landlock: Add ruleset and domain management
A Landlock ruleset is mainly a red-black tree with Landlock rules as nodes. This enables quick update and lookup to match a requested access, e.g. to a file. A ruleset is usable through a dedicated file descriptor (cf. following commit implementing syscalls) which enables a process to create and populate a ruleset with new rules. A domain is a ruleset tied to a set of processes. This group of rules defines the security policy enforced on these processes and their future children. A domain can transition to a new domain which is the intersection of all its constraints and those of a ruleset provided by the current process. This modification only impact the current process. This means that a process can only gain more constraints (i.e. lose accesses) over time. Cc: James Morris <jmorris@namei.org> Signed-off-by: Mickaël Salaün <mic@linux.microsoft.com> Acked-by: Serge Hallyn <serge@hallyn.com> Reviewed-by: Kees Cook <keescook@chromium.org> Reviewed-by: Jann Horn <jannh@google.com> Link: https://lore.kernel.org/r/20210422154123.13086-3-mic@digikod.net Signed-off-by: James Morris <jamorris@linux.microsoft.com>
This commit is contained in:
Mickaël Salaün
James Morris
parent
90945448e9
commit
ae271c1b14
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@ -1,3 +1,3 @@
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obj-$(CONFIG_SECURITY_LANDLOCK) := landlock.o
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landlock-y := object.o
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landlock-y := object.o ruleset.o
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@ -0,0 +1,17 @@
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/* SPDX-License-Identifier: GPL-2.0-only */
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/*
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* Landlock LSM - Limits for different components
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*
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* Copyright © 2016-2020 Mickaël Salaün <mic@digikod.net>
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* Copyright © 2018-2020 ANSSI
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*/
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#ifndef _SECURITY_LANDLOCK_LIMITS_H
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#define _SECURITY_LANDLOCK_LIMITS_H
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#include <linux/limits.h>
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#define LANDLOCK_MAX_NUM_LAYERS 64
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#define LANDLOCK_MAX_NUM_RULES U32_MAX
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#endif /* _SECURITY_LANDLOCK_LIMITS_H */
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@ -0,0 +1,469 @@
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// SPDX-License-Identifier: GPL-2.0-only
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/*
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* Landlock LSM - Ruleset management
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*
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* Copyright © 2016-2020 Mickaël Salaün <mic@digikod.net>
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* Copyright © 2018-2020 ANSSI
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*/
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#include <linux/bits.h>
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#include <linux/bug.h>
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#include <linux/compiler_types.h>
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#include <linux/err.h>
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#include <linux/errno.h>
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#include <linux/kernel.h>
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#include <linux/lockdep.h>
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#include <linux/overflow.h>
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#include <linux/rbtree.h>
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#include <linux/refcount.h>
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#include <linux/slab.h>
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#include <linux/spinlock.h>
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#include <linux/workqueue.h>
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#include "limits.h"
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#include "object.h"
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#include "ruleset.h"
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static struct landlock_ruleset *create_ruleset(const u32 num_layers)
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{
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struct landlock_ruleset *new_ruleset;
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new_ruleset = kzalloc(struct_size(new_ruleset, fs_access_masks,
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num_layers), GFP_KERNEL_ACCOUNT);
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if (!new_ruleset)
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return ERR_PTR(-ENOMEM);
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refcount_set(&new_ruleset->usage, 1);
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mutex_init(&new_ruleset->lock);
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new_ruleset->root = RB_ROOT;
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new_ruleset->num_layers = num_layers;
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/*
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* hierarchy = NULL
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* num_rules = 0
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* fs_access_masks[] = 0
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*/
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return new_ruleset;
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}
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struct landlock_ruleset *landlock_create_ruleset(const u32 fs_access_mask)
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{
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struct landlock_ruleset *new_ruleset;
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/* Informs about useless ruleset. */
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if (!fs_access_mask)
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return ERR_PTR(-ENOMSG);
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new_ruleset = create_ruleset(1);
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if (!IS_ERR(new_ruleset))
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new_ruleset->fs_access_masks[0] = fs_access_mask;
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return new_ruleset;
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}
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static void build_check_rule(void)
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{
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const struct landlock_rule rule = {
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.num_layers = ~0,
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};
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BUILD_BUG_ON(rule.num_layers < LANDLOCK_MAX_NUM_LAYERS);
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}
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static struct landlock_rule *create_rule(
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struct landlock_object *const object,
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const struct landlock_layer (*const layers)[],
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const u32 num_layers,
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const struct landlock_layer *const new_layer)
