[PATCH v5 21/24] selftests/landlock: Add tests for audit and LANDLOCK_RESTRICT_SELF_QUIET

Mickaël Salaün
2025-01-31T16:32:25Z

Add audit_test.c to check with and without LANDLOCK_RESTRICT_SELF_*
flags against the two Landlock audit record types:
AUDIT_LANDLOCK_ACCESS and AUDIT_LANDLOCK_DOMAIN.

Tests are run with audit filters to ensure the audit records come from
the test program. Moreover, because there can only be one audit
process, tests would failed if run in parallel. Because of audit
limitations, tests can only be run in the initial namespace.

The audit test helpers were inspired by libaudit and
tools/testing/selftests/net/netfilter/audit_logread.c

Cc: Günther Noack <gnoack@google.com>
Cc: Paul Moore <paul@paul-moore.com>
Cc: Phil Sutter <phil@nwl.cc>
Signed-off-by: Mickaël Salaün <mic@digikod.net>
Link: https://lore.kernel.org/r/20250131163059.1139617-22-mic@digikod.net
---

Changes since v4:
- Update with the new landlock_restrict_self()'s flags, the new audit
rule types, and message fields.
- Simplify audit_filter_exe() and audit_init_filter_exe().
- Test with kill() instead of umount().
- Test domain deallocation events.

Changes since v3:
- Improve audit_request() to check Netlink errors and handle multiple
replies.
- Make audit_filter_exe() more generic to handle several audit rule
lists.
- Merge audit_init_state() into audit_init() and create
audit_init_with_exe_filter() to handle AUDIT_EXE_LANDLOCK_DENY with an
arbitrary path.
- Add matches_log_dom_info().

Changes since v2:
- New patch.
---
tools/testing/selftests/landlock/audit.h | 358 ++++++++++++++++++
tools/testing/selftests/landlock/audit_test.c | 204 ++++++++++
tools/testing/selftests/landlock/common.h | 2 +
tools/testing/selftests/landlock/config | 1 +
4 files changed, 565 insertions(+)
create mode 100644 tools/testing/selftests/landlock/audit.h
create mode 100644 tools/testing/selftests/landlock/audit_test.c

