// SPDX-License-Identifier: GPL-2.0-only
/*
* Landlock LSM - Ruleset management
*
* Copyright © 2016-2020 Mickaël Salaün <[email protected]>
* 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, 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_inode = RB_ROOT;
#if IS_ENABLED(CONFIG_INET)
new_ruleset->root_net_port = RB_ROOT;
#endif /* IS_ENABLED(CONFIG_INET) */
new_ruleset->num_layers = num_layers;
/*
* hierarchy = NULL
* num_rules = 0
* access_masks[] = 0
*/
return new_ruleset;
}
struct landlock_ruleset *
landlock_create_ruleset(const access_mask_t fs_access_mask,
const access_mask_t net_access_mask,
const access_mask_t scope_mask)
{
struct landlock_ruleset *new_ruleset;
/* Informs about useless ruleset. */
if (!fs_access_mask && !net_access_mask && !scope_mask)
return ERR_PTR(-ENOMSG);
new_ruleset = create_ruleset(1);
if (IS_ERR(new_ruleset))
return new_ruleset;
if (fs_access_mask)
landlock_add_fs_access_mask(new_ruleset, fs_access_mask, 0);
if (net_access_mask)
landlock_add_net_access_mask(new_ruleset, net_access_mask, 0);
if (scope_mask)
landlock_add_scope_mask(new_ruleset, scope_mask, 0);
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 bool is_object_pointer(const enum landlock_key_type key_type)
{
switch (key_type) {
case LANDLOCK_KEY_INODE:
return true;
#if IS_ENABLED(CONFIG_INET)
case LANDLOCK_KEY_NET_PORT:
return false;
#endif /* IS_ENABLED(CONFIG_INET) */
default:
WARN_ON_ONCE(1);
return false;
}
}
static struct landlock_rule *
create_rule(const struct landlock_id id,
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);
if (is_object_pointer(id.type)) {
/* This should be catched by insert_rule(). */
WARN_ON_ONCE(!id.key.object);
landlock_get_object(id.key.object);
}
new_rule->key = id.key;
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 struct rb_root *get_root(struct landlock_ruleset *const ruleset,
const enum landlock_key_type key_type)
{
switch (key_type) {
case LANDLOCK_KEY_INODE:
return &ruleset->root_inode;
#if IS_ENABLED(CONFIG_INET)
case LANDLOCK_KEY_NET_PORT:
return &ruleset->root_net_port;
#endif /* IS_ENABLED(CONFIG_INET) */
default:
WARN_ON_ONCE(1);
return ERR_PTR(-EINVAL);
}
}
static void free_rule(struct landlock_rule *const rule,
const enum landlock_key_type key_type)
{
might_sleep();
if (!rule)
return;
if (is_object_pointer(key_type))
landlock_put_object(rule->key.object);
kfree(rule);
}
static void build_check_ruleset(void)
{
const struct landlock_ruleset ruleset = {
.num_rules = ~0,
.num_layers = ~0,
};
BUILD_BUG_ON(ruleset.num_rules < LANDLOCK_MAX_NUM_RULES);
BUILD_BUG_ON(ruleset.num_layers < LANDLOCK_MAX_NUM_LAYERS);
}
/**
* insert_rule - Create and insert a rule in a ruleset
*
* @ruleset: The ruleset to be updated.