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{
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struct landlock_rule *new_rule;
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u32 new_num_layers;
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build_check_rule();
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if (new_layer) {
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/* Should already be checked by landlock_merge_ruleset(). */
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if (WARN_ON_ONCE(num_layers >= LANDLOCK_MAX_NUM_LAYERS))
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return ERR_PTR(-E2BIG);
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new_num_layers = num_layers + 1;
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} else {
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new_num_layers = num_layers;
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}
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new_rule = kzalloc(struct_size(new_rule, layers, new_num_layers),
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GFP_KERNEL_ACCOUNT);
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if (!new_rule)
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return ERR_PTR(-ENOMEM);
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RB_CLEAR_NODE(&new_rule->node);
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landlock_get_object(object);
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new_rule->object = object;
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new_rule->num_layers = new_num_layers;
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/* Copies the original layer stack. */
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memcpy(new_rule->layers, layers,
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flex_array_size(new_rule, layers, num_layers));
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if (new_layer)
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/* Adds a copy of @new_layer on the layer stack. */
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new_rule->layers[new_rule->num_layers - 1] = *new_layer;
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return new_rule;
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}
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static void free_rule(struct landlock_rule *const rule)
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{
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might_sleep();
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if (!rule)
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return;
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landlock_put_object(rule->object);
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kfree(rule);
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}
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static void build_check_ruleset(void)
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{
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const struct landlock_ruleset ruleset = {
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.num_rules = ~0,
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.num_layers = ~0,
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};
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BUILD_BUG_ON(ruleset.num_rules < LANDLOCK_MAX_NUM_RULES);
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BUILD_BUG_ON(ruleset.num_layers < LANDLOCK_MAX_NUM_LAYERS);
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}
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/**
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* insert_rule - Create and insert a rule in a ruleset
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*
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* @ruleset: The ruleset to be updated.
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* @object: The object to build the new rule with. The underlying kernel
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* object must be held by the caller.
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* @layers: One or multiple layers to be copied into the new rule.
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* @num_layers: The number of @layers entries.
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*
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* When user space requests to add a new rule to a ruleset, @layers only
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* contains one entry and this entry is not assigned to any level. In this
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* case, the new rule will extend @ruleset, similarly to a boolean OR between
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* access rights.
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*
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* When merging a ruleset in a domain, or copying a domain, @layers will be
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* added to @ruleset as new constraints, similarly to a boolean AND between
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* access rights.
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*/
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static int insert_rule(struct landlock_ruleset *const ruleset,
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struct landlock_object *const object,
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const struct landlock_layer (*const layers)[],
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size_t num_layers)
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{
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struct rb_node **walker_node;
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struct rb_node *parent_node = NULL;
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struct landlock_rule *new_rule;
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might_sleep();
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lockdep_assert_held(&ruleset->lock);
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if (WARN_ON_ONCE(!object || !layers))
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return -ENOENT;
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walker_node = &(ruleset->root.rb_node);
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while (*walker_node) {
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struct landlock_rule *const this = rb_entry(*walker_node,
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struct landlock_rule, node);
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if (this->object != object) {
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parent_node = *walker_node;
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if (this->object < object)
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walker_node = &((*walker_node)->rb_right);
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else
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walker_node = &((*walker_node)->rb_left);
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continue;
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}
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/* Only a single-level layer should match an existing rule. */
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if (WARN_ON_ONCE(num_layers != 1))
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return -EINVAL;
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/* If there is a matching rule, updates it. */
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if ((*layers)[0].level == 0) {
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/*
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* Extends access rights when the request comes from
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* landlock_add_rule(2), i.e. @ruleset is not a domain.
