Re: [RFC PATCH v4 03/15] landlock: landlock_find/insert_rule refactoring

[Konstantin Meskhidze <konstantin.meskhidze@huawei.com>]

3/16/2022 11:27 AM, Mickaël Salaün пишет:
> 
> On 09/03/2022 14:44, Konstantin Meskhidze wrote:
>> A new object union added to support a socket port
>> rule type. To support it landlock_insert_rule() and
>> landlock_find_rule() were refactored. Now adding
>> or searching a rule in a ruleset depends on a
>> rule_type argument provided in refactored
>> functions mentioned above.
>>
>> Signed-off-by: Konstantin Meskhidze <konstantin.meskhidze@huawei.com>
>> ---
>>
>> Changes since v3:
>> * Split commit.
>> * Refactoring landlock_insert_rule and landlock_find_rule functions.
>> * Rename new_ruleset->root_inode.
>>
>> ---
>>   security/landlock/fs.c      |   5 +-
>>   security/landlock/ruleset.c | 108 +++++++++++++++++++++++++-----------
>>   security/landlock/ruleset.h |  26 +++++----
>>   3 files changed, 94 insertions(+), 45 deletions(-)
>>
>> diff --git a/security/landlock/fs.c b/security/landlock/fs.c
>> index 97f5c455f5a7..1497948d754f 100644
>> --- a/security/landlock/fs.c
>> +++ b/security/landlock/fs.c
>> @@ -168,7 +168,7 @@ int landlock_append_fs_rule(struct 
>> landlock_ruleset *const ruleset,
>>       if (IS_ERR(object))
>>           return PTR_ERR(object);
>>       mutex_lock(&ruleset->lock);
>> -    err = landlock_insert_rule(ruleset, object, access_rights);
>> +    err = landlock_insert_rule(ruleset, object, 0, access_rights, 
>> LANDLOCK_RULE_PATH_BENEATH);
> 
> For consistency, please use 80 columns everywhere.

