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SubjectRe: + 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
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.

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