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*/
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if (WARN_ON_ONCE(this->num_layers != 1))
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return -EINVAL;
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if (WARN_ON_ONCE(this->layers[0].level != 0))
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return -EINVAL;
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this->layers[0].access |= (*layers)[0].access;
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return 0;
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}
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if (WARN_ON_ONCE(this->layers[0].level == 0))
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return -EINVAL;
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/*
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* Intersects access rights when it is a merge between a
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* ruleset and a domain.
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*/
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new_rule = create_rule(object, &this->layers, this->num_layers,
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&(*layers)[0]);
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if (IS_ERR(new_rule))
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return PTR_ERR(new_rule);
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rb_replace_node(&this->node, &new_rule->node, &ruleset->root);
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free_rule(this);
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return 0;
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}
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/* There is no match for @object. */
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build_check_ruleset();
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if (ruleset->num_rules >= LANDLOCK_MAX_NUM_RULES)
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return -E2BIG;
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new_rule = create_rule(object, layers, num_layers, NULL);
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if (IS_ERR(new_rule))
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return PTR_ERR(new_rule);
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rb_link_node(&new_rule->node, parent_node, walker_node);
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rb_insert_color(&new_rule->node, &ruleset->root);
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ruleset->num_rules++;
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return 0;
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}
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static void build_check_layer(void)
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{
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const struct landlock_layer layer = {
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.level = ~0,
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};
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BUILD_BUG_ON(layer.level < LANDLOCK_MAX_NUM_LAYERS);
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}
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/* @ruleset must be locked by the caller. */
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int landlock_insert_rule(struct landlock_ruleset *const ruleset,
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struct landlock_object *const object, const u32 access)
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{
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struct landlock_layer layers[] = {{
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.access = access,
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/* When @level is zero, insert_rule() extends @ruleset. */
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.level = 0,
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}};
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build_check_layer();
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return insert_rule(ruleset, object, &layers, ARRAY_SIZE(layers));
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}
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static inline void get_hierarchy(struct landlock_hierarchy *const hierarchy)
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{
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if (hierarchy)
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refcount_inc(&hierarchy->usage);
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}
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static void put_hierarchy(struct landlock_hierarchy *hierarchy)
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{
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while (hierarchy && refcount_dec_and_test(&hierarchy->usage)) {
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const struct landlock_hierarchy *const freeme = hierarchy;
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hierarchy = hierarchy->parent;
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kfree(freeme);
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}
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}
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static int merge_ruleset(struct landlock_ruleset *const dst,
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struct landlock_ruleset *const src)
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{
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struct landlock_rule *walker_rule, *next_rule;
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int err = 0;
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might_sleep();
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/* Should already be checked by landlock_merge_ruleset() */
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if (WARN_ON_ONCE(!src))
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return 0;
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/* Only merge into a domain. */
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if (WARN_ON_ONCE(!dst || !dst->hierarchy))
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return -EINVAL;
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/* Locks @dst first because we are its only owner. */
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mutex_lock(&dst->lock);
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mutex_lock_nested(&src->lock, SINGLE_DEPTH_NESTING);
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/* Stacks the new layer. */
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if (WARN_ON_ONCE(src->num_layers != 1 || dst->num_layers < 1)) {
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err = -EINVAL;
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goto out_unlock;
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}
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dst->fs_access_masks[dst->num_layers - 1] = src->fs_access_masks[0];
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/* Merges the @src tree. */
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rbtree_postorder_for_each_entry_safe(walker_rule, next_rule,
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&src->root, node) {
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struct landlock_layer layers[] = {{
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.level = dst->num_layers,
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}};
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if (WARN_ON_ONCE(walker_rule->num_layers != 1)) {
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err = -EINVAL;
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goto out_unlock;
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}
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if (WARN_ON_ONCE(walker_rule->layers[0].level != 0)) {
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err = -EINVAL;
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goto out_unlock;
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}
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layers[0].access = walker_rule->layers[0].access;
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err = insert_rule(dst, walker_rule->object, &layers,
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ARRAY_SIZE(layers));
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if (err)
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goto out_unlock;
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}
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out_unlock:
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mutex_unlock(&src->lock);
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mutex_unlock(&dst->lock);
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return err;
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}
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static int inherit_ruleset(struct landlock_ruleset *const parent,
