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-rw-r--r--security/landlock/ruleset.c475
1 files changed, 475 insertions, 0 deletions
diff --git a/security/landlock/ruleset.c b/security/landlock/ruleset.c
new file mode 100644
index 000000000..996484f98
--- /dev/null
+++ b/security/landlock/ruleset.c
@@ -0,0 +1,475 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Landlock LSM - Ruleset management
+ *
+ * Copyright © 2016-2020 Mickaël Salaün <mic@digikod.net>
+ * Copyright © 2018-2020 ANSSI
+ */
+
+#include <linux/bits.h>
+#include <linux/bug.h>
+#include <linux/compiler_types.h>
+#include <linux/err.h>
+#include <linux/errno.h>
+#include <linux/kernel.h>
+#include <linux/lockdep.h>
+#include <linux/overflow.h>
+#include <linux/rbtree.h>
+#include <linux/refcount.h>
+#include <linux/slab.h>
+#include <linux/spinlock.h>
+#include <linux/workqueue.h>
+
+#include "limits.h"
+#include "object.h"
+#include "ruleset.h"
+
+static struct landlock_ruleset *create_ruleset(const u32 num_layers)
+{
+ struct landlock_ruleset *new_ruleset;
+
+ new_ruleset =
+ kzalloc(struct_size(new_ruleset, fs_access_masks, num_layers),
+ GFP_KERNEL_ACCOUNT);
+ if (!new_ruleset)
+ return ERR_PTR(-ENOMEM);
+ refcount_set(&new_ruleset->usage, 1);
+ mutex_init(&new_ruleset->lock);
+ new_ruleset->root = RB_ROOT;
+ new_ruleset->num_layers = num_layers;
+ /*
+ * hierarchy = NULL
+ * num_rules = 0
+ * fs_access_masks[] = 0
+ */
+ return new_ruleset;
+}
+
+struct landlock_ruleset *
+landlock_create_ruleset(const access_mask_t fs_access_mask)
+{
+ struct landlock_ruleset *new_ruleset;
+
+ /* Informs about useless ruleset. */
+ if (!fs_access_mask)
+ return ERR_PTR(-ENOMSG);
+ new_ruleset = create_ruleset(1);
+ if (!IS_ERR(new_ruleset))
+ new_ruleset->fs_access_masks[0] = fs_access_mask;
+ return new_ruleset;
+}
+
+static void build_check_rule(void)
+{
+ const struct landlock_rule rule = {
+ .num_layers = ~0,
+ };
+
+ BUILD_BUG_ON(rule.num_layers < LANDLOCK_MAX_NUM_LAYERS);
+}
+
+static struct landlock_rule *
+create_rule(struct landlock_object *const object,
+ const struct landlock_layer (*const layers)[], const u32 num_layers,
+ const struct landlock_layer *const new_layer)
+{
+ struct landlock_rule *new_rule;
+ u32 new_num_layers;
+
+ build_check_rule();
+ if (new_layer) {
+ /* Should already be checked by landlock_merge_ruleset(). */
+ if (WARN_ON_ONCE(num_layers >= LANDLOCK_MAX_NUM_LAYERS))
+ return ERR_PTR(-E2BIG);
+ new_num_layers = num_layers + 1;
+ } else {
+ new_num_layers = num_layers;
+ }
+ new_rule = kzalloc(struct_size(new_rule, layers, new_num_layers),
+ GFP_KERNEL_ACCOUNT);
+ if (!new_rule)
+ return ERR_PTR(-ENOMEM);
+ RB_CLEAR_NODE(&new_rule->node);
+ landlock_get_object(object);
+ new_rule->object = object;
+ new_rule->num_layers = new_num_layers;
+ /* Copies the original layer stack. */
+ memcpy(new_rule->layers, layers,
+ flex_array_size(new_rule, layers, num_layers));
+ if (new_layer)
+ /* Adds a copy of @new_layer on the layer stack. */
+ new_rule->layers[new_rule->num_layers - 1] = *new_layer;
+ return new_rule;
+}
+
+static void free_rule(struct landlock_rule *const rule)
+{
+ might_sleep();
+ if (!rule)
+ return;
+ landlock_put_object(rule->object);
+ kfree(rule);
+}
+
+static void build_check_ruleset(void)
+{
+ const struct landlock_ruleset ruleset = {
+ .num_rules = ~0,
+ .num_layers = ~0,
+ };
+ typeof(ruleset.fs_access_masks[0]) fs_access_mask = ~0;
+
+ BUILD_BUG_ON(ruleset.num_rules < LANDLOCK_MAX_NUM_RULES);
+ BUILD_BUG_ON(ruleset.num_layers < LANDLOCK_MAX_NUM_LAYERS);
+ BUILD_BUG_ON(fs_access_mask < LANDLOCK_MASK_ACCESS_FS);
+}
+
+/**
+ * insert_rule - Create and insert a rule in a ruleset
+ *
+ * @ruleset: The ruleset to be updated.