   Ok. I got it.
> 
>>       mutex_unlock(&ruleset->lock);
>>       /*
>>        * No need to check for an error because landlock_insert_rule()
>> @@ -195,7 +195,8 @@ static inline u64 unmask_layers(
>>       inode = d_backing_inode(path->dentry);
>>       rcu_read_lock();
>>       rule = landlock_find_rule(domain,
>> -            rcu_dereference(landlock_inode(inode)->object));
>> +            (uintptr_t)rcu_dereference(landlock_inode(inode)->object),
>> +            LANDLOCK_RULE_PATH_BENEATH);
>>       rcu_read_unlock();
>>       if (!rule)
>>           return layer_mask;
>> diff --git a/security/landlock/ruleset.c b/security/landlock/ruleset.c
>> index a6212b752549..971685c48641 100644
>> --- a/security/landlock/ruleset.c
>> +++ b/security/landlock/ruleset.c
>> @@ -34,7 +34,7 @@ static struct landlock_ruleset *create_ruleset(const 
>> u32 num_layers)
>>           return ERR_PTR(-ENOMEM);
>>       refcount_set(&new_ruleset->usage, 1);
>>       mutex_init(&new_ruleset->lock);
>> -    new_ruleset->root = RB_ROOT;
>> +    new_ruleset->root_inode = RB_ROOT;
>>       new_ruleset->num_layers = num_layers;
>>       /*
>>        * hierarchy = NULL
>> @@ -81,10 +81,12 @@ static void build_check_rule(void)
>>   }
>>
>>   static struct landlock_rule *create_rule(
>> -        struct landlock_object *const object,
>> +        struct landlock_object *const object_ptr,
>> +        const uintptr_t object_data,
>>           const struct landlock_layer (*const layers)[],
>>           const u32 num_layers,
>> -        const struct landlock_layer *const new_layer)
>> +        const struct landlock_layer *const new_layer,
>> +        const u16 rule_type)
>>   {
>>       struct landlock_rule *new_rule;
>>       u32 new_num_layers;
>> @@ -103,8 +105,16 @@ static struct landlock_rule *create_rule(
>>       if (!new_rule)
>>           return ERR_PTR(-ENOMEM);
>>       RB_CLEAR_NODE(&new_rule->node);
>> -    landlock_get_object(object);
>> -    new_rule->object = object;
>> +
>> +    switch (rule_type) {
>> +    case LANDLOCK_RULE_PATH_BENEATH:
>> +        landlock_get_object(object_ptr);
>> +        new_rule->object.ptr = object_ptr;
>> +        break;
>> +    default:
>> +        return ERR_PTR(-EINVAL);
> 
> This would lead to memory leak. You should at least add a 
> WARN_ON_ONCE(1) here, but a proper solution would be to remove the use 
> of rule_type and only rely on object_ptr and object_data values. You can 
> also add a WARN_ON_ONCE(object_ptr && object_data).
> 
>  
   But rule_type is needed here in coming commits to support network
   rules. For LANDLOCK_RULE_PATH_BENEATH rule type landlock_get_object() 
is used but for LANDLOCK_RULE_NET_SERVICE is not. Using rule type is 
convenient for distinguising between fs and network rules.
>> +    }
>> +
>>       new_rule->num_layers = new_num_layers;
>>       /* Copies the original layer stack. */
>>       memcpy(new_rule->layers, layers,
>> @@ -120,7 +130,7 @@ static void free_rule(struct landlock_rule *const 
>> rule)
>>       might_sleep();
>>       if (!rule)
>>           return;
>> -    landlock_put_object(rule->object);
>> +    landlock_put_object(rule->object.ptr);
>>       kfree(rule);
>>   }
>>
>> @@ -156,26 +166,38 @@ static void build_check_ruleset(void)
>>    * access rights.
>>    */
>>   static int insert_rule(struct landlock_ruleset *const ruleset,
>> -        struct landlock_object *const object,
>> +        struct landlock_object *const object_ptr,
>> +        const uintptr_t object_data,
>>           const struct landlock_layer (*const layers)[],
>> -        size_t num_layers)
>> +        size_t num_layers, u16 rule_type)
>>   {
>>       struct rb_node **walker_node;
>>       struct rb_node *parent_node = NULL;
>>       struct landlock_rule *new_rule;
>> +    uintptr_t object;
>> +    struct rb_root *root;
>>
>>       might_sleep();
>>       lockdep_assert_held(&ruleset->lock);
>> -    if (WARN_ON_ONCE(!object || !layers))
>> -        return -ENOENT;
> 
> You can leave this code here.

  But anyway in coming commits with network rules this code will be 
moved into case LANDLOCK_RULE_PATH_BENEATH: ....
> 
>> -    walker_node = &(ruleset->root.rb_node);
>> +    /* Choose rb_tree structure depending on a rule type */
>> +    switch (rule_type) {
>> +    case LANDLOCK_RULE_PATH_BENEATH:
>> +        if (WARN_ON_ONCE(!object_ptr || !layers))
>> +            return -ENOENT;
>> +        object = (uintptr_t)object_ptr;
>> +        root = &ruleset->root_inode;
>> +        break;
>> +    default:
>> +        return -EINVAL;
>> +    }
>> +    walker_node = &root->rb_node;
>>       while (*walker_node) {
>>           struct landlock_rule *const this = rb_entry(*walker_node,
>>                   struct landlock_rule, node);
>>
>> -        if (this->object != object) {
>> +        if (this->object.data != object) {
>>               parent_node = *walker_node;
>> -            if (this->object < object)
>> +            if (this->object.data < object)
>>                   walker_node = &((*walker_node)->rb_right);
>>               else
>>                   walker_node = &((*walker_node)->rb_left);
>> @@ -207,11 +229,15 @@ static int insert_rule(struct landlock_ruleset 
>> *const ruleset,
>>            * 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]);
>> +        switch (rule_type) {
>> +        case LANDLOCK_RULE_PATH_BENEATH:
> 
> Same here and for the following code, you should replace such 
> switch/case with an if (object_ptr).
>    What about coming commits with network rule_type support?
> 
>> +            new_rule = create_rule(object_ptr, 0, &this->layers, 
>> this->num_layers,
>> +                           &(*layers)[0], rule_type);
>> +            break;
>> +        }
>>           if (IS_ERR(new_rule))
>>               return PTR_ERR(new_rule);
>> -        rb_replace_node(&this->node, &new_rule->node, &ruleset->root);
>> +        rb_replace_node(&this->node, &new_rule->node, 
>> &ruleset->root_inode);
> 
> Use the root variable here. Same for the following code and patches.

