[PATCH] page_mkwrite caller race fix
After do_wp_page has tested page_mkwrite, it must release old_page after
acquiring page table lock, not before: at some stage that ordering got
reversed, leaving a (very unlikely) window in which old_page might be
truncated, freed, and reused in the same position.
Signed-off-by: Hugh Dickins <hugh@veritas.com>
Acked-by: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/memory.c b/mm/memory.c
index ef09f0a..0047d3a 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1531,8 +1531,6 @@
if (vma->vm_ops->page_mkwrite(vma, old_page) < 0)
goto unwritable_page;
- page_cache_release(old_page);
-
/*
* Since we dropped the lock we need to revalidate
* the PTE as someone else may have changed it. If
@@ -1541,6 +1539,7 @@
*/
page_table = pte_offset_map_lock(mm, pmd, address,
&ptl);
+ page_cache_release(old_page);
if (!pte_same(*page_table, orig_pte))
goto unlock;
}