ip_mroute: Make privilege checking more consistent

- The v6 socket option and ioctl handlers had no privilege checks at
  all.  The socket options, I believe, can only be reached via a raw
  socket, but a jailed root user with a raw socket shouldn't be able to
  configure multicast routing in a non-VNET jail.  The ioctls can only
  be used to fetch stats.
- Delete a bogus comment in X_mrt_ioctl(), one can issue multicast
  routing ioctls against any socket.  Note that the call path is
  soo_ioctl()->rtioctl_fib()->mrt_ioctl().

I think all of the mroute privilege checks should be done within the
ip(6)_mroute code, but let's first make the v4 and v6 modules
consistent.

Reviewed by:	glebius
MFC after:	2 weeks
Sponsored by:	Stormshield
Sponsored by:	Klara, Inc.
Differential Revision:	https://reviews.freebsd.org/D54982

sys/netinet/ip_mroute.c

@@ -546,11 +546,6 @@ X_mrt_ioctl(u_long cmd, caddr_t data, int fibnum __unused)
 {
 	int error;
 
-	/*
-	 * Currently the only function calling this ioctl routine is rtioctl_fib().
-	 * Typically, only root can create the raw socket in order to execute
-	 * this ioctl method, however the request might be coming from a prison
-	 */
 	error = priv_check(curthread, PRIV_NETINET_MROUTE);
 	if (error)
 		return (error);

sys/netinet6/ip6_mroute.c

@@ -89,6 +89,7 @@
 #include <sys/mbuf.h>
 #include <sys/module.h>
 #include <sys/domain.h>
+#include <sys/priv.h>
 #include <sys/protosw.h>
 #include <sys/sdt.h>
 #include <sys/signalvar.h>
@@ -458,24 +459,26 @@ X_ip6_mrouter_get(struct socket *so, struct sockopt *sopt)
 static int
 X_mrt6_ioctl(u_long cmd, caddr_t data)
 {
-	int ret;
-
-	ret = EINVAL;
+	int error;
 
+	error = priv_check(curthread, PRIV_NETINET_MROUTE);
+	if (error)
+		return (error);
+	error = EINVAL;
 	switch (cmd) {
 	case SIOCGETSGCNT_IN6:
-		ret = get_sg_cnt((struct sioc_sg_req6 *)data);
+		error = get_sg_cnt((struct sioc_sg_req6 *)data);
 		break;
 
 	case SIOCGETMIFCNT_IN6:
-		ret = get_mif6_cnt((struct sioc_mif_req6 *)data);
+		error = get_mif6_cnt((struct sioc_mif_req6 *)data);
 		break;
 
 	default:
 		break;
 	}
 
-	return (ret);
+	return (error);
 }
 
 /*

sys/netinet6/raw_ip6.c

@@ -604,6 +604,9 @@ rip6_ctloutput(struct socket *so, struct sockopt *sopt)
 		case MRT6_ADD_MFC:
 		case MRT6_DEL_MFC:
 		case MRT6_PIM:
+			error = priv_check(curthread, PRIV_NETINET_MROUTE);
+			if (error != 0)
+				return (error);
 			if (inp->inp_ip_p != IPPROTO_ICMPV6)
 				return (EOPNOTSUPP);
 			error = ip6_mrouter_get ?  ip6_mrouter_get(so, sopt) :
@@ -627,6 +630,9 @@ rip6_ctloutput(struct socket *so, struct sockopt *sopt)
 		case MRT6_ADD_MFC:
 		case MRT6_DEL_MFC:
 		case MRT6_PIM:
+			error = priv_check(curthread, PRIV_NETINET_MROUTE);
+			if (error != 0)
+				return (error);
 			if (inp->inp_ip_p != IPPROTO_ICMPV6)
 				return (EOPNOTSUPP);
 			error = ip6_mrouter_set ?  ip6_mrouter_set(so, sopt) :