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

[Mickaël Salaün <mic@xxxxxxxxxxx>]

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@xxxxxxxxxx>
> > > > > ---
> > > > >
> > > > > 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.