We rely on vma->vm_ops == NULL to detect anonymous VMA: see
vma_is_anonymous(), but some drivers doesn't set ->vm_ops.
As result we can end up with anonymous page in private file mapping.
That's 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@xxxxxxxxxxxxxxx>
---
mm/mmap.c | 8 ++++++++
1 file changed, 8 insertions(+)
diff --git a/mm/mmap.c b/mm/mmap.c
index 2e98784d5b7c..a82a02853cbc 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) {
--
2.1.4
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