diff --git a/tools/testing/selftests/landlock/audit.h b/tools/testing/selftests/landlock/audit.h
new file mode 100644
index 000000000000..65b0adb950a0
--- /dev/null
+++ b/tools/testing/selftests/landlock/audit.h
@@ -0,0 +1,358 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Landlock audit helpers
+ *
+ * Copyright © 2024-2025 Microsoft Corporation
+ */
+
+#define _GNU_SOURCE
+#include <errno.h>
+#include <linux/audit.h>
+#include <linux/limits.h>
+#include <linux/netlink.h>
+#include <regex.h>
+#include <stdbool.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/socket.h>
+
+#define REGEX_LANDLOCK_PREFIX "^audit([0-9.:]\\+): domain=[0-9a-f]\\+"
+
+struct audit_filter {
+ __u32 record_type;
+ size_t exe_len;
+ char exe[PATH_MAX];
+};
+
+struct audit_message {
+ struct nlmsghdr header;
+ union {
+ struct audit_status status;
+ struct audit_features features;
+ struct audit_rule_data rule;
+ struct nlmsgerr err;
+ char data[PATH_MAX + 200];
+ };
+};
+
+static int audit_send(const int fd, const struct audit_message *const msg)
+{
+ struct sockaddr_nl addr = {
+ .nl_family = AF_NETLINK,
+ };
+ int ret;
+
+ do {
+ ret = sendto(fd, msg, msg->header.nlmsg_len, 0,
+ (struct sockaddr *)&addr, sizeof(addr));
+ } while (ret < 0 && errno == EINTR);
+
+ if (ret < 0)
+ return -errno;
+
+ if (ret != msg->header.nlmsg_len)
+ return -E2BIG;
+
+ return 0;
+}
+
+static int audit_recv(const int fd, struct audit_message *msg)
+{
+ struct sockaddr_nl addr;
+ socklen_t addrlen = sizeof(addr);
+ struct audit_message msg_tmp;
+ int err;
+
+ if (!msg)
+ msg = &msg_tmp;
+
+ do {
+ err = recvfrom(fd, msg, sizeof(*msg), 0,
+ (struct sockaddr *)&addr, &addrlen);
+ } while (err < 0 && errno == EINTR);
+
+ if (err < 0)
+ return -errno;
+
+ if (addrlen != sizeof(addr) || addr.nl_pid != 0)
+ return -EINVAL;
+
+ /* Checks Netlink error or end of messages. */
+ if (msg->header.nlmsg_type == NLMSG_ERROR)
+ return msg->err.error;
+
+ return 0;
+}
+
+static int audit_request(const int fd,
+ const struct audit_message *const request,
+ struct audit_message *reply)
+{
+ struct audit_message msg_tmp;
+ bool first_reply = true;
+ int err;
+
+ err = audit_send(fd, request);
+ if (err)
+ return err;
+
+ if (!reply)
+ reply = &msg_tmp;
+
+ do {
+ if (first_reply)
+ first_reply = false;
+ else
+ reply = &msg_tmp;
+
+ err = audit_recv(fd, reply);
+ if (err)
+ return err;
+ } while (reply->header.nlmsg_type != NLMSG_ERROR &&
+ reply->err.msg.nlmsg_type != request->header.nlmsg_type);
+
+ return reply->err.error;
+}
+
+static int audit_filter_exe(const int audit_fd,
+ const struct audit_filter *const filter,
+ const __u16 type)
+{
+ struct audit_message msg = {
+ .header = {
+ .nlmsg_len = NLMSG_SPACE(sizeof(msg.rule)) +
+ NLMSG_ALIGN(filter->exe_len),
+ .nlmsg_type = type,
+ .nlmsg_flags = NLM_F_REQUEST | NLM_F_ACK,
+ },
+ .rule = {
+ .flags = AUDIT_FILTER_EXCLUDE,
+ .action = AUDIT_NEVER,
+ .field_count = 1,
+ .fields[0] = filter->record_type,
+ .fieldflags[0] = AUDIT_NOT_EQUAL,
+ .values[0] = filter->exe_len,
+ .buflen = filter->exe_len,
+ }
+ };
+
+ if (filter->record_type != AUDIT_EXE)
+ return -EINVAL;
+
+ memcpy(msg.rule.buf, filter->exe, filter->exe_len);
+ return audit_request(audit_fd, &msg, NULL);
+}
+
+static int audit_filter_drop(const int audit_fd, const __u16 type)
+{
+ struct audit_message msg = {
+ .header = {
+ .nlmsg_len = NLMSG_SPACE(sizeof(msg.rule)),
+ .nlmsg_type = type,
+ .nlmsg_flags = NLM_F_REQUEST | NLM_F_ACK,
+ },
+ .rule = {
+ .flags = AUDIT_FILTER_EXCLUDE,
+ .action = AUDIT_NEVER,
+ .field_count = 1,
+ .fields[0] = AUDIT_MSGTYPE,
