A Landlock domain is a set of eBPF programs. There is a list for each
different program types that can be run on a specific Landlock hook
(e.g. ptrace). A domain is tied to a set of subjects (i.e. tasks). A
Landlock program should not try (nor be able) to infer which subject is
currently enforced, but to have a unique security policy for all
subjects tied to the same domain. This make the reasoning much easier
and help avoid pitfalls.
The next commits tie a domain to a task's credentials thanks to
seccomp(2), but we could use cgroups or a security file-system to
enforce a sysadmin-defined policy .
Signed-off-by: Mickaël Salaün <mic@xxxxxxxxxxx>
Cc: Alexei Starovoitov <ast@xxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
Cc: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
Cc: James Morris <jmorris@xxxxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: Serge E. Hallyn <serge@xxxxxxxxxx>
Cc: Will Drewry <wad@xxxxxxxxxxxx>
---
Changes since v10:
* rename files and names to clearly define a domain
* create a standalone patch to ease review
---
security/landlock/Makefile | 3 +-
security/landlock/common.h | 38 +++++
security/landlock/domain_manage.c | 265 ++++++++++++++++++++++++++++++
security/landlock/domain_manage.h | 23 +++
4 files changed, 328 insertions(+), 1 deletion(-)
create mode 100644 security/landlock/domain_manage.c
create mode 100644 security/landlock/domain_manage.h
diff --git a/security/landlock/Makefile b/security/landlock/Makefile
index 682b798c6b76..dd5f70185778 100644
--- a/security/landlock/Makefile
+++ b/security/landlock/Makefile
@@ -1,4 +1,5 @@
obj-$(CONFIG_SECURITY_LANDLOCK) := landlock.o
landlock-y := \
- bpf_verify.o bpf_ptrace.o
+ bpf_verify.o bpf_ptrace.o \
+ domain_manage.o
diff --git a/security/landlock/common.h b/security/landlock/common.h
index 0234c4bc4acd..fb2990eb5fb4 100644
--- a/security/landlock/common.h
+++ b/security/landlock/common.h
@@ -11,11 +11,49 @@
#include <linux/bpf.h>
#include <linux/filter.h>
+#include <linux/refcount.h>
enum landlock_hook_type {
LANDLOCK_HOOK_PTRACE = 1,
};
+#define _LANDLOCK_HOOK_LAST LANDLOCK_HOOK_PTRACE
+
+struct landlock_prog_list {
+ struct landlock_prog_list *prev;
+ struct bpf_prog *prog;
+ refcount_t usage;
+};
+
+/**
+ * struct landlock_domain - Landlock programs enforced on a set of tasks
+ *
+ * When prepending a new program, if &struct landlock_domain is shared with
+ * other tasks, then duplicate it and prepend the program to this new &struct
+ * landlock_domain.
+ *
+ * @usage: reference count to manage the object lifetime. When a task needs to
+ * add Landlock programs and if @usage is greater than 1, then the
+ * task must duplicate &struct landlock_domain to not change the
+ * children's programs as well.
+ * @programs: array of non-NULL &struct landlock_prog_list pointers
+ */
+struct landlock_domain {
+ struct landlock_prog_list *programs[_LANDLOCK_HOOK_LAST];
+ refcount_t usage;
+};
+
+/**
+ * get_hook_index - get an index for the programs of struct landlock_prog_set
+ *
+ * @type: a Landlock hook type
+ */
+static inline size_t get_hook_index(enum landlock_hook_type type)
+{
+ /* type ID > 0 for loaded programs */
+ return type - 1;
+}
+
static inline enum landlock_hook_type get_hook_type(const struct bpf_prog *prog)
{
switch (prog->expected_attach_type) {
diff --git a/security/landlock/domain_manage.c b/security/landlock/domain_manage.c
new file mode 100644
index 000000000000..c955b9c95c84
--- /dev/null
+++ b/security/landlock/domain_manage.c
@@ -0,0 +1,265 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Landlock LSM - domain management
+ *
+ * Copyright © 2016-2019 Mickaël Salaün <mic@xxxxxxxxxxx>
+ * Copyright © 2018-2019 ANSSI
+ */
+
+#include <linux/err.h>
+#include <linux/errno.h>
+#include <linux/refcount.h>
+#include <linux/slab.h>
+#include <linux/spinlock.h>
+
+#include "common.h"
+#include "domain_manage.h"
+
+void landlock_get_domain(struct landlock_domain *dom)
+{
+ if (!dom)
+ return;
+ refcount_inc(&dom->usage);
+}
+
+static void put_landlock_prog_list(struct landlock_prog_list *prog_list)
+{
+ struct landlock_prog_list *orig = prog_list;
+
+ /* clean up single-reference branches iteratively */
+ while (orig && refcount_dec_and_test(&orig->usage)) {
+ struct landlock_prog_list *freeme = orig;
+
+ if (orig->prog)
+ bpf_prog_put(orig->prog);
+ orig = orig->prev;
+ kfree(freeme);
+ }
+}
+
+void landlock_put_domain(struct landlock_domain *domain)
+{
+ if (domain && refcount_dec_and_test(&domain->usage)) {
+ size_t i;
+
+ for (i = 0; i < ARRAY_SIZE(domain->programs); i++)
+ put_landlock_prog_list(domain->programs[i]);
+ kfree(domain);
+ }
+}
+
+static struct landlock_domain *new_landlock_domain(void)
+{
+ struct landlock_domain *domain;
+
+ /* array filled with NULL values */
+ domain = kzalloc(sizeof(*domain), GFP_KERNEL);
+ if (!domain)
+ return ERR_PTR(-ENOMEM);
+ refcount_set(&domain->usage, 1);
+ return domain;
+}
+
+/**
+ * store_landlock_prog - prepend and deduplicate a Landlock prog_list
+ *
+ * Prepend @prog to @init_domain while ignoring @prog if they are already in
+ * @ref_domain. Whatever is the result of this function call, you can call
+ * bpf_prog_put(@prog) after.
