KASAN: null-ptr-deref Write in binder_update_page_range

[Minchan Kim]

Thanks, Martijn,

Greg, could you have a look to pick up?

On Mon, Aug 27, 2018 at 03:35:24PM +0200, Martijn Coenen wrote:
> Thanks Minchan!
> 
> On Thu, Aug 23, 2018 at 7:29 AM, Minchan Kim <minchan at kernel.org> wrote:
> > Signed-off-by: Todd Kjos <tkjos at google.com>
> > Signed-off-by: Minchan Kim <minchan at kernel.org>
> Reviewed-by: Martijn Coenen <maco at android.com>
> 
> > ---
> >  drivers/android/binder_alloc.c | 43 +++++++++++++++++++++++++++-------
> >  1 file changed, 35 insertions(+), 8 deletions(-)
> >
> > diff --git a/drivers/android/binder_alloc.c b/drivers/android/binder_alloc.c
> > index 3f3b7b253445..64fd96eada31 100644
> > --- a/drivers/android/binder_alloc.c
> > +++ b/drivers/android/binder_alloc.c
> > @@ -332,6 +332,35 @@ static int binder_update_page_range(struct binder_alloc *alloc, int allocate,
> >         return vma ? -ENOMEM : -ESRCH;
> >  }
> >
> > +
> > +static inline void binder_alloc_set_vma(struct binder_alloc *alloc,
> > +               struct vm_area_struct *vma)
> > +{
> > +       if (vma)
> > +               alloc->vma_vm_mm = vma->vm_mm;
> > +       /*
> > +        * If we see alloc->vma is not NULL, buffer data structures set up
> > +        * completely. Look at smp_rmb side binder_alloc_get_vma.
> > +        * We also want to guarantee new alloc->vma_vm_mm is always visible
> > +        * if alloc->vma is set.
> > +        */
> > +       smp_wmb();
> > +       alloc->vma = vma;
> > +}
> > +
> > +static inline struct vm_area_struct *binder_alloc_get_vma(
> > +               struct binder_alloc *alloc)
> > +{
> > +       struct vm_area_struct *vma = NULL;
> > +
> > +       if (alloc->vma) {
> > +               /* Look at description in binder_alloc_set_vma */
> > +               smp_rmb();
> > +               vma = alloc->vma;
> > +       }
> > +       return vma;
> > +}
> > +
> >  static struct binder_buffer *binder_alloc_new_buf_locked(
> >                                 struct binder_alloc *alloc,
> >                                 size_t data_size,
> > @@ -348,7 +377,7 @@ static struct binder_buffer *binder_alloc_new_buf_locked(
> >         size_t size, data_offsets_size;
> >         int ret;
> >
> > -       if (alloc->vma == NULL) {
> > +       if (!binder_alloc_get_vma(alloc)) {
> >                 binder_alloc_debug(BINDER_DEBUG_USER_ERROR,
> >                                    "%d: binder_alloc_buf, no vma\n",
> >                                    alloc->pid);
> > @@ -723,9 +752,7 @@ int binder_alloc_mmap_handler(struct binder_alloc *alloc,
> >         buffer->free = 1;
> >         binder_insert_free_buffer(alloc, buffer);
> >         alloc->free_async_space = alloc->buffer_size / 2;
> > -       barrier();
> > -       alloc->vma = vma;
> > -       alloc->vma_vm_mm = vma->vm_mm;
> > +       binder_alloc_set_vma(alloc, vma);
> >         mmgrab(alloc->vma_vm_mm);
> >
> >         return 0;
> > @@ -754,10 +781,10 @@ void binder_alloc_deferred_release(struct binder_alloc *alloc)
> >         int buffers, page_count;
> >         struct binder_buffer *buffer;
> >
> > -       BUG_ON(alloc->vma);
> > -
> >         buffers = 0;
> >         mutex_lock(&alloc->mutex);
> > +       BUG_ON(alloc->vma);
> > +
> >         while ((n = rb_first(&alloc->allocated_buffers))) {
> >                 buffer = rb_entry(n, struct binder_buffer, rb_node);
> >
> > @@ -900,7 +927,7 @@ int binder_alloc_get_allocated_count(struct binder_alloc *alloc)
> >   */
> >  void binder_alloc_vma_close(struct binder_alloc *alloc)
> >  {
> > -       WRITE_ONCE(alloc->vma, NULL);
> > +       binder_alloc_set_vma(alloc, NULL);
> >  }
> >
> >  /**
> > @@ -935,7 +962,7 @@ enum lru_status binder_alloc_free_page(struct list_head *item,
> >
> >         index = page - alloc->pages;
> >         page_addr = (uintptr_t)alloc->buffer + index * PAGE_SIZE;
> > -       vma = alloc->vma;
> > +       vma = binder_alloc_get_vma(alloc);
> >         if (vma) {
> >                 if (!mmget_not_zero(alloc->vma_vm_mm))
> >                         goto err_mmget;
> > --
> > 2.18.0.1017.ga543ac7ca45-goog
> >
> >
> >
> >