+ .fieldflags[0] = AUDIT_NOT_EQUAL,
+ .values[0] = AUDIT_LANDLOCK_DOMAIN,
+ }
+ };
+
+ return audit_request(audit_fd, &msg, NULL);
+}
+
+static int audit_set_status(int fd, __u32 key, __u32 val)
+{
+ const struct audit_message msg = {
+ .header = {
+ .nlmsg_len = NLMSG_SPACE(sizeof(msg.status)),
+ .nlmsg_type = AUDIT_SET,
+ .nlmsg_flags = NLM_F_REQUEST | NLM_F_ACK,
+ },
+ .status = {
+ .mask = key,
+ .enabled = key == AUDIT_STATUS_ENABLED ? val : 0,
+ .pid = key == AUDIT_STATUS_PID ? val : 0,
+ }
+ };
+
+ return audit_request(fd, &msg, NULL);
+}
+
+static int audit_match_record(int audit_fd, const __u16 type,
+ const char *const pattern)
+{
+ struct audit_message msg;
+ int ret, err = 0;
+ bool matches_record = !type;
+ regex_t regex;
+
+ ret = regcomp(&regex, pattern, 0);
+ if (ret)
+ return -EINVAL;
+
+ do {
+ memset(&msg, 0, sizeof(msg));
+ err = audit_recv(audit_fd, &msg);
+ if (err)
+ goto out;
+
+ if (msg.header.nlmsg_type == type)
+ matches_record = true;
+ } while (!matches_record);
+
+ ret = regexec(&regex, msg.data, 0, NULL, 0);
+ if (ret) {
+ printf("DATA: %s\n", msg.data);
+ printf("ERROR: no match for pattern: %s\n", pattern);
+ err = -ENOENT;
+ }
+
+out:
+ regfree(&regex);
+ return err;
+}
+
+struct audit_records {
+ size_t access;
+ size_t domain;
+};
+
+static void audit_count_records(int audit_fd, struct audit_records *records)
+{
+ struct audit_message msg;
+
+ records->access = 0;
+ records->domain = 0;
+
+ do {
+ memset(&msg, 0, sizeof(msg));
+ if (audit_recv(audit_fd, &msg))
+ return;
+
+ switch (msg.header.nlmsg_type) {
+ case AUDIT_LANDLOCK_ACCESS:
+ records->access++;
+ break;
+ case AUDIT_LANDLOCK_DOMAIN:
+ records->domain++;
+ break;
+ }
+ } while (true);
+}
+
+static int audit_init(void)
+{
+ const struct timeval tv = {
+ .tv_usec = 1,
+ };
+ int fd, err;
+
+ fd = socket(PF_NETLINK, SOCK_RAW, NETLINK_AUDIT);
+ if (fd < 0)
+ return -errno;
+
+ err = audit_set_status(fd, AUDIT_STATUS_ENABLED, 1);
+ if (err)
+ return err;
+
+ err = audit_set_status(fd, AUDIT_STATUS_PID, getpid());
+ if (err)
+ return err;
+
+ /* Sets a timeout for negative tests. */
+ err = setsockopt(fd, SOL_SOCKET, SO_RCVTIMEO, &tv, sizeof(tv));
+ if (err)
+ return -errno;
+
+ return fd;
+}
+
+static int audit_init_filter_exe(struct audit_filter *filter, const char *path)
+{
+ char *absolute_path = NULL;
+
+ // TODO: Make sure there is no rule already filtering.
+
+ filter->record_type = AUDIT_EXE;
+
+ if (!path) {
+ filter->exe_len = readlink("/proc/self/exe", filter->exe,
+ sizeof(filter->exe) - 1);
+ if (filter->exe_len < 0)
+ return -errno;
+
+ return 0;
+ }
+
+ absolute_path = realpath(path, NULL);
+ if (!absolute_path)
+ return -errno;
+
+ /* No need for the terminating NULL byte. */
+ filter->exe_len = strlen(absolute_path);
+ if (filter->exe_len > sizeof(filter->exe))
+ return -E2BIG;
+
+ memcpy(filter->exe, absolute_path, filter->exe_len);
+ free(absolute_path);
+ return 0;
+}
+
+static int audit_cleanup(int audit_fd, struct audit_filter *filter)
+{
+ struct audit_filter new_filter;
+
+ if (audit_fd < 0 || !filter) {
+ int err;
+
+ /*
+ * Simulates audit_init_with_exe_filter() when called from
+ * FIXTURE_TEARDOWN_PARENT().
+ */
+ audit_fd = audit_init();
+ if (audit_fd < 0)
+ return audit_fd;
+
+ filter = &new_filter;
+ err = audit_init_filter_exe(filter, NULL);
+ if (err)
+ return err;
+ }
+
+ /* Filters might not be in place. */
+ audit_filter_exe(audit_fd, filter, AUDIT_DEL_RULE);
+ audit_filter_drop(audit_fd, AUDIT_DEL_RULE);
+
+ /*
+ * Because audit_cleanup() might not be called by the test auditd
+ * process, it might not be possible to explicitly set it. Anyway,
