Revert partially the commit 21b1273

[tcpdump] / print-cdp.c

diff --git a/print-cdp.c b/print-cdp.c
index 12f2d4bf51262925c6797ac8ec420b5bdaaf9b56..0ab646e51dee71dd63296ee4bd1b9c80a58ac94a 100644 (file)
--- a/print-cdp.c
+++ b/print-cdp.c
@@ -21,31 +21,33 @@
  * Code by Gert Doering, SpaceNet GmbH, [email protected]
  *
  * Reference documentation:
  * Code by Gert Doering, SpaceNet GmbH, [email protected]
  *
  * Reference documentation:

- *    http://www.cisco.com/univercd/cc/td/doc/product/lan/trsrb/frames.htm
+ *    https://web.archive.org/web/20000914194913/http://www.cisco.com/univercd/cc/td/doc/product/lan/trsrb/frames.pdf

  */
 
  */
 

-#ifndef lint
-static const char rcsid[] _U_ =
-    "@(#) $Header: /tcpdump/master/tcpdump/print-cdp.c,v 1.25 2004-10-07 14:53:11 hannes Exp $";
-#endif
+/* \summary: Cisco Discovery Protocol (CDP) printer */

 
 #ifdef HAVE_CONFIG_H
 
 #ifdef HAVE_CONFIG_H

-#include "config.h"
+#include <config.h>

 #endif
 
 #endif
 

-#include <tcpdump-stdinc.h>
+#include "netdissect-stdinc.h"

 
 

-#include <stdio.h>

 #include <string.h>
 
 #include <string.h>
 

-#include "interface.h"
+#include "netdissect.h"

 #include "addrtoname.h"
 #include "addrtoname.h"

-#include "extract.h"                   /* must come after interface.h */
+#include "extract.h"

 #include "nlpid.h"
 
 #include "nlpid.h"
 

-static const char tstr[] = "[|cdp]";

 
 

-#define CDP_HEADER_LEN  4
+#define CDP_HEADER_LEN             4
+#define CDP_HEADER_VERSION_OFFSET  0
+#define CDP_HEADER_TTL_OFFSET      1
+#define CDP_HEADER_CHECKSUM_OFFSET 2
+
+#define CDP_TLV_HEADER_LEN  4
+#define CDP_TLV_TYPE_OFFSET 0
+#define CDP_TLV_LEN_OFFSET  2

 
 static const struct tok cdp_tlv_values[] = {
     { 0x01,             "Device-ID"},
 
 static const struct tok cdp_tlv_values[] = {
     { 0x01,             "Device-ID"},


@@ -59,8 +61,8 @@ static const struct tok cdp_tlv_values[] = {
     { 0x09,             "VTP Management Domain"},
     { 0x0a,             "Native VLAN ID"},
     { 0x0b,             "Duplex"},
     { 0x09,             "VTP Management Domain"},
     { 0x0a,             "Native VLAN ID"},
     { 0x0b,             "Duplex"},

-    { 0x0e,             "ATA-186 VoIP VLAN request"},
-    { 0x0f,             "ATA-186 VoIP VLAN assignment"},
+    { 0x0e,             "ATA-186 VoIP VLAN assignment"},
+    { 0x0f,             "ATA-186 VoIP VLAN request"},

     { 0x10,             "power consumption"},
     { 0x11,             "MTU"},
     { 0x12,             "AVVID trust bitmap"},
     { 0x10,             "power consumption"},
     { 0x11,             "MTU"},
     { 0x12,             "AVVID trust bitmap"},


@@ -83,158 +85,207 @@ static const struct tok cdp_capability_values[] = {
     { 0, NULL }
 };
 
     { 0, NULL }
 };
 

-static int cdp_print_addr(const u_char *, int);
-static int cdp_print_prefixes(const u_char *, int);
-static unsigned long cdp_get_number(const u_char *, int);
+static int cdp_print_addr(netdissect_options *, const u_char *, u_int);
+static int cdp_print_prefixes(netdissect_options *, const u_char *, u_int);
+static unsigned int cdp_get_number(netdissect_options *, const u_char *, u_int);

 
 void
 
 void

-cdp_print(const u_char *pptr, u_int length, u_int caplen)
+cdp_print(netdissect_options *ndo,
+          const u_char *pptr, u_int length, u_int caplen)

