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473 lines
12 KiB
473 lines
12 KiB
// 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 <[email protected]> |
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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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typeof(ruleset.fs_access_masks[0]) fs_access_mask = ~0; |
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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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BUILD_BUG_ON(fs_access_mask < LANDLOCK_MASK_ACCESS_FS); |
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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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.access = ~0, |
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}; |
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BUILD_BUG_ON(layer.level < LANDLOCK_MAX_NUM_LAYERS); |
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BUILD_BUG_ON(layer.access < LANDLOCK_MASK_ACCESS_FS); |
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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: |
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landlock_put_ruleset(new_dom); |
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return ERR_PTR(err); |
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} |
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/* |
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* The returned access has the same lifetime as @ruleset. |
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*/ |
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const struct landlock_rule *landlock_find_rule( |
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const struct landlock_ruleset *const ruleset, |
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const struct landlock_object *const object) |
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{ |
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const struct rb_node *node; |
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if (!object) |
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return NULL; |
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node = ruleset->root.rb_node; |
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while (node) { |
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struct landlock_rule *this = rb_entry(node, |
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struct landlock_rule, node); |
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if (this->object == object) |
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return this; |
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if (this->object < object) |
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node = node->rb_right; |
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else |
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node = node->rb_left; |
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} |
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return NULL; |
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}
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