[PATCH AUTOSEL 4.9 13/73] signal/pid_namespace: Fix reboot_pid_ns to use send_sig not force_sig

[Sasha Levin]

From: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx>

[ Upstream commit f9070dc94542093fd516ae4ccea17ef46a4362c5 ]

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@xxxxxxx>
Cc: Serge Hallyn <serge@xxxxxxxxxx>
Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
Fixes: cf3f89214ef6 ("pidns: add reboot_pid_ns() to handle the reboot syscall")
Signed-off-by: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 kernel/pid_namespace.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/pid_namespace.c b/kernel/pid_namespace.c
index 3976dd57db78..0eab538841fd 100644
--- a/kernel/pid_namespace.c
+++ b/kernel/pid_namespace.c
@@ -344,7 +344,7 @@ int reboot_pid_ns(struct pid_namespace *pid_ns, int cmd)
 	}
 
 	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);
-- 
2.20.1