Merge tag 'trace-v7.3-rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-tracegrafted

Pull tracing fixes from Steven Rostedt:

 - Don't destroy user event fields when removal fails

   User event fields are destroyed before the event is removed from
   visibility. But that can fail leaving the still visible event with no
   fields. Move the destroying of the fields to after the event is
   successfully removed from visibility.

 - Initialize function graph state is fork before calling
   copy_exec_state()

   For non-CLONE_VM forks, copy_exec_state() allocates a new
   task_exec_state. If that allocation fails, ftrace_graph_exit_task()
   will free the tasks ret_stack pointer. Since that pointer is still
   using the parent's ret_stack, it mistakenly frees the parent's
   pointer too.

   Call ftrace_graph_init() on the task first which will NULL out the
   new tasks's ret_stack and if the copy fails, it will not free
   anything.

 - Remove FGRAPH_MAX_INDEX

   The macro FGRAPH_MAX_INDEX was added but never used. Remove it.

 - Save ent_size in function graph printing of nested functions

   The function graph tracer needs to look at the next event to see if
   the next event is the return of the current function entry. If it is,
   it prints a single line:

	ktime_get();

   Otherwise it prints it like a nested function:

	tick_nohz_irq_exit() {
	    ktime_get();
	    kcpustat_irq_exit();
	}

   In order to look at the next event, it must save the current event so
   that it has the information to print from it. It saves the event in
   the iterator descriptor called "ent". What it doesn't save is the
   ent_size of the event which is now used to know if the function graph
   arguments are to be printed. The peek doesn't save the size so the
   size used happens to be that of the size of the last event that was
   seen.

   Save the entry event size in the iterator descriptor so that the
   correct size is used.

 - Fix several errors with freeing data in the histogram code

   The histogram code had a lot of leaked or or incorrect accounting
   when failures happen. Correct them.

 - Fix histogram regression of .percent and .graph modifiers

   Up until 6.3 histogram values could have "percent" or "graph"
   modifiers that changed how they were printed. But a change that added
   restricting histograms values from being strings, stack traces and
   other modifiers inadvertently prevented them from using the percent
   and graph modifiers, which were legal use cases for values.

   Put back the percent and graph modifiers.

 - Fix various typos in the comments

 - Set the trace_clock before initializing a histogram with clock
   argument

   The histogram API allows the user to specific which trace clock to
   use via a "clock=" string. The histogram is set up first before the
   clock is checked. If the passed in clock is not valid, it exits
   without fully fixing up the histogram leaving it on the list and a
   use-after-free can trigger.

   Update the clock argument first and if it fails then exit gracefully
   before the histogram trigger is placed on any lists.

 - Restore :mod: trailer after parsing in ftrace_set_clr_event

   The function ftrace_set_clr_event() modifies the parse string and
   needs to put it back to what was passed in. It searches for ":mod:"
   via a strsep() but fails to put back the first ':' in the string.

   Add back the ':' in the passed in string.

 - Take trace_array reference when opening a tracer options file

   The options files are dynamically created and some tracers add their
   own options. When a tracer adds their own list of options, the
   trace_array holding them has an array to hold the list of options for
   each tracer. This array increases in size via a krealloc(), and the
   new entry gets a newly allocated array to hold the options of the new
   tracer being added.

   The element in each entry of the tracer's option array holds a
   pointer back to the trace_array, a pointer to the tracer it is
   associated to, a pointer to the flags of the option.

   The issue is that these arrays are freed when the trace_array is
   freed when its instance it represents is removed from the instances
   directory. There's a race that an open of one of these options files
   can happen when the instance is being removed.

   Add a new helper function to be called by the open function of the
   options file to iterate all existing trace_arrays under a lock and
   find the one that has the given option element in one of it's tracer
   arrays. If found, then update the associated trace_array's reference
   counter to keep it from being freed. If not found, have the open call
   return -ENODEV.

 - Disable interrupts when acquiring the lock in rb_wake_up_waiters()

   The function rb_wake_up_waiters() assumes it will be called in
   interrupt context and does not disable irqs when taking
   cpu_buffer->reader_lock, which can be called in hard interrupt
   context. The issue is in PREEMPT_RT, this function is called in
   thread context leaving this lock open to a deadlock.

   Take the lock with interrupts disabled.

 - Use rcu_assign_pointer() for tmp_ops filter hash

   The tmp_ops used in update_ftrace_direct_mod() assigns its
   filter_hash field directly, but that field is annotated as __rcu and
   sparse complains. Assign it with rcu_assign_pointer()

 - Fix use-after-free in enable_trigger_private_data_free()

   The trace_event_call is accessed through the event_trigger_data's
   trace_event_file pointer to put the trace_event_call on freeing. The
   issue is that the trace_event_file data may have been freed already
   causing a use-after-free. Add a field to the event_trigger_data that
   points directly to the trace_event_call so that it can decrement its
   reference directly without needing to go through the
   trace_event_file.

