Re: [PATCH] mm/mempolicy: Avoid use uninitialized preferred_node

[Yisheng Xie]

Hi Alexander ,

On 2018/3/9 18:49, Alexander Potapenko wrote:
> On Fri, Mar 9, 2018 at 6:21 AM, Yisheng Xie <xieyisheng1@xxxxxxxxxx> wrote:
>> Alexander reported an use of uninitialized memory in __mpol_equal(),
>> which is caused by incorrect use of preferred_node.
>>
>> When mempolicy in mode MPOL_PREFERRED with flags MPOL_F_LOCAL, it use
>> numa_node_id() instead of preferred_node, however, __mpol_equeue() use
>> preferred_node without check whether it is MPOL_F_LOCAL or not.
>>
>> Reported-by: Alexander Potapenko <glider@xxxxxxxxxx>
>> Signed-off-by: Yisheng Xie <xieyisheng1@xxxxxxxxxx>
> Tested-by: Alexander Potapenko <glider@xxxxxxxxxx>

Thanks,
> 
> I confirm that the patch fixes the problem. Thanks for the quick turnaround!
> Any idea which commit had introduced the bug in the first place?

IIUC, It is introduce by:
Fixes: fc36b8d3d819 (mempolicy: use MPOL_F_LOCAL to Indicate Preferred Local Policy)

Thanks
Yisheng
>> ---
>>  mm/mempolicy.c | 3 +++
>>  1 file changed, 3 insertions(+)
>>
>> diff --git a/mm/mempolicy.c b/mm/mempolicy.c
>> index d879f1d..641545e 100644
>> --- a/mm/mempolicy.c
>> +++ b/mm/mempolicy.c
>> @@ -2124,6 +2124,9 @@ bool __mpol_equal(struct mempolicy *a, struct mempolicy *b)
>>         case MPOL_INTERLEAVE:
>>                 return !!nodes_equal(a->v.nodes, b->v.nodes);
>>         case MPOL_PREFERRED:
>> +               /* a's flags is the same as b's */
>> +               if (a->flags & MPOL_F_LOCAL)
>> +                       return true;
>>                 return a->v.preferred_node == b->v.preferred_node;
>>         default:
>>                 BUG();
>> --
>> 1.8.3.1
>>
> 
> 
>