[Devel] Re: [PATCH 1/3] Signal semantics for /sbin/init

[Oleg Nesterov]

On 09/13, Cedric Le Goater wrote:
>
> Oleg Nesterov wrote:
> > On 09/10, sukadev at us.ibm.com wrote:
> >> (This is Oleg's patch with my pid ns additions. Compiled and unit tested
> >> on 2.6.23-rc4-mm1 with other patches in this set. Oleg pls update this
> >> patch if necessary and sign-off)
> > 
> > Sukadev, my apologies. This patch does need some changes,
> > 
> >> Notes:
> >>
> >> 	- Blocked signals are never ignored, so init still can receive
> >> 	  a pending blocked signal after sigprocmask(SIG_UNBLOCK).
> >> 	  Easy to fix, but probably we can ignore this issue.
> > 
> > I was wrong. This should be fixed right now. I _think_ this is easy,
> > and I was going to finish this patch yesterday, but - sorry! - I just
> > can't switch to "kernel mode" these days, I am fighting with some urgent
> > tasks on my paid job.
> > 
> To respect the current init semantic,

The current init semantic is broken in many ways ;)

> shouldn't we discard any unblockable 
> signal (STOP and KILL) sent by a process to its pid namespace init process ? 
> Then, all other signals should be handled appropriately by the pid namespace 
> init. 

Yes, I think you are probably right, this should be enough in practice. After all,
only root can send the signal to /sbin/init. On my machine, /proc/1/status shows
that init doesn't have a handler for non-ignored SIGUNUSED == 31, though.

But who knows? The kernel promises some guarantees, it is not good to break them.
Perhaps some strange non-standard environment may suffer.

> We are assuming that the pid namespace init is not doing anything silly and 
> I guess it's OK if the consequences are only on the its pid namespace and 
> not the whole system.

The sub-namespace case is very easy afaics, we only need the "signal comes from
the parent namespace" check, not a problem if we make the decision on the sender's
path, like this patch does.

Oleg.

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