Re: [RFC] nodemask: Consider MAX_NUMNODES inside node_isset

[Anshuman Khandual]

On 01/03/2017 02:47 PM, Michal Hocko wrote:
> On Tue 03-01-17 14:37:09, Anshuman Khandual wrote:
>> On 01/03/2017 02:14 PM, Michal Hocko wrote:
>>> On Tue 03-01-17 13:57:53, Anshuman Khandual wrote:
>>>> node_isset can give incorrect result if the node number is beyond the
>>>> bitmask size (MAX_NUMNODES in this case) which is not checked inside
>>>> test_bit. Hence check for the bit limits (MAX_NUMNODES) inside the
>>>> node_isset function before calling test_bit.
>>> Could you be more specific when such a thing might happen? Have you seen
>>> any in-kernel user who would give such a bogus node?
>>
>> Have not seen this through any in-kernel use case. While rebasing the CDM
>> zonelist rebuilding series,
> 
> Then fix this particular code path...

Yeah I did.

> 
>> I came across this through an error path when
>> a bogus node value of 256 (MAX_NUMNODES on POWER) is received when we call
>> first_node() on an empty nodemask (which itself seems weird as well).
> 
> Does calling first_node on an empty nodemask make any sense? If there is
> a risk then I would expect nodes_empty() check before doing any mask
> related operations.

Hmm, you are right. All these checks should be done by the caller not
these nodemask helper functions.