netfilter: nf_ct_sctp: minimal multihoming support

Currently nf_conntrack_proto_sctp module handles only packets between
primary addresses used to establish the connection. Any packets between
secondary addresses are classified as invalid so that usual firewall
configurations drop them. Allowing HEARTBEAT and HEARTBEAT-ACK chunks to
establish a new conntrack would allow traffic between secondary
addresses to pass through. A more sophisticated solution based on the
addresses advertised in the initial handshake (and possibly also later
dynamic address addition and removal) would be much harder to implement.
Moreover, in general we cannot assume to always see the initial
handshake as it can be routed through a different path.

The patch adds two new conntrack states:

SCTP_CONNTRACK_HEARTBEAT_SENT - a HEARTBEAT chunk seen but not acked
SCTP_CONNTRACK_HEARTBEAT_ACKED - a HEARTBEAT acked by HEARTBEAT-ACK

State transition rules:

- HEARTBEAT_SENT responds to usual chunks the same way as NONE (so that
the behaviour changes as little as possible)
- HEARTBEAT_ACKED responds to usual chunks the same way as ESTABLISHED
does, except the resulting state is HEARTBEAT_ACKED rather than
ESTABLISHED
- previously existing states except NONE are preserved when HEARTBEAT or
HEARTBEAT-ACK is seen
- NONE (in the initial direction) changes to HEARTBEAT_SENT on HEARTBEAT
and to CLOSED on HEARTBEAT-ACK
- HEARTBEAT_SENT changes to HEARTBEAT_ACKED on HEARTBEAT-ACK in the
reply direction
- HEARTBEAT_SENT and HEARTBEAT_ACKED are preserved on HEARTBEAT and
HEARTBEAT-ACK otherwise

Normally, vtag is set from the INIT chunk for the reply direction and
from the INIT-ACK chunk for the originating direction (i.e. each of
these defines vtag value for the opposite direction). For secondary
conntracks, we can't rely on seeing INIT/INIT-ACK and even if we have
seen them, we would need to connect two different conntracks. Therefore
simplified logic is applied: vtag of first packet in each direction
(HEARTBEAT in the originating and HEARTBEAT-ACK in reply direction) is
saved and all following packets in that direction are compared with this
saved value. While INIT and INIT-ACK define vtag for the opposite
direction, vtags extracted from HEARTBEAT and HEARTBEAT-ACK are always
for their direction.

Default timeout values for new states are

HEARTBEAT_SENT: 30 seconds (default hb_interval)
HEARTBEAT_ACKED: 210 seconds (hb_interval * path_max_retry + max_rto)

(We cannot expect to see the shutdown sequence so that, unlike
ESTABLISHED, the HEARTBEAT_ACKED timeout shouldn't be too long.)

Signed-off-by: Michal Kubecek <[e-mail]>
Signed-off-by: Pablo Neira Ayuso <[e-mail]>

include/uapi/linux/netfilter/nf_conntrack_sctp.h

···
 	SCTP_CONNTRACK_SHUTDOWN_SENT,
 	SCTP_CONNTRACK_SHUTDOWN_RECD,
 	SCTP_CONNTRACK_SHUTDOWN_ACK_SENT,
+	SCTP_CONNTRACK_HEARTBEAT_SENT,
+	SCTP_CONNTRACK_HEARTBEAT_ACKED,
 	SCTP_CONNTRACK_MAX
 };
 

include/uapi/linux/netfilter/nfnetlink_cttimeout.h

···
 	CTA_TIMEOUT_SCTP_SHUTDOWN_SENT,
 	CTA_TIMEOUT_SCTP_SHUTDOWN_RECD,
 	CTA_TIMEOUT_SCTP_SHUTDOWN_ACK_SENT,
+	CTA_TIMEOUT_SCTP_HEARTBEAT_SENT,
+	CTA_TIMEOUT_SCTP_HEARTBEAT_ACKED,
 	__CTA_TIMEOUT_SCTP_MAX
 };
 #define CTA_TIMEOUT_SCTP_MAX (__CTA_TIMEOUT_SCTP_MAX - 1)

net/netfilter/nf_conntrack_proto_sctp.c

···
 	"SHUTDOWN_SENT",
 	"SHUTDOWN_RECD",
 	"SHUTDOWN_ACK_SENT",
+	"HEARTBEAT_SENT",
+	"HEARTBEAT_ACKED",
 };
 
