Linux 3.2.83

[Ben Hutchings]

I'm announcing the release of the 3.2.83 kernel.

All users of the 3.2 kernel series should upgrade.

The updated 3.2.y git tree can be found at:
        https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git linux-3.2.y
and can be browsed at the normal kernel.org git web browser:
        https://git.kernel.org/?p=linux/kernel/git/stable/linux-stable.git

The diff from 3.2.82 is attached to this message.

Ben.

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

 Makefile           |  2 +-
 include/linux/mm.h |  1 +
 mm/memory.c        | 39 ++++++++++++++++++++++++++++-----------
 3 files changed, 30 insertions(+), 12 deletions(-)

Ben Hutchings (1):
      Linux 3.2.83

Michal Hocko (1):
      mm, gup: close FOLL MAP_PRIVATE race

diff --git a/Makefile b/Makefile
index b6fa6316ef75..716cdade034d 100644
--- a/Makefile
+++ b/Makefile
@@ -1,6 +1,6 @@
 VERSION = 3
 PATCHLEVEL = 2
-SUBLEVEL = 82
+SUBLEVEL = 83
 EXTRAVERSION =
 NAME = Saber-toothed Squirrel
 
diff --git a/include/linux/mm.h b/include/linux/mm.h
index e5ee683b0ad3..16394da01d2d 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1527,6 +1527,7 @@ struct page *follow_page(struct vm_area_struct *, unsigned long address,
 #define FOLL_MLOCK	0x40	/* mark page as mlocked */
 #define FOLL_SPLIT	0x80	/* don't return transhuge pages, split them */
 #define FOLL_HWPOISON	0x100	/* check page is hwpoisoned */
+#define FOLL_COW	0x4000	/* internal GUP flag */
 
 typedef int (*pte_fn_t)(pte_t *pte, pgtable_t token, unsigned long addr,
 			void *data);
diff --git a/mm/memory.c b/mm/memory.c
index 675b211296fd..2917e9b2e4d4 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1427,6 +1427,24 @@ int zap_vma_ptes(struct vm_area_struct *vma, unsigned long address,
 }
 EXPORT_SYMBOL_GPL(zap_vma_ptes);
 
+static inline bool can_follow_write_pte(pte_t pte, struct page *page,
+					unsigned int flags)
+{
+	if (pte_write(pte))
+		return true;
+
+	/*
+	 * Make sure that we are really following CoWed page. We do not really
+	 * have to care about exclusiveness of the page because we only want
+	 * to ensure that once COWed page hasn't disappeared in the meantime
+	 * or it hasn't been merged to a KSM page.
+	 */
+	if ((flags & FOLL_FORCE) && (flags & FOLL_COW))
+		return page && PageAnon(page) && !PageKsm(page);
+
+	return false;
+}
+
 /**
  * follow_page - look up a page descriptor from a user-virtual address
  * @vma: vm_area_struct mapping @address
@@ -1509,10 +1527,13 @@ split_fallthrough:
 	pte = *ptep;
 	if (!pte_present(pte))
 		goto no_page;
-	if ((flags & FOLL_WRITE) && !pte_write(pte))
-		goto unlock;
 
 	page = vm_normal_page(vma, address, pte);
+	if ((flags & FOLL_WRITE) && !can_follow_write_pte(pte, page, flags)) {
+		pte_unmap_unlock(ptep, ptl);
+		return NULL;
+	}
+
 	if (unlikely(!page)) {
 		if ((flags & FOLL_DUMP) ||
 		    !is_zero_pfn(pte_pfn(pte)))
@@ -1555,7 +1576,7 @@ split_fallthrough:
 			unlock_page(page);
 		}
 	}
-unlock:
+
 	pte_unmap_unlock(ptep, ptl);
 out:
 	return page;
@@ -1789,17 +1810,13 @@ int __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
 				 * The VM_FAULT_WRITE bit tells us that
 				 * do_wp_page has broken COW when necessary,
 				 * even if maybe_mkwrite decided not to set
-				 * pte_write. We can thus safely do subsequent
-				 * page lookups as if they were reads. But only
-				 * do so when looping for pte_write is futile:
-				 * in some cases userspace may also be wanting
-				 * to write to the gotten user page, which a
-				 * read fault here might prevent (a readonly
-				 * page might get reCOWed by userspace write).
+				 * pte_write. We cannot simply drop FOLL_WRITE
+				 * here because the COWed page might be gone by
+				 * the time we do the subsequent page lookups.
 				 */
 				if ((ret & VM_FAULT_WRITE) &&
 				    !(vma->vm_flags & VM_WRITE))
-					foll_flags &= ~FOLL_WRITE;
+					foll_flags |= FOLL_COW;
 
 				cond_resched();
 			}

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