rework on the ICMP MPLS extension code:

- preserve the snapend pointer as it may get overwritten by calling the IP printer
- protect against infinite loops inside the MPLS extension printer.
- detect present of an MPLS extension header by introducing a length field to the ICMP header
  as per draft-bonica-internet-icmp-08.

diff --git a/print-icmp.c b/print-icmp.c
index bd6470d4669849fbe3fb6eb504eee2afe1c6f097..a6c0811007e2b7f952ed083efe7b046a5f6902bc 100644 (file)
--- a/print-icmp.c
+++ b/print-icmp.c
@@ -21,7 +21,7 @@
 
 #ifndef lint
 static const char rcsid[] _U_ =
-    "@(#) $Header: /tcpdump/master/tcpdump/print-icmp.c,v 1.83 2005-07-01 16:10:02 hannes Exp $ (LBL)";
+    "@(#) $Header: /tcpdump/master/tcpdump/print-icmp.c,v 1.84 2006-12-12 10:48:43 hannes Exp $ (LBL)";
 #endif
 
 #ifdef HAVE_CONFIG_H
@@ -62,20 +62,12 @@ struct icmp {
                        u_int16_t icd_seq;
                } ih_idseq;
                u_int32_t ih_void;
-
-               /* ICMP_UNREACH_NEEDFRAG -- Path MTU Discovery (RFC1191) */
-               struct ih_pmtu {
-                       u_int16_t ipm_void;
-                       u_int16_t ipm_nextmtu;
-               } ih_pmtu;
        } icmp_hun;
 #define        icmp_pptr       icmp_hun.ih_pptr
 #define        icmp_gwaddr     icmp_hun.ih_gwaddr
 #define        icmp_id         icmp_hun.ih_idseq.icd_id
 #define        icmp_seq        icmp_hun.ih_idseq.icd_seq
 #define        icmp_void       icmp_hun.ih_void
-#define        icmp_pmvoid     icmp_hun.ih_pmtu.ipm_void
-#define        icmp_nextmtu    icmp_hun.ih_pmtu.ipm_nextmtu
        union {
                struct id_ts {
                        u_int32_t its_otime;
@@ -86,12 +78,6 @@ struct icmp {
                        struct ip idi_ip;
                        /* options and then 64 bits of data */
                } id_ip;
-                struct mpls_ext {
-                    u_int8_t legacy_header[128]; /* extension header starts 128 bytes after ICMP header */
-                    u_int8_t version_res[2];
-                    u_int8_t checksum[2];
-                    u_int8_t data[1];
-                } mpls_ext;
                u_int32_t id_mask;
                u_int8_t id_data[1];
        } icmp_dun;
@@ -101,9 +87,6 @@ struct icmp {
 #define        icmp_ip         icmp_dun.id_ip.idi_ip
 #define        icmp_mask       icmp_dun.id_mask
 #define        icmp_data       icmp_dun.id_data
-#define        icmp_mpls_ext_version   icmp_dun.mpls_ext.version_res
-#define        icmp_mpls_ext_checksum  icmp_dun.mpls_ext.checksum
-#define        icmp_mpls_ext_data      icmp_dun.mpls_ext.data
 };
 
 #define ICMP_MPLS_EXT_EXTRACT_VERSION(x) (((x)&0xf0)>>4) 
@@ -118,7 +101,7 @@ struct icmp {
  * ip header length.
  */
 #define        ICMP_MINLEN     8                               /* abs minimum */
-#define ICMP_EXTD_MINLEN (156 - sizeof (struct ip))     /* draft-bonica-icmp-mpls-02 */
+#define ICMP_EXTD_MINLEN (156 - sizeof (struct ip))     /* draft-bonica-internet-icmp-08 */
 #define        ICMP_TSLEN      (8 + 3 * sizeof (u_int32_t))    /* timestamp */
 #define        ICMP_MASKLEN    12                              /* address mask */
 #define        ICMP_ADVLENMIN  (8 + sizeof (struct ip) + 8)    /* min */
@@ -173,7 +156,9 @@ struct icmp {
        (type) == ICMP_IREQ || (type) == ICMP_IREQREPLY || \
        (type) == ICMP_MASKREQ || (type) == ICMP_MASKREPLY)
 #define        ICMP_MPLS_EXT_TYPE(type) \
-       ((type) == ICMP_UNREACH || (type) == ICMP_TIMXCEED)
+       ((type) == ICMP_UNREACH || \
+         (type) == ICMP_TIMXCEED || \
+         (type) == ICMP_PARAMPROB)
 /* rfc1700 */
 #ifndef ICMP_UNREACH_NET_UNKNOWN
 #define ICMP_UNREACH_NET_UNKNOWN       6       /* destination net unknown */
@@ -276,7 +261,48 @@ struct id_rdiscovery {
        u_int32_t ird_pref;
 };
 
