[Devel] Re: [PATCH 2/4] signals: send_signal: use si_fromuser() to detect from_ancestor_ns

[Sukadev Bhattiprolu]

Oleg Nesterov [oleg at redhat.com] wrote:
| Change send_signal() to use si_fromuser(). From now SEND_SIG_NOINFO
| triggers the "from_ancestor_ns" check.
| 
| This fixes reparent_thread()->group_send_sig_info(pdeath_signal)
| behaviour, before this patch send_signal() does not detect the
| cross-namespace case when the child of the dying parent belongs
| to the sub-namespace.
| 
| This patch can affect the behaviour of send_sig(), kill_pgrp() and
| kill_pid() when the caller sends the signal to the sub-namespace
| with "priv == 0" but surprisingly all callers seem to use them
| correctly, including disassociate_ctty(on_exit).
| 
| Except: drivers/staging/comedi/drivers/addi-data/*.c incorrectly
| use send_sig(priv => 0). But his is minor and should be fixed
| anyway.
| 
| Reported-by: Daniel Lezcano <dlezcano at fr.ibm.com>
| Signed-off-by: Oleg Nesterov <oleg at redhat.com>
| ---
| 
|  kernel/signal.c |    5 ++---
|  1 file changed, 2 insertions(+), 3 deletions(-)
| 
| --- TTT_32/kernel/signal.c~FU_2_SEND_SIGNAL	2009-10-04 02:21:55.000000000 +0200
| +++ TTT_32/kernel/signal.c	2009-10-04 03:09:44.000000000 +0200
| @@ -928,9 +928,8 @@ static int send_signal(int sig, struct s
|  	int from_ancestor_ns = 0;
| 
|  #ifdef CONFIG_PID_NS
| -	if (!is_si_special(info) && SI_FROMUSER(info) &&
| -			task_pid_nr_ns(current, task_active_pid_ns(t)) <= 0)
| -		from_ancestor_ns = 1;
| +	from_ancestor_ns = si_fromuser(info) &&
| +			   !task_pid_nr_ns(current, task_active_pid_ns(t));

Makes sense. And we had mentioned earlier that container-init is immune
to suicide but should we add a check for 'current == t' above to cover the

	send_sig(SIGKILL, current, 0);

in load_aout_binary() and friends

	from_ancestor_ns = si_fromuser(info) && (current == t ||
				!task_pid_nr_ns(current, task_active_pid_ns(t)));

Sukadev.
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