signal: send_sig_all no longer needs SEND_SIG_FORCED

mainline inclusion
from mainline-4.20
commit b16503baa891
category: bugfix
bugzilla: 6354
CVE: NA
-------------------------------------------------

Now that send_signal always delivers SEND_SIG_PRIV signals to a pid
namespace init it is no longer necessary to use SEND_SIG_FORCED when
calling do_send_sig_info to ensure that pid namespace inits are
signaled and possibly killed.  Using SEND_SIG_PRIV is sufficient.

So use SEND_SIG_PRIV so that userspace when it receives a SIGTERM can
tell that the kernel sent the signal and not some random userspace
application.

Fixes: b82c3287 ("sysrq: use SEND_SIG_FORCED instead of force_sig()")
Reviewed-by: NThomas Gleixner <tglx@linutronix.de>
Signed-off-by: N"Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: NHongbo Yao <yaohongbo@huawei.com>
Reviewed-by: NYang Yingliang <yangyingliang@huawei.com>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>

drivers/tty/sysrq.c

@@ -348,7 +348,7 @@ static void send_sig_all(int sig)
 		if (is_global_init(p))
 			continue;
 
-		do_send_sig_info(sig, SEND_SIG_FORCED, p, PIDTYPE_MAX);
+		do_send_sig_info(sig, SEND_SIG_PRIV, p, PIDTYPE_MAX);
 	}
 	read_unlock(&tasklist_lock);
 }