Re: + c-r-prctl-add-ability-to-set-new-mm_struct-exe_file-update-after-mm- num_exe_file_vmas-removal.patch added to -mm tree

[Konstantin Khlebnikov <khlebnikov@openvz.org>]

Oleg Nesterov wrote:
> On 04/20, Cyrill Gorcunov wrote:
>>
>> Guys, while I more-less agree with Matt about single-shot behaviour
>>
>> [ let me copy my and his email
>>
>>    >>  With mm->exe_file this prctl option become a one-shot
>>    >>  only, and while at moment our user-space tool can perfectly
>>    >>  live with that I thought that there is no strict need to
>>    >>  limit the option this way from the very beginning.
>>    >>
>>    >  As far as backward compatibility, isn't it better to lift that restriction
>>    >  later rather than add it? I think the latter would very likely "break"
>>    >  things whereas the former would not.
>>    >
>>    >  I also prefer that restriction because it establishes a bound on how
>>    >  frequently the symlink can change. Keeping it a one-shot deal makes the
>>    >  values that show up in tools like top more reliable for admins.
>> ]
>>
>> I guess maybe it's time to drop one-shot requirement and as result
>> we can drop MMF_EXE_FILE_CHANGED bit completely,
>
> Plus perhaps we can remove this for_each_vma check?
>
>> making overall code
>> simplier?
>
> Personally I'd certainly prefer this ;)
>
>
>
> But let me repeat to avoid the confusion. I am fine either way,
> I am not going to discuss this again unless I see something which
> looks technically wrong. And the current MMF_EXE_FILE_CHANGED
> doesn't look right even if the problem is minor.

Yeah, whole this protection does not protect anything and can be easily bypassed.
For example task can re-execute itself and change exe-file again and again.

>
> Oleg.
>