Fix a few issues related to the legacy 4.4 BSD multicast APIs.

IPv4 addresses can and do change during normal operation. Testing by
pfSense developers exposed an issue where OpenOSPFD was using the IPv4
address to leave the OSPF link-scope multicast groups on a dynamic
OpenVPN tun interface, rather than using RFC 3678 with the interface
index, which won't be raced when the interface's addresses change.

In inp_join_group():
 If we are already a member of an ASM group, and IP_ADD_MEMBERSHIP or
 MCAST_JOIN_GROUP ioctls are re-issued, return EADDRINUSE as per the
 legacy 4.4BSD multicast API. This bends RFC 3678 slightly, but does
 not violate POLA for apps using the old API.
 It also stops us falling through to kicking IGMP state transactions
 in what is otherwise a no-op case.
 [This has already been dealt with in HEAD, but make it explicit before
  we MFC the change to 8.]

In inp_leave_group():
 Fix a bogus conditional.
 Move the ifp null check to ioctls MCAST_LEAVE* in the switch..case
 where it actually belongs.
 If an interface was specified, by primary IPv4 address, for ioctl
 IP_DROP_MEMBERSHIP or MCAST_LEAVE_GROUP (an ASM full leave operation),
 then and only then should we look up the ifp from the IPv4 address in
 mreqs.imr_interface.
 If not, we fall through to imo_match_group() as before, but only in
 the IP_DROP_MEMBERSHIP case.

With these changes, the legacy 4.4BSD multicast API idempotence should
be mostly preserved in the SSM enabled IPv4 stack.

Found by:	ermal (with pfSense)
MFC after:	3 days

1 files changed, 19 insertions, 7 deletions

diff --git a/sys/netinet/in_mcast.c b/sys/netinet/in_mcast.c
index 1f658da..4edf309 100644
--- a/sys/netinet/in_mcast.c
+++ b/sys/netinet/in_mcast.c
@@ -1999,9 +1999,12 @@ inp_join_group(struct inpcb *inp, struct sockopt *sopt)
 			}
 		} else {
 			/*
-			 * MCAST_JOIN_GROUP alone, on any existing membership,
-			 * is rejected, to stop the same inpcb tying up
-			 * multiple refs to the in_multi.
+			 * MCAST_JOIN_GROUP on an existing exclusive
+			 * membership is an error; return EADDRINUSE
+			 * to preserve 4.4BSD API idempotence, and
+			 * avoid tedious detour to code below.
+			 * NOTE: This is bending RFC 3678 a bit.
+			 *
 			 * On an existing inclusive membership, this is also
 			 * an error; if you want to change filter mode,
 			 * you must use the userland API setsourcefilter().
@@ -2010,6 +2013,8 @@ inp_join_group(struct inpcb *inp, struct sockopt *sopt)
 			 * is atomic with allocation of a membership.
 			 */
 			error = EINVAL;
+			if (imf->imf_st[1] == MCAST_EXCLUDE)
+				error = EADDRINUSE;
 			goto out_inp_locked;
 		}
 	}
@@ -2186,7 +2191,14 @@ inp_leave_group(struct inpcb *inp, struct sockopt *sopt)
 			ssa->sin.sin_addr = mreqs.imr_sourceaddr;
 		}
 
-		if (!in_nullhost(gsa->sin.sin_addr))
+		/*
+		 * Attempt to look up hinted ifp from interface address.
+		 * Fallthrough with null ifp iff lookup fails, to
+		 * preserve 4.4BSD mcast API idempotence.
+		 * XXX NOTE WELL: The RFC 3678 API is preferred because
+		 * using an IPv4 address as a key is racy.
+		 */
+		if (!in_nullhost(mreqs.imr_interface))
 			INADDR_TO_IFP(mreqs.imr_interface, ifp);
 
 		CTR3(KTR_IGMPV3, "%s: imr_interface = %s, ifp = %p",
@@ -2222,6 +2234,9 @@ inp_leave_group(struct inpcb *inp, struct sockopt *sopt)
 			return (EADDRNOTAVAIL);
 
 		ifp = ifnet_byindex(gsr.gsr_interface);
+
+		if (ifp == NULL)
+			return (EADDRNOTAVAIL);
 		break;
 
 	default:
@@ -2234,9 +2249,6 @@ inp_leave_group(struct inpcb *inp, struct sockopt *sopt)
 	if (!IN_MULTICAST(ntohl(gsa->sin.sin_addr.s_addr)))
 		return (EINVAL);
 
-	if (ifp == NULL)
-		return (EADDRNOTAVAIL);
-
 	/*
 	 * Find the membership in the membership array.
 	 */