CVE-2017-13010/BEEP: Do bounds checking when comparing strings.

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

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

print-beep.c

@@ -28,9 +28,17 @@
  */
 
 static int
-l_strnstart(const char *tstr1, u_int tl1, const char *str2, u_int l2)
+l_strnstart(netdissect_options *ndo, const char *tstr1, u_int tl1,
+    const char *str2, u_int l2)
 {
-
+	if (!ND_TTEST2(*str2, tl1)) {
+		/*
+		 * We don't have tl1 bytes worth of captured data
+		 * for the string, so we can't check for this
+		 * string.
+		 */
+		return 0;
+	}
 	if (tl1 > l2)
 		return 0;
 
@@ -41,19 +49,19 @@ void
 beep_print(netdissect_options *ndo, const u_char *bp, u_int length)
 {
 
-	if (l_strnstart("MSG", 4, (const char *)bp, length)) /* A REQuest */
+	if (l_strnstart(ndo, "MSG", 4, (const char *)bp, length)) /* A REQuest */
 		ND_PRINT((ndo, " BEEP MSG"));
-	else if (l_strnstart("RPY ", 4, (const char *)bp, length))
+	else if (l_strnstart(ndo, "RPY ", 4, (const char *)bp, length))
 		ND_PRINT((ndo, " BEEP RPY"));
-	else if (l_strnstart("ERR ", 4, (const char *)bp, length))
+	else if (l_strnstart(ndo, "ERR ", 4, (const char *)bp, length))
 		ND_PRINT((ndo, " BEEP ERR"));
-	else if (l_strnstart("ANS ", 4, (const char *)bp, length))
+	else if (l_strnstart(ndo, "ANS ", 4, (const char *)bp, length))
 		ND_PRINT((ndo, " BEEP ANS"));
-	else if (l_strnstart("NUL ", 4, (const char *)bp, length))
+	else if (l_strnstart(ndo, "NUL ", 4, (const char *)bp, length))
 		ND_PRINT((ndo, " BEEP NUL"));
-	else if (l_strnstart("SEQ ", 4, (const char *)bp, length))
+	else if (l_strnstart(ndo, "SEQ ", 4, (const char *)bp, length))
 		ND_PRINT((ndo, " BEEP SEQ"));
-	else if (l_strnstart("END", 4, (const char *)bp, length))
+	else if (l_strnstart(ndo, "END", 4, (const char *)bp, length))
 		ND_PRINT((ndo, " BEEP END"));
 	else
 		ND_PRINT((ndo, " BEEP (payload or undecoded)"));

tests/TESTLIST

@@ -440,6 +440,7 @@ 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
 ipv6-mobility-header-oobr	ipv6-mobility-header-oobr.pcap	ipv6-mobility-header-oobr.out
+beep-oobr		beep-oobr.pcap			beep-oobr.out
 
 # bad packets from Kamil Frankowicz
 snmp-heapoverflow-1	snmp-heapoverflow-1.pcap	snmp-heapoverflow-1.out

tests/beep-oobr.out

@@ -0,0 +1,2 @@
+unknown ip 3
+IP6 3030:3030:3030:3030:3030:3030:3030:3030.10288 > 3030:3030:3030:3030:3030:3030:3030:3030.12336: Flags [.U], seq 808464432:808476740, ack 808464432, win 12336, urg 12336, options [eol], length 12308 BEEP (payload or undecoded)