Re: [PATCH] LANDLOCK: use kmem_cache for landlock_object

[Paul Moore]

On Wed, Mar 27, 2024 at 7:26 PM Ayush Tiwari <ayushtiw0110@xxxxxxxxx> wrote:
>
> Use kmem_cache replace kzalloc() calls with kmem_cache_zalloc() for
> struct landlock_object and update the related dependencies.
>
> Signed-off-by: Ayush Tiwari <ayushtiw0110@xxxxxxxxx>
> ---
>  security/landlock/fs.c     |  2 +-
>  security/landlock/object.c | 14 ++++++++++++--
>  security/landlock/object.h |  4 ++++
>  security/landlock/setup.c  |  2 ++
>  4 files changed, 19 insertions(+), 3 deletions(-)

Hi Ayush,

Mickaël has the final say on Landlock patches, but I had a few
comments that I've included below ...

> diff --git a/security/landlock/fs.c b/security/landlock/fs.c
> index fc520a06f9af..227dd67dd902 100644
> --- a/security/landlock/fs.c
> +++ b/security/landlock/fs.c
> @@ -124,7 +124,7 @@ static struct landlock_object *get_inode_object(struct inode *const inode)
>         if (unlikely(rcu_access_pointer(inode_sec->object))) {
>                 /* Someone else just created the object, bail out and retry. */
>                 spin_unlock(&inode->i_lock);
> -               kfree(new_object);
> +               kmem_cache_free(landlock_object_cache, new_object);

See my comment below, but you may want to wrap this in a Landlock
object API function.

>                 rcu_read_lock();
>                 goto retry;
> diff --git a/security/landlock/object.c b/security/landlock/object.c
> index 1f50612f0185..df1354215617 100644
> --- a/security/landlock/object.c
> +++ b/security/landlock/object.c
> @@ -17,6 +17,15 @@
>
>  #include "object.h"
>
> +struct kmem_cache *landlock_object_cache;
> +
> +void __init landlock_object_init(void)
> +{
> +       landlock_object_cache = kmem_cache_create(
> +               "landlock_object_cache", sizeof(struct landlock_object), 0,
> +               SLAB_PANIC, NULL);

The comments in include/linux/slab.h suggest using the KMEM_CACHE()
macro, instead of kmem_cache_create(), as a best practice for creating
slab caches.

> +}
> +
>  struct landlock_object *
>  landlock_create_object(const struct landlock_object_underops *const underops,
>                        void *const underobj)
> @@ -25,7 +34,8 @@ landlock_create_object(const struct landlock_object_underops *const underops,
>
>         if (WARN_ON_ONCE(!underops || !underobj))
>                 return ERR_PTR(-ENOENT);
> -       new_object = kzalloc(sizeof(*new_object), GFP_KERNEL_ACCOUNT);
> +       new_object =
> +               kmem_cache_zalloc(landlock_object_cache, GFP_KERNEL_ACCOUNT);

If the line is too long, you might want to consider splitting the
function parameters like this:

  new_object = kmem_cache_zalloc(landlock_object_cache,
                                 GFP_KERNEL_ACCOUNT);

>         if (!new_object)
>                 return ERR_PTR(-ENOMEM);
>         refcount_set(&new_object->usage, 1);
> @@ -62,6 +72,6 @@ void landlock_put_object(struct landlock_object *const object)
>                  * @object->underobj to @object (if it still exists).
>                  */
>                 object->underops->release(object);
> -               kfree_rcu(object, rcu_free);
> +               kmem_cache_free(landlock_object_cache, object);
>         }
>  }
> diff --git a/security/landlock/object.h b/security/landlock/object.h
> index 5f28c35e8aa8..8ba1af3ddc2e 100644
> --- a/security/landlock/object.h
> +++ b/security/landlock/object.h
> @@ -13,6 +13,10 @@
>  #include <linux/refcount.h>
>  #include <linux/spinlock.h>
>
> +extern struct kmem_cache *landlock_object_cache;

This really is a decision for Mickaël, but you may want to make
@landlock_object_cache private to object.c and create functions to
manage it as needed, e.g. put/free operations.

> +void __init landlock_object_init(void);
> +
>  struct landlock_object;
>
>  /**
> diff --git a/security/landlock/setup.c b/security/landlock/setup.c
> index f6dd33143b7f..a5fca4582ee1 100644

-- 
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