CVE-2017-13048/RSVP: fix decoding of Fast Reroute objects

In rsvp_obj_print() the case block for Class-Num 205 (FAST_REROUTE) from
RFC 4090 Section 4.1 could over-read accessing the buffer contents before
making the bounds check. Rearrange those steps the correct way around.

This fixes a buffer over-read discovered by Bhargava Shastry,
SecT/TU Berlin.

Add a test using the capture file supplied by the reporter(s).

print-rsvp.c

@@ -1472,12 +1472,12 @@ rsvp_obj_print(netdissect_options *ndo,
         case RSVP_OBJ_FASTREROUTE:
             /* the differences between c-type 1 and 7 are minor */
             obj_ptr.rsvp_obj_frr = (const struct rsvp_obj_frr_t *)obj_tptr;
-            bw.i = EXTRACT_32BITS(obj_ptr.rsvp_obj_frr->bandwidth);
 
             switch(rsvp_obj_ctype) {
             case RSVP_CTYPE_1: /* new style */
                 if (obj_tlen < sizeof(struct rsvp_obj_frr_t))
                     return-1;
+                bw.i = EXTRACT_32BITS(obj_ptr.rsvp_obj_frr->bandwidth);
                 ND_PRINT((ndo, "%s  Setup Priority: %u, Holding Priority: %u, Hop-limit: %u, Bandwidth: %.10g Mbps",
                        ident,
                        (int)obj_ptr.rsvp_obj_frr->setup_prio,
@@ -1496,6 +1496,7 @@ rsvp_obj_print(netdissect_options *ndo,
             case RSVP_CTYPE_TUNNEL_IPV4: /* old style */
                 if (obj_tlen < 16)
                     return-1;
+                bw.i = EXTRACT_32BITS(obj_ptr.rsvp_obj_frr->bandwidth);
                 ND_PRINT((ndo, "%s  Setup Priority: %u, Holding Priority: %u, Hop-limit: %u, Bandwidth: %.10g Mbps",
                        ident,
                        (int)obj_ptr.rsvp_obj_frr->setup_prio,

tests/TESTLIST

@@ -565,6 +565,7 @@ hncp_dhcpv4data-oobr	hncp_dhcpv4data-oobr.pcap	hncp_dhcpv4data-oobr.out -v -c1
 vqp-oobr		vqp-oobr.pcap			vqp-oobr.out		-v -c1
 bgp_pmsi_tunnel-oobr	bgp_pmsi_tunnel-oobr.pcap	bgp_pmsi_tunnel-oobr.out -v -c1
 bgp_mvpn_6_and_7	bgp_mvpn_6_and_7.pcap		bgp_mvpn_6_and_7.out	-v -c1
+rsvp_fast_reroute-oobr	rsvp_fast_reroute-oobr.pcap	rsvp_fast_reroute-oobr.out -v -c1
 
 # bad packets from Katie Holly
 mlppp-oobr		mlppp-oobr.pcap			mlppp-oobr.out

tests/rsvp_fast_reroute-oobr.out

@@ -0,0 +1,6 @@
+IP (tos 0x0, ttl 224, id 17920, offset 0, flags [none], proto RSVP (46), length 42024, bad cksum 3700 (->fc41)!)
+    0.203.243.128 > 0.26.0.0: 
+	RSVPv1 Path Message (1), Flags: [Refresh reduction capable], length: 41218, ttl: 227, checksum: 0x00f4
+	  Fast Re-Route Object (205) Flags: [ignore and forward if unknown], Class-Type: Unknown (0), length: 4
+	  Fast Re-Route Object (205) Flags: [ignore and forward if unknown], Class-Type: Unknown (0), length: 4
+		 [|rsvp]