xen/gntdev: avoid out of bounds access in case of partial gntdev_mmap()

In case gntdev_mmap() succeeds only partially in mapping grant pages
it will leave some vital information uninitialized needed later for
cleanup. This will lead to an out of bounds array access when unmapping
the already mapped pages.

So just initialize the data needed for unmapping the pages a little bit
earlier.

Cc: <stable@vger.kernel.org>
Reported-by: Arthur Borsboom <arthurborsboom@gmail.com>
Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>

diff --git a/drivers/xen/gntdev.c b/drivers/xen/gntdev.c
index 82360594fa8e49bcbad179a6bb349564286cf203..57efbd3b053b37ca43816483dd3364c3c48a761e 100644 (file)
--- a/drivers/xen/gntdev.c
+++ b/drivers/xen/gntdev.c
@@ -1024,6 +1024,7 @@ static int gntdev_mmap(struct file *flip, struct vm_area_struct *vma)
        mutex_unlock(&priv->lock);
 
        if (use_ptemod) {
+               map->pages_vm_start = vma->vm_start;
                err = apply_to_page_range(vma->vm_mm, vma->vm_start,
                                          vma->vm_end - vma->vm_start,
                                          find_grant_ptes, map);
@@ -1061,7 +1062,6 @@ static int gntdev_mmap(struct file *flip, struct vm_area_struct *vma)
                                            set_grant_ptes_as_special, NULL);
                }
 #endif
-               map->pages_vm_start = vma->vm_start;
        }
 
        return 0;