Code: unsigned int munlock_vma_page(struct page *page)
{
 	unsigned int nr_pages;
 	struct zone *zone = page_zone(page);
 
 	BUG_ON(!PageLocked(page));
 
 	/*
	 * Serialize with any parallel __split_huge_page_refcount() which
	 * might otherwise copy PageMlocked to part of the tail pages before
	 * we clear it in the head page. It also stabilizes hpage_nr_pages().
	 */
	spin_lock_irq(&zone->lru_lock);

	nr_pages = hpage_nr_pages(page);
	if (!TestClearPageMlocked(page))
		goto unlock_out;

	__mod_zone_page_state(zone, NR_MLOCK, -nr_pages);

	if (__munlock_isolate_lru_page(page, true)) {
		spin_unlock_irq(&zone->lru_lock);
		__munlock_isolated_page(page);
		goto out;
	}
	__munlock_isolation_failed(page);

unlock_out:
	spin_unlock_irq(&zone->lru_lock);

out:
	return nr_pages - 1;
}

Vulnerability Type: DoS 
CWE ID: CWE-264
Summary: The try_to_unmap_cluster function in mm/rmap.c in the Linux kernel before 3.14.3 does not properly consider which pages must be locked, which allows local users to cause a denial of service (system crash) by triggering a memory-usage pattern that requires removal of page-table mappings.
Commit Message: mm: try_to_unmap_cluster() should lock_page() before mlocking

A BUG_ON(!PageLocked) was triggered in mlock_vma_page() by Sasha Levin
fuzzing with trinity.  The call site try_to_unmap_cluster() does not lock
the pages other than its check_page parameter (which is already locked).

The BUG_ON in mlock_vma_page() is not documented and its purpose is
somewhat unclear, but apparently it serializes against page migration,
which could otherwise fail to transfer the PG_mlocked flag.  This would
not be fatal, as the page would be eventually encountered again, but
NR_MLOCK accounting would become distorted nevertheless.  This patch adds
a comment to the BUG_ON in mlock_vma_page() and munlock_vma_page() to that
effect.

The call site try_to_unmap_cluster() is fixed so that for page !=
check_page, trylock_page() is attempted (to avoid possible deadlocks as we
already have check_page locked) and mlock_vma_page() is performed only
upon success.  If the page lock cannot be obtained, the page is left
without PG_mlocked, which is again not a problem in the whole unevictable
memory design.

Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Bob Liu <bob.liu@oracle.com>
Reported-by: Sasha Levin <sasha.levin@oracle.com>
Cc: Wanpeng Li <liwanp@linux.vnet.ibm.com>
Cc: Michel Lespinasse <walken@google.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Acked-by: Rik van Riel <riel@redhat.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Hugh Dickins <hughd@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>