mm: make sure all file VMAs have ->vm_ops set

We rely on vma->vm_ops == NULL to detect anonymous VMA: see
vma_is_anonymous(), but some drivers doesn't set ->vm_ops.

As a result we can end up with anonymous page in private file mapping.
That should not lead to serious misbehaviour, but nevertheless is wrong.

Let's fix by setting up dummy ->vm_ops for file mmapping if f_op->mmap()
didn't set its own.

The patch also adds sanity check into __vma_link_rb(). It will help
catch broken VMAs which inserted directly into mm_struct via
insert_vm_struct().

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Reviewed-by: Oleg Nesterov <oleg@redhat.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 8 insertions, 0 deletions

diff --git a/mm/mmap.c b/mm/mmap.c
index c739d6db7193..971dd2cb77d2 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -612,6 +612,8 @@ static unsigned long count_vma_pages_range(struct mm_struct *mm,
 void __vma_link_rb(struct mm_struct *mm, struct vm_area_struct *vma,
                 struct rb_node **rb_link, struct rb_node *rb_parent)
 {
+        WARN_ONCE(vma->vm_file && !vma->vm_ops, "missing vma->vm_ops");
+
         /* Update tracking information for the gap following the new vma. */
         if (vma->vm_next)
                 vma_gap_update(vma->vm_next);
@@ -1636,6 +1638,12 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
                  */
                 WARN_ON_ONCE(addr != vma->vm_start);
 
+                /* All file mapping must have ->vm_ops set */
+                if (!vma->vm_ops) {
+                        static const struct vm_operations_struct dummy_ops = {};
+                        vma->vm_ops = &dummy_ops;
+                }
+
                 addr = vma->vm_start;
                 vm_flags = vma->vm_flags;
         } else if (vm_flags & VM_SHARED) {