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 v11:
* remove old code from previous refactoring (removing the program
chaining concept) and simplify program prepending (reported by Serge
E. Hallyn):
* simplify landlock_prepend_prog() and merge it with
store_landlock_prog()
* add new_prog_list() and rework new_landlock_domain()
* remove the extra page allocation checks, only rely on the eBPF
program checks
* replace the -EINVAL for the duplicate program check with the -EEXIST
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 | 173 ++++++++++++++++++++++++++++++
security/landlock/domain_manage.h | 23 ++++
4 files changed, 236 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..8b7ce988a221
--- /dev/null
+++ b/security/landlock/domain_manage.c
@@ -0,0 +1,173 @@
+// 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_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_prog_list(domain->programs[i]);
+ kfree(domain);
+ }
+}
+
+static struct landlock_prog_list *new_prog_list(struct bpf_prog *prog)
+{
+ struct landlock_prog_list *new_list;
+
+ if (WARN_ON(IS_ERR_OR_NULL(prog)))
+ return ERR_PTR(-EFAULT);
+ if (prog->type != BPF_PROG_TYPE_LANDLOCK_HOOK)
+ return ERR_PTR(-EINVAL);
+ prog = bpf_prog_inc(prog);
+ if (IS_ERR(prog))
+ return ERR_CAST(prog);
+ new_list = kzalloc(sizeof(*new_list), GFP_KERNEL);
+ if (!new_list) {
+ bpf_prog_put(prog);
+ return ERR_PTR(-ENOMEM);
+ }
+ new_list->prog = prog;
+ refcount_set(&new_list->usage, 1);
+ return new_list;
+}
+
+/* @prog can legitimately be NULL */
+static struct landlock_domain *new_landlock_domain(struct bpf_prog *prog)
+{
+ struct landlock_domain *new_domain;
+ struct landlock_prog_list *new_list;
+ size_t hook;
+
+ /* programs[] filled with NULL values */
+ new_domain = kzalloc(sizeof(*new_domain), GFP_KERNEL);
+ if (!new_domain)
+ return ERR_PTR(-ENOMEM);
+ refcount_set(&new_domain->usage, 1);
+ if (!prog)
+ return new_domain;
+ new_list = new_prog_list(prog);
+ if (IS_ERR(new_list)) {
+ kfree(new_domain);
+ return ERR_CAST(new_list);
+ }
+ hook = get_hook_index(get_hook_type(prog));
+ new_domain->programs[hook] = new_list;
+ return new_domain;
+}
+
+/**
+ * landlock_prepend_prog - attach a Landlock program to @current_domain
+ *
+ * Prepend @prog to @current_domain if @prog is not already in @current_domain.
+ *
+ * @current_domain: landlock_domain pointer which is garantee to not be
+ * modified elsewhere. This pointer should not be used nor
+ * put/freed after the call.
+ * @prog: non-NULL Landlock program to prepend to @current_domain. @prog will
+ * be owned by landlock_prepend_prog(). You can then call
+ * bpf_prog_put(@prog) after.
+ *
+ * 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 *oneref_domain;
+ struct landlock_prog_list *new_list, *walker;
+ size_t hook;
+
+ if (WARN_ON(!prog))
+ return ERR_PTR(-EFAULT);
+ if (prog->type != BPF_PROG_TYPE_LANDLOCK_HOOK)
+ return ERR_PTR(-EINVAL);
+
+ /*
+ * Each domain contains an array of prog_list pointers. If a domain is
+ * used by more than one credential, then this domain is first
+ * duplicated and then @prog is prepended to this new domain. We then
+ * have the garantee that a domain is immutable when shared, and it can
+ * only be modified if it is referenced only once (by the modifier).
+ */
+ if (!current_domain)
+ return new_landlock_domain(prog);
+
+ hook = get_hook_index(get_hook_type(prog));
+ /* check for similar program */
+ for (walker = current_domain->programs[hook]; walker;
+ walker = walker->prev) {
+ /* don't allow duplicate programs */
+ if (prog == walker->prog)
+ return ERR_PTR(-EEXIST);
+ }
+
+ new_list = new_prog_list(prog);
+ if (IS_ERR(new_list))
+ return ERR_CAST(new_list);
+
+ /* duplicate the domain if not referenced only once */
+ if (refcount_read(¤t_domain->usage) == 1) {
+ oneref_domain = current_domain;
+ } else {
+ size_t i;
+
+ oneref_domain = new_landlock_domain(NULL);
+ if (IS_ERR(oneref_domain)) {
+ put_prog_list(new_list);
+ return oneref_domain;
+ }
+ for (i = 0; i < ARRAY_SIZE(oneref_domain->programs); i++) {
+ oneref_domain->programs[i] =
+ current_domain->programs[i];
+ if (oneref_domain->programs[i])
+ refcount_inc(&oneref_domain->programs[i]->usage);
+ }
+ landlock_put_domain(current_domain);
+ /* @current_domain may be a dangling pointer now */
+ current_domain = NULL;
+ }
+
+ /* no need to increment usage (pointer replacement) */
+ new_list->prev = oneref_domain->programs[hook];
+ oneref_domain->programs[hook] = new_list;
+ return oneref_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