+ * @object: The object to build the new rule with. The underlying kernel
+ * object must be held by the caller.
+ * @layers: One or multiple layers to be copied into the new rule.
+ * @num_layers: The number of @layers entries.
+ *
+ * When user space requests to add a new rule to a ruleset, @layers only
+ * contains one entry and this entry is not assigned to any level. In this
+ * case, the new rule will extend @ruleset, similarly to a boolean OR between
+ * access rights.
+ *
+ * When merging a ruleset in a domain, or copying a domain, @layers will be
+ * added to @ruleset as new constraints, similarly to a boolean AND between
+ * access rights.
+ */
+static int insert_rule(struct landlock_ruleset *const ruleset,
+ struct landlock_object *const object,
+ const struct landlock_layer (*const layers)[],
+ size_t num_layers)
+{
+ struct rb_node **walker_node;
+ struct rb_node *parent_node = NULL;
+ struct landlock_rule *new_rule;
+
+ might_sleep();
+ lockdep_assert_held(&ruleset->lock);
+ if (WARN_ON_ONCE(!object || !layers))
+ return -ENOENT;
+ walker_node = &(ruleset->root.rb_node);
+ while (*walker_node) {
+ struct landlock_rule *const this =
+ rb_entry(*walker_node, struct landlock_rule, node);
+
+ if (this->object != object) {
+ parent_node = *walker_node;
+ if (this->object < object)
+ walker_node = &((*walker_node)->rb_right);
+ else
+ walker_node = &((*walker_node)->rb_left);
+ continue;
+ }
+
+ /* Only a single-level layer should match an existing rule. */
+ if (WARN_ON_ONCE(num_layers != 1))
+ return -EINVAL;
+
+ /* If there is a matching rule, updates it. */
+ if ((*layers)[0].level == 0) {
+ /*
+ * Extends access rights when the request comes from
+ * landlock_add_rule(2), i.e. @ruleset is not a domain.
+ */
+ if (WARN_ON_ONCE(this->num_layers != 1))
+ return -EINVAL;
+ if (WARN_ON_ONCE(this->layers[0].level != 0))
+ return -EINVAL;
+ this->layers[0].access |= (*layers)[0].access;
+ return 0;
+ }
+
+ if (WARN_ON_ONCE(this->layers[0].level == 0))
+ return -EINVAL;
+
+ /*
+ * Intersects access rights when it is a merge between a
+ * ruleset and a domain.
