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

[Arnd Bergmann <arnd@arndb.de>]

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