 {
 {

-       int type, len, i, j;
-        const u_char *tptr;
+       u_int type, len, i;
+       const u_char *tptr;

 
 

+       ndo->ndo_protocol = "cdp";

        if (caplen < CDP_HEADER_LEN) {
        if (caplen < CDP_HEADER_LEN) {

-               printf("%s", tstr);
+               nd_print_trunc(ndo);

                return;
        }
 
                return;
        }
 

-        tptr = pptr; /* temporary pointer */
+       tptr = pptr; /* temporary pointer */

 
 

-        if (!TTEST2(*tptr, CDP_HEADER_LEN))
-                goto trunc;
-       printf("CDPv%u, ttl: %us", *tptr, *(tptr+1));
-        if (vflag)
-                printf(", checksum: %u (unverified), length %u", EXTRACT_16BITS(tptr), length);
+       ND_TCHECK_LEN(tptr, CDP_HEADER_LEN);
+       ND_PRINT("CDPv%u, ttl: %us",
+                                          GET_U_1((tptr + CDP_HEADER_VERSION_OFFSET)),
+                                          GET_U_1(tptr + CDP_HEADER_TTL_OFFSET));
+       if (ndo->ndo_vflag)
+               ND_PRINT(", checksum: 0x%04x (unverified), length %u",
+                        GET_BE_U_2(tptr + CDP_HEADER_CHECKSUM_OFFSET),
+                        length);

        tptr += CDP_HEADER_LEN;
 
        while (tptr < (pptr+length)) {
        tptr += CDP_HEADER_LEN;
 
        while (tptr < (pptr+length)) {

+               ND_TCHECK_LEN(tptr, CDP_TLV_HEADER_LEN); /* read out Type and Length */
+               type = GET_BE_U_2(tptr + CDP_TLV_TYPE_OFFSET);
+               len  = GET_BE_U_2(tptr + CDP_TLV_LEN_OFFSET); /* object length includes the 4 bytes header length */
+               if (len < CDP_TLV_HEADER_LEN) {
+                   if (ndo->ndo_vflag)
+                       ND_PRINT("\n\t%s (0x%02x), TLV length: %u byte%s (too short)",
+                              tok2str(cdp_tlv_values,"unknown field type", type),
+                              type,
+                              len,
+                              PLURAL_SUFFIX(len)); /* plural */
+                   else
+                       ND_PRINT(", %s TLV length %u too short",
+                              tok2str(cdp_tlv_values,"unknown field type", type),
+                              len);
+                   break;
+               }
+               tptr += CDP_TLV_HEADER_LEN;
+               len -= CDP_TLV_HEADER_LEN;

 
 

-                if (!TTEST2(*tptr, 4)) /* read out Type and Length */
-                    goto trunc;
-               type = EXTRACT_16BITS(tptr);
-               len  = EXTRACT_16BITS(tptr+2); /* object length includes the 4 bytes header length */
-                tptr += 4;
-                len -= 4;
-
-               if (!TTEST2(*tptr, len))
-                       goto trunc;
+               ND_TCHECK_LEN(tptr, len);

 
 

-                if (vflag || type == 1) { /* in non-verbose mode just print Device-ID */
+               if (ndo->ndo_vflag || type == 1) { /* in non-verbose mode just print Device-ID */

 
 

-                    if (vflag)
-                        printf("\n\t%s (0x%02x), length: %u byte%s: ",
-                               tok2str(cdp_tlv_values,"unknown field type", type),
-                               type,
-                               len,
-                               PLURAL_SUFFIX(len)); /* plural */
+                   if (ndo->ndo_vflag)
+                       ND_PRINT("\n\t%s (0x%02x), value length: %u byte%s: ",
+                              tok2str(cdp_tlv_values,"unknown field type", type),
+                              type,
+                              len,
+                              PLURAL_SUFFIX(len)); /* plural */

 
 

-                    switch (type) {
+                   switch (type) {

 
 

-                    case 0x01: /* Device-ID */
-                        if (!vflag)
-                            printf(", Device-ID ");
-                        printf("'");
-                        fn_printn(tptr, len, NULL);
-                        printf("'");
+                   case 0x01: /* Device-ID */
+                       if (!ndo->ndo_vflag)
+                           ND_PRINT(", Device-ID ");
+                       ND_PRINT("'");
+                       (void)nd_printn(ndo, tptr, len, NULL);
+                       ND_PRINT("'");

