1 files changed, 5 insertions, 2 deletions

diff --git a/mm/rmap.c b/mm/rmap.c
index 377d417ec15f..2e034a0b89ab 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -225,7 +225,9 @@ vma_address(struct page *page, struct vm_area_struct *vma)
 
 /*
  * At what user virtual address is page expected in vma? checking that the
- * page matches the vma: currently only used by unuse_process, on anon pages.
+ * page matches the vma: currently only used on anon pages, by unuse_vma;
+ * and by extraordinary checks on anon pages in VM_UNPAGED vmas, taking
+ * care that an mmap of /dev/mem might window free and foreign pages.
  */
 unsigned long page_address_in_vma(struct page *page, struct vm_area_struct *vma)
 {
@@ -234,7 +236,8 @@ unsigned long page_address_in_vma(struct page *page, struct vm_area_struct *vma)
                     (void *)page->mapping - PAGE_MAPPING_ANON)
                         return -EFAULT;
         } else if (page->mapping && !(vma->vm_flags & VM_NONLINEAR)) {
-                if (vma->vm_file->f_mapping != page->mapping)
+                if (!vma->vm_file ||
+                    vma->vm_file->f_mapping != page->mapping)
                         return -EFAULT;
         } else
                 return -EFAULT;