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[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>
This commit is contained in:
Hugh Dickins 2007-02-10 01:43:00 -08:00 committed by Linus Torvalds
parent f05b6284ee
commit c3704ceb4a
1 changed files with 1 additions and 2 deletions
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3
mm/memory.c
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@ -1531,8 +1531,6 @@ static int do_wp_page(struct mm_struct *mm, struct vm_area_struct *vma,
if (vma->vm_ops->page_mkwrite(vma, old_page) < 0) if (vma->vm_ops->page_mkwrite(vma, old_page) < 0)
goto unwritable_page; goto unwritable_page;
page_cache_release(old_page);
/* /*
* Since we dropped the lock we need to revalidate * Since we dropped the lock we need to revalidate
* the PTE as someone else may have changed it. If * the PTE as someone else may have changed it. If
@ -1541,6 +1539,7 @@ static int do_wp_page(struct mm_struct *mm, struct vm_area_struct *vma,
*/ */
page_table = pte_offset_map_lock(mm, pmd, address, page_table = pte_offset_map_lock(mm, pmd, address,
&ptl); &ptl);
page_cache_release(old_page);
if (!pte_same(*page_table, orig_pte)) if (!pte_same(*page_table, orig_pte))
goto unlock; goto unlock;
} }