+ */
+ new_rule = create_rule(object, &this->layers, this->num_layers,
+ &(*layers)[0]);
+ if (IS_ERR(new_rule))
+ return PTR_ERR(new_rule);
+ rb_replace_node(&this->node, &new_rule->node, &ruleset->root);
+ free_rule(this);
+ return 0;
+ }
+
+ /* There is no match for @object. */
+ build_check_ruleset();
+ if (ruleset->num_rules >= LANDLOCK_MAX_NUM_RULES)
+ return -E2BIG;
+ new_rule = create_rule(object, layers, num_layers, NULL);
+ if (IS_ERR(new_rule))
+ return PTR_ERR(new_rule);
+ rb_link_node(&new_rule->node, parent_node, walker_node);
+ rb_insert_color(&new_rule->node, &ruleset->root);
+ ruleset->num_rules++;
+ return 0;
+}
+
+static void build_check_layer(void)
+{
+ const struct landlock_layer layer = {
+ .level = ~0,
+ .access = ~0,
+ };
+
+ BUILD_BUG_ON(layer.level < LANDLOCK_MAX_NUM_LAYERS);
+ BUILD_BUG_ON(layer.access < LANDLOCK_MASK_ACCESS_FS);
+}
+
+/* @ruleset must be locked by the caller. */
+int landlock_insert_rule(struct landlock_ruleset *const ruleset,
+ struct landlock_object *const object,
+ const access_mask_t access)
+{
+ struct landlock_layer layers[] = { {
+ .access = access,
+ /* When @level is zero, insert_rule() extends @ruleset. */
+ .level = 0,
+ } };
+
+ build_check_layer();
+ return insert_rule(ruleset, object, &layers, ARRAY_SIZE(layers));
+}
+
+static inline void get_hierarchy(struct landlock_hierarchy *const hierarchy)
+{
+ if (hierarchy)
+ refcount_inc(&hierarchy->usage);
+}
+
+static void put_hierarchy(struct landlock_hierarchy *hierarchy)
+{
+ while (hierarchy && refcount_dec_and_test(&hierarchy->usage)) {
+ const struct landlock_hierarchy *const freeme = hierarchy;
+
+ hierarchy = hierarchy->parent;
+ kfree(freeme);
+ }
+}
+
+static int merge_ruleset(struct landlock_ruleset *const dst,
+ struct landlock_ruleset *const src)
+{
+ struct landlock_rule *walker_rule, *next_rule;
+ int err = 0;
+
+ might_sleep();
+ /* Should already be checked by landlock_merge_ruleset() */
+ if (WARN_ON_ONCE(!src))
+ return 0;
+ /* Only merge into a domain. */
+ if (WARN_ON_ONCE(!dst || !dst->hierarchy))
+ return -EINVAL;
+
+ /* Locks @dst first because we are its only owner. */
+ mutex_lock(&dst->lock);
+ mutex_lock_nested(&src->lock, SINGLE_DEPTH_NESTING);
+
+ /* Stacks the new layer. */
+ if (WARN_ON_ONCE(src->num_layers != 1 || dst->num_layers < 1)) {
+ err = -EINVAL;
+ goto out_unlock;
+ }
+ dst->fs_access_masks[dst->num_layers - 1] = src->fs_access_masks[0];
+
+ /* Merges the @src tree. */
+ rbtree_postorder_for_each_entry_safe(walker_rule, next_rule, &src->root,
+ node) {
+ struct landlock_layer layers[] = { {
+ .level = dst->num_layers,
+ } };
+
+ if (WARN_ON_ONCE(walker_rule->num_layers != 1)) {
+ err = -EINVAL;
+ goto out_unlock;
+ }
+ if (WARN_ON_ONCE(walker_rule->layers[0].level != 0)) {
+ err = -EINVAL;
+ goto out_unlock;
+ }
+ layers[0].access = walker_rule->layers[0].access;
+ err = insert_rule(dst, walker_rule->object, &layers,
+ ARRAY_SIZE(layers));
+ if (err)
+ goto out_unlock;
+ }
+
+out_unlock:
+ mutex_unlock(&src->lock);
+ mutex_unlock(&dst->lock);
+ return err;
+}
+
+static int inherit_ruleset(struct landlock_ruleset *const parent,
+ struct landlock_ruleset *const child)
+{
+ struct landlock_rule *walker_rule, *next_rule;
+ int err = 0;
+
+ might_sleep();
+ if (!parent)
