[for-3.18,7/7] mm: avoid setting up anonymous pages into file mapping

Message ID 1493832958-12489-8-git-send-email-amit.pundir@linaro.org
State New
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Series
  • Security fixes picked from android security bulletins
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Commit Message

Amit Pundir May 3, 2017, 5:35 p.m.
From: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>


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.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>

Acked-by: Oleg Nesterov <oleg@redhat.com>

Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Willy Tarreau <w@1wt.eu>
Cc: stable@vger.kernel.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

(cherry picked from commit 6b7339f4c31ad69c8e9c0b2859276e22cf72176d)
Signed-off-by: Amit Pundir <amit.pundir@linaro.org>

---
 mm/memory.c | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

-- 
2.7.4

Patch

diff --git a/mm/memory.c b/mm/memory.c
index e8e3cf7bd247..6ca26c332712 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -2629,6 +2629,10 @@  static int do_anonymous_page(struct mm_struct *mm, struct vm_area_struct *vma,
 
 	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;
@@ -3033,6 +3037,9 @@  static int do_linear_fault(struct mm_struct *mm, struct vm_area_struct *vma,
 			- 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);
@@ -3198,11 +3205,9 @@  static int handle_pte_fault(struct mm_struct *mm,
 	entry = ACCESS_ONCE(*pte);
 	if (!pte_present(entry)) {
 		if (pte_none(entry)) {
-			if (vma->vm_ops) {
-				if (likely(vma->vm_ops->fault))
-					return do_linear_fault(mm, vma, address,
+			if (vma->vm_ops)
+				return do_linear_fault(mm, vma, address,
 						pte, pmd, flags, entry);
-			}
 			return do_anonymous_page(mm, vma, address,
 						 pte, pmd, flags);
 		}