-/* draft-bonica-icmp-mpls-02 */
+/*
+ * draft-bonica-internet-icmp-08
+ *
+ * The Destination Unreachable, Time Exceeded
+ * and Parameter Problem messages are slighly changed as per
+ * the above draft. A new Length field gets added to give
+ * the caller an idea about the length of the piggypacked
+ * IP packet before the MPLS extension header starts.
+ *
+ * The Length field represents length of the padded "original datagram"
+ * field  measured in 32-bit words.
+ *
+ * 0                   1                   2                   3
+ * 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+ * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ * |     Type      |     Code      |          Checksum             |
+ * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ * |     unused    |    Length     |          unused               |
+ * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ * |      Internet Header + leading octets of original datagram    |
+ * |                                                               |
+ * |                           //                                  |
+ * |                                                               |
+ * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ */
+
+struct icmp_ext_t {
+    u_int8_t icmp_type;
+    u_int8_t icmp_code;
+    u_int8_t icmp_checksum[2];
+    u_int8_t icmp_reserved;
+    u_int8_t icmp_length;
+    u_int8_t icmp_reserved2[2];
+    u_int8_t icmp_ext_legacy_header[128]; /* extension header starts 128 bytes after ICMP header */
+    u_int8_t icmp_ext_version_res[2];
+    u_int8_t icmp_ext_checksum[2];
+    u_int8_t icmp_ext_data[1];
+};
+
+struct icmp_mpls_ext_common_header_t {
+};
+
 struct icmp_mpls_ext_object_header_t {
     u_int8_t length[2];
     u_int8_t class_num;
@@ -312,17 +338,20 @@ icmp_print(const u_char *bp, u_int plen, const u_char *bp2, int fragmented)
 {
        char *cp;
        const struct icmp *dp;
+        const struct icmp_ext_t *ext_dp;
        const struct ip *ip;
        const char *str, *fmt;
        const struct ip *oip;
        const struct udphdr *ouh;
         const u_int8_t *obj_tptr;
         u_int32_t raw_label;
+        const u_char *snapend_save;
        const struct icmp_mpls_ext_object_header_t *icmp_mpls_ext_object_header;
        u_int hlen, dport, mtu, obj_tlen, obj_class_num, obj_ctype;
        char buf[MAXHOSTNAMELEN + 100];
 
        dp = (struct icmp *)bp;
+        ext_dp = (struct icmp_ext_t *)bp;
        ip = (struct ip *)bp2;
        str = buf;
 
@@ -544,35 +573,48 @@ icmp_print(const u_char *bp, u_int plen, const u_char *bp2, int fragmented)
                        }
                }
        }
+
+        /*
+         * print the remnants of the IP packet.
+         * save the snaplength as this may get overidden in the IP printer.
+         */
        if (vflag >= 1 && !ICMP_INFOTYPE(dp->icmp_type)) {
                bp += 8;
                (void)printf("\n\t");
                ip = (struct ip *)bp;
                snaplen = snapend - bp;
+                snapend_save = snapend;
                ip_print(gndo, bp, EXTRACT_16BITS(&ip->ip_len));
+                snapend = snapend_save;
        }
 
-        if (vflag >= 1 && plen > ICMP_EXTD_MINLEN && ICMP_MPLS_EXT_TYPE(dp->icmp_type)) {
+        /*
+         * Check if the extended ICMP header indicates that there is
+         * MPLS extension header present for the "interesting" ICMP types.
+         */
+        if (vflag >= 1 && plen > ICMP_EXTD_MINLEN &&
+            ext_dp->icmp_length && ICMP_MPLS_EXT_TYPE(dp->icmp_type)) {
 
-            TCHECK(*(dp->icmp_mpls_ext_version));
-            printf("\n\tMPLS extension v%u",ICMP_MPLS_EXT_EXTRACT_VERSION(*(dp->icmp_mpls_ext_version)));
+            TCHECK(*ext_dp);
+            printf("\n\tMPLS extension v%u",
+                   ICMP_MPLS_EXT_EXTRACT_VERSION(*(ext_dp->icmp_ext_version_res)));
             
             /*
              * Sanity checking of the header.
              */
-            if (ICMP_MPLS_EXT_EXTRACT_VERSION(*(dp->icmp_mpls_ext_version)) != ICMP_MPLS_EXT_VERSION) {
+            if (ICMP_MPLS_EXT_EXTRACT_VERSION(*(ext_dp->icmp_ext_version_res)) !=
+                ICMP_MPLS_EXT_VERSION) {
                 printf(" packet not supported");
                 return;
             }
 
             hlen = plen - ICMP_EXTD_MINLEN;
-            TCHECK2(*(dp->icmp_mpls_ext_checksum), 2);
             printf(", checksum 0x%04x (unverified), length %u", /* FIXME */
-                   EXTRACT_16BITS(dp->icmp_mpls_ext_checksum),
+                   EXTRACT_16BITS(ext_dp->icmp_ext_checksum),
                    hlen);
 
             hlen -= 4; /* subtract common header size */
-            obj_tptr = (u_int8_t *)dp->icmp_mpls_ext_data;
+            obj_tptr = (u_int8_t *)ext_dp->icmp_ext_data;
 
             while (hlen > sizeof(struct icmp_mpls_ext_object_header_t)) {
 
@@ -590,8 +632,12 @@ icmp_print(const u_char *bp, u_int plen, const u_char *bp2, int fragmented)
                        obj_tlen);
 
                 hlen-=sizeof(struct icmp_mpls_ext_object_header_t); /* length field includes tlv header */
-                if (obj_tlen < sizeof(struct icmp_mpls_ext_object_header_t))
-                    break;
+
+                /* infinite loop protection */                
+                if ((obj_class_num == 0) ||
+                    (obj_tlen < sizeof(struct icmp_mpls_ext_object_header_t))) {
+                    return;
+                }
                 obj_tlen-=sizeof(struct icmp_mpls_ext_object_header_t);
 
                 switch (obj_class_num) {