linux-kernel - Re: [PATCHv2] signal: protect SIGNAL_UNKILLABLE from unintentional clearing.

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Date:   Thu, 5 Jan 2017 19:18:59 +0100
From:   Oleg Nesterov <oleg@...hat.com>
To:     Jamie Iles <jamie.iles@...cle.com>
Cc:     linux-kernel@...r.kernel.org,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCHv2] signal: protect SIGNAL_UNKILLABLE from unintentional
 clearing.

On 01/04, Jamie Iles wrote:
>
> This can result in init becoming stoppable/killable after tracing.  For
> example, running:
>
>   while true; do kill -STOP 1; done &
>   strace -p 1
>
> and then stopping strace and the kill loop will result in init being
> left in state TASK_STOPPED.  Sending SIGCONT to init will resume it, but
> init will now respond to future SIGSTOP signals rather than ignoring
> them.

and to SIGKILL.

Another problem is that /sbin/init should ignore SIGKILL even when ptraced,
but this needs another patch, will try to do tomorrow. And yet another problem
with force_sig(), it should probably take ptrace and/or SIGTRAP into account.

Thanks Jamie,

Acked-by: Oleg Nesterov <oleg@...hat.com>