 #define SECS  * HZ
···
 	[SCTP_CONNTRACK_SHUTDOWN_SENT]		= 300 SECS / 1000,
 	[SCTP_CONNTRACK_SHUTDOWN_RECD]		= 300 SECS / 1000,
 	[SCTP_CONNTRACK_SHUTDOWN_ACK_SENT]	= 3 SECS,
+	[SCTP_CONNTRACK_HEARTBEAT_SENT]		= 30 SECS,
+	[SCTP_CONNTRACK_HEARTBEAT_ACKED]	= 210 SECS,
 };
 
 #define sNO SCTP_CONNTRACK_NONE
···
 #define	sSS SCTP_CONNTRACK_SHUTDOWN_SENT
 #define	sSR SCTP_CONNTRACK_SHUTDOWN_RECD
 #define	sSA SCTP_CONNTRACK_SHUTDOWN_ACK_SENT
+#define	sHS SCTP_CONNTRACK_HEARTBEAT_SENT
+#define	sHA SCTP_CONNTRACK_HEARTBEAT_ACKED
 #define	sIV SCTP_CONNTRACK_MAX
 
 /*
···
 		    to that of the SHUTDOWN chunk.
 CLOSED            - We have seen a SHUTDOWN_COMPLETE chunk in the direction of
 		    the SHUTDOWN chunk. Connection is closed.
+HEARTBEAT_SENT    - We have seen a HEARTBEAT in a new flow.
+HEARTBEAT_ACKED   - We have seen a HEARTBEAT-ACK in the direction opposite to
+		    that of the HEARTBEAT chunk. Secondary connection is
+		    established.
 */
 
 /* TODO
···
  - Check the error type in the reply dir before transitioning from
 cookie echoed to closed.
  - Sec 5.2.4 of RFC 2960
- - Multi Homing support.
+ - Full Multi Homing support.
 */
 