  What about your suggestion to use 2 rb_tress to support different 
rule_types:
	 1. root_inode - for filesystem objects
          2. root_net_port - for network port objects
????

> 
> 
>>           free_rule(this);
>>           return 0;
>>       }
>> @@ -220,11 +246,15 @@ static int insert_rule(struct landlock_ruleset 
>> *const ruleset,
>>       build_check_ruleset();
>>       if (ruleset->num_rules >= LANDLOCK_MAX_NUM_RULES)
>>           return -E2BIG;
>> -    new_rule = create_rule(object, layers, num_layers, NULL);
>> +    switch (rule_type) {
>> +    case LANDLOCK_RULE_PATH_BENEATH:
>> +        new_rule = create_rule(object_ptr, 0, layers, num_layers, 
>> NULL, rule_type);
>> +        break;
>> +    }
>>       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);
>> +    rb_insert_color(&new_rule->node, &ruleset->root_inode);
>>       ruleset->num_rules++;
>>       return 0;
>>   }
>> @@ -242,7 +272,9 @@ static void build_check_layer(void)
>>
>>   /* @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_object *const object_ptr,
>> +        const uintptr_t object_data,
>> +        const u32 access, const u16 rule_type)
>>   {
>>       struct landlock_layer layers[] = {{
>>           .access = access,
>> @@ -251,7 +283,8 @@ int landlock_insert_rule(struct landlock_ruleset 
>> *const ruleset,
>>       }};
>>
>>       build_check_layer();
>> -    return insert_rule(ruleset, object, &layers, ARRAY_SIZE(layers));
>> +    return insert_rule(ruleset, object_ptr, object_data, &layers,
>> +               ARRAY_SIZE(layers), rule_type);
>>   }
>>
>>   static inline void get_hierarchy(struct landlock_hierarchy *const 
>> hierarchy)
>> @@ -297,7 +330,7 @@ static int merge_ruleset(struct landlock_ruleset 
>> *const dst,
>>
>>       /* Merges the @src tree. */
>>       rbtree_postorder_for_each_entry_safe(walker_rule, next_rule,
>> -            &src->root, node) {
>> +            &src->root_inode, node) {
>>           struct landlock_layer layers[] = {{
>>               .level = dst->num_layers,
>>           }};
>> @@ -311,8 +344,8 @@ static int merge_ruleset(struct landlock_ruleset 
>> *const dst,
>>               goto out_unlock;
>>           }
>>           layers[0].access = walker_rule->layers[0].access;
>> -        err = insert_rule(dst, walker_rule->object, &layers,
>> -                ARRAY_SIZE(layers));
>> +        err = insert_rule(dst, walker_rule->object.ptr, 0, &layers,
>> +                ARRAY_SIZE(layers), LANDLOCK_RULE_PATH_BENEATH);
>>           if (err)
>>               goto out_unlock;
>>       }
>> @@ -323,6 +356,8 @@ static int merge_ruleset(struct landlock_ruleset 
>> *const dst,
>>       return err;
>>   }
>>
>> +
>> +
> 
> Useless lines.

