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    SubjectRe: [PATCH 2/4] signals: send_signal: use si_fromuser() to detect from_ancestor_ns
    Oleg Nesterov [oleg@redhat.com] wrote:
    | On 10/05, Sukadev Bhattiprolu wrote:
    | >
    | > Oleg Nesterov [oleg@redhat.com] wrote:
    | > |
    | > | --- 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)));
    |
    | I don't think so.
    |
    | First of all, this is just ugly. If we need this check we should change
    | the callers, not send_signal().

    Well, all I am saying is that the check

    !task_pid_nr_ns(current, task_active_pid_ns(t)))

    excludes container-init sending signal to itself - task_pid_nr_ns() above
    would return 1 for container-init and 'from_ancestor_ns' would be 0.

    But sure, we could use force_sig_info() in caller.

    |
    | But more importantly, I disagree with "container-init is immune to suicide"
    | above. This is another issue I was going to discuss later, lets do this now.

    Ok :-)

    |
    | When load_elf_binary() does send_sig(SIGKILL, current) init must die, because
    | we have no option. Exec failed, but we can't return to user-space with the
    | error code, it is too late.
    |

    Hence the SIGKILL - I agree with this.


    | So, imho this patch also fixes this case by accident,

    This part I am not sure. But as mentioned above, from_ancestor_ns is 0
    and the SIGKILL will not queued right ?


    | but I think it would
    | be better to change load_aout_binary/etc to use force_sig_info() to make
    | the code more explicit.
    |
    | What do you think?
    |
    | Oleg.


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