Patch "mm: avoid setting up anonymous pages into file mapping" has been added to the 4.1-stable tree

This is a note to let you know that I've just added the patch titled

mm: avoid setting up anonymous pages into file mapping

to the 4.1-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
mm-avoid-setting-up-anonymous-pages-into-file-mapping.patch
and it can be found in the queue-4.1 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: "Kirill A. Shutemov" <[email protected]>
Date: Mon, 6 Jul 2015 23:18:37 +0300
Subject: mm: avoid setting up anonymous pages into file mapping

From: "Kirill A. Shutemov" <[email protected]>

commit 6b7339f4c31ad69c8e9c0b2859276e22cf72176d upstream.

Reading page fault handler code I've noticed that under right circumstances kernel would map anonymous pages into file mappings: if the VMA doesn't have vm_ops->fault() and the VMA wasn't fully populated on ->mmap(), kernel would handle page fault to not populated pte with do_anonymous_page().

Let's change page fault handler to use do_anonymous_page() only on anonymous VMA (->vm_ops == NULL) and make sure that the VMA is not shared.

For file mappings without vm_ops->fault() or shred VMA without vm_ops, page fault on pte_none() entry would lead to SIGBUS.

---
 mm/memory.c |   20 +++++++++++++-------
 1 file changed, 13 insertions(+), 7 deletions(-)

@@ -2669,6 +2669,10 @@ static int do_anonymous_page(struct mm_s
 
 	pte_unmap(page_table);
 
+	/* File mapping without ->vm_ops ? */
+	if (vma->vm_flags & VM_SHARED)
+		return VM_FAULT_SIGBUS;
+
 	/* Check if we need to add a guard page to the stack */
 	if (check_stack_guard_page(vma, address) < 0)
 		return VM_FAULT_SIGSEGV;

@@ -3097,6 +3101,9 @@ static int do_fault(struct mm_struct *mm
 			- vma->vm_start) >> PAGE_SHIFT) + vma->vm_pgoff;
 
 	pte_unmap(page_table);
+	/* The VMA was not fully populated on mmap() or missing VM_DONTEXPAND */
+	if (!vma->vm_ops->fault)
+		return VM_FAULT_SIGBUS;
 	if (!(flags & FAULT_FLAG_WRITE))
 		return do_read_fault(mm, vma, address, pmd, pgoff, flags,
 				orig_pte);

@@ -3242,13 +3249,12 @@ static int handle_pte_fault(struct mm_st
 	barrier();
 	if (!pte_present(entry)) {
 		if (pte_none(entry)) {
-			if (vma->vm_ops) {
-				if (likely(vma->vm_ops->fault))
-					return do_fault(mm, vma, address, pte,
-							pmd, flags, entry);
-			}
-			return do_anonymous_page(mm, vma, address,
-						 pte, pmd, flags);
+			if (vma->vm_ops)
+				return do_fault(mm, vma, address, pte, pmd,
+						flags, entry);
+
+			return do_anonymous_page(mm, vma, address, pte, pmd,
+					flags);
 		}
 		return do_swap_page(mm, vma, address,
 					pte, pmd, flags, entry);

Patches currently in stable-queue which might be from [email protected] are

queue-4.1/mm-avoid-setting-up-anonymous-pages-into-file-mapping.patch