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signal: Always ignore SIGKILL and SIGSTOP sent to the global init

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[ Upstream commit 86989c41b5 ]

If the first process started (aka /sbin/init) receives a SIGKILL it
will panic the system if it is delivered.  Making the system unusable
and undebugable.  It isn't much better if the first process started
receives SIGSTOP.

So always ignore SIGSTOP and SIGKILL sent to init.

This is done in a separate clause in sig_task_ignored as force_sig_info
can clear SIG_UNKILLABLE and this protection should work even then.

Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
Eric W. Biederman
2018-07-19 19:47:27 -05:00
committed by Chris
parent 5633e4d2f6
commit cfc8bafc18
1 changed files with 4 additions and 0 deletions
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4
kernel/signal.c
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@@ -71,6 +71,10 @@ static int sig_task_ignored(struct task_struct *t, int sig, bool force)
handler = sig_handler(t, sig);
/* SIGKILL and SIGSTOP may not be sent to the global init */
if (unlikely(is_global_init(t) && sig_kernel_only(sig)))
return true;
if (unlikely(t->signal->flags & SIGNAL_UNKILLABLE) &&
handler == SIG_DFL && !(force && sig_kernel_only(sig)))
return 1;