From: Denis Ovsienko <denis@ovsienko.info>
Date: Thu, 10 Dec 2020 01:02:52 +0000 (+0000)
Subject: MPLS: Modernize packet parsing style.
X-Git-Tag: tcpdump-4.99-bp~19
X-Git-Url: https://git.tcpdump.org/tcpdump/commitdiff_plain/f39bfb7d9df502dbba065519e51e44ffb902c747

MPLS: Modernize packet parsing style.

Enable ND_LONGJMP_FROM_TCHECK. Remove both ND_TCHECK*() instances
because they are redundant. Report invalid packets as invalid, not
truncated. Test whether the invalid packet is entirely in the buffer.
Replace a long switch block with a ternary assignment.
---

diff --git a/print-mpls.c b/print-mpls.c
index 4351507e..b8820aa9 100644
--- a/print-mpls.c
+++ b/print-mpls.c
@@ -34,6 +34,7 @@
 
 #include "netdissect-stdinc.h"
 
+#define ND_LONGJMP_FROM_TCHECK
 #include "netdissect.h"
 #include "extract.h"
 #include "mpls.h"
@@ -62,15 +63,15 @@ mpls_print(netdissect_options *ndo, const u_char *bp, u_int length)
 	const u_char *p;
 	uint32_t label_entry;
 	uint16_t label_stack_depth = 0;
+	uint8_t first;
 	enum mpls_packet_type pt = PT_UNKNOWN;
 
 	ndo->ndo_protocol = "mpls";
 	p = bp;
 	nd_print_protocol_caps(ndo);
 	do {
-		ND_TCHECK_LEN(p, sizeof(label_entry));
 		if (length < sizeof(label_entry))
-			goto trunc;
+			goto invalid;
 		label_entry = GET_BE_U_4(p);
 		ND_PRINT("%s(label %u",
 		       (label_stack_depth && ndo->ndo_vflag) ? "\n\t" : " ",
@@ -128,56 +129,17 @@ mpls_print(netdissect_options *ndo, const u_char *bp, u_int length)
 		 * Cisco sends control-plane traffic MPLS-encapsulated in
 		 * this fashion.
 		 */
-		ND_TCHECK_1(p);
 		if (length < 1) {
 			/* nothing to print */
 			return;
 		}
-		switch(GET_U_1(p)) {
-
-		case 0x45:
-		case 0x46:
-		case 0x47:
-		case 0x48:
-		case 0x49:
-		case 0x4a:
-		case 0x4b:
-		case 0x4c:
-		case 0x4d:
-		case 0x4e:
-		case 0x4f:
-			pt = PT_IPV4;
-			break;
-
-		case 0x60:
-		case 0x61:
-		case 0x62:
-		case 0x63:
-		case 0x64:
-		case 0x65:
-		case 0x66:
-		case 0x67:
-		case 0x68:
-		case 0x69:
-		case 0x6a:
-		case 0x6b:
-		case 0x6c:
-		case 0x6d:
-		case 0x6e:
-		case 0x6f:
-			pt = PT_IPV6;
-			break;
-
-		case 0x81:
-		case 0x82:
-		case 0x83:
-			pt = PT_OSI;
-			break;
-
-		default:
+		first = GET_U_1(p);
+		pt =
+			(first >= 0x45 && first <= 0x4f) ? PT_IPV4 :
+			(first >= 0x60 && first <= 0x6f) ? PT_IPV6 :
+			(first >= 0x81 && first <= 0x83) ? PT_OSI :
 			/* ok bail out - we did not figure out what it is*/
-			break;
-		}
+			PT_UNKNOWN;
 	}
 
 	/*
@@ -206,6 +168,7 @@ mpls_print(netdissect_options *ndo, const u_char *bp, u_int length)
 	}
 	return;
 
-trunc:
-	nd_print_trunc(ndo);
+invalid:
+	nd_print_invalid(ndo);
+	ND_TCHECK_LEN(p, length);
 }