 - Fix accounting of buffer data remote headers

   trace_buffer_desc_size() and trace_remote_alloc_buffer() undercount
   the number of pages is needed for the asked for size as it doesn't
   take into account the meta data on each page. Add a helper function
   to do the calculation properly and use that in these functions.

 - Catch nr_page_va overflow in ring_buffer_desc sizing

   The number of pages per remote ring buffer is capped by
   ring_buffer_desc::nr_page_va (32 bits). A buffer_size large enough to
   overflow that field would silently allocate a descriptor smaller than
   what was asked for.

 - Do not resize the subbuf order if any per_cpu buffer is disabled

   The mmapping of ring buffers disables resizing the subbuffers, but it
   is done per-cpu whereas the subbuf size change is done for all the
   per_cpu buffers under the buffer->mutex. It could change the size of
   some while the mapping is happening on others. Have the resize of the
   subbuf order check all the per_cpu buffers under the lock to see if
   any of them is disabled before starting and causing an inconsistency
   between buffers that are being mapped.

* tag 'trace-v7.3-rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace: (25 commits)
  ring-buffer: Check resize_disabled before publishing the new subbuf order
  tracing/remotes: Catch nr_page_va overflow in ring_buffer_desc sizing
  tracing/remotes: Account for ring buffer page header in size calculation
  tracing: Don't dereference trace_event_file in deferred trigger free
  ftrace: Use rcu_assign_pointer() for tmp_ops filter hash
  ring-buffer: Acquire the lock with irqsave in rb_wake_up_waiters()
  tracing: Take trace_array reference when opening a tracer options file
  tracing: Fix ring_buffer_read_page_size() kernel-doc
  tracing: Restore :mod: trailer after parsing in ftrace_set_clr_event()
  tracing: Fix memory corruption from a "STACKTRACE" histogram key
  tracing: Fix memory corruption from the histogram stacktrace modifier
  tracing: Undo the registration when enabling the histogram trigger fails
  tracing: Take the reference before publishing the named histogram trigger
  tracing: Set the trace clock before registering the histogram trigger
  tracing: Fix typo "preceeded" in comment
  tracing: Fix typo "availabe" in comment
  tracing: Let histogram values keep the percent and graph modifiers
  tracing: Keep the entry count when the histogram stats allocation fails
  tracing: Free histogram the field rejected for a bad modifier
  tracing: Free histogram the var ref when its initialization fails
  ...

