mm/huge_memory.c: fix potential NULL pointer dereference

commit a8f531ebc33052642b4bd7b812eedf397108ce64 upstream.

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 <huawei.libin@huawei.com>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Reviewed-by: Wanpeng Li <liwanp@linux.vnet.ibm.com>
Reviewed-by: Michal Hocko <mhocko@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 362c329b83fe7441b4d2119c1e164a54c58fc860..b92d0ce428b1dda83fc8ea30311506c7a1dfdcd7 100644 (file)
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2286,6 +2286,8 @@ 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)