 /* SCTP conntrack state transitions */
-static const u8 sctp_conntracks[2][9][SCTP_CONNTRACK_MAX] = {
+static const u8 sctp_conntracks[2][11][SCTP_CONNTRACK_MAX] = {
 	{
 /*	ORIGINAL	*/
-/*                  sNO, sCL, sCW, sCE, sES, sSS, sSR, sSA */
-/* init         */ {sCW, sCW, sCW, sCE, sES, sSS, sSR, sSA},
-/* init_ack     */ {sCL, sCL, sCW, sCE, sES, sSS, sSR, sSA},
-/* abort        */ {sCL, sCL, sCL, sCL, sCL, sCL, sCL, sCL},
-/* shutdown     */ {sCL, sCL, sCW, sCE, sSS, sSS, sSR, sSA},
-/* shutdown_ack */ {sSA, sCL, sCW, sCE, sES, sSA, sSA, sSA},
-/* error        */ {sCL, sCL, sCW, sCE, sES, sSS, sSR, sSA},/* Can't have Stale cookie*/
-/* cookie_echo  */ {sCL, sCL, sCE, sCE, sES, sSS, sSR, sSA},/* 5.2.4 - Big TODO */
-/* cookie_ack   */ {sCL, sCL, sCW, sCE, sES, sSS, sSR, sSA},/* Can't come in orig dir */
-/* shutdown_comp*/ {sCL, sCL, sCW, sCE, sES, sSS, sSR, sCL}
+/*                  sNO, sCL, sCW, sCE, sES, sSS, sSR, sSA, sHS, sHA */
+/* init         */ {sCW, sCW, sCW, sCE, sES, sSS, sSR, sSA, sCW, sHA},
+/* init_ack     */ {sCL, sCL, sCW, sCE, sES, sSS, sSR, sSA, sCL, sHA},
+/* abort        */ {sCL, sCL, sCL, sCL, sCL, sCL, sCL, sCL, sCL, sCL},
+/* shutdown     */ {sCL, sCL, sCW, sCE, sSS, sSS, sSR, sSA, sCL, sSS},
+/* shutdown_ack */ {sSA, sCL, sCW, sCE, sES, sSA, sSA, sSA, sSA, sHA},
+/* error        */ {sCL, sCL, sCW, sCE, sES, sSS, sSR, sSA, sCL, sHA},/* Can't have Stale cookie*/
+/* cookie_echo  */ {sCL, sCL, sCE, sCE, sES, sSS, sSR, sSA, sCL, sHA},/* 5.2.4 - Big TODO */
+/* cookie_ack   */ {sCL, sCL, sCW, sCE, sES, sSS, sSR, sSA, sCL, sHA},/* Can't come in orig dir */
+/* shutdown_comp*/ {sCL, sCL, sCW, sCE, sES, sSS, sSR, sCL, sCL, sHA},
+/* heartbeat    */ {sHS, sCL, sCW, sCE, sES, sSS, sSR, sSA, sHS, sHA},
+/* heartbeat_ack*/ {sCL, sCL, sCW, sCE, sES, sSS, sSR, sSA, sHS, sHA}
 	},
 	{
 /*	REPLY	*/
-/*                  sNO, sCL, sCW, sCE, sES, sSS, sSR, sSA */
-/* init         */ {sIV, sCL, sCW, sCE, sES, sSS, sSR, sSA},/* INIT in sCL Big TODO */
-/* init_ack     */ {sIV, sCL, sCW, sCE, sES, sSS, sSR, sSA},
-/* abort        */ {sIV, sCL, sCL, sCL, sCL, sCL, sCL, sCL},
-/* shutdown     */ {sIV, sCL, sCW, sCE, sSR, sSS, sSR, sSA},
-/* shutdown_ack */ {sIV, sCL, sCW, sCE, sES, sSA, sSA, sSA},
-/* error        */ {sIV, sCL, sCW, sCL, sES, sSS, sSR, sSA},
-/* cookie_echo  */ {sIV, sCL, sCW, sCE, sES, sSS, sSR, sSA},/* Can't come in reply dir */
-/* cookie_ack   */ {sIV, sCL, sCW, sES, sES, sSS, sSR, sSA},
-/* shutdown_comp*/ {sIV, sCL, sCW, sCE, sES, sSS, sSR, sCL}
+/*                  sNO, sCL, sCW, sCE, sES, sSS, sSR, sSA, sHS, sHA */
+/* init         */ {sIV, sCL, sCW, sCE, sES, sSS, sSR, sSA, sIV, sHA},/* INIT in sCL Big TODO */
+/* init_ack     */ {sIV, sCL, sCW, sCE, sES, sSS, sSR, sSA, sIV, sHA},
+/* abort        */ {sIV, sCL, sCL, sCL, sCL, sCL, sCL, sCL, sIV, sCL},
+/* shutdown     */ {sIV, sCL, sCW, sCE, sSR, sSS, sSR, sSA, sIV, sSR},
+/* shutdown_ack */ {sIV, sCL, sCW, sCE, sES, sSA, sSA, sSA, sIV, sHA},
+/* error        */ {sIV, sCL, sCW, sCL, sES, sSS, sSR, sSA, sIV, sHA},
+/* cookie_echo  */ {sIV, sCL, sCW, sCE, sES, sSS, sSR, sSA, sIV, sHA},/* Can't come in reply dir */
+/* cookie_ack   */ {sIV, sCL, sCW, sES, sES, sSS, sSR, sSA, sIV, sHA},
+/* shutdown_comp*/ {sIV, sCL, sCW, sCE, sES, sSS, sSR, sCL, sIV, sHA},
+/* heartbeat    */ {sIV, sCL, sCW, sCE, sES, sSS, sSR, sSA, sHS, sHA},
+/* heartbeat_ack*/ {sIV, sCL, sCW, sCE, sES, sSS, sSR, sSA, sHA, sHA}
 	}
 };
 
