.handled_access_fs = LANDLOCK_ACCESS_FS_READ_FILE,
+	};
+	const char *const dev_null_path = "/dev/null";
+	int ruleset_fd;
+
+	if (self->skip_test)
+		SKIP(return, "this filesystem is not supported (test)");
+
+	/* Checks without Landlock. */
+	EXPECT_EQ(0, test_open(dev_null_path, O_RDONLY | O_CLOEXEC));
+	EXPECT_EQ(0, test_open(variant->file_path, O_RDONLY | O_CLOEXEC));
+
+	ruleset_fd = create_ruleset(_metadata, LANDLOCK_ACCESS_FS_READ_FILE,
+				    layer1_allow_read_file);
+	EXPECT_LE(0, ruleset_fd);
+	enforce_ruleset(_metadata, ruleset_fd);
+	EXPECT_EQ(0, close(ruleset_fd));
+
+	EXPECT_EQ(EACCES, test_open(dev_null_path, O_RDONLY | O_CLOEXEC));
+	EXPECT_EQ(0, test_open(variant->file_path, O_RDONLY | O_CLOEXEC));
+
+	/* Forbids directory reading. */
+	ruleset_fd =
+		landlock_create_ruleset(&layer2_deny_everything_attr,
+					sizeof(layer2_deny_everything_attr), 0);
+	EXPECT_LE(0, ruleset_fd);
+	enforce_ruleset(_metadata, ruleset_fd);
+	EXPECT_EQ(0, close(ruleset_fd));
+
+	/* Checks with Landlock and forbidden access. */
+	EXPECT_EQ(EACCES, test_open(dev_null_path, O_RDONLY | O_CLOEXEC));
+	EXPECT_EQ(EACCES, test_open(variant->file_path, O_RDONLY | O_CLOEXEC));
+}
+
+/* Matrix of tests to check file hierarchy evaluation. */
+
+TEST_F_FORK(layout3_fs, tag_inode_dir_parent)
+{
+	/* The current directory must not be the root for this test. */
+	layer3_fs_tag_inode(_metadata, self, variant, ".");
+}
+
+TEST_F_FORK(layout3_fs, tag_inode_dir_mnt)
+{
+	layer3_fs_tag_inode(_metadata, self, variant, TMP_DIR);
+}
+
+TEST_F_FORK(layout3_fs, tag_inode_dir_child)
+{
+	layer3_fs_tag_inode(_metadata, self, variant, self->dir_path);
+}
+
+TEST_F_FORK(layout3_fs, tag_inode_file)
+{
+	layer3_fs_tag_inode(_metadata, self, variant, variant->file_path);
+}
+
+/* Light version of layout1.release_inodes */
+TEST_F_FORK(layout3_fs, release_inodes)
+{
+	const struct rule layer1[] = {
+		{
+			.path = TMP_DIR,
+			.access = LANDLOCK_ACCESS_FS_READ_DIR,
+		},
+		{},
+	};
+	int ruleset_fd;
+
+	if (self->skip_test)
+		SKIP(return, "this filesystem is not supported (test)");
+
+	/* Clean up for the teardown to not fail. */
+	if (self->has_created_file)
+		EXPECT_EQ(0, remove_path(variant->file_path));
+
+	if (self->has_created_dir)
+		/* Don't check for error because of cgroup specificities. */
+		remove_path(self->dir_path);
+
+	ruleset_fd =
+		create_ruleset(_metadata, LANDLOCK_ACCESS_FS_READ_DIR, layer1);
+	ASSERT_LE(0, ruleset_fd);
+
+	/* Unmount the filesystem while it is being used by a ruleset. */
+	set_cap(_metadata, CAP_SYS_ADMIN);
+	ASSERT_EQ(0, umount(TMP_DIR));
+	clear_cap(_metadata, CAP_SYS_ADMIN);
+
+	/* Replaces with a new mount point to simplify FIXTURE_TEARDOWN. */
+	set_cap(_metadata, CAP_SYS_ADMIN);
+	ASSERT_EQ(0, mount("tmp", TMP_DIR, "tmpfs", 0, "size=4m,mode=700"));
+	clear_cap(_metadata, CAP_SYS_ADMIN);
+
+	enforce_ruleset(_metadata, ruleset_fd);
+	ASSERT_EQ(0, close(ruleset_fd));
+
+	/* Checks that access to the new mount point is denied. */
+	ASSERT_EQ(EACCES, test_open(TMP_DIR, O_RDONLY));
+}
+
 TEST_HARNESS_MAIN
-- 
2.39.2