CVE-2017-11543/Make sure the SLIP direction octet is valid.

Report if it's not, and don't use it as an out-of-bounds index into an
array.

This fixes a buffer overflow discovered by Wilfried Kirsch.

Add a test using the capture file supplied by the reporter(s), modified
so the capture file won't be rejected as an invalid capture.

print-sl.c

@@ -131,8 +131,21 @@ sliplink_print(netdissect_options *ndo,
 	u_int hlen;
 
 	dir = p[SLX_DIR];
-	ND_PRINT((ndo, dir == SLIPDIR_IN ? "I " : "O "));
+	switch (dir) {
 
+	case SLIPDIR_IN:
+		ND_PRINT((ndo, "I "));
+		break;
+
+	case SLIPDIR_OUT:
+		ND_PRINT((ndo, "O "));
+		break;
+
+	default:
+		ND_PRINT((ndo, "Invalid direction %d ", dir));
+		dir = -1;
+		break;
+	}
 	if (ndo->ndo_nflag) {
 		/* XXX just dump the header */
 		register int i;
@@ -155,13 +168,21 @@ sliplink_print(netdissect_options *ndo,
 		 * has restored the IP header copy to IPPROTO_TCP.
 		 */
 		lastconn = ((const struct ip *)&p[SLX_CHDR])->ip_p;
+		ND_PRINT((ndo, "utcp %d: ", lastconn));
+		if (dir == -1) {
+			/* Direction is bogus, don't use it */
+			return;
+		}
 		hlen = IP_HL(ip);
 		hlen += TH_OFF((const struct tcphdr *)&((const int *)ip)[hlen]);
 		lastlen[dir][lastconn] = length - (hlen << 2);
-		ND_PRINT((ndo, "utcp %d: ", lastconn));
 		break;
 
 	default:
+		if (dir == -1) {
+			/* Direction is bogus, don't use it */
+			return;
+		}
 		if (p[SLX_CHDR] & TYPE_COMPRESSED_TCP) {
 			compressed_sl_print(ndo, &p[SLX_CHDR], ip,
 			    length, dir);

tests/TESTLIST

@@ -439,6 +439,9 @@ stp-v4-length-sigsegv	stp-v4-length-sigsegv.pcap	stp-v4-length-sigsegv.out
 hoobr_pimv1		hoobr_pimv1.pcap		hoobr_pimv1.out
 hoobr_safeputs		hoobr_safeputs.pcap		hoobr_safeputs.out
 
+# bad packets from Wilfried Kirsch
+slip-bad-direction	slip-bad-direction.pcap		slip-bad-direction.out	-ve
+
 # RTP tests
 # fuzzed pcap
 rtp-seg-fault-1  rtp-seg-fault-1.pcap  rtp-seg-fault-1.out  -v -T rtp

tests/slip-bad-direction.out

@@ -0,0 +1 @@
+Invalid direction 231 e7.e7.e7.e7.e7.e7.e7.e7.e7.e7.e7.e7.e7.e7.e7: ip v14