3 files changed, 721 insertions, 0 deletions

diff --git a/samples/landlock/.gitignore b/samples/landlock/.gitignore
new file mode 100644
index 000000000..f43668b2d
--- /dev/null
+++ b/samples/landlock/.gitignore
@@ -0,0 +1 @@
+/sandboxer
diff --git a/samples/landlock/Makefile b/samples/landlock/Makefile
new file mode 100644
index 000000000..5d601e51c
--- /dev/null
+++ b/samples/landlock/Makefile
@@ -0,0 +1,13 @@
+# SPDX-License-Identifier: BSD-3-Clause
+
+userprogs-always-y := sandboxer
+
+userccflags += -I usr/include
+
+.PHONY: all clean
+
+all:
+	$(MAKE) -C ../.. samples/landlock/
+
+clean:
+	$(MAKE) -C ../.. M=samples/landlock/ clean
diff --git a/samples/landlock/sandboxer.c b/samples/landlock/sandboxer.c
new file mode 100644
index 000000000..030583273
--- /dev/null
+++ b/samples/landlock/sandboxer.c
@@ -0,0 +1,707 @@
+// SPDX-License-Identifier: BSD-3-Clause
+/*
+ * Simple Landlock sandbox manager able to execute a process restricted by
+ * user-defined file system and network access control policies.
+ *
+ * Copyright © 2017-2020 Mickaël Salaün <mic@digikod.net>
+ * Copyright © 2020 ANSSI
+ */
+
+#define _GNU_SOURCE
+#define __SANE_USERSPACE_TYPES__
+#include <arpa/inet.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <linux/landlock.h>
+#include <linux/socket.h>
+#include <stddef.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/prctl.h>
+#include <sys/stat.h>
+#include <sys/syscall.h>
+#include <unistd.h>
+#include <stdbool.h>
+
+#if defined(__GLIBC__)
+#include <linux/prctl.h>
+#endif
+
+#ifndef landlock_create_ruleset
+static inline int
+landlock_create_ruleset(const struct landlock_ruleset_attr *const attr,
+			const size_t size, const __u32 flags)
+{
+	return syscall(__NR_landlock_create_ruleset, attr, size, flags);
+}
+#endif
+
+#ifndef landlock_add_rule
+static inline int landlock_add_rule(const int ruleset_fd,
+				    const enum landlock_rule_type rule_type,
+				    const void *const rule_attr,
+				    const __u32 flags)
+{
+	return syscall(__NR_landlock_add_rule, ruleset_fd, rule_type, rule_attr,
+		       flags);
+}
+#endif
+
+#ifndef landlock_restrict_self
+static inline int landlock_restrict_self(const int ruleset_fd,
+					 const __u32 flags)
+{
+	return syscall(__NR_landlock_restrict_self, ruleset_fd, flags);
+}
+#endif
+
+#define ENV_FS_RO_NAME "LL_FS_RO"
+#define ENV_FS_RW_NAME "LL_FS_RW"
+#define ENV_FS_QUIET_NAME "LL_FS_QUIET"
+#define ENV_TCP_BIND_NAME "LL_TCP_BIND"
+#define ENV_TCP_CONNECT_NAME "LL_TCP_CONNECT"
+#define ENV_NET_QUIET_NAME "LL_NET_QUIET"
+#define ENV_SCOPED_NAME "LL_SCOPED"
+#define ENV_QUIET_ACCESS_NAME "LL_QUIET_ACCESS"
+#define ENV_FORCE_LOG_NAME "LL_FORCE_LOG"
+#define ENV_UDP_BIND_NAME "LL_UDP_BIND"
+#define ENV_UDP_CONNECT_SEND_NAME "LL_UDP_CONNECT_SEND"
+#define ENV_DELIMITER ":"
+
+static int str2num(const char *numstr, __u64 *num_dst)
+{
+	char *endptr = NULL;
+	int err = 0;
+	__u64 num;
+
+	errno = 0;
+	num = strtoull(numstr, &endptr, 10);
+	if (errno != 0)
+		err = errno;
+	/* Was the string empty, or not entirely parsed successfully? */
+	else if ((*numstr == '\0') || (*endptr != '\0'))
+		err = EINVAL;
+	else
+		*num_dst = num;
+
+	return err;
+}
+
+static int parse_path(char *env_path, const char ***const path_list)
+{
+	int i, num_paths = 0;
+
+	if (env_path) {
+		num_paths++;
+		for (i = 0; env_path[i]; i++) {
+			if (env_path[i] == ENV_DELIMITER[0])
+				num_paths++;
+		}
+	}
+	*path_list = malloc(num_paths * sizeof(**path_list));
+	if (!*path_list)
+		return -1;
+
+	for (i = 0; i < num_paths; i++)
+		(*path_list)[i] = strsep(&env_path, ENV_DELIMITER);
+
+	return num_paths;
+}
+
+/* clang-format off */
+
+#define ACCESS_FILE ( \
+	LANDLOCK_ACCESS_FS_EXECUTE | \
+	LANDLOCK_ACCESS_FS_WRITE_FILE | \
+	LANDLOCK_ACCESS_FS_READ_FILE | \
+	LANDLOCK_ACCESS_FS_TRUNCATE | \
+	LANDLOCK_ACCESS_FS_IOCTL_DEV | \