+ return 0;
+
+ /* Locks @child first because we are its only owner. */
+ mutex_lock(&child->lock);
+ mutex_lock_nested(&parent->lock, SINGLE_DEPTH_NESTING);
+
+ /* Copies the @parent tree. */
+ rbtree_postorder_for_each_entry_safe(walker_rule, next_rule,
+ &parent->root, node) {
+ err = insert_rule(child, walker_rule->object,
+ &walker_rule->layers,
+ walker_rule->num_layers);
+ if (err)
+ goto out_unlock;
+ }
+
+ if (WARN_ON_ONCE(child->num_layers <= parent->num_layers)) {
+ err = -EINVAL;
+ goto out_unlock;
+ }
+ /* Copies the parent layer stack and leaves a space for the new layer. */
+ memcpy(child->fs_access_masks, parent->fs_access_masks,
+ flex_array_size(parent, fs_access_masks, parent->num_layers));
+
+ if (WARN_ON_ONCE(!parent->hierarchy)) {
+ err = -EINVAL;
+ goto out_unlock;
+ }
+ get_hierarchy(parent->hierarchy);
+ child->hierarchy->parent = parent->hierarchy;
+
+out_unlock:
+ mutex_unlock(&parent->lock);
+ mutex_unlock(&child->lock);
+ return err;
+}
+
+static void free_ruleset(struct landlock_ruleset *const ruleset)
+{
+ struct landlock_rule *freeme, *next;
+
+ might_sleep();
+ rbtree_postorder_for_each_entry_safe(freeme, next, &ruleset->root, node)
+ free_rule(freeme);
+ put_hierarchy(ruleset->hierarchy);
+ kfree(ruleset);
+}
+
+void landlock_put_ruleset(struct landlock_ruleset *const ruleset)
+{
+ might_sleep();
+ if (ruleset && refcount_dec_and_test(&ruleset->usage))
+ free_ruleset(ruleset);
+}
+
+static void free_ruleset_work(struct work_struct *const work)
+{
+ struct landlock_ruleset *ruleset;
+
+ ruleset = container_of(work, struct landlock_ruleset, work_free);
+ free_ruleset(ruleset);
+}
+
+void landlock_put_ruleset_deferred(struct landlock_ruleset *const ruleset)
+{
+ if (ruleset && refcount_dec_and_test(&ruleset->usage)) {
+ INIT_WORK(&ruleset->work_free, free_ruleset_work);
+ schedule_work(&ruleset->work_free);
+ }
+}
+
+/**
+ * landlock_merge_ruleset - Merge a ruleset with a domain
+ *
+ * @parent: Parent domain.
+ * @ruleset: New ruleset to be merged.
+ *
+ * Returns the intersection of @parent and @ruleset, or returns @parent if
+ * @ruleset is empty, or returns a duplicate of @ruleset if @parent is empty.
+ */
+struct landlock_ruleset *
+landlock_merge_ruleset(struct landlock_ruleset *const parent,
+ struct landlock_ruleset *const ruleset)
+{
+ struct landlock_ruleset *new_dom;
+ u32 num_layers;
+ int err;
+
+ might_sleep();
+ if (WARN_ON_ONCE(!ruleset || parent == ruleset))
+ return ERR_PTR(-EINVAL);
+
+ if (parent) {
+ if (parent->num_layers >= LANDLOCK_MAX_NUM_LAYERS)
+ return ERR_PTR(-E2BIG);
+ num_layers = parent->num_layers + 1;
+ } else {
+ num_layers = 1;
+ }
+
+ /* Creates a new domain... */
+ new_dom = create_ruleset(num_layers);
+ if (IS_ERR(new_dom))
+ return new_dom;
+ new_dom->hierarchy =
+ kzalloc(sizeof(*new_dom->hierarchy), GFP_KERNEL_ACCOUNT);
+ if (!new_dom->hierarchy) {
+ err = -ENOMEM;
+ goto out_put_dom;
+ }
+ refcount_set(&new_dom->hierarchy->usage, 1);
+
+ /* ...as a child of @parent... */
+ err = inherit_ruleset(parent, new_dom);
+ if (err)
+ goto out_put_dom;
+
+ /* ...and including @ruleset. */
+ err = merge_ruleset(new_dom, ruleset);
+ if (err)
+ goto out_put_dom;
+
+ return new_dom;
+
+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;
+}