···
 		pr_debug("SCTP_CID_SHUTDOWN_COMPLETE\n");
 		i = 8;
 		break;
+	case SCTP_CID_HEARTBEAT:
+		pr_debug("SCTP_CID_HEARTBEAT");
+		i = 9;
+		break;
+	case SCTP_CID_HEARTBEAT_ACK:
+		pr_debug("SCTP_CID_HEARTBEAT_ACK");
+		i = 10;
+		break;
 	default:
-		/* Other chunks like DATA, SACK, HEARTBEAT and
-		its ACK do not cause a change in state */
+		/* Other chunks like DATA or SACK do not change the state */
 		pr_debug("Unknown chunk type, Will stay in %s\n",
 			 sctp_conntrack_names[cur_state]);
 		return cur_state;
···
 	    !test_bit(SCTP_CID_COOKIE_ECHO, map) &&
 	    !test_bit(SCTP_CID_ABORT, map) &&
 	    !test_bit(SCTP_CID_SHUTDOWN_ACK, map) &&
+	    !test_bit(SCTP_CID_HEARTBEAT, map) &&
+	    !test_bit(SCTP_CID_HEARTBEAT_ACK, map) &&
 	    sh->vtag != ct->proto.sctp.vtag[dir]) {
 		pr_debug("Verification tag check failed\n");
 		goto out;
···
 			/* Sec 8.5.1 (D) */
 			if (sh->vtag != ct->proto.sctp.vtag[dir])
 				goto out_unlock;
+		} else if (sch->type == SCTP_CID_HEARTBEAT ||
+			   sch->type == SCTP_CID_HEARTBEAT_ACK) {
+			if (ct->proto.sctp.vtag[dir] == 0) {
+				pr_debug("Setting vtag %x for dir %d\n",
+					 sh->vtag, dir);
+				ct->proto.sctp.vtag[dir] = sh->vtag;
+			} else if (sh->vtag != ct->proto.sctp.vtag[dir]) {
+				pr_debug("Verification tag check failed\n");
+				goto out_unlock;
+			}
 		}
 
 		old_state = ct->proto.sctp.state;
···
 				/* Sec 8.5.1 (A) */
 				return false;
 			}
+		} else if (sch->type == SCTP_CID_HEARTBEAT) {
+			pr_debug("Setting vtag %x for secondary conntrack\n",
+				 sh->vtag);
+			ct->proto.sctp.vtag[IP_CT_DIR_ORIGINAL] = sh->vtag;
 		}
 		/* If it is a shutdown ack OOTB packet, we expect a return
 		   shutdown complete, otherwise an ABORT Sec 8.4 (5) and (8) */
···
 	[CTA_TIMEOUT_SCTP_SHUTDOWN_SENT]	= { .type = NLA_U32 },
 	[CTA_TIMEOUT_SCTP_SHUTDOWN_RECD]	= { .type = NLA_U32 },
 	[CTA_TIMEOUT_SCTP_SHUTDOWN_ACK_SENT]	= { .type = NLA_U32 },
+	[CTA_TIMEOUT_SCTP_HEARTBEAT_SENT]	= { .type = NLA_U32 },
+	[CTA_TIMEOUT_SCTP_HEARTBEAT_ACKED]	= { .type = NLA_U32 },
 };
 #endif /* CONFIG_NF_CT_NETLINK_TIMEOUT */
 
···
 	},
 	{
 		.procname	= "nf_conntrack_sctp_timeout_shutdown_ack_sent",
+		.maxlen		= sizeof(unsigned int),
+		.mode		= 0644,
+		.proc_handler	= proc_dointvec_jiffies,
+	},
+	{
+		.procname	= "nf_conntrack_sctp_timeout_heartbeat_sent",
+		.maxlen		= sizeof(unsigned int),
+		.mode		= 0644,
+		.proc_handler	= proc_dointvec_jiffies,
+	},
+	{
+		.procname	= "nf_conntrack_sctp_timeout_heartbeat_acked",
 		.maxlen		= sizeof(unsigned int),
 		.mode		= 0644,
 		.proc_handler	= proc_dointvec_jiffies,
···
 	pn->ctl_table[4].data = &sn->timeouts[SCTP_CONNTRACK_SHUTDOWN_SENT];
 	pn->ctl_table[5].data = &sn->timeouts[SCTP_CONNTRACK_SHUTDOWN_RECD];
 	pn->ctl_table[6].data = &sn->timeouts[SCTP_CONNTRACK_SHUTDOWN_ACK_SENT];
+	pn->ctl_table[7].data = &sn->timeouts[SCTP_CONNTRACK_HEARTBEAT_SENT];
+	pn->ctl_table[8].data = &sn->timeouts[SCTP_CONNTRACK_HEARTBEAT_ACKED];
 #endif
 	return 0;
 }