+ *
+ * @init_domain: empty domain to prepend to
+ * @ref_domain: domain to check for duplicate programs
+ * @prog: program to prepend
+ *
+ * Return -errno on error or 0 if @prog was successfully stored.
+ */
+static int store_landlock_prog(struct landlock_domain *init_domain,
+ const struct landlock_domain *ref_domain,
+ struct bpf_prog *prog)
+{
+ struct landlock_prog_list *tmp_list = NULL;
+ int err;
+ size_t hook;
+ enum landlock_hook_type last_type;
+ struct bpf_prog *new = prog;
+
+ /* allocate all the memory we need */
+ struct landlock_prog_list *new_list;
+
+ last_type = get_hook_type(new);
+
+ /* ignore duplicate programs */
+ if (ref_domain) {
+ struct landlock_prog_list *ref;
+
+ hook = get_hook_index(get_hook_type(new));
+ for (ref = ref_domain->programs[hook]; ref;
+ ref = ref->prev) {
+ if (ref->prog == new)
+ return -EINVAL;
+ }
+ }
+
+ new = bpf_prog_inc(new);
+ if (IS_ERR(new)) {
+ err = PTR_ERR(new);
+ goto put_tmp_list;
+ }
+ new_list = kzalloc(sizeof(*new_list), GFP_KERNEL);
+ if (!new_list) {
+ bpf_prog_put(new);
+ err = -ENOMEM;
+ goto put_tmp_list;
+ }
+ /* ignore Landlock types in this tmp_list */
+ new_list->prog = new;
+ new_list->prev = tmp_list;
+ refcount_set(&new_list->usage, 1);
+ tmp_list = new_list;
+
+ if (!tmp_list)
+ /* inform user space that this program was already added */
+ return -EEXIST;
+
+ /* properly store the list (without error cases) */
+ while (tmp_list) {
+ struct landlock_prog_list *new_list;
+
+ new_list = tmp_list;
+ tmp_list = tmp_list->prev;
+ /* do not increment the previous prog list usage */
+ hook = get_hook_index(get_hook_type(new_list->prog));
+ new_list->prev = init_domain->programs[hook];
+ /* no need to add from the last program to the first because
+ * each of them are a different Landlock type */
+ smp_store_release(&init_domain->programs[hook], new_list);
+ }
+ return 0;
+
+put_tmp_list:
+ put_landlock_prog_list(tmp_list);
+ return err;
+}
+
+/* limit Landlock programs set to 256KB */
+#define LANDLOCK_PROGRAMS_MAX_PAGES (1 << 6)
+
+/**
+ * landlock_prepend_prog - attach a Landlock prog_list to @current_domain
+ *
+ * Whatever is the result of this function call, you can call
+ * bpf_prog_put(@prog) after.
+ *
+ * @current_domain: landlock_domain pointer, must be (RCU-)locked (if needed)
+ * to prevent a concurrent put/free. This pointer must not be
+ * freed after the call.
+ * @prog: non-NULL Landlock prog_list to prepend to @current_domain. @prog will
+ * be owned by landlock_prepend_prog() and freed if an error happened.
+ *
+ * Return @current_domain or a new pointer when OK. Return a pointer error
+ * otherwise.
