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Subject[RFC][PATCH 2/6][v3] Protect init from unwanted signals more

From: Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>
Date: Fri, 19 Dec 2008 13:12:45 -0800
Subject: [RFC][PATCH 2/6][v3] Protect init from unwanted signals more

(This is a modified version of the patch submitted by Oleg Nesterov
http://lkml.org/lkml/2008/11/18/249 and tries to address comments
that came up in that discussion)

init ignores the SIG_DFL signals but we queue them anyway, including
SIGKILL. This is mostly OK, the signal will be dropped silently when
dequeued, but the pending SIGKILL has 2 bad implications:

- it implies fatal_signal_pending(), so we confuse things
like wait_for_completion_killable/lock_page_killable.

- for the sub-namespace inits, the pending SIGKILL can
mask (legacy_queue) the subsequent SIGKILL from the
parent namespace which must kill cinit reliably.
(preparation, cinits don't have SIGNAL_UNKILLABLE yet)

The patch can't help when init is ptraced, but ptracing of init is
not "safe" anyway.

Signed-off-by: Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>
---
kernel/signal.c | 16 +++++++++++++---
1 files changed, 13 insertions(+), 3 deletions(-)
diff --git a/kernel/signal.c b/kernel/signal.c
index 7945e71..55f41b6 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -53,10 +53,21 @@ static int sig_handler_ignored(void __user *handler, int sig)
(handler == SIG_DFL && sig_kernel_ignore(sig));
}

-static int sig_ignored(struct task_struct *t, int sig)
+static int sig_task_ignored(struct task_struct *t, int sig)
{
void __user *handler;

+ handler = sig_handler(t, sig);
+
+ if (unlikely(t->signal->flags & SIGNAL_UNKILLABLE) &&
+ (handler == SIG_IGN || handler == SIG_DFL))
+ return 1;
+
+ return sig_handler_ignored(handler, sig);
+}
+
+static int sig_ignored(struct task_struct *t, int sig)
+{
/*
* Blocked signals are never ignored, since the
* signal handler may change by the time it is
@@ -65,8 +76,7 @@ static int sig_ignored(struct task_struct *t, int sig)
if (sigismember(&t->blocked, sig) || sigismember(&t->real_blocked, sig))
return 0;

- handler = sig_handler(t, sig);
- if (!sig_handler_ignored(handler, sig))
+ if (!sig_task_ignored(t, sig))
return 0;

/*
--
1.5.2.5


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