                        break;
                        break;

-                    case 0x02: /* Address */
-                        if (cdp_print_addr(tptr, len) < 0)
-                            goto trunc;
+                   case 0x02: /* Address */
+                       if (cdp_print_addr(ndo, tptr, len) < 0)
+                           goto trunc;

                        break;
                        break;

-                    case 0x03: /* Port-ID */
-                        printf("'");
-                        fn_printn(tptr, len, NULL);
-                        printf("'");
+                   case 0x03: /* Port-ID */
+                       ND_PRINT("'");
+                       (void)nd_printn(ndo, tptr, len, NULL);
+                       ND_PRINT("'");

                        break;
                        break;

-                    case 0x04: /* Capabilities */
-                       printf("(0x%08x): %s",
-                               EXTRACT_32BITS(tptr),
-                               bittok2str(cdp_capability_values, "none",EXTRACT_32BITS(tptr)));
+                   case 0x04: /* Capabilities */
+                       if (len < 4)
+                           goto trunc;
+                       ND_PRINT("(0x%08x): %s",
+                              GET_BE_U_4(tptr),
+                              bittok2str(cdp_capability_values, "none", GET_BE_U_4(tptr)));

                        break;
                        break;

-                    case 0x05: /* Version */
-                        printf("\n\t  ");
-                        for (i=0;i<len;i++) {
-                            j = *(tptr+i);
-                            putchar(j);
-                            if (j == 0x0a) /* lets rework the version string to get a nice identation */
-                                printf("\t  ");
-                        }
+                   case 0x05: /* Version */
+                       ND_PRINT("\n\t  ");
+                       for (i=0;i<len;i++) {
+                           u_char c;
+
+                           c = GET_U_1(tptr + i);
+                           if (c == '\n') /* lets rework the version string to
+                                             get a nice indentation */
+                               ND_PRINT("\n\t  ");
+                           else
+                               fn_print_char(ndo, c);
+                       }

                        break;
                        break;

-                    case 0x06: /* Platform */
-                        printf("'");
-                        fn_printn(tptr, len, NULL);
-                        printf("'");
+                   case 0x06: /* Platform */
+                       ND_PRINT("'");
+                       (void)nd_printn(ndo, tptr, len, NULL);
+                       ND_PRINT("'");

                        break;
                        break;

-                    case 0x07: /* Prefixes */
-                       if (cdp_print_prefixes(tptr, len) < 0)
-                            goto trunc;
+                   case 0x07: /* Prefixes */
+                       if (cdp_print_prefixes(ndo, tptr, len) < 0)
+                           goto trunc;

                        break;
                        break;

-                    case 0x08: /* Protocol Hello Option - not documented */
+                   case 0x08: /* Protocol Hello Option - not documented */

                        break;
                        break;

-                    case 0x09: /* VTP Mgmt Domain  - not documented */
-                        printf("'");
-                        fn_printn(tptr, len, NULL);
-                        printf("'");
+                   case 0x09: /* VTP Mgmt Domain  - CDPv2 */
+                       ND_PRINT("'");
+                       (void)nd_printn(ndo, tptr, len, NULL);
+                       ND_PRINT("'");

                        break;
                        break;

-                    case 0x0a: /* Native VLAN ID - not documented */
-                       printf("%d",EXTRACT_16BITS(tptr));
+                   case 0x0a: /* Native VLAN ID - CDPv2 */
+                       if (len < 2)
+                           goto trunc;
+                       ND_PRINT("%u", GET_BE_U_2(tptr));

                        break;
                        break;

-                    case 0x0b: /* Duplex - not documented */
-                       printf("%s", *(tptr) ? "full": "half");
+                   case 0x0b: /* Duplex - CDPv2 */
+                       if (len < 1)
+                           goto trunc;
+                       ND_PRINT("%s", GET_U_1(tptr) ? "full": "half");

                        break;
 
                        break;
 

