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From:   Arnd Bergmann <arnd@arndb.de>
Date:   Mon, 17 Jun 2019 16:04:14 +0200
Message-ID: <CAK8P3a0+jOW==OOx_CLj=TCsG5EBK2ni6kw1+PexJLAC2NEp_g@mail.gmail.com>
Subject: Re: [BUG]: mm/vmalloc: uninitialized variable access in pcpu_get_vm_areas
To:     Roman Penyaev <rpenyaev@suse.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>
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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

static void
insert_vmap_area_augment(struct vmap_area *va,
        struct rb_node *from, struct rb_root *root,
        struct list_head *head)
{
        struct rb_node **link;
        struct rb_node *parent;

        if (from)
                link = find_va_links(va, NULL, from, &parent);
        else
                link = find_va_links(va, root, NULL, &parent);

        link_va(va, root, parent, link, head);
        augment_tree_propagate_from(va);
}

static __always_inline struct rb_node **
find_va_links(struct vmap_area *va,
        struct rb_root *root, struct rb_node *from,
        struct rb_node **parent)
{
       ...
                       if (va->va_start < tmp_va->va_end &&
                                va->va_end <= tmp_va->va_start)
       ...
}

static __always_inline void
link_va(struct vmap_area *va, struct rb_root *root,
        struct rb_node *parent, struct rb_node **link, struct list_head *head)
{
        ...
        rb_link_node(&va->rb_node, parent, link);
        ...
}

       Arnd