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Message-ID: <20210204033057.GB29022@mail.hallyn.com>
Date: Wed, 3 Feb 2021 21:30:57 -0600
From: "Serge E. Hallyn" <serge@...lyn.com>
To: Mickaël Salaün <mic@...ikod.net>
Cc: James Morris <jmorris@...ei.org>, Jann Horn <jannh@...gle.com>,
"Serge E . Hallyn" <serge@...lyn.com>,
Al Viro <viro@...iv.linux.org.uk>,
Andrew Morton <akpm@...ux-foundation.org>,
Andy Lutomirski <luto@...capital.net>,
Anton Ivanov <anton.ivanov@...bridgegreys.com>,
Arnd Bergmann <arnd@...db.de>,
Casey Schaufler <casey@...aufler-ca.com>,
Jeff Dike <jdike@...toit.com>, Jonathan Corbet <corbet@....net>,
Kees Cook <keescook@...omium.org>,
Michael Kerrisk <mtk.manpages@...il.com>,
Richard Weinberger <richard@....at>, Shuah Khan <shuah@...nel.org>,
Vincent Dagonneau <vincent.dagonneau@....gouv.fr>,
kernel-hardening@...ts.openwall.com, linux-api@...r.kernel.org,
linux-arch@...r.kernel.org, linux-doc@...r.kernel.org,
linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-kselftest@...r.kernel.org,
linux-security-module@...r.kernel.org, x86@...nel.org,
Mickaël Salaün <mic@...ux.microsoft.com>
Subject: Re: [PATCH v28 02/12] landlock: Add ruleset and domain management
On Tue, Feb 02, 2021 at 05:27:00PM +0100, Mickaël Salaün wrote:
> From: Mickaël Salaün <mic@...ux.microsoft.com>
>
> 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@...ei.org>
> Cc: Jann Horn <jannh@...gle.com>
> Cc: Kees Cook <keescook@...omium.org>
> Cc: Serge E. Hallyn <serge@...lyn.com>
Acked-by: Serge Hallyn <serge@...lyn.com>
> Signed-off-by: Mickaël Salaün <mic@...ux.microsoft.com>
> ---
>
> Changes since v27:
> * Fix domains with layers of non-overlapping access rights.
> * Add stricter limit checks (same semantic).
> * Change the grow direction of a rule layer stack to make it the same as
> the new ruleset fs_access_masks stack (cosmetic change).
> * Cosmetic fix for a comment block.
>
> Changes since v26:
> * Fix spelling.
>
> Changes since v25:
> * Add build-time checks for the num_layers and num_rules variables
> according to LANDLOCK_MAX_NUM_LAYERS and LANDLOCK_MAX_NUM_RULES, and
> move these limits to a dedicated file.
> * Cosmetic variable renames.
>
> Changes since v24:
> * Update struct landlock_rule with a layer stack. This reverts "Always
> intersect access rights" from v24 and also adds the ability to tie
> access rights with their policy layer. As noted by Jann Horn, always
> intersecting access rights made some use cases uselessly more
> difficult to handle in user space. Thanks to this new stack, we still
> have a deterministic policy behavior whatever their level in the stack
> of policies, while using a "union" of accesses when building a
> ruleset. The implementation use a FAM to keep the access checks quick
> and memory efficient (4 bytes per layer per inode). Update
> insert_rule() accordingly.
>
> Changes since v23:
> * Always intersect access rights. Following the filesystem change
> logic, make ruleset updates more consistent by always intersecting
> access rights (boolean AND) instead of combining them (boolean OR) for
> the same layer. This defensive approach could also help avoid user
> space to inadvertently allow multiple access rights for the same
> object (e.g. write and execute access on a path hierarchy) instead of
> dealing with such inconsistency. This can happen when there is no
> deduplication of objects (e.g. paths and underlying inodes) whereas
> they get different access rights with landlock_add_rule(2).
