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

[Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>]

Oleg Nesterov [oleg@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@fr.ibm.com>
| Signed-off-by: Oleg Nesterov <oleg@redhat.com>

Since, addressing the problem of container-init sending SIGKILL to itself
would have to be a separate patch:

Reviewed-by: Sukadev Bhattiprolu <sukadev@us.ibm.com>