+	LANDLOCK_ACCESS_FS_RESOLVE_UNIX)
+
+/* clang-format on */
+
+static int populate_ruleset_fs(const char *const env_var, const int ruleset_fd,
+			       const __u64 allowed_access, __u32 flags)
+{
+	int num_paths, i, ret = 1;
+	char *env_path_name;
+	const char **path_list = NULL;
+	struct landlock_path_beneath_attr path_beneath = {
+		.parent_fd = -1,
+	};
+
+	env_path_name = getenv(env_var);
+	if (!env_path_name) {
+		/* Prevents users to forget a setting. */
+		fprintf(stderr, "Missing environment variable %s\n", env_var);
+		return 1;
+	}
+	env_path_name = strdup(env_path_name);
+	unsetenv(env_var);
+	num_paths = parse_path(env_path_name, &path_list);
+	if (num_paths < 0) {
+		fprintf(stderr, "Failed to allocate memory\n");
+		goto out_free_name;
+	}
+	if (num_paths == 1 && path_list[0][0] == '\0') {
+		/*
+		 * Allows to not use all possible restrictions (e.g. use
+		 * LL_FS_RO without LL_FS_RW).
+		 */
+		ret = 0;
+		goto out_free_name;
+	}
+
+	for (i = 0; i < num_paths; i++) {
+		struct stat statbuf;
+
+		path_beneath.parent_fd = open(path_list[i], O_PATH | O_CLOEXEC);
+		if (path_beneath.parent_fd < 0) {
+			fprintf(stderr, "Failed to open \"%s\": %s\n",
+				path_list[i], strerror(errno));
+			continue;
+		}
+		if (fstat(path_beneath.parent_fd, &statbuf)) {
+			fprintf(stderr, "Failed to stat \"%s\": %s\n",
+				path_list[i], strerror(errno));
+			close(path_beneath.parent_fd);
+			goto out_free_name;
+		}
+		path_beneath.allowed_access = allowed_access;
+		if (!S_ISDIR(statbuf.st_mode))
+			path_beneath.allowed_access &= ACCESS_FILE;
+		if (landlock_add_rule(ruleset_fd, LANDLOCK_RULE_PATH_BENEATH,
+				      &path_beneath, flags)) {
+			fprintf(stderr,
+				"Failed to update the ruleset with \"%s\": %s\n",
+				path_list[i], strerror(errno));
+			close(path_beneath.parent_fd);
+			goto out_free_name;
+		}
+		close(path_beneath.parent_fd);
+	}
+	ret = 0;
+
+out_free_name:
+	free(path_list);
+	free(env_path_name);
+	return ret;
+}
+
+static int populate_ruleset_net(const char *const env_var, const int ruleset_fd,
+				const __u64 allowed_access, __u32 flags)
+{
+	int ret = 1;
+	char *env_port_name, *env_port_name_next, *strport;
+	struct landlock_net_port_attr net_port = {
+		.allowed_access = allowed_access,
+	};
+
+	env_port_name = getenv(env_var);
+	if (!env_port_name)
+		return 0;
+	env_port_name = strdup(env_port_name);
+	unsetenv(env_var);
+
+	env_port_name_next = env_port_name;
+	while ((strport = strsep(&env_port_name_next, ENV_DELIMITER))) {
+		__u64 port;
+
+		if (strcmp(strport, "") == 0)
+			continue;
+
+		if (str2num(strport, &port)) {
+			fprintf(stderr, "Failed to parse port at \"%s\"\n",
+				strport);
+			goto out_free_name;
+		}
+		net_port.port = port;
+		if (landlock_add_rule(ruleset_fd, LANDLOCK_RULE_NET_PORT,
+				      &net_port, flags)) {
+			fprintf(stderr,
+				"Failed to update the ruleset with port \"%llu\": %s\n",
+				net_port.port, strerror(errno));
+			goto out_free_name;
+		}
+	}
+	ret = 0;
+
+out_free_name:
+	free(env_port_name);
+	return ret;
+}
+
+/* Returns true on error, false otherwise. */
+static bool check_ruleset_scope(const char *const env_var,
+				struct landlock_ruleset_attr *ruleset_attr)
+{
+	char *env_type_scope, *env_type_scope_next, *ipc_scoping_name;
+	bool error = false;
+	bool abstract_scoping = false;
+	bool signal_scoping = false;
+
+	/* Scoping is not supported by Landlock ABI */
+	if (!(ruleset_attr->scoped &
+	      (LANDLOCK_SCOPE_ABSTRACT_UNIX_SOCKET | LANDLOCK_SCOPE_SIGNAL)))
+		goto out_unset;
+
+	env_type_scope = getenv(env_var);
+	/* Scoping is not supported by the user */
+	if (!env_type_scope || strcmp("", env_type_scope) == 0)
+		goto out_unset;
+
+	env_type_scope = strdup(env_type_scope);
+	env_type_scope_next = env_type_scope;
+	while ((ipc_scoping_name =
+			strsep(&env_type_scope_next, ENV_DELIMITER))) {