> * Add extra checks to make sure that:
> - there is always an (allocated) object in each used rules;
> - when updating a ruleset with a new rule (i.e. not merging two
> rulesets), the ruleset doesn't contain multiple layers.
> * Hide merge parameter from the public landlock_insert_rule() API. This
> helps avoid misuse of this function.
> * Replace a remaining hardcoded 1 with SINGLE_DEPTH_NESTING.
>
> Changes since v22:
> * Explicitely use RB_ROOT and SINGLE_DEPTH_NESTING (suggested by Jann
> Horn).
> * Improve comments and fix spelling (suggested by Jann Horn).
>
> Changes since v21:
> * Add and clean up comments.
>
> Changes since v18:
> * Account rulesets to kmemcg.
> * Remove struct holes.
> * Cosmetic changes.
>
> Changes since v17:
> * Move include/uapi/linux/landlock.h and _LANDLOCK_ACCESS_FS_* to a
> following patch.
>
> Changes since v16:
> * Allow enforcement of empty ruleset, which enables deny-all policies.
>
> Changes since v15:
> * Replace layer_levels and layer_depth with a bitfield of layers, cf.
> filesystem commit.
> * Rename the LANDLOCK_ACCESS_FS_{UNLINK,RMDIR} with
> LANDLOCK_ACCESS_FS_REMOVE_{FILE,DIR} because it makes sense to use
> them for the action of renaming a file or a directory, which may lead
> to the removal of the source file or directory. Removes the
> LANDLOCK_ACCESS_FS_{LINK_TO,RENAME_FROM,RENAME_TO} which are now
> replaced with LANDLOCK_ACCESS_FS_REMOVE_{FILE,DIR} and
> LANDLOCK_ACCESS_FS_MAKE_* .
> * Update the documentation accordingly and highlight how the access
> rights are taken into account.
> * Change nb_rules from atomic_t to u32 because it is not use anymore by
> show_fdinfo().
> * Add safeguard for level variables types.
> * Check max number of rules.
> * Replace struct landlock_access (self and beneath bitfields) with one
> bitfield.
> * Remove useless variable.
> * Add comments.
>
> Changes since v14:
> * Simplify the object, rule and ruleset management at the expense of a
> less aggressive memory freeing (contributed by Jann Horn, with
> additional modifications):
> - Make a domain immutable (remove the opportunistic cleaning).
> - Remove RCU pointers.
> - Merge struct landlock_ref and struct landlock_ruleset_elem into
> landlock_rule: get ride of rule's RCU.
> - Adjust union.
> - Remove the landlock_insert_rule() check about a new object with the
> same address as a previously disabled one, because it is not
> possible to disable a rule anymore.
> Cf. https://lore.kernel.org/lkml/CAG48ez21bEn0wL1bbmTiiu8j9jP5iEWtHOwz4tURUJ+ki0ydYw@mail.gmail.com/
> * Fix nested domains by implementing a notion of layer level and depth:
> - Update landlock_insert_rule() to manage such layers.
> - Add an inherit_ruleset() helper to properly create a new domain.
> - Rename landlock_find_access() to landlock_find_rule() and return a
> full rule reference.
> - Add a layer_level and a layer_depth fields to struct landlock_rule.
> - Add a top_layer_level field to struct landlock_ruleset.
> * Remove access rights that may be required for FD-only requests:
> truncate, getattr, lock, chmod, chown, chgrp, ioctl. This will be
> handle in a future evolution of Landlock, but right now the goal is to
> lighten the code to ease review.
> * Remove LANDLOCK_ACCESS_FS_OPEN and rename
> LANDLOCK_ACCESS_FS_{READ,WRITE} with a FILE suffix.
> * Rename LANDLOCK_ACCESS_FS_READDIR to match the *_FILE pattern.
> * Remove LANDLOCK_ACCESS_FS_MAP which was useless.
> * Fix memory leak in put_hierarchy() (reported by Jann Horn).
> * Fix user-after-free and rename free_ruleset() (reported by Jann Horn).
