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    Subject[PATCH 1/4] signal: give SEND_SIG_FORCED more power to beat SIGNAL_UNKILLABLE
    force_sig_info() and friends have the special semantics for
    synchronous signals, this interface should not be used if the
    target is not current. And it needs the fixes, in particular
    the clearing of SIGNAL_UNKILLABLE is not exactly right.

    However there are callers which have to use force_ exactly because
    it clears SIGNAL_UNKILLABLE and thus it can kill the CLONE_NEWPID
    tasks, although this is almost always is wrong by various reasons.

    With this patch SEND_SIG_FORCED ignores SIGNAL_UNKILLABLE, like
    we do if the signal comes from the ancestor namespace.

    This makes the naming in prepare_signal() paths insane, fixed by
    the next cleanup.

    Note: this only affects SIGKILL/SIGSTOP, but this is enough for
    force_sig() abusers.

    Signed-off-by: Oleg Nesterov <>
    kernel/signal.c | 3 ++-
    1 files changed, 2 insertions(+), 1 deletions(-)

    diff --git a/kernel/signal.c b/kernel/signal.c
    index c73c428..bfb2b97 100644
    --- a/kernel/signal.c
    +++ b/kernel/signal.c
    @@ -1059,7 +1059,8 @@ static int __send_signal(int sig, struct siginfo *info, struct task_struct *t,


    - if (!prepare_signal(sig, t, from_ancestor_ns))
    + if (!prepare_signal(sig, t,
    + from_ancestor_ns || (info == SEND_SIG_FORCED)))
    return 0;

    pending = group ? &t->signal->shared_pending : &t->pending;

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