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struct landlock_ruleset *const child)
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{
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struct landlock_rule *walker_rule, *next_rule;
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int err = 0;
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might_sleep();
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if (!parent)
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return 0;
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/* Locks @child first because we are its only owner. */
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mutex_lock(&child->lock);
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mutex_lock_nested(&parent->lock, SINGLE_DEPTH_NESTING);
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/* Copies the @parent tree. */
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rbtree_postorder_for_each_entry_safe(walker_rule, next_rule,
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&parent->root, node) {
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err = insert_rule(child, walker_rule->object,
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&walker_rule->layers, walker_rule->num_layers);
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if (err)
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goto out_unlock;
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}
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if (WARN_ON_ONCE(child->num_layers <= parent->num_layers)) {
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err = -EINVAL;
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goto out_unlock;
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}
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/* Copies the parent layer stack and leaves a space for the new layer. */
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memcpy(child->fs_access_masks, parent->fs_access_masks,
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flex_array_size(parent, fs_access_masks, parent->num_layers));
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if (WARN_ON_ONCE(!parent->hierarchy)) {
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err = -EINVAL;
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goto out_unlock;
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}
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get_hierarchy(parent->hierarchy);
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child->hierarchy->parent = parent->hierarchy;
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out_unlock:
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mutex_unlock(&parent->lock);
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mutex_unlock(&child->lock);
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return err;
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}
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static void free_ruleset(struct landlock_ruleset *const ruleset)
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{
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struct landlock_rule *freeme, *next;
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might_sleep();
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rbtree_postorder_for_each_entry_safe(freeme, next, &ruleset->root,
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node)
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free_rule(freeme);
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put_hierarchy(ruleset->hierarchy);
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kfree(ruleset);
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}
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void landlock_put_ruleset(struct landlock_ruleset *const ruleset)
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{
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might_sleep();
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if (ruleset && refcount_dec_and_test(&ruleset->usage))
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free_ruleset(ruleset);
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}
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static void free_ruleset_work(struct work_struct *const work)
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{
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struct landlock_ruleset *ruleset;
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ruleset = container_of(work, struct landlock_ruleset, work_free);
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free_ruleset(ruleset);
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}
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void landlock_put_ruleset_deferred(struct landlock_ruleset *const ruleset)
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{
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if (ruleset && refcount_dec_and_test(&ruleset->usage)) {
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INIT_WORK(&ruleset->work_free, free_ruleset_work);
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schedule_work(&ruleset->work_free);
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}
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}
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/**
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* landlock_merge_ruleset - Merge a ruleset with a domain
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*
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* @parent: Parent domain.
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* @ruleset: New ruleset to be merged.
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*
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* Returns the intersection of @parent and @ruleset, or returns @parent if
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* @ruleset is empty, or returns a duplicate of @ruleset if @parent is empty.
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*/
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struct landlock_ruleset *landlock_merge_ruleset(
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struct landlock_ruleset *const parent,
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struct landlock_ruleset *const ruleset)
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{
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struct landlock_ruleset *new_dom;
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u32 num_layers;
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int err;
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might_sleep();
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if (WARN_ON_ONCE(!ruleset || parent == ruleset))
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return ERR_PTR(-EINVAL);
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if (parent) {
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if (parent->num_layers >= LANDLOCK_MAX_NUM_LAYERS)
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return ERR_PTR(-E2BIG);
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num_layers = parent->num_layers + 1;
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} else {
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num_layers = 1;
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}
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/* Creates a new domain... */
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new_dom = create_ruleset(num_layers);
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if (IS_ERR(new_dom))
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return new_dom;
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new_dom->hierarchy = kzalloc(sizeof(*new_dom->hierarchy),
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GFP_KERNEL_ACCOUNT);
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if (!new_dom->hierarchy) {
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err = -ENOMEM;
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goto out_put_dom;
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}
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refcount_set(&new_dom->hierarchy->usage, 1);
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/* ...as a child of @parent... */
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err = inherit_ruleset(parent, new_dom);
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if (err)
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goto out_put_dom;
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/* ...and including @ruleset. */
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err = merge_ruleset(new_dom, ruleset);
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if (err)
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goto out_put_dom;
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return new_dom;
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||||
out_put_dom:
|
||||
landlock_put_ruleset(new_dom);
|
||||
return ERR_PTR(err);
|
||||
}
|
||||
|
||||
/*
|
||||
* The returned access has the same lifetime as @ruleset.
