Re: [PATCH v6 02/17] landlock: refactors landlock_find/insert_rule

["Mickaël Salaün" <mic@digikod.net>]

On 08/07/2022 16:14, Konstantin Meskhidze (A) wrote:
> 
> 
> 7/8/2022 4:59 PM, Mickaël Salaün пишет:
>>
>> On 08/07/2022 15:10, Konstantin Meskhidze (A) wrote:
>>>
>>>
>>> 7/7/2022 7:44 PM, Mickaël Salaün пишет:
>>>>
>>>> On 21/06/2022 10:22, Konstantin Meskhidze wrote:
>>>>> Adds a new object union to support a socket port
>>>>> rule type. Refactors landlock_insert_rule() and
>>>>> landlock_find_rule() to support coming network
>>>>> modifications. 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 v5:
>>>>> * Formats code with clang-format-14.
>>>>>
>>>>> Changes since v4:
>>>>> * Refactors insert_rule() and create_rule() functions by deleting
>>>>> rule_type from their arguments list, it helps to reduce useless code.
>>>>>
>>>>> Changes since v3:
>>>>> * Splits commit.
>>>>> * Refactors landlock_insert_rule and landlock_find_rule functions.
>>>>> * Rename new_ruleset->root_inode.
>>>>>
>>>>> ---
>>>>>   security/landlock/fs.c      |   7 ++-
>>>>>   security/landlock/ruleset.c | 105 
>>>>> ++++++++++++++++++++++++++----------
>>>>>   security/landlock/ruleset.h |  27 +++++-----
>>>>>   3 files changed, 96 insertions(+), 43 deletions(-)
>>>>>
>>>>> diff --git a/security/landlock/fs.c b/security/landlock/fs.c
>>>>> index e6da08ed99d1..46aedc2a05a8 100644
>>>>> --- a/security/landlock/fs.c
>>>>> +++ b/security/landlock/fs.c
>>>>> @@ -173,7 +173,8 @@ 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);
>>>>>       mutex_unlock(&ruleset->lock);
>>>>>       /*
>>>>>        * No need to check for an error because landlock_insert_rule()
>>>>> @@ -204,7 +205,9 @@ find_rule(const struct landlock_ruleset *const 
>>>>> domain,
>>>>>       inode = d_backing_inode(dentry);
>>>>>       rcu_read_lock();
>>>>>       rule = landlock_find_rule(
>>>>> -        domain, rcu_dereference(landlock_inode(inode)->object));
>>>>> +        domain,
>>>>> +        (uintptr_t)rcu_dereference(landlock_inode(inode)->object),
>>>>> +        LANDLOCK_RULE_PATH_BENEATH);
>>>>>       rcu_read_unlock();
>>>>>       return rule;
>>>>>   }
>>>>> diff --git a/security/landlock/ruleset.c b/security/landlock/ruleset.c
>>>>> index a3fd58d01f09..5f13f8a12aee 100644
>>>>> --- a/security/landlock/ruleset.c
>>>>> +++ b/security/landlock/ruleset.c
>>>>> @@ -35,7 +35,7 @@ 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
>>>>> @@ -69,7 +69,8 @@ static void build_check_rule(void)
>>>>>   }
>>>>>
>>>>>   static struct landlock_rule *
>>>>> -create_rule(struct landlock_object *const object,
>>>>> +create_rule(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)
>>>>>   {
>>>>> @@ -90,8 +91,15 @@ create_rule(struct landlock_object *const object,
>>>>>       if (!new_rule)
>>>>>           return ERR_PTR(-ENOMEM);
>>>>>       RB_CLEAR_NODE(&new_rule->node);
>>>>> -    landlock_get_object(object);
>>>>> -    new_rule->object = object;
>>>>> +
>>>>> +    if (object_ptr) {
>>>>> +        landlock_get_object(object_ptr);
>>>>> +        new_rule->object.ptr = object_ptr;
>>>>> +    } else if (object_ptr && object_data) {
>>>>
>>>> Something is wrong with this second check: else + object_ptr?
>>>
>>>   Sorry. Do you mean logical error here? I got your point.
>>>   You are right!
>>>
>>>   I think it must be refactored like this:
>>>
>>>      if (object_ptr && !object_data) {
>>>          landlock_get_object(object_ptr);
>>>          new_rule->object.ptr = object_ptr;
>>>      } else if (object_ptr && object_data) {
>>>          ...
>>>      }
>>
>> There is indeed a logical error but this doesn't fix everything. Please
>> include my previous suggestion instead.
>>
>     By the way, in the next commits I have fixed this logic error.
> Anyway I will refactor this one also. Thanks.
>>
>>> Plus, I will add a test for this case.
>>
>> That would be great but I don't think this code is reachable from user
>> space. I think that would require kunit but I may be missing something.
>> How would you test this?
> 
> You are correct. I checked it. It's impossible to reach this line from 
> userpace (insert both object_ptr and object_data). But create_rule() 
> must be used carefuly by other developers (if any in future). Do you 
> think if its possible to have some internal kernel tests that could 
> handle this issue?

We can use kunit tests for such kernel functions, but in this case I'm 
not sure what could be tested. I started working on bringing kunit tests 
to Landlock but it's not ready yet. Please list all non-userspace tests 
you can think about.