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Subject[PATCH 2.6.32 54/62] mm: avoid setting up anonymous pages into file mapping
2.6.32-longterm review patch.  If anyone has any objections, please let me know.

------------------

From: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>

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.

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>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
(cherry picked from commit e2506476534cff7bb3697fbe0654fdefd101bc80)

Signed-off-by: Willy Tarreau <w@1wt.eu>
---
mm/memory.c | 13 +++++++++----
1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/mm/memory.c b/mm/memory.c
index 085b068..e36dee2 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -2727,6 +2727,10 @@ 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_SIGBUS;
@@ -2979,6 +2983,9 @@ 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;
return __do_fault(mm, vma, address, pmd, pgoff, flags, orig_pte);
}

@@ -3037,11 +3044,9 @@ static inline int handle_pte_fault(struct mm_struct *mm,
entry = *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);
}
--
1.7.12.2.21.g234cd45.dirty




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