Re: [PATCH v6] Added PR_SET_PROCTITLE_AREA option for prctl()

[Ingo Molnar <mingo@elte.hu>]

* KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> wrote:

> > > 
> > > * KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> wrote:
> > > 
> > > > > The feature looks useful, but the choice of a prctl as an API is strange 
> > > > > - it limits us to the current task only - while the ability to set 
> > > > > arguments for another task looks a more generic (and potentially more 
> > > > > useful) solution.
> > > > 
> > > > No. It's impossible.
> > > > /proc/{pid}/cmdline read user process's memory. iow, this prctl() don't
> > > > receive string, it receive virtual address itself. [...]
> > > 
> > > it's not 'impossible' at all, you yourself mention ptrace:
> > 
> > Ah yes, 'impossible' was wrong word. but it doesn't works intentionally.
> > 
> > 1. setproctitle() unaware application continue to see argv[0] directly.
> >   it makes some inconsistent behavior. 
> > 2. proc title (i.e. string) injection need to map new page as process title area.
> >    implicit mapping increasing makes new trouble
> >    - mihgt cause to exceed max_map_count awhile after.
> >    - might cause leak proc title area (who know when it should be freed?)
> > 
> > I think reasonable way is 1. send signal (or use another inter process
> > communication way) to target process 2. target process change own proc title
> > themself.
> > 
> > Plus, I haven't seen the use-case of changin another task. iow I doubt
> > it's worth to change lots code.
> 
> if your mention is strongly, can you please explain your expected use 
> case?

I have no strong opinion - i just raised the possibility. We try to 
avoid special-purpose APIs for new syscalls - we try to design them in a 
generic way.

	Ingo