linux-kernel - Re: [PATCH] block: don't embed integrity

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Date:   Fri, 10 Mar 2023 15:42:42 +0200
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Mirsad Todorovac <mirsad.todorovac@....unizg.hr>
Cc:     Thomas Weißschuh <linux@...ssschuh.net>,
        Jens Axboe <axboe@...nel.dk>, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH] block: don't embed integrity_kobj into gendisk

On Fri, Mar 10, 2023 at 09:52:51AM +0100, Mirsad Todorovac wrote:
> Hi, Thomas,
> 
> The good news is that the
> 
> "kobject: 'integrity' (000000001aa7f87a): does not have a release() function"
> 
> is now removed:
> 
> https://domac.alu.hr/~mtodorov/linux/bugreports/integrity/fix/20230310_082429.jpg
> 
> On 3/10/23 00:26, Thomas Weißschuh wrote:
> > On Thu, Mar 09, 2023 at 10:46:50PM +0100, Mirsad Goran Todorovac wrote:
> > > On 09. 03. 2023. 22:23, Thomas Weißschuh wrote:
> > > 
> > > Very well, but who then destroys the cache crated here:
> > > 
> > > security/integrity/iint.c:177-179
> > > > 177         iint_cache =
> > > > 178             kmem_cache_create("iint_cache", sizeof(struct integrity_iint_cache),
> > > > 179                               0, SLAB_PANIC, init_once);
> > > 
> > > I assumed that it must have been done from iint.c because iint_cache is
> > > static?
> > 
> > It doesn't seem like anything destroys this cache.
> > 
> > I'm not sure this is a problem though as iint.c can not be built as module.
> 
> Maybe I was just scolded when I relied on exit() to do the memory deallocation
> from heap automatically in userspace programs. :-/
> 
> I suppose this cache is destroyed when virtual Linux machine is shutdown.
> 
> Still, it might seem prudent for all of the objects to be destroyed before shutting
> down the kernel, assuring the call of proper destructors, and in the right order.
> 
> > At least it's not a problem with kobjects as those are not used here.
> 
> I begin to understand.
> 
> security/integrity/iint.c:
> 175 static int __init integrity_iintcache_init(void)
> 176 {
> 177         iint_cache =
> 178             kmem_cache_create("iint_cache", sizeof(struct integrity_iint_cache),
> 179                               0, SLAB_PANIC, init_once);
> 180         return 0;
> 181 }
> 182 DEFINE_LSM(integrity) = {
> 183         .name = "integrity",
> 184         .init = integrity_iintcache_init,
> 185 };
> 
> and struct lsm_info
> 
> include/linux/lsm_hooks.h:
> 1721 struct lsm_info {
> 1722         const char *name;       /* Required. */
> 1723         enum lsm_order order;   /* Optional: default is LSM_ORDER_MUTABLE */
> 1724         unsigned long flags;    /* Optional: flags describing LSM */
> 1725         int *enabled;           /* Optional: controlled by CONFIG_LSM */
> 1726         int (*init)(void);      /* Required. */
> 1727         struct lsm_blob_sizes *blobs; /* Optional: for blob sharing. */
> 1728 };
> 
> Here a proper destructor might be prudent to add.
> 
> Naive try could be like this:
> 
> diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
> index 6e156d2acffc..d5a6ab9b5eb2 100644
> --- a/include/linux/lsm_hooks.h
> +++ b/include/linux/lsm_hooks.h
> @@ -1724,6 +1724,7 @@ struct lsm_info {
>         unsigned long flags;    /* Optional: flags describing LSM */
>         int *enabled;           /* Optional: controlled by CONFIG_LSM */
>         int (*init)(void);      /* Required. */
> +       int (*release)(void);   /* Release associated resources */
>         struct lsm_blob_sizes *blobs; /* Optional: for blob sharing. */
>  };
> 
> diff --git a/security/integrity/iint.c b/security/integrity/iint.c
> index 8638976f7990..3f69eb702b2e 100644
> --- a/security/integrity/iint.c
> +++ b/security/integrity/iint.c
> @@ -179,9 +179,16 @@ static int __init integrity_iintcache_init(void)
>                               0, SLAB_PANIC, init_once);
>         return 0;
>  }
> +
> +static int __exit integrity_iintcache_release(void)
> +{
> +       kmem_cache_destroy(iint_cache);
> +}
> +
>  DEFINE_LSM(integrity) = {
>         .name = "integrity",
>         .init = integrity_iintcache_init,
> +       .release = integrity_iintcache_release,
>  };
> 
> However, I lack insight of who should invoke .release() on 'integrity',
> in 10.7 million lines of *.c and *.h files. Obviously, now no one is
> expecting .release in LSM modules. But there might be a need for the
> proper cleanup.
> 
> For it is not a kobject as you already observed? :-/

I think you may prepare a formal patch and Cc to Greg KH, who knows
the kobject code well and this warning in particular.

I believe, even if a dead code, the destructor to have is a good code
behaviour, since it is might be called on the __exitcall.

-- 
With Best Regards,
Andy Shevchenko