|
||||
*/
|
||||
const struct landlock_rule *landlock_find_rule(
|
||||
const struct landlock_ruleset *const ruleset,
|
||||
const struct landlock_object *const object)
|
||||
{
|
||||
const struct rb_node *node;
|
||||
|
||||
if (!object)
|
||||
return NULL;
|
||||
node = ruleset->root.rb_node;
|
||||
while (node) {
|
||||
struct landlock_rule *this = rb_entry(node,
|
||||
struct landlock_rule, node);
|
||||
|
||||
if (this->object == object)
|
||||
return this;
|
||||
if (this->object < object)
|
||||
node = node->rb_right;
|
||||
else
|
||||
node = node->rb_left;
|
||||
}
|
||||
return NULL;
|
||||
}
|
||||
|
|
@ -0,0 +1,165 @@
|
|||
/* SPDX-License-Identifier: GPL-2.0-only */
|
||||
/*
|
||||
* Landlock LSM - Ruleset management
|
||||
*
|
||||
* Copyright © 2016-2020 Mickaël Salaün <mic@digikod.net>
|
||||
* Copyright © 2018-2020 ANSSI
|
||||
*/
|
||||
|
||||
#ifndef _SECURITY_LANDLOCK_RULESET_H
|
||||
#define _SECURITY_LANDLOCK_RULESET_H
|
||||
|
||||
#include <linux/mutex.h>
|
||||
#include <linux/rbtree.h>
|
||||
#include <linux/refcount.h>
|
||||
#include <linux/workqueue.h>
|
||||
|
||||
#include "object.h"
|
||||
|
||||
/**
|
||||
* struct landlock_layer - Access rights for a given layer
|
||||
*/
|
||||
struct landlock_layer {
|
||||
/**
|
||||
* @level: Position of this layer in the layer stack.
|
||||
*/
|
||||
u16 level;
|
||||
/**
|
||||
* @access: Bitfield of allowed actions on the kernel object. They are
|
||||
* relative to the object type (e.g. %LANDLOCK_ACTION_FS_READ).
|
||||
*/
|
||||
u16 access;
|
||||
};
|
||||
|
||||
/**
|
||||
* struct landlock_rule - Access rights tied to an object
|
||||
*/
|
||||
struct landlock_rule {
|
||||
/**
|
||||
* @node: Node in the ruleset's red-black tree.
|
||||
*/
|
||||
struct rb_node node;
|
||||
/**
|
||||
* @object: Pointer to identify a kernel object (e.g. an inode). This
|
||||
* is used as a key for this ruleset element. This pointer is set once
|
||||
* and never modified. It always points to an allocated object because
|
||||
* each rule increments the refcount of its object.
|
||||
*/
|
||||
struct landlock_object *object;
|
||||
/**
|
||||
* @num_layers: Number of entries in @layers.
|
||||
*/
|
||||
u32 num_layers;
|
||||
/**
|
||||
* @layers: Stack of layers, from the latest to the newest, implemented
|
||||
* as a flexible array member (FAM).
|
||||
*/
|
||||
struct landlock_layer layers[];
|
||||
};
|
||||
|
||||
/**
|
||||
* struct landlock_hierarchy - Node in a ruleset hierarchy
|
||||
*/
|
||||
struct landlock_hierarchy {
|
||||
/**
|
||||
* @parent: Pointer to the parent node, or NULL if it is a root
|
||||
* Landlock domain.
|
||||
*/
|
||||
struct landlock_hierarchy *parent;
|
||||
/**
|
||||
* @usage: Number of potential children domains plus their parent
|
||||
* domain.
