Re: [PATCH] mm: Fix potential NULL pointer dereference

[Libin <huawei.libin@huawei.com>]

On 2013/7/24 12:35, Wanpeng Li wrote:
> On Wed, Jul 24, 2013 at 12:22:08PM +0800, Wanpeng Li wrote:
>> On Wed, Jul 24, 2013 at 11:48:19AM +0800, Libin wrote:
>>> find_vma may return NULL, thus check the return
>>> value to avoid NULL pointer dereference.
>>>
>>
>> When can this happen since down_read(&mm->mmap_sem) is held?
>>
> 
> Between mmap_sem read lock released and write lock held I think.
> 

Yes, In khugepaged_alloc_page mmap_sem read lock was released.
Thanks for your reply.
Libin.

>>> Signed-off-by: Libin <huawei.libin@huawei.com>
>>> ---
>>> mm/huge_memory.c | 2 ++
>>> 1 file changed, 2 insertions(+)
>>>
>>> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
>>> index 243e710..d4423f4 100644
>>> --- a/mm/huge_memory.c
>>> +++ b/mm/huge_memory.c
>>> @@ -2294,6 +2294,8 @@ 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)
>>> -- 
>>> 1.8.2.1
>>>
>>>
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>>
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> 
> 
> .
> 


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