+		if (strcmp("a", ipc_scoping_name) == 0 && !abstract_scoping) {
+			abstract_scoping = true;
+		} else if (strcmp("s", ipc_scoping_name) == 0 &&
+			   !signal_scoping) {
+			signal_scoping = true;
+		} else {
+			fprintf(stderr, "Unknown or duplicate scope \"%s\"\n",
+				ipc_scoping_name);
+			error = true;
+			goto out_free_name;
+		}
+	}
+
+out_free_name:
+	free(env_type_scope);
+
+out_unset:
+	if (!abstract_scoping)
+		ruleset_attr->scoped &= ~LANDLOCK_SCOPE_ABSTRACT_UNIX_SOCKET;
+	if (!signal_scoping)
+		ruleset_attr->scoped &= ~LANDLOCK_SCOPE_SIGNAL;
+
+	unsetenv(env_var);
+	return error;
+}
+
+/* clang-format off */
+
+#define ACCESS_FS_ROUGHLY_READ ( \
+	LANDLOCK_ACCESS_FS_EXECUTE | \
+	LANDLOCK_ACCESS_FS_READ_FILE | \
+	LANDLOCK_ACCESS_FS_READ_DIR)
+
+#define ACCESS_FS_ROUGHLY_WRITE ( \
+	LANDLOCK_ACCESS_FS_WRITE_FILE | \
+	LANDLOCK_ACCESS_FS_REMOVE_DIR | \
+	LANDLOCK_ACCESS_FS_REMOVE_FILE | \
+	LANDLOCK_ACCESS_FS_MAKE_CHAR | \
+	LANDLOCK_ACCESS_FS_MAKE_DIR | \
+	LANDLOCK_ACCESS_FS_MAKE_REG | \
+	LANDLOCK_ACCESS_FS_MAKE_SOCK | \
+	LANDLOCK_ACCESS_FS_MAKE_FIFO | \
+	LANDLOCK_ACCESS_FS_MAKE_BLOCK | \
+	LANDLOCK_ACCESS_FS_MAKE_SYM | \
+	LANDLOCK_ACCESS_FS_REFER | \
+	LANDLOCK_ACCESS_FS_TRUNCATE | \
+	LANDLOCK_ACCESS_FS_IOCTL_DEV | \
+	LANDLOCK_ACCESS_FS_RESOLVE_UNIX)
+
+/* clang-format on */
+
+/*
+ * Parses ENV_QUIET_ACCESS_NAME and sets the quiet_access_fs, quiet_access_net
+ * and quiet_scoped masks of @ruleset_attr accordingly.
+ */
+static int add_quiet_access(const char *const env_var,
+			    struct landlock_ruleset_attr *const ruleset_attr)
+{
+	char *env_quiet_access, *env_quiet_access_next, *str_access;
+
+	env_quiet_access = getenv(env_var);
+	if (!env_quiet_access)
+		return 0;
+
+	env_quiet_access = strdup(env_quiet_access);
+	env_quiet_access_next = env_quiet_access;
+	unsetenv(env_var);
+
+	while ((str_access = strsep(&env_quiet_access_next, ENV_DELIMITER))) {
+		if (strcmp(str_access, "") == 0)
+			continue;
+		else if (strcmp(str_access, "all") == 0) {
+			ruleset_attr->quiet_access_fs =
+				ruleset_attr->handled_access_fs;
+			ruleset_attr->quiet_access_net =
+				ruleset_attr->handled_access_net;
+			ruleset_attr->quiet_scoped = ruleset_attr->scoped;
+		} else if (strcmp(str_access, "read") == 0)
+			ruleset_attr->quiet_access_fs |= ACCESS_FS_ROUGHLY_READ;
+		else if (strcmp(str_access, "write") == 0)
+			ruleset_attr->quiet_access_fs |=
+				ACCESS_FS_ROUGHLY_WRITE;
+		else if (strcmp(str_access, "tcp_bind") == 0)
+			ruleset_attr->quiet_access_net |=
+				LANDLOCK_ACCESS_NET_BIND_TCP;
+		else if (strcmp(str_access, "tcp_connect") == 0)
+			ruleset_attr->quiet_access_net |=
+				LANDLOCK_ACCESS_NET_CONNECT_TCP;
+		else if (strcmp(str_access, "udp_bind") == 0)
+			ruleset_attr->quiet_access_net |=
+				LANDLOCK_ACCESS_NET_BIND_UDP;
+		else if (strcmp(str_access, "udp_connect") == 0)
+			ruleset_attr->quiet_access_net |=
+				LANDLOCK_ACCESS_NET_CONNECT_SEND_UDP;
+		else if (strcmp(str_access, "abstract_unix_socket") == 0)
+			ruleset_attr->quiet_scoped |=
+				LANDLOCK_SCOPE_ABSTRACT_UNIX_SOCKET;
+		else if (strcmp(str_access, "signal") == 0)
+			ruleset_attr->quiet_scoped |= LANDLOCK_SCOPE_SIGNAL;
+		else {
+			fprintf(stderr, "Unknown quiet access \"%s\"\n",
+				str_access);
+			free(env_quiet_access);
+			return -1;
+		}
+	}
+
+	free(env_quiet_access);
+	ruleset_attr->quiet_access_fs &= ruleset_attr->handled_access_fs;
+	ruleset_attr->quiet_access_net &= ruleset_attr->handled_access_net;
+	ruleset_attr->quiet_scoped &= ruleset_attr->scoped;
+	return 0;
+}
+
+#define LANDLOCK_ABI_LAST 11
+
+#define XSTR(s) #s
+#define STR(s) XSTR(s)
+
+/* clang-format off */
+
+static const char help[] =
+	"usage: " ENV_FS_RO_NAME "=\"...\" " ENV_FS_RW_NAME "=\"...\" "
+	"[other environment variables] %1$s <cmd> [args]...\n"
+	"\n"
+	"Execute the given command in a restricted environment.\n"