-                    /* http://www.cisco.com/univercd/cc/td/doc/product/voice/ata/atarn/186rn21m.htm
-                     * plus more details from other sources
-                     */
-                    case 0x0e: /* ATA-186 VoIP VLAN request - incomplete doc. */
-                       printf("app %d, vlan %d",
-                               *(tptr), EXTRACT_16BITS(tptr+1));
+                   /* https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cata/186/2_12_m/english/release/notes/186rn21m.html
+                    * plus more details from other sources
+                    *
+                    * There are apparently versions of the request with both
+                    * 2 bytes and 3 bytes of value.  The 3 bytes of value
+                    * appear to be a 1-byte application type followed by a
+                    * 2-byte VLAN ID; the 2 bytes of value are unknown
+                    * (they're 0x20 0x00 in some captures I've seen; that
+                    * is not a valid VLAN ID, as VLAN IDs are 12 bits).
+                    *
+                    * The replies all appear to be 3 bytes long.
+                    */
+                   case 0x0e: /* ATA-186 VoIP VLAN assignment - incomplete doc. */
+                       if (len < 3)
+                           goto trunc;
+                       ND_PRINT("app %u, vlan %u", GET_U_1(tptr),
+                                GET_BE_U_2(tptr + 1));
+                       break;
+                   case 0x0f: /* ATA-186 VoIP VLAN request - incomplete doc. */
+                       if (len < 2)
+                           goto trunc;
+                       if (len == 2)
+                           ND_PRINT("unknown 0x%04x", GET_BE_U_2(tptr));
+                       else
+                           ND_PRINT("app %u, vlan %u", GET_U_1(tptr),
+                                    GET_BE_U_2(tptr + 1));

                        break;
                        break;

-                    case 0x10: /* ATA-186 VoIP VLAN assignment - incomplete doc. */
-                       printf("%1.2fW",
-                               cdp_get_number(tptr, len)/1000.0 );
+                   case 0x10: /* Power - not documented */
+                       ND_PRINT("%1.2fW", cdp_get_number(ndo, tptr, len) / 1000.0);

                        break;
                        break;

-                    case 0x11: /* MTU - not documented */
-                       printf("%u bytes", EXTRACT_32BITS(tptr));
+                   case 0x11: /* MTU - not documented */
+                       if (len < 4)
+                           goto trunc;
+                       ND_PRINT("%u bytes", GET_BE_U_4(tptr));

                        break;
                        break;

-                    case 0x12: /* AVVID trust bitmap - not documented */
-                       printf("0x%02x", *(tptr) );
+                   case 0x12: /* AVVID trust bitmap - not documented */
+                       if (len < 1)
+                           goto trunc;
+                       ND_PRINT("0x%02x", GET_U_1(tptr));

                        break;
                        break;

-                    case 0x13: /* AVVID untrusted port CoS - not documented */
-                       printf("0x%02x", *(tptr));
+                   case 0x13: /* AVVID untrusted port CoS - not documented */
+                       if (len < 1)
+                           goto trunc;
+                       ND_PRINT("0x%02x", GET_U_1(tptr));

                        break;
                        break;

-                    case 0x14: /* System Name - not documented */
-                        printf("'");
-                        fn_printn(tptr, len, NULL);
-                        printf("'");
+                   case 0x14: /* System Name - not documented */
+                       ND_PRINT("'");
+                       (void)nd_printn(ndo, tptr, len, NULL);
+                       ND_PRINT("'");

                        break;
                        break;

-                    case 0x16: /* System Object ID - not documented */
-                       if (cdp_print_addr(tptr, len) < 0)
+                   case 0x16: /* System Object ID - not documented */
+                       if (cdp_print_addr(ndo, tptr, len) < 0)

                                goto trunc;
                        break;
                                goto trunc;
                        break;

-                    case 0x17: /* Physical Location - not documented */
-                       printf("0x%02x", *(tptr));
+                   case 0x17: /* Physical Location - not documented */
+                       if (len < 1)
+                           goto trunc;
+                       ND_PRINT("0x%02x", GET_U_1(tptr));

                        if (len > 1) {
                        if (len > 1) {

-                               printf("/");
-                               fn_printn(tptr + 1, len - 1, NULL);
-                       }
+                               ND_PRINT("/");
+                               (void)nd_printn(ndo, tptr + 1, len - 1, NULL);
+                       }

                        break;
                        break;