+ */
+struct landlock_domain *landlock_prepend_prog(
+ struct landlock_domain *current_domain,
+ struct bpf_prog *prog)
+{
+ struct landlock_domain *new_domain = current_domain;
+ unsigned long pages;
+ int err;
+ size_t i;
+ struct landlock_domain tmp_domain = {};
+
+ if (prog->type != BPF_PROG_TYPE_LANDLOCK_HOOK)
+ return ERR_PTR(-EINVAL);
+
+ /* validate memory size allocation */
+ pages = prog->pages;
+ if (current_domain) {
+ size_t i;
+
+ for (i = 0; i < ARRAY_SIZE(current_domain->programs); i++) {
+ struct landlock_prog_list *walker_p;
+
+ for (walker_p = current_domain->programs[i];
+ walker_p; walker_p = walker_p->prev)
+ pages += walker_p->prog->pages;
+ }
+ /* count a struct landlock_domain if we need to allocate one */
+ if (refcount_read(¤t_domain->usage) != 1)
+ pages += round_up(sizeof(*current_domain), PAGE_SIZE)
+ / PAGE_SIZE;
+ }
+ if (pages > LANDLOCK_PROGRAMS_MAX_PAGES)
+ return ERR_PTR(-E2BIG);
+
+ /* ensure early that we can allocate enough memory for the new
+ * prog_lists */
+ err = store_landlock_prog(&tmp_domain, current_domain, prog);
+ if (err)
+ return ERR_PTR(err);
+
+ /*
+ * Each task_struct points to an array of prog list pointers. These
+ * tables are duplicated when additions are made (which means each
+ * table needs to be refcounted for the processes using it). When a new
+ * table is created, all the refcounters on the prog_list are bumped
+ * (to track each table that references the prog). When a new prog is
+ * added, it's just prepended to the list for the new table to point
+ * at.
+ *
+ * Manage all the possible errors before this step to not uselessly
+ * duplicate current_domain and avoid a rollback.
+ */
+ if (!new_domain) {
+ /*
+ * If there is no Landlock domain used by the current task,
+ * then create a new one.
+ */
+ new_domain = new_landlock_domain();
+ if (IS_ERR(new_domain))
+ goto put_tmp_lists;
+ } else if (refcount_read(¤t_domain->usage) > 1) {
+ /*
+ * If the current task is not the sole user of its Landlock
+ * domain, then duplicate it.
+ */
+ new_domain = new_landlock_domain();
+ if (IS_ERR(new_domain))
+ goto put_tmp_lists;
+ for (i = 0; i < ARRAY_SIZE(new_domain->programs); i++) {
+ new_domain->programs[i] =
+ READ_ONCE(current_domain->programs[i]);
+ if (new_domain->programs[i])
+ refcount_inc(&new_domain->programs[i]->usage);
+ }
+
+ /*
+ * Landlock domain from the current task will not be freed here
+ * because the usage is strictly greater than 1. It is only
+ * prevented to be freed by another task thanks to the caller
+ * of landlock_prepend_prog() which should be locked if needed.
+ */
+ landlock_put_domain(current_domain);
+ }
+
+ /* prepend tmp_domain to new_domain */
+ for (i = 0; i < ARRAY_SIZE(tmp_domain.programs); i++) {
+ /* get the last new list */
+ struct landlock_prog_list *last_list =
+ tmp_domain.programs[i];
+
+ if (last_list) {
+ while (last_list->prev)
+ last_list = last_list->prev;
+ /* no need to increment usage (pointer replacement) */
+ last_list->prev = new_domain->programs[i];
+ new_domain->programs[i] = tmp_domain.programs[i];
+ }
+ }
+ return new_domain;
+
+put_tmp_lists:
+ for (i = 0; i < ARRAY_SIZE(tmp_domain.programs); i++)
+ put_landlock_prog_list(tmp_domain.programs[i]);
+ return new_domain;
+}
diff --git a/security/landlock/domain_manage.h b/security/landlock/domain_manage.h
new file mode 100644
index 000000000000..5b5b49f6e3e8
--- /dev/null
+++ b/security/landlock/domain_manage.h
@@ -0,0 +1,23 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Landlock LSM - domain management headers
+ *
+ * Copyright © 2016-2019 Mickaël Salaün <mic@xxxxxxxxxxx>
+ * Copyright © 2018-2019 ANSSI
+ */
+
+#ifndef _SECURITY_LANDLOCK_DOMAIN_MANAGE_H
+#define _SECURITY_LANDLOCK_DOMAIN_MANAGE_H
+
+#include <linux/filter.h>
+
+#include "common.h"
+
+void landlock_get_domain(struct landlock_domain *dom);
+void landlock_put_domain(struct landlock_domain *dom);
+
+struct landlock_domain *landlock_prepend_prog(
+ struct landlock_domain *current_domain,
+ struct bpf_prog *prog);
+
+#endif /* _SECURITY_LANDLOCK_DOMAIN_MANAGE_H */
--
2.23.0
