SCTP: Allow ADD_IP to work with AUTH for backward compatibility.

This patch adds a tunable that will allow ADD_IP to work without
AUTH for backward compatibility.  The default value is off since
the default value for ADD_IP is off as well.  People who need
to use ADD-IP with older implementations take risks of connection
hijacking and should consider upgrading or turning this tunable on.

Signed-off-by: Vlad Yasevich <vladislav.yasevich@hp.com>

net/sctp/sysctl.c

@@ -263,6 +263,15 @@ static ctl_table sctp_table[] = {
 		.proc_handler	= &proc_dointvec,
 		.strategy	= &sysctl_intvec
 	},
+	{
+		.ctl_name	= CTL_UNNUMBERED,
+		.procname	= "addip_noauth_enable",
+		.data		= &sctp_addip_noauth,
+		.maxlen		= sizeof(int),
+		.mode		= 0644,
+		.proc_handler	= &proc_dointvec,
+		.strategy	= &sysctl_intvec
+	},
 	{ .ctl_name = 0 }
 };