+ * AUDIT_STATUS_ENABLED will implicitly be set to 0 when the auditd
+ * process will exit.
+ */
+ return close(audit_fd);
+}
+
+static int audit_init_with_exe_filter(struct audit_filter *filter)
+{
+ int fd, err;
+
+ fd = audit_init();
+ if (fd < 0)
+ return fd;
+
+ err = audit_init_filter_exe(filter, NULL);
+ if (err)
+ return err;
+
+ err = audit_filter_exe(fd, filter, AUDIT_ADD_RULE);
+ if (err)
+ return err;
+
+ return fd;
+}
diff --git a/tools/testing/selftests/landlock/audit_test.c b/tools/testing/selftests/landlock/audit_test.c
new file mode 100644
index 000000000000..44131fb6e3d3
--- /dev/null
+++ b/tools/testing/selftests/landlock/audit_test.c
@@ -0,0 +1,204 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Landlock tests - Audit
+ *
+ * Copyright © 2024-2025 Microsoft Corporation
+ */
+
+#define _GNU_SOURCE
+#include <errno.h>
+#include <linux/landlock.h>
+#include <sys/mount.h>
+#include <sys/prctl.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+#include <unistd.h>
+
+#include "audit.h"
+#include "common.h"
+
+static int matches_log_domain_allocated(struct __test_metadata *const _metadata,
+ int audit_fd)
+{
+ return audit_match_record(
+ audit_fd, AUDIT_LANDLOCK_DOMAIN,
+ REGEX_LANDLOCK_PREFIX
+ " status=allocated mode=enforcing pid=[0-9]\\+ uid=[0-9]\\+"
+ " exe=\"[^\"]\\+\" comm=\"audit_test\"$");
+}
+
+static int
+matches_log_domain_deallocated(struct __test_metadata *const _metadata,
+ int audit_fd, unsigned int num_denials)
+{
+ static const char log_template[] = REGEX_LANDLOCK_PREFIX
+ " status=deallocated denials=%u$";
+ char log_match[sizeof(log_template) + 10];
+ int log_match_len;
+
+ log_match_len = snprintf(log_match, sizeof(log_match), log_template,
+ num_denials);
+ if (log_match_len > sizeof(log_match))
+ return -E2BIG;
+
+ return audit_match_record(audit_fd, AUDIT_LANDLOCK_DOMAIN, log_match);
+}
+
+static int matches_log_signal(struct __test_metadata *const _metadata,
+ int audit_fd, const pid_t opid)
+{
+ static const char log_template[] = REGEX_LANDLOCK_PREFIX
+ " blockers=scope\\.signal opid=%d ocomm=\"audit_test\"$";
+ char log_match[sizeof(log_template) + 10];
+ int log_match_len;
+
+ log_match_len =
+ snprintf(log_match, sizeof(log_match), log_template, opid);
+ if (log_match_len > sizeof(log_match))
+ return -E2BIG;
+
+ return audit_match_record(audit_fd, AUDIT_LANDLOCK_ACCESS, log_match);
+}
+
+FIXTURE(audit_fork)
+{
+ struct audit_filter audit_filter;
+ int audit_fd;
+};
+
+FIXTURE_VARIANT(audit_fork)
+{
+ const int restrict_flags;
+};
+
+/* clang-format off */
+FIXTURE_VARIANT_ADD(audit_fork, default) {
+ /* clang-format on */
+ .restrict_flags = 0,
+};
+
+/* clang-format off */
+FIXTURE_VARIANT_ADD(audit_fork, quiet) {
+ /* clang-format on */
+ .restrict_flags = LANDLOCK_RESTRICT_SELF_QUIET,
+};
+
+/* clang-format off */
+FIXTURE_VARIANT_ADD(audit_fork, quiet_subdomains) {
+ /* clang-format on */
+ .restrict_flags = LANDLOCK_RESTRICT_SELF_QUIET_SUBDOMAINS,
+};
+
+/* clang-format off */
+FIXTURE_VARIANT_ADD(audit_fork, log_cross_exec) {
+ /* clang-format on */
+ .restrict_flags = LANDLOCK_RESTRICT_SELF_LOG_CROSS_EXEC,
+};
+
+FIXTURE_SETUP(audit_fork)
+{
+ disable_caps(_metadata);
+ set_cap(_metadata, CAP_AUDIT_CONTROL);
+ self->audit_fd = audit_init_with_exe_filter(&self->audit_filter);
+ EXPECT_LE(0, self->audit_fd)
+ {
+ const char *error_msg;
+
+ /* kill "$(auditctl -s | sed -ne 's/^pid \([0-9]\+\)$/\1/p')" */
+ if (self->audit_fd == -EEXIST)
+ error_msg = "socket already in use (e.g. auditd)";
+ else
+ error_msg = strerror(-self->audit_fd);
