CVE-2017-13008/IEEE 802.11: Fix TIM bitmap copy to copy from p + offset.

offset has already been advanced to point to the bitmap; we shouldn't
add the amount to advance again.

This fixes a buffer over-read discovered by Brian 'geeknik' Carpenter.

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

While we're at it, remove some redundant tests - we've already checked,
before the case statement, whether we have captured the entire
information element and whether the entire information element is
present in the on-the-wire packet; in the cases for particular IEs, we
only need to make sure we don't go past the end of the IE.

print-802_11.c

@@ -1039,10 +1039,6 @@ parse_elements(netdissect_options *ndo,
 			if (ssid.length != 0) {
 				if (ssid.length > sizeof(ssid.ssid) - 1)
 					return 0;
-				if (!ND_TTEST2(*(p + offset), ssid.length))
-					return 0;
-				if (length < ssid.length)
-					return 0;
 				memcpy(&ssid.ssid, p + offset, ssid.length);
 				offset += ssid.length;
 				length -= ssid.length;
@@ -1068,10 +1064,6 @@ parse_elements(netdissect_options *ndo,
 				if (challenge.length >
 				    sizeof(challenge.text) - 1)
 					return 0;
-				if (!ND_TTEST2(*(p + offset), challenge.length))
-					return 0;
-				if (length < challenge.length)
-					return 0;
 				memcpy(&challenge.text, p + offset,
 				    challenge.length);
 				offset += challenge.length;
@@ -1097,10 +1089,6 @@ parse_elements(netdissect_options *ndo,
 			if (rates.length != 0) {
 				if (rates.length > sizeof rates.rate)
 					return 0;
-				if (!ND_TTEST2(*(p + offset), rates.length))
-					return 0;
-				if (length < rates.length)
-					return 0;
 				memcpy(&rates.rate, p + offset, rates.length);
 				offset += rates.length;
 				length -= rates.length;
@@ -1189,7 +1177,7 @@ parse_elements(netdissect_options *ndo,
 			offset += 3;
 			length -= 3;
 
-			memcpy(tim.bitmap, p + offset + 3, tim.length - 3);
+			memcpy(tim.bitmap, p + offset, tim.length - 3);
 			offset += tim.length - 3;
 			length -= tim.length - 3;
 			/*

tests/TESTLIST

@@ -438,6 +438,7 @@ ipv6-rthdr-oobr		ipv6-rthdr-oobr.pcap		ipv6-rthdr-oobr.out
 ieee802.11_tim_ie_oobr	ieee802.11_tim_ie_oobr.pcap	ieee802.11_tim_ie_oobr.out
 decnet-shorthdr-oobr	decnet-shorthdr-oobr.pcap	decnet-shorthdr-oobr.out
 isakmp-3948-oobr-2	isakmp-3948-oobr-2.pcap		isakmp-3948-oobr-2.out
+ieee802.11_rates_oobr	ieee802.11_rates_oobr.pcap	ieee802.11_rates_oobr.out
 
 # bad packets from Kamil Frankowicz
 snmp-heapoverflow-1	snmp-heapoverflow-1.pcap	snmp-heapoverflow-1.out

tests/ieee802.11_rates_oobr.out

@@ -0,0 +1 @@
+fhset 48 fhpat 48 48dBm signal 48dB signal 48dB noise [|802.11]Beacon IBSS, PRIVACY[|802.11]