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

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Message-ID: <CAK8P3a0+jOW==OOx_CLj=TCsG5EBK2ni6kw1+PexJLAC2NEp_g@mail.gmail.com>
Date:   Mon, 17 Jun 2019 16:04:14 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Roman Penyaev <rpenyaev@...e.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 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

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