2017-08-15 11:28:21

by Jamie Iles

Subject: [PATCH] signal: don't remove SIGNAL_UNKILLABLE for traced tasks.

When forcing a signal, SIGNAL_UNKILLABLE is removed to prevent recursive
faults, but this is undesirable when tracing. For example, debugging an
init process (whether global or namespace), hitting a breakpoint and
SIGTRAP will force SIGTRAP and then remove SIGNAL_UNKILLABLE.
Everything continues fine, but then once debugging has finished, the
init process is left killable which is unlikely what the user expects,
resulting in either an accidentally killed init or an init that stops
reaping zombies.

Cc: Andrew Morton <[email protected]>
Cc: Oleg Nesterov <[email protected]>
Signed-off-by: Jamie Iles <[email protected]>
---
kernel/signal.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/kernel/signal.c b/kernel/signal.c
index 7e33f8c583e6..ed804a470dcd 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -1194,7 +1194,11 @@ force_sig_info(int sig, struct siginfo *info, struct task_struct *t)
recalc_sigpending_and_wake(t);
}
}
- if (action->sa.sa_handler == SIG_DFL)
+ /*
+ * Don't clear SIGNAL_UNKILLABLE for traced tasks, users won't expect
+ * debugging to leave init killable.
+ */
+ if (action->sa.sa_handler == SIG_DFL && !t->ptrace)
t->signal->flags &= ~SIGNAL_UNKILLABLE;
ret = specific_send_sig_info(sig, info, t);
spin_unlock_irqrestore(&t->sighand->siglock, flags);
--
2.13.3

2017-08-15 16:17:01

by Oleg Nesterov

Subject: Re: [PATCH] signal: don't remove SIGNAL_UNKILLABLE for traced tasks.

On 08/15, Jamie Iles wrote:
>
> --- a/kernel/signal.c
> +++ b/kernel/signal.c
> @@ -1194,7 +1194,11 @@ force_sig_info(int sig, struct siginfo *info, struct task_struct *t)
> recalc_sigpending_and_wake(t);
> }
> }
> - if (action->sa.sa_handler == SIG_DFL)
> + /*
> + * Don't clear SIGNAL_UNKILLABLE for traced tasks, users won't expect
> + * debugging to leave init killable.
> + */
> + if (action->sa.sa_handler == SIG_DFL && !t->ptrace)
> t->signal->flags &= ~SIGNAL_UNKILLABLE;
> ret = specific_send_sig_info(sig, info, t);
> spin_unlock_irqrestore(&t->sighand->siglock, flags);

Acked-by: Oleg Nesterov <[email protected]>