> * Replace the for loops with rbtree_postorder_for_each_entry_safe().
> * Constify variables.
> * Only use refcount_inc() through getter helpers.
> * Change Landlock_insert_ruleset_access() to
> Landlock_insert_ruleset_rule().
> * Rename landlock_put_ruleset_enqueue() to landlock_put_ruleset_deferred().
> * Improve kernel documentation and add a warning about the unhandled
> access/syscall families.
> * Move ABI check to syscall.c .
>
> Changes since v13:
> * New implementation, inspired by the previous inode eBPF map, but
> agnostic to the underlying kernel object.
>
> Previous changes:
> https://lore.kernel.org/lkml/20190721213116.23476-7-mic@digikod.net/
> ---
> security/landlock/Makefile | 2 +-
> security/landlock/limits.h | 17 ++
> security/landlock/ruleset.c | 469 ++++++++++++++++++++++++++++++++++++
> security/landlock/ruleset.h | 165 +++++++++++++
> 4 files changed, 652 insertions(+), 1 deletion(-)
> create mode 100644 security/landlock/limits.h
> create mode 100644 security/landlock/ruleset.c
> create mode 100644 security/landlock/ruleset.h
>
> diff --git a/security/landlock/Makefile b/security/landlock/Makefile
> index cb6deefbf4c0..d846eba445bb 100644
> --- a/security/landlock/Makefile
> +++ b/security/landlock/Makefile
> @@ -1,3 +1,3 @@
> obj-$(CONFIG_SECURITY_LANDLOCK) := landlock.o
>
> -landlock-y := object.o
> +landlock-y := object.o ruleset.o
> diff --git a/security/landlock/limits.h b/security/landlock/limits.h
> new file mode 100644
> index 000000000000..b734f597bb0e
> --- /dev/null
> +++ b/security/landlock/limits.h
> @@ -0,0 +1,17 @@
> +/* SPDX-License-Identifier: GPL-2.0-only */
> +/*
> + * Landlock LSM - Limits for different components
> + *
> + * Copyright © 2016-2020 Mickaël Salaün <mic@...ikod.net>
> + * Copyright © 2018-2020 ANSSI
> + */
> +
> +#ifndef _SECURITY_LANDLOCK_LIMITS_H
> +#define _SECURITY_LANDLOCK_LIMITS_H
> +
> +#include <linux/limits.h>
> +
> +#define LANDLOCK_MAX_NUM_LAYERS 64
> +#define LANDLOCK_MAX_NUM_RULES U32_MAX
> +
> +#endif /* _SECURITY_LANDLOCK_LIMITS_H */
> diff --git a/security/landlock/ruleset.c b/security/landlock/ruleset.c
> new file mode 100644
> index 000000000000..59c86126ea1c
> --- /dev/null
> +++ b/security/landlock/ruleset.c
> @@ -0,0 +1,469 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * Landlock LSM - Ruleset management
> + *
> + * Copyright © 2016-2020 Mickaël Salaün <mic@...ikod.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 u32 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 put_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,
> + };
> +
> + 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.
> + * @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);
> + put_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,
> + };
> +
> + BUILD_BUG_ON(layer.level < LANDLOCK_MAX_NUM_LAYERS);
> +}
> +
> +/* @ruleset must be locked by the caller. */
> +int landlock_insert_rule(struct landlock_ruleset *const ruleset,
> + struct landlock_object *const object, const u32 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)
> + put_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;
> +}
> diff --git a/security/landlock/ruleset.h b/security/landlock/ruleset.h
> new file mode 100644
> index 000000000000..6b1198458b37
> --- /dev/null
> +++ b/security/landlock/ruleset.h
> @@ -0,0 +1,165 @@
> +/* SPDX-License-Identifier: GPL-2.0-only */
> +/*
> + * Landlock LSM - Ruleset management
> + *
> + * Copyright © 2016-2020 Mickaël Salaün <mic@...ikod.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: Guards 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 */
> --
> 2.30.0
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