|
||||
*/
|
||||
refcount_t usage;
|
||||
};
|
||||
|
||||
/**
|
||||
* struct landlock_ruleset - Landlock ruleset
|
||||
*
|
||||
* This data structure must contain unique entries, be updatable, and quick to
|
||||
* match an object.
|
||||
*/
|
||||
struct landlock_ruleset {
|
||||
/**
|
||||
* @root: Root of a red-black tree containing &struct landlock_rule
|
||||
* nodes. Once a ruleset is tied to a process (i.e. as a domain), this
|
||||
* tree is immutable until @usage reaches zero.
|
||||
*/
|
||||
struct rb_root root;
|
||||
/**
|
||||
* @hierarchy: Enables hierarchy identification even when a parent
|
||||
* domain vanishes. This is needed for the ptrace protection.
|
||||
*/
|
||||
struct landlock_hierarchy *hierarchy;
|
||||
union {
|
||||
/**
|
||||
* @work_free: Enables to free a ruleset within a lockless
|
||||
* section. This is only used by
|
||||
* landlock_put_ruleset_deferred() when @usage reaches zero.
|
||||
* The fields @lock, @usage, @num_rules, @num_layers and
|
||||
* @fs_access_masks are then unused.
|
||||
*/
|
||||
struct work_struct work_free;
|
||||
struct {
|
||||
/**
|
||||
* @lock: Protects against concurrent modifications of
|
||||
* @root, if @usage is greater than zero.
|
||||
*/
|
||||
struct mutex lock;
|
||||
/**
|
||||
* @usage: Number of processes (i.e. domains) or file
|
||||
* descriptors referencing this ruleset.
|
||||
*/
|
||||
refcount_t usage;
|
||||
/**
|
||||
* @num_rules: Number of non-overlapping (i.e. not for
|
||||
* the same object) rules in this ruleset.
|
||||
*/
|
||||
u32 num_rules;
|
||||
/**
|
||||
* @num_layers: Number of layers that are used in this
|
||||
* ruleset. This enables to check that all the layers
|
||||
* allow an access request. A value of 0 identifies a
|
||||
* non-merged ruleset (i.e. not a domain).
|
||||
*/
|
||||
u32 num_layers;
|
||||
/**
|
||||
* @fs_access_masks: Contains the subset of filesystem
|
||||
* actions that are restricted by a ruleset. A domain
|
||||
* saves all layers of merged rulesets in a stack
|
||||
* (FAM), starting from the first layer to the last
|
||||
* one. These layers are used when merging rulesets,
|
||||
* for user space backward compatibility (i.e.
|
||||
* future-proof), and to properly handle merged
|
||||
* rulesets without overlapping access rights. These
|
||||
* layers are set once and never changed for the
|
||||
* lifetime of the ruleset.
|
||||
*/
|
||||
u16 fs_access_masks[];
|
||||
};
|
||||
};
|
||||
};
|
||||
|
||||
struct landlock_ruleset *landlock_create_ruleset(const u32 fs_access_mask);
|
||||
|
||||
void landlock_put_ruleset(struct landlock_ruleset *const ruleset);
|
||||
void landlock_put_ruleset_deferred(struct landlock_ruleset *const ruleset);
|
||||
|
||||
int landlock_insert_rule(struct landlock_ruleset *const ruleset,
|
||||
struct landlock_object *const object, const u32 access);
|
||||
|
||||
struct landlock_ruleset *landlock_merge_ruleset(
|
||||
struct landlock_ruleset *const parent,
|
||||
struct landlock_ruleset *const ruleset);
|
||||
|
||||
const struct landlock_rule *landlock_find_rule(
|
||||
const struct landlock_ruleset *const ruleset,
|
||||
const struct landlock_object *const object);
|
||||
|
||||
static inline void landlock_get_ruleset(struct landlock_ruleset *const ruleset)
|
||||
{
|
||||
if (ruleset)
|
||||
refcount_inc(&ruleset->usage);
|
||||
}
|
||||
|
||||
#endif /* _SECURITY_LANDLOCK_RULESET_H */
|
||||
Loading…
Reference in New Issue