[PATCH 7/7][v8] SI_USER: Masquerade si_pid when crossing pid ns boundary

[Oleg Nesterov]

On 02/19, Eric W. Biederman wrote:
>
> Oleg Nesterov <oleg at redhat.com> writes:
> >
> > SI_FROMUSER() == T, unless we have more (hopefully not) in-kernel
> > users which send SI_FROMUSER() signals, .si_pid must be valid?
>
> So the argument is that while things such as force_sig_info(SIGSEGV)
> don't have a si_pid we don't care because from_ancestor_ns  == 0.
>
> Interesting.  Then I don't know if we have any kernel senders
> that cross the namespace boundaries.
>
> That said I still object to this code.
>
> sys_kill(-pgrp, SIGUSR1)
>   kill_something_info(SIGUSR1, &info, 0)
>     __kill_pgrp_info(SIGUSR1, &info task_pgrp(current))
>       group_send_sig_info(SIGUSR1, &info, tsk)
>         __group_send_sig_info(SIGUSR1, &info, tsk)
>           send_signal(SIGUSR1, &info, tsk, 1)
>             __send_signal(SIGUSR1, &info, tsk, 1)
>
>
> Process groups and sessions can have processes in multiple pid
> namespaces, which is very useful for not messing up your controlling
> terminal.
>
> In which case sys_kill cannot possibly set the si_pid value correct
> and from_ancestor_ns is not enough either.

(I know, I shouldn't reply today because I am already sleeping ;)

Why? send_signal() should calculate the correct value of
from_parent and pass it to __send_signal(). If it is true, then
we clear .si_pid in the copied siginfo (which was already queued).
We don't mangle the original siginfo.

This happens for each process we send the signal.

Or I misunderstood you?

Oleg.