linux-kernel - [PATCH 3.16 05/47] signal/pid_namespace: Fix reboot_pid_ns to use send_sig not force

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Message-ID: <lsq.1572026582.524233753@decadent.org.uk>
Date:   Fri, 25 Oct 2019 19:03:06 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, Denis Kirjanov <kda@...ux-powerpc.org>,
        "Daniel Lezcano" <daniel.lezcano@...e.fr>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        "Oleg Nesterov" <oleg@...hat.com>,
        "Serge Hallyn" <serge@...lyn.com>
Subject: [PATCH 3.16 05/47] signal/pid_namespace: Fix reboot_pid_ns to use
 send_sig not force_sig

3.16.76-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: "Eric W. Biederman" <ebiederm@...ssion.com>

commit f9070dc94542093fd516ae4ccea17ef46a4362c5 upstream.

The locking in force_sig_info is not prepared to deal with a task that
exits or execs (as sighand may change).  The is not a locking problem
in force_sig as force_sig is only built to handle synchronous
exceptions.

Further the function force_sig_info changes the signal state if the
signal is ignored, or blocked or if SIGNAL_UNKILLABLE will prevent the
delivery of the signal.  The signal SIGKILL can not be ignored and can
not be blocked and SIGNAL_UNKILLABLE won't prevent it from being
delivered.

So using force_sig rather than send_sig for SIGKILL is confusing
and pointless.

Because it won't impact the sending of the signal and and because
using force_sig is wrong, replace force_sig with send_sig.

Cc: Daniel Lezcano <daniel.lezcano@...e.fr>
Cc: Serge Hallyn <serge@...lyn.com>
Cc: Oleg Nesterov <oleg@...hat.com>
Fixes: cf3f89214ef6 ("pidns: add reboot_pid_ns() to handle the reboot syscall")
Signed-off-by: "Eric W. Biederman" <ebiederm@...ssion.com>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 kernel/pid_namespace.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/kernel/pid_namespace.c
+++ b/kernel/pid_namespace.c
@@ -304,7 +304,7 @@ int reboot_pid_ns(struct pid_namespace *
 	}

 	read_lock(&tasklist_lock);
-	force_sig(SIGKILL, pid_ns->child_reaper);
+	send_sig(SIGKILL, pid_ns->child_reaper, 1);
 	read_unlock(&tasklist_lock);

 	do_exit(0);