   Got it. Thanks.
> 
> 
>>   static int inherit_ruleset(struct landlock_ruleset *const parent,
>>           struct landlock_ruleset *const child)
>>   {
>> @@ -339,9 +374,10 @@ static int inherit_ruleset(struct 
>> landlock_ruleset *const parent,
>>
>>       /* 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);
>> +            &parent->root_inode, node) {
>> +        err = insert_rule(child, walker_rule->object.ptr, 0,
>> +                &walker_rule->layers, walker_rule->num_layers,
>> +                LANDLOCK_RULE_PATH_BENEATH);
>>           if (err)
>>               goto out_unlock;
>>       }
>> @@ -372,7 +408,7 @@ 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,
>> +    rbtree_postorder_for_each_entry_safe(freeme, next, 
>> &ruleset->root_inode,
>>               node)
>>           free_rule(freeme);
>>       put_hierarchy(ruleset->hierarchy);
>> @@ -465,20 +501,28 @@ struct landlock_ruleset *landlock_merge_ruleset(
>>    */
>>   const struct landlock_rule *landlock_find_rule(
>>           const struct landlock_ruleset *const ruleset,
>> -        const struct landlock_object *const object)
>> +        const uintptr_t object_data, const u16 rule_type)
>>   {
>>       const struct rb_node *node;
>>
>> -    if (!object)
>> +    if (!object_data)
> 
> object_data can be 0. You need to add a test with such value.
> 
> We need to be sure that this change cannot affect the current FS code.

  I got it. I will refactor it.
> 
> 
>>           return NULL;
>> -    node = ruleset->root.rb_node;
>> +
>> +    switch (rule_type) {
>> +    case LANDLOCK_RULE_PATH_BENEATH:
>> +        node = ruleset->root_inode.rb_node;
>> +        break;
>> +    default:
>> +        return ERR_PTR(-EINVAL);
> 
> This is a bug. There is no check for such value. You need to check and 
> update all call sites to catch such errors. Same for all new use of 
> ERR_PTR().

Sorry, I did not get your point.
Do you mean I should check the correctness of rule_type in above 
function which calls landlock_find_rule() ??? Why can't I add such check 
here?

> 
> 
>> +    }
>> +
>>       while (node) {
>>           struct landlock_rule *this = rb_entry(node,
>>                   struct landlock_rule, node);
>>
>> -        if (this->object == object)
>> +        if (this->object.data == object_data)
>>               return this;
>> -        if (this->object < object)
>> +        if (this->object.data < object_data)
>>               node = node->rb_right;
>>           else
>>               node = node->rb_left;
>> diff --git a/security/landlock/ruleset.h b/security/landlock/ruleset.h
>> index bc87e5f787f7..088b8d95f653 100644
>> --- a/security/landlock/ruleset.h
>> +++ b/security/landlock/ruleset.h
>> @@ -50,15 +50,17 @@ struct landlock_rule {
>>        */
>>       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.
>> +     * @object: A union to identify either a kernel object (e.g. an 
>> inode) or
>> +     * a socket port object.
> 
> …or a raw data value (e.g. a network socket port).
> 
  Ok. I will mofdify this line
> 
>> This is used as a key for this ruleset element.
>> +     * This pointer is set once and never modified. It always points 
>> to an
> 
> s/This pointer/@object.ptr/

  Ok. I got it.
> 
> 
>> +     * allocated object because each rule increments the refcount of its
>> +     * object (for inodes);
>>        */
>> +     union {
>> +        struct landlock_object *ptr;
>> +        uintptr_t data;
>> +     } object;
>> +
>>       u32 num_layers;
>>       /**
>>        * @layers: Stack of layers, from the latest to the newest, 
>> implemented
>> @@ -95,7 +97,7 @@ struct landlock_ruleset {
>>        * 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;
>> +    struct rb_root root_inode;
>>       /**
>>        * @hierarchy: Enables hierarchy identification even when a parent
>>        * domain vanishes.  This is needed for the ptrace protection.
>> @@ -157,7 +159,9 @@ 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_object *const object_ptr,
>> +             const uintptr_t object_data,
>> +             const u32 access, const u16 rule_type);
>>
>>   struct landlock_ruleset *landlock_merge_ruleset(
>>           struct landlock_ruleset *const parent,
>> @@ -165,7 +169,7 @@ struct landlock_ruleset *landlock_merge_ruleset(
>>
>>   const struct landlock_rule *landlock_find_rule(
>>           const struct landlock_ruleset *const ruleset,
>> -        const struct landlock_object *const object);
>> +        const uintptr_t object_data, const u16 rule_type);
>>
>>   static inline void landlock_get_ruleset(struct landlock_ruleset 
>> *const ruleset)
>>   {
>> -- 
>> 2.25.1
>>
> .