+	"Multi-valued settings (lists of ports, paths, scopes) are colon-delimited.\n"
+	"\n"
+	"Mandatory settings:\n"
+	"* " ENV_FS_RO_NAME ": paths allowed to be used in a read-only way\n"
+	"* " ENV_FS_RW_NAME ": paths allowed to be used in a read-write way\n"
+	"\n"
+	"Optional settings (when not set, their associated access check "
+	"is always allowed, which is different from an empty string which "
+	"means an empty list):\n"
+	"* " ENV_TCP_BIND_NAME ": ports allowed to bind (server)\n"
+	"* " ENV_TCP_CONNECT_NAME ": ports allowed to connect (client)\n"
+	"* " ENV_UDP_BIND_NAME ": local UDP ports allowed to bind (server: "
+	"prepare to receive on port / client: set as source port)\n"
+	"* " ENV_UDP_CONNECT_SEND_NAME ": remote UDP ports allowed to connect "
+	"or send to (client: use as destination port / server: receive only from it)\n"
+	"(caution: sending requires being able to bind to a local source port)\n"
+	"* " ENV_SCOPED_NAME ": actions denied on the outside of the landlock domain\n"
+	"  - \"a\" to restrict opening abstract unix sockets\n"
+	"  - \"s\" to restrict sending signals\n"
+	"\n"
+	"A sandboxer should not log denied access requests to avoid spamming logs, "
+	"but to test audit we can set " ENV_FORCE_LOG_NAME "=1\n"
+	ENV_FS_QUIET_NAME " and " ENV_NET_QUIET_NAME ", both optional, can then be used "
+	"to make access to some denied paths or network ports not trigger audit logging.\n"
+	ENV_QUIET_ACCESS_NAME " can be used to specify which accesses should be quieted "
+	"(required when " ENV_FS_QUIET_NAME " or " ENV_NET_QUIET_NAME " is set):\n"
+	"  - \"all\" to quiet all of the accesses below\n"
+	"  - \"read\" to quiet all file/dir read accesses\n"
+	"  - \"write\" to quiet all file/dir write accesses\n"
+	"  - \"tcp_bind\" to quiet tcp bind denials\n"
+	"  - \"tcp_connect\" to quiet tcp connect denials\n"
+	"  - \"udp_bind\" to quiet udp bind denials\n"
+	"  - \"udp_connect\" to quiet udp connect / send denials\n"
+	"  - \"abstract_unix_socket\" to quiet abstract unix socket denials\n"
+	"  - \"signal\" to quiet signal denials\n"
+	"\n"
+	"Example:\n"
+	ENV_FS_RO_NAME "=\"${PATH}:/lib:/usr:/proc:/etc:/dev/urandom\" "
+	ENV_FS_RW_NAME "=\"/dev/null:/dev/full:/dev/zero:/dev/pts:/tmp\" "
+	ENV_TCP_BIND_NAME "=\"9418\" "
+	ENV_TCP_CONNECT_NAME "=\"80:443\" "
+	ENV_UDP_CONNECT_SEND_NAME "=\"53\" "
+	ENV_SCOPED_NAME "=\"a:s\" "
+	"%1$s bash -i\n"
+	"\n"
+	"This sandboxer can use Landlock features up to ABI version "
+	STR(LANDLOCK_ABI_LAST) ".\n";
+
+/* clang-format on */
+
+int main(const int argc, char *const argv[], char *const *const envp)
+{
+	const char *cmd_path;
+	char *const *cmd_argv;
+	int ruleset_fd, abi;
+	char *env_port_name, *env_force_log;
+	__u64 access_fs_ro = ACCESS_FS_ROUGHLY_READ,
+	      access_fs_rw = ACCESS_FS_ROUGHLY_READ | ACCESS_FS_ROUGHLY_WRITE;
+
+	struct landlock_ruleset_attr ruleset_attr = {
+		.handled_access_fs = access_fs_rw,
+		.handled_access_net = LANDLOCK_ACCESS_NET_BIND_TCP |
+				      LANDLOCK_ACCESS_NET_CONNECT_TCP |
+				      LANDLOCK_ACCESS_NET_BIND_UDP |
+				      LANDLOCK_ACCESS_NET_CONNECT_SEND_UDP,
+		.scoped = LANDLOCK_SCOPE_ABSTRACT_UNIX_SOCKET |
+			  LANDLOCK_SCOPE_SIGNAL,
+		.quiet_access_fs = 0,
+		.quiet_access_net = 0,
+		.quiet_scoped = 0,
+	};
+	bool quiet_supported = true;
+	int supported_restrict_flags = LANDLOCK_RESTRICT_SELF_LOG_NEW_EXEC_ON |
+				       LANDLOCK_RESTRICT_SELF_NO_NEW_PRIVS;
+	int set_restrict_flags = LANDLOCK_RESTRICT_SELF_NO_NEW_PRIVS;
+
+	if (argc < 2) {
+		fprintf(stderr, help, argv[0]);
+		return 1;
+	}
+
+	abi = landlock_create_ruleset(NULL, 0, LANDLOCK_CREATE_RULESET_VERSION);
+	if (abi < 0) {
+		const int err = errno;
+
+		perror("Failed to check Landlock compatibility");
+		switch (err) {
+		case ENOSYS:
+			fprintf(stderr,
+				"Hint: Landlock is not supported by the current kernel. "