+ TH_LOG("Failed to initialize audit: %s", error_msg);
+ }
+ clear_cap(_metadata, CAP_AUDIT_CONTROL);
+}
+
+FIXTURE_TEARDOWN(audit_fork)
+{
+ set_cap(_metadata, CAP_AUDIT_CONTROL);
+ EXPECT_EQ(0, audit_cleanup(self->audit_fd, &self->audit_filter));
+ clear_cap(_metadata, CAP_AUDIT_CONTROL);
+}
+
+TEST_F(audit_fork, flags)
+{
+ int status;
+ pid_t child;
+ struct audit_records records;
+
+ child = fork();
+ ASSERT_LE(0, child);
+ if (child == 0) {
+ const struct landlock_ruleset_attr ruleset_attr = {
+ .scoped = LANDLOCK_SCOPE_SIGNAL,
+ };
+ int ruleset_fd;
+
+ /* Add filesystem restrictions. */
+ ruleset_fd = landlock_create_ruleset(&ruleset_attr,
+ sizeof(ruleset_attr), 0);
+ ASSERT_LE(0, ruleset_fd);
+ EXPECT_EQ(0, prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0));
+ ASSERT_EQ(0, landlock_restrict_self(ruleset_fd,
+ variant->restrict_flags));
+ EXPECT_EQ(0, close(ruleset_fd));
+
+ /* First signal checks to test log entries. */
+ EXPECT_EQ(-1, kill(getppid(), 0));
+ EXPECT_EQ(EPERM, errno);
+
+ if (variant->restrict_flags & LANDLOCK_RESTRICT_SELF_QUIET) {
+ EXPECT_EQ(-EAGAIN,
+ matches_log_signal(_metadata, self->audit_fd,
+ getppid()));
+ } else {
+ EXPECT_EQ(0,
+ matches_log_signal(_metadata, self->audit_fd,
+ getppid()));
+
+ /* Checks domain information records. */
+ EXPECT_EQ(0, matches_log_domain_allocated(
+ _metadata, self->audit_fd));
+ }
+
+ /* Second signal checks to test audit_count_records(). */
+ EXPECT_EQ(-1, kill(getppid(), 0));
+ EXPECT_EQ(EPERM, errno);
+
+ /* Makes sure there is no superfluous logged records. */
+ audit_count_records(self->audit_fd, &records);
+ if (variant->restrict_flags & LANDLOCK_RESTRICT_SELF_QUIET) {
+ EXPECT_EQ(0, records.access);
+ } else {
+ EXPECT_EQ(1, records.access);
+ }
+ EXPECT_EQ(0, records.domain);
+
+ /* Updates filter rules to match the drop record. */
+ set_cap(_metadata, CAP_AUDIT_CONTROL);
+ EXPECT_EQ(0, audit_filter_drop(self->audit_fd, AUDIT_ADD_RULE));
+ EXPECT_EQ(0,
+ audit_filter_exe(self->audit_fd, &self->audit_filter,
+ AUDIT_DEL_RULE));
+ clear_cap(_metadata, CAP_AUDIT_CONTROL);
+
+ _exit(_metadata->exit_code);
+ return;
+ }
+
+ ASSERT_EQ(child, waitpid(child, &status, 0));
+ if (WIFSIGNALED(status) || !WIFEXITED(status) ||
+ WEXITSTATUS(status) != EXIT_SUCCESS)
+ _metadata->exit_code = KSFT_FAIL;
+
+ if (variant->restrict_flags & LANDLOCK_RESTRICT_SELF_QUIET) {
+ EXPECT_EQ(-EAGAIN, matches_log_domain_deallocated(
+ _metadata, self->audit_fd, 0));
+ } else {
+ EXPECT_EQ(0, matches_log_domain_deallocated(_metadata,
+ self->audit_fd, 2));
+ }
+}
+
+TEST_HARNESS_MAIN
diff --git a/tools/testing/selftests/landlock/common.h b/tools/testing/selftests/landlock/common.h
index a604ea5d8297..ea7c4f9638b0 100644
--- a/tools/testing/selftests/landlock/common.h
+++ b/tools/testing/selftests/landlock/common.h
@@ -11,6 +11,7 @@
#include <errno.h>
#include <linux/securebits.h>
#include <sys/capability.h>
+#include <sys/prctl.h>
#include <sys/socket.h>
#include <sys/un.h>
#include <sys/wait.h>
@@ -37,6 +38,7 @@ static void _init_caps(struct __test_metadata *const _metadata, bool drop_all)
/* Only these three capabilities are useful for the tests. */
const cap_value_t caps[] = {
/* clang-format off */
+ CAP_AUDIT_CONTROL,
CAP_DAC_OVERRIDE,
CAP_MKNOD,
CAP_NET_ADMIN,
diff --git a/tools/testing/selftests/landlock/config b/tools/testing/selftests/landlock/config
index 29af19c4e9f9..3d4eb994d62b 100644
--- a/tools/testing/selftests/landlock/config
+++ b/tools/testing/selftests/landlock/config
@@ -1,3 +1,4 @@
+CONFIG_AUDIT=y
CONFIG_CGROUPS=y
CONFIG_CGROUP_SCHED=y
CONFIG_INET=y
--
2.48.1