Patch "ksm: fix unlocked iteration over vmas in cmp_and_merge_page()" has been added to the 4.13-stable tree

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

ksm: fix unlocked iteration over vmas in cmp_and_merge_page()

to the 4.13-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:
ksm-fix-unlocked-iteration-over-vmas-in-cmp_and_merge_page.patch
and it can be found in the queue-4.13 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 Tkhai <[email protected]>
Date: Tue, 3 Oct 2017 16:14:27 -0700
Subject: ksm: fix unlocked iteration over vmas in cmp_and_merge_page()

From: Kirill Tkhai <[email protected]>

commit 4b22927f0cbd58303aac689e378d20bf56267a39 upstream.

In this place mm is unlocked, so vmas or list may change. Down read mmap_sem to protect them from modifications.

---
 mm/ksm.c |    5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

@@ -1990,6 +1990,7 @@ static void stable_tree_append(struct rm
  */
 static void cmp_and_merge_page(struct page *page, struct rmap_item *rmap_item)
 {
+	struct mm_struct *mm = rmap_item->mm;
 	struct rmap_item *tree_rmap_item;
 	struct page *tree_page = NULL;
 	struct stable_node *stable_node;

@@ -2062,9 +2063,11 @@ static void cmp_and_merge_page(struct pa
 	if (ksm_use_zero_pages && (checksum == zero_checksum)) {
 		struct vm_area_struct *vma;
 
-		vma = find_mergeable_vma(rmap_item->mm, rmap_item->address);
+		down_read(&mm->mmap_sem);
+		vma = find_mergeable_vma(mm, rmap_item->address);
 		err = try_to_merge_one_page(vma, page,
 					    ZERO_PAGE(rmap_item->address));
+		up_read(&mm->mmap_sem);
 		/*
 		 * In case of failure, the page was not really empty, so we
 		 * need to continue. Otherwise we're done.

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

queue-4.13/ksm-fix-unlocked-iteration-over-vmas-in-cmp_and_merge_page.patch