+				"To support it, build the kernel with "
+				"CONFIG_SECURITY_LANDLOCK=y and prepend "
+				"\"landlock,\" to the content of CONFIG_LSM.\n");
+			break;
+		case EOPNOTSUPP:
+			fprintf(stderr,
+				"Hint: Landlock is currently disabled. "
+				"It can be enabled in the kernel configuration by "
+				"prepending \"landlock,\" to the content of CONFIG_LSM, "
+				"or at boot time by setting the same content to the "
+				"\"lsm\" kernel parameter.\n");
+			break;
+		}
+		return 1;
+	}
+
+	/* Best-effort security. */
+	switch (abi) {
+	case 1:
+		/*
+		 * Removes LANDLOCK_ACCESS_FS_REFER for ABI < 2
+		 *
+		 * Note: The "refer" operations (file renaming and linking
+		 * across different directories) are always forbidden when using
+		 * Landlock with ABI 1.
+		 *
+		 * If only ABI 1 is available, this sandboxer knowingly forbids
+		 * refer operations.
+		 *
+		 * If a program *needs* to do refer operations after enabling
+		 * Landlock, it can not use Landlock at ABI level 1.  To be
+		 * compatible with different kernel versions, such programs
+		 * should then fall back to not restrict themselves at all if
+		 * the running kernel only supports ABI 1.
+		 */
+		ruleset_attr.handled_access_fs &= ~LANDLOCK_ACCESS_FS_REFER;
+		__attribute__((fallthrough));
+	case 2:
+		/* Removes LANDLOCK_ACCESS_FS_TRUNCATE for ABI < 3 */
+		ruleset_attr.handled_access_fs &= ~LANDLOCK_ACCESS_FS_TRUNCATE;
+		__attribute__((fallthrough));
+	case 3:
+		/* Removes network support for ABI < 4 */
+		ruleset_attr.handled_access_net &=
+			~(LANDLOCK_ACCESS_NET_BIND_TCP |
+			  LANDLOCK_ACCESS_NET_CONNECT_TCP);
+		__attribute__((fallthrough));
+	case 4:
+		/* Removes LANDLOCK_ACCESS_FS_IOCTL_DEV for ABI < 5 */
+		ruleset_attr.handled_access_fs &= ~LANDLOCK_ACCESS_FS_IOCTL_DEV;
+
+		__attribute__((fallthrough));
+	case 5:
+		/* Removes LANDLOCK_SCOPE_* for ABI < 6 */
+		ruleset_attr.scoped &= ~(LANDLOCK_SCOPE_ABSTRACT_UNIX_SOCKET |
+					 LANDLOCK_SCOPE_SIGNAL);
+		__attribute__((fallthrough));
+	case 6:
+		/* Removes LANDLOCK_RESTRICT_SELF_LOG_NEW_EXEC_ON for ABI < 7 */
+		supported_restrict_flags &=
+			~LANDLOCK_RESTRICT_SELF_LOG_NEW_EXEC_ON;
+		__attribute__((fallthrough));
+	case 7:
+	case 8:
+		/* Removes LANDLOCK_ACCESS_FS_RESOLVE_UNIX for ABI < 9 */
+		ruleset_attr.handled_access_fs &=
+			~LANDLOCK_ACCESS_FS_RESOLVE_UNIX;
+		__attribute__((fallthrough));
+	case 9:
+		/* Removes UDP support for ABI < 10 */
+		ruleset_attr.handled_access_net &=
+			~(LANDLOCK_ACCESS_NET_BIND_UDP |
+			  LANDLOCK_ACCESS_NET_CONNECT_SEND_UDP);
+		/* Removes quiet flags for ABI < 10 later on. */
+		quiet_supported = false;
+		__attribute__((fallthrough));
+	case 10:
+		/* Removes LANDLOCK_RESTRICT_SELF_NO_NEW_PRIVS for ABI < 11 */
+		supported_restrict_flags &=
+			~LANDLOCK_RESTRICT_SELF_NO_NEW_PRIVS;
+		set_restrict_flags &= ~LANDLOCK_RESTRICT_SELF_NO_NEW_PRIVS;
+
+		/* Must be printed for any ABI < LANDLOCK_ABI_LAST. */
+		fprintf(stderr,
+			"Hint: You should update the running kernel "
+			"to leverage Landlock features "
+			"provided by ABI version %d (instead of %d).\n",
+			LANDLOCK_ABI_LAST, abi);
+		__attribute__((fallthrough));
+	case LANDLOCK_ABI_LAST:
+		break;
+	default:
+		fprintf(stderr,
+			"Hint: You should update this sandboxer "
+			"to leverage Landlock features "
+			"provided by ABI version %d (instead of %d).\n",
+			abi, LANDLOCK_ABI_LAST);
+	}
+	access_fs_ro &= ruleset_attr.handled_access_fs;
+	access_fs_rw &= ruleset_attr.handled_access_fs;
+
+	/* Removes bind access attribute if not supported by a user. */
+	env_port_name = getenv(ENV_TCP_BIND_NAME);
+	if (!env_port_name) {
+		ruleset_attr.handled_access_net &=
+			~LANDLOCK_ACCESS_NET_BIND_TCP;
+	}
+	/* Removes connect access attribute if not supported by a user. */
+	env_port_name = getenv(ENV_TCP_CONNECT_NAME);
+	if (!env_port_name) {
