CVE-2017-13025/IPv6 mobility: Add a bounds check before fetching data

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), modified
so the capture file won't cause 'tcpdump: pcap_loop: truncated dump file'

extract.h

@@ -281,3 +281,6 @@ EXTRACT_64BITS(const void *p)
 
 #define ND_TTEST_64BITS(p) ND_TTEST2(*(p), 8)
 #define ND_TCHECK_64BITS(p) ND_TCHECK2(*(p), 8)
+
+#define ND_TTEST_128BITS(p) ND_TTEST2(*(p), 16)
+#define ND_TCHECK_128BITS(p) ND_TCHECK2(*(p), 16)

print-mobility.c

@@ -159,6 +159,7 @@ mobility_opt_print(netdissect_options *ndo,
 				ND_PRINT((ndo, "(altcoa: trunc)"));
 				goto trunc;
 			}
+			ND_TCHECK_128BITS(&bp[i+2]);
 			ND_PRINT((ndo, "(alt-CoA: %s)", ip6addr_string(ndo, &bp[i+2])));
 			break;
 		case IP6MOPT_NONCEID:

tests/TESTLIST

@@ -526,6 +526,7 @@ icmp6_mobileprefix_asan	icmp6_mobileprefix_asan.pcap	icmp6_mobileprefix_asan.out
 ip_printroute_asan	ip_printroute_asan.pcap		ip_printroute_asan.out	-v
 mobility_opt_asan	mobility_opt_asan.pcap		mobility_opt_asan.out	-v
 mobility_opt_asan_2	mobility_opt_asan_2.pcap	mobility_opt_asan_2.out	-v
+mobility_opt_asan_3	mobility_opt_asan_3.pcap	mobility_opt_asan_3.out	-v
 
 # RTP tests
 # fuzzed pcap

tests/mobility_opt_asan_3.out

@@ -0,0 +1,2 @@
+IP6 (class 0x50, flowlabel 0x00004, hlim 0, next-header Mobile IP (old) (62) payload length: 7168) d400:7fa1:200:400::6238:2949 > 9675:86dd:7300:2c:1c7f:ffff:ffc3:b2a1: mobility: CoT nonce id=0x74 Care-of Init Cookie=80570f80:00000004[|MOBILITY]
+IP6 (class 0x50, flowlabel 0x00004, hlim 0, next-header Mobile IP (old) (62) payload length: 7168) ffc3:b2a1:200:400::6238:2949 > 9675:86dd:73f0:2c:1c7f:ffff:ebc3:b2a1: mobility: BU seq#=39837 lifetime=261452[|MOBILITY]