Re: [PATCH] slub/memcg: Cure the brainless abuse of sysfs attributes

[David Rientjes]

On Sat, 20 May 2017, Thomas Gleixner wrote:

> memcg_propagate_slab_attrs() abuses the sysfs attribute file functions to
> propagate settings from the root kmem_cache to a newly created
> kmem_cache. It does that with:
> 
>      attr->show(root, buf);
>      attr->store(new, buf, strlen(bug);
> 
> Aside of being a lazy and absurd hackery this is broken because it does not
> check the return value of the show() function.
> 
> Some of the show() functions return 0 w/o touching the buffer. That means in
> such a case the store function is called with the stale content of the
> previous show(). That causes nonsense like invoking kmem_cache_shrink() on
> a newly created kmem_cache. In the worst case it would cause handing in an
> uninitialized buffer.
> 
> This should be rewritten proper by adding a propagate() callback to those
> slub_attributes which must be propagated and avoid that insane conversion
> to and from ASCII, but that's too large for a hot fix.
> 
> Check at least the return value of the show() function, so calling store()
> with stale content is prevented.
> 
> Reported-by: Steven Rostedt <rostedt@xxxxxxxxxxx>
> Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx

Acked-by: David Rientjes <rientjes@xxxxxxxxxx>