+		ruleset_attr.handled_access_net &=
+			~LANDLOCK_ACCESS_NET_CONNECT_TCP;
+	}
+	/* Removes UDP bind access control if not supported by a user. */
+	env_port_name = getenv(ENV_UDP_BIND_NAME);
+	if (!env_port_name) {
+		ruleset_attr.handled_access_net &=
+			~LANDLOCK_ACCESS_NET_BIND_UDP;
+	}
+	/* Removes UDP connect/send access control if not supported by a user. */
+	env_port_name = getenv(ENV_UDP_CONNECT_SEND_NAME);
+	if (!env_port_name) {
+		ruleset_attr.handled_access_net &=
+			~LANDLOCK_ACCESS_NET_CONNECT_SEND_UDP;
+	}
+
+	if (check_ruleset_scope(ENV_SCOPED_NAME, &ruleset_attr))
+		return 1;
+
+	/* Enables optional logs. */
+	env_force_log = getenv(ENV_FORCE_LOG_NAME);
+	if (env_force_log) {
+		if (strcmp(env_force_log, "1") != 0) {
+			fprintf(stderr, "Unknown value for " ENV_FORCE_LOG_NAME
+					" (only \"1\" is handled)\n");
+			return 1;
+		}
+		if (!(supported_restrict_flags &
+		      LANDLOCK_RESTRICT_SELF_LOG_NEW_EXEC_ON)) {
+			fprintf(stderr,
+				"Audit logs not supported by current kernel\n");
+			return 1;
+		}
+		set_restrict_flags |= LANDLOCK_RESTRICT_SELF_LOG_NEW_EXEC_ON;
+		unsetenv(ENV_FORCE_LOG_NAME);
+	}
+
+	/* Set the quiet access masks. */
+	if (quiet_supported) {
+		if ((getenv(ENV_FS_QUIET_NAME) || getenv(ENV_NET_QUIET_NAME)) &&
+		    !getenv(ENV_QUIET_ACCESS_NAME)) {
+			fprintf(stderr,
+				"%s must be set (e.g. to \"all\") when %s or %s is used\n",
+				ENV_QUIET_ACCESS_NAME, ENV_FS_QUIET_NAME,
+				ENV_NET_QUIET_NAME);
+			return 1;
+		}
+		if (add_quiet_access(ENV_QUIET_ACCESS_NAME, &ruleset_attr))
+			return 1;
+	} else if (getenv(ENV_FS_QUIET_NAME) || getenv(ENV_NET_QUIET_NAME) ||
+		   getenv(ENV_QUIET_ACCESS_NAME)) {
+		fprintf(stderr,
+			"Quiet flags not supported by current kernel\n");
+		return 1;
+	}
+
+	ruleset_fd =
+		landlock_create_ruleset(&ruleset_attr, sizeof(ruleset_attr), 0);
+	if (ruleset_fd < 0) {
+		perror("Failed to create a ruleset");
+		return 1;
+	}
+
+	if (populate_ruleset_fs(ENV_FS_RO_NAME, ruleset_fd, access_fs_ro, 0))
+		goto err_close_ruleset;
+	if (populate_ruleset_fs(ENV_FS_RW_NAME, ruleset_fd, access_fs_rw, 0))
+		goto err_close_ruleset;
+
+	/* Don't require this env to be present. */
+	if (quiet_supported && getenv(ENV_FS_QUIET_NAME)) {
+		if (populate_ruleset_fs(ENV_FS_QUIET_NAME, ruleset_fd, 0,
+					LANDLOCK_ADD_RULE_QUIET))
+			goto err_close_ruleset;
+	}
+
+	if (populate_ruleset_net(ENV_TCP_BIND_NAME, ruleset_fd,
+				 LANDLOCK_ACCESS_NET_BIND_TCP, 0)) {
+		goto err_close_ruleset;
+	}
+	if (populate_ruleset_net(ENV_TCP_CONNECT_NAME, ruleset_fd,
+				 LANDLOCK_ACCESS_NET_CONNECT_TCP, 0)) {
+		goto err_close_ruleset;
+	}
+	if (populate_ruleset_net(ENV_UDP_BIND_NAME, ruleset_fd,
+				 LANDLOCK_ACCESS_NET_BIND_UDP, 0)) {
+		goto err_close_ruleset;
+	}
+	if (populate_ruleset_net(ENV_UDP_CONNECT_SEND_NAME, ruleset_fd,
+				 LANDLOCK_ACCESS_NET_CONNECT_SEND_UDP, 0)) {
+		goto err_close_ruleset;
+	}
+
+	if (quiet_supported) {
+		if (populate_ruleset_net(ENV_NET_QUIET_NAME, ruleset_fd, 0,
+					 LANDLOCK_ADD_RULE_QUIET)) {
+			goto err_close_ruleset;
+		}
+	}
+
+	if (!(set_restrict_flags & LANDLOCK_RESTRICT_SELF_NO_NEW_PRIVS) &&
+	    prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0)) {
+		perror("Failed to restrict privileges");
+		goto err_close_ruleset;
+	}
+	if (landlock_restrict_self(ruleset_fd, set_restrict_flags)) {
+		perror("Failed to enforce ruleset");
+		goto err_close_ruleset;
+	}
+	close(ruleset_fd);
+
+	cmd_path = argv[1];
+	cmd_argv = argv + 1;
+	fprintf(stderr, "Executing the sandboxed command...\n");
+	execvpe(cmd_path, cmd_argv, envp);
+	fprintf(stderr, "Failed to execute \"%s\": %s\n", cmd_path,
+		strerror(errno));
+	fprintf(stderr, "Hint: access to the binary, the interpreter or "
+			"shared libraries may be denied.\n");
+	return 1;
+
+err_close_ruleset:
+	close(ruleset_fd);
+	return 1;
+}