* @id: The ID to build the new rule with. The underlying kernel object, if
* any, 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,
const struct landlock_id id,
const struct landlock_layer (*const layers)[],
const size_t num_layers)
{
struct rb_node **walker_node;
struct rb_node *parent_node = NULL;
struct landlock_rule *new_rule;
struct rb_root *root;
might_sleep();
lockdep_assert_held(&ruleset->lock);
if (WARN_ON_ONCE(!layers))
return -ENOENT;
if (is_object_pointer(id.type) && WARN_ON_ONCE(!id.key.object))
return -ENOENT;
root = get_root(ruleset, id.type);
if (IS_ERR(root))
return PTR_ERR(root);
walker_node = &root->rb_node;
while (*walker_node) {
struct landlock_rule *const this =
rb_entry(*walker_node, struct landlock_rule, node);
if (this->key.data != id.key.data) {
parent_node = *walker_node;
if (this->key.data < id.key.data)
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(id, &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, root);
free_rule(this, id.type);
return 0;
}
/* There is no match for @id. */
build_check_ruleset();
if (ruleset->num_rules >= LANDLOCK_MAX_NUM_RULES)
return -E2BIG;
new_rule = create_rule(id, 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, 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,
const struct landlock_id id,
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, id, &layers, ARRAY_SIZE(layers));
}
static 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_tree(struct landlock_ruleset *const dst,
struct landlock_ruleset *const src,
const enum landlock_key_type key_type)
{
struct landlock_rule *walker_rule, *next_rule;
struct rb_root *src_root;
int err = 0;
might_sleep();
lockdep_assert_held(&dst->lock);
lockdep_assert_held(&src->lock);
src_root = get_root(src, key_type);
if (IS_ERR(src_root))
return PTR_ERR(src_root);
/* 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,
} };
const struct landlock_id id = {
.key = walker_rule->key,
.type = key_type,
};
if (WARN_ON_ONCE(walker_rule->num_layers != 1))
return -EINVAL;
if (WARN_ON_ONCE(walker_rule->layers[0].level != 0))
return -EINVAL;
layers[0].access = walker_rule->layers[0].access;
err = insert_rule(dst, id, &layers, ARRAY_SIZE(layers));
if (err)
return err;
}
return err;
}
static int merge_ruleset(struct landlock_ruleset *const dst,
struct landlock_ruleset *const src)
{
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->access_masks[dst->num_layers - 1] = src->access_masks[0];
/* Merges the @src inode tree. */
err = merge_tree(dst, src, LANDLOCK_KEY_INODE);
if (err)
goto out_unlock;
#if IS_ENABLED(CONFIG_INET)
/* Merges the @src network port tree. */
err = merge_tree(dst, src, LANDLOCK_KEY_NET_PORT);
if (err)
goto out_unlock;
#endif /* IS_ENABLED(CONFIG_INET) */
out_unlock:
mutex_unlock(&src->lock);
mutex_unlock(&dst->lock);
return err;
}
static int inherit_tree(struct landlock_ruleset *const parent,
struct landlock_ruleset *const child,
const enum landlock_key_type key_type)
{
struct landlock_rule *walker_rule, *next_rule;
struct rb_root *parent_root;
int err = 0;
might_sleep();
lockdep_assert_held(&parent->lock);
lockdep_assert_held(&child->lock);
parent_root = get_root(parent, key_type);
if (IS_ERR(parent_root))
return PTR_ERR(parent_root);
/* Copies the @parent inode or network tree. */
rbtree_postorder_for_each_entry_safe(walker_rule, next_rule,
parent_root, node) {
const struct landlock_id id = {
.key = walker_rule->key,
.type = key_type,
};
err = insert_rule(child, id, &walker_rule->layers,
walker_rule->num_layers);
if (err)
return err;
}
return err;
}
static int inherit_ruleset(struct landlock_ruleset *const parent,
struct landlock_ruleset *const child)
{
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 inode tree. */
err = inherit_tree(parent, child, LANDLOCK_KEY_INODE);
if (err)
goto out_unlock;
#if IS_ENABLED(CONFIG_INET)
/* Copies the @parent network port tree. */
err = inherit_tree(parent, child, LANDLOCK_KEY_NET_PORT);
if (err)
goto out_unlock;
#endif /* IS_ENABLED(CONFIG_INET) */
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->access_masks, parent->access_masks,
flex_array_size(parent, 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_inode,
node)
free_rule(freeme, LANDLOCK_KEY_INODE);
#if IS_ENABLED(CONFIG_INET)
rbtree_postorder_for_each_entry_safe(freeme, next,
&ruleset->root_net_port, node)
free_rule(freeme, LANDLOCK_KEY_NET_PORT);
#endif /* IS_ENABLED(CONFIG_INET) */
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_id id)
{
const struct rb_root *root;
const struct rb_node *node;
root = get_root((struct landlock_ruleset *)ruleset, id.type);
if (IS_ERR(root))
return NULL;
node = root->rb_node;
while (node) {
struct landlock_rule *this =
rb_entry(node, struct landlock_rule, node);
if (this->key.data == id.key.data)
return this;
if (this->key.data < id.key.data)
node = node->rb_right;
else
node = node->rb_left;
}
return NULL;
}
/*
* @layer_masks is read and may be updated according to the access request and
* the matching rule.
