Re: [BUG]: mm/vmalloc: uninitialized variable access in pcpu_get_vm_areas

From: Roman Penyaev <rpenyaev@suse.de>
To: Arnd Bergmann <arnd@arndb.de>
Cc: "Uladzislau Rezki (Sony)" <urezki@gmail.com>,
	Roman Gushchin <guro@fb.com>, Michal Hocko <mhocko@suse.com>,
	Matthew Wilcox <willy@infradead.org>,
	Thomas Garnier <thgarnie@google.com>,
	Oleksiy Avramchenko <oleksiy.avramchenko@sonymobile.com>,
	Steven Rostedt <rostedt@goodmis.org>,
	Joel Fernandes <joelaf@google.com>,
	Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@elte.hu>,
	Tejun Heo <tj@kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Stephen Rothwell <sfr@canb.auug.org.au>,
	Rick Edgecombe <rick.p.edgecombe@intel.com>,
	Andrey Ryabinin <aryabinin@virtuozzo.com>,
	Mike Rapoport <rppt@linux.ibm.com>, Linux-MM <linux-mm@kvack.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [BUG]: mm/vmalloc: uninitialized variable access in pcpu_get_vm_areas
Date: Mon, 17 Jun 2019 16:40:31 +0200	[thread overview]
Message-ID: <a05a92b2fdc7c8b7850e9e7c63f8e9e6@suse.de> (raw)
In-Reply-To: <CAK8P3a0+jOW==OOx_CLj=TCsG5EBK2ni6kw1+PexJLAC2NEp_g@mail.gmail.com>

On 2019-06-17 16:04, Arnd Bergmann wrote:
> On Mon, Jun 17, 2019 at 3:49 PM Roman Penyaev <rpenyaev@suse.de> wrote:
>> >               augment_tree_propagate_from(va);
>> >
>> > -             if (type == NE_FIT_TYPE)
>> > -                     insert_vmap_area_augment(lva, &va->rb_node,
>> > -                             &free_vmap_area_root, &free_vmap_area_list);
>> > -     }
>> > -
>> >       return 0;
>> >  }
>> 
>> 
>> Hi Arnd,
>> 
>> Seems the proper fix is just setting lva to NULL.  The only place
>> where lva is allocated and then used is when type == NE_FIT_TYPE,
>> so according to my shallow understanding of the code everything
>> should be fine.
> 
> I don't see how NULL could work here. insert_vmap_area_augment()
> passes the va pointer into find_va_links() and link_va(), both of
> which dereference the pointer, see

Exactly, but insert_vmap_area_augement() accepts 'va', not 'lva',
but in your variant 'va' is already freed (see type == FL_FIT_TYPE
branch, on top of that function).  So that should be use-after-free.

--
Roman