From a8f531ebc33052642b4bd7b812eedf397108ce64 Mon Sep 17 00:00:00 2001 From: Libin Date: Wed, 11 Sep 2013 14:20:38 -0700 Subject: [PATCH] mm/huge_memory.c: fix potential NULL pointer dereference In collapse_huge_page() there is a race window between releasing the mmap_sem read lock and taking the mmap_sem write lock, so find_vma() may return NULL. So check the return value to avoid NULL pointer dereference. collapse_huge_page khugepaged_alloc_page up_read(&mm->mmap_sem) down_write(&mm->mmap_sem) vma = find_vma(mm, address) Signed-off-by: Libin Acked-by: Kirill A. Shutemov Reviewed-by: Wanpeng Li Reviewed-by: Michal Hocko Cc: # v3.0+ Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/huge_memory.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/mm/huge_memory.c b/mm/huge_memory.c index 8b7fc2025e04..963e14c0486f 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -2296,6 +2296,8 @@ static void collapse_huge_page(struct mm_struct *mm, goto out; vma = find_vma(mm, address); + if (!vma) + goto out; hstart = (vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK; hend = vma->vm_end & HPAGE_PMD_MASK; if (address < hstart || address + HPAGE_PMD_SIZE > hend)