* @masks_array_size must be equal to ARRAY_SIZE(*layer_masks).
*
* Returns true if the request is allowed (i.e. relevant layer masks for the
* request are empty).
*/
bool landlock_unmask_layers(const struct landlock_rule *const rule,
const access_mask_t access_request,
layer_mask_t (*const layer_masks)[],
const size_t masks_array_size)
{
size_t layer_level;
if (!access_request || !layer_masks)
return true;
if (!rule)
return false;
/*
* An access is granted if, for each policy layer, at least one rule
* encountered on the pathwalk grants the requested access,
* regardless of its position in the layer stack. We must then check
* the remaining layers for each inode, from the first added layer to
* the last one. When there is multiple requested accesses, for each
* policy layer, the full set of requested accesses may not be granted
* by only one rule, but by the union (binary OR) of multiple rules.
* E.g. /a/b <execute> + /a <read> => /a/b <execute + read>
*/
for (layer_level = 0; layer_level < rule->num_layers; layer_level++) {
const struct landlock_layer *const layer =
&rule->layers[layer_level];
const layer_mask_t layer_bit = BIT_ULL(layer->level - 1);
const unsigned long access_req = access_request;
unsigned long access_bit;
bool is_empty;
/*
* Records in @layer_masks which layer grants access to each
* requested access.
*/
is_empty = true;
for_each_set_bit(access_bit, &access_req, masks_array_size) {
if (layer->access & BIT_ULL(access_bit))
(*layer_masks)[access_bit] &= ~layer_bit;
is_empty = is_empty && !(*layer_masks)[access_bit];
}
if (is_empty)
return true;
}
return false;
}
typedef access_mask_t
get_access_mask_t(const struct landlock_ruleset *const ruleset,
const u16 layer_level);
/**
* landlock_init_layer_masks - Initialize layer masks from an access request
*
* Populates @layer_masks such that for each access right in @access_request,
* the bits for all the layers are set where this access right is handled.
*
* @domain: The domain that defines the current restrictions.
* @access_request: The requested access rights to check.
* @layer_masks: It must contain %LANDLOCK_NUM_ACCESS_FS or
* %LANDLOCK_NUM_ACCESS_NET elements according to @key_type.
* @key_type: The key type to switch between access masks of different types.
*
* Returns: An access mask where each access right bit is set which is handled
* in any of the active layers in @domain.
*/
access_mask_t
landlock_init_layer_masks(const struct landlock_ruleset *const domain,
const access_mask_t access_request,
layer_mask_t (*const layer_masks)[],
const enum landlock_key_type key_type)
{
access_mask_t handled_accesses = 0;
size_t layer_level, num_access;
get_access_mask_t *get_access_mask;
switch (key_type) {
case LANDLOCK_KEY_INODE:
get_access_mask = landlock_get_fs_access_mask;
num_access = LANDLOCK_NUM_ACCESS_FS;
break;
#if IS_ENABLED(CONFIG_INET)
case LANDLOCK_KEY_NET_PORT:
get_access_mask = landlock_get_net_access_mask;
num_access = LANDLOCK_NUM_ACCESS_NET;
break;
#endif /* IS_ENABLED(CONFIG_INET) */
default:
WARN_ON_ONCE(1);
return 0;
}
memset(layer_masks, 0,
array_size(sizeof((*layer_masks)[0]), num_access));
/* An empty access request can happen because of O_WRONLY | O_RDWR. */
if (!access_request)
return 0;
/* Saves all handled accesses per layer. */
for (layer_level = 0; layer_level < domain->num_layers; layer_level++) {
const unsigned long access_req = access_request;
const access_mask_t access_mask =
get_access_mask(domain, layer_level);
unsigned long access_bit;
for_each_set_bit(access_bit, &access_req, num_access) {
if (BIT_ULL(access_bit) & access_mask) {
(*layer_masks)[access_bit] |=
BIT_ULL(layer_level);
handled_accesses |= BIT_ULL(access_bit);
}
}
}
return handled_accesses;
}
Codebase Browser
linux