linux-kernel - Re: [BUG]: mm/vmalloc: uninitialized variable access in pcpu_get_vm

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Date:   Mon, 17 Jun 2019 16:40:31 +0200
From:   Roman Penyaev <rpenyaev@...e.de>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     "Uladzislau Rezki (Sony)" <urezki@...il.com>,
        Roman Gushchin <guro@...com>, Michal Hocko <mhocko@...e.com>,
        Matthew Wilcox <willy@...radead.org>,
        Thomas Garnier <thgarnie@...gle.com>,
        Oleksiy Avramchenko <oleksiy.avramchenko@...ymobile.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Joel Fernandes <joelaf@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...e.hu>, Tejun Heo <tj@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Rick Edgecombe <rick.p.edgecombe@...el.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Linux-MM <linux-mm@...ck.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [BUG]: mm/vmalloc: uninitialized variable access in
 pcpu_get_vm_areas

On 2019-06-17 16:04, Arnd Bergmann wrote:
> On Mon, Jun 17, 2019 at 3:49 PM Roman Penyaev <rpenyaev@...e.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