-                    default:
-                        print_unknown_data(gndo,tptr,"\n\t  ",len);
-                       break;
-                    }
-                }
-               /* avoid infinite loop */
-               if (len == 0)
+                   default:
+                       print_unknown_data(ndo, tptr, "\n\t  ", len);

                        break;
                        break;

+                   }
+               }

                tptr = tptr+len;
        }
                tptr = tptr+len;
        }

-        if (vflag < 1)
-            printf(", length %u",caplen);
+       if (ndo->ndo_vflag < 1)
+           ND_PRINT(", length %u", caplen);

 
        return;
 trunc:
 
        return;
 trunc:

-       printf("%s", tstr);
+       nd_print_trunc(ndo);

 }
 
 /*
 }
 
 /*


@@ -249,34 +300,36 @@ trunc:
 #define PT_IEEE_802_2          2       /* IEEE 802.2 LLC header */
 
 static int
 #define PT_IEEE_802_2          2       /* IEEE 802.2 LLC header */
 
 static int

-cdp_print_addr(const u_char * p, int l)
+cdp_print_addr(netdissect_options *ndo,
+              const u_char * p, u_int l)

 {
 {

-       int pt, pl, al, num;
+       u_int pt, pl, al, num;

        const u_char *endp = p + l;
        const u_char *endp = p + l;

-#ifdef INET6

        static const u_char prot_ipv6[] = {
                0xaa, 0xaa, 0x03, 0x00, 0x00, 0x00, 0x86, 0xdd
        };
        static const u_char prot_ipv6[] = {
                0xaa, 0xaa, 0x03, 0x00, 0x00, 0x00, 0x86, 0xdd
        };

-#endif

 
 

-       TCHECK2(*p, 2);
-       num = EXTRACT_32BITS(p);
+       ND_TCHECK_4(p);
+       if (p + 4 > endp)
+               goto trunc;
+       num = GET_BE_U_4(p);

        p += 4;
 
        p += 4;
 

-       while (p < endp && num >= 0) {
-               TCHECK2(*p, 2);
+       while (p < endp && num != 0) {
+               ND_TCHECK_2(p);

                if (p + 2 > endp)
                        goto trunc;
                if (p + 2 > endp)
                        goto trunc;

-               pt = p[0];              /* type of "protocol" field */
-               pl = p[1];              /* length of "protocol" field */
+               pt = GET_U_1(p);                /* type of "protocol" field */
+               pl = GET_U_1(p + 1);    /* length of "protocol" field */

                p += 2;
 
                p += 2;
 

-               TCHECK2(p[pl], 2);
+               ND_TCHECK_2(p + pl);

                if (p + pl + 2 > endp)
                        goto trunc;
                if (p + pl + 2 > endp)
                        goto trunc;

-               al = EXTRACT_16BITS(&p[pl]);    /* address length */
+               al = GET_BE_U_2(p + pl);        /* address length */

 
 

-               if (pt == PT_NLPID && pl == 1 && *p == NLPID_IP && al == 4) {
+               if (pt == PT_NLPID && pl == 1 && GET_U_1(p) == NLPID_IP &&
+                   al == 4) {

                        /*
                         * IPv4: protocol type = NLPID, protocol length = 1
                         * (1-byte NLPID), protocol = 0xcc (NLPID for IPv4),
                        /*
                         * IPv4: protocol type = NLPID, protocol length = 1
                         * (1-byte NLPID), protocol = 0xcc (NLPID for IPv4),


@@ -284,15 +337,11 @@ cdp_print_addr(const u_char * p, int l)
                         */
                        p += 3;
 
                         */
                        p += 3;
 

-                       TCHECK2(*p, 4);

                        if (p + 4 > endp)
                                goto trunc;
                        if (p + 4 > endp)
                                goto trunc;

-                       printf("IPv4 (%u) %s",
-                               num,
-                               ipaddr_string(p));
+                       ND_PRINT("IPv4 (%u) %s", num, GET_IPADDR_STRING(p));

                        p += 4;
                }
                        p += 4;
                }

-#ifdef INET6

                else if (pt == PT_IEEE_802_2 && pl == 8 &&
                    memcmp(p, prot_ipv6, 8) == 0 && al == 16) {
                        /*
                else if (pt == PT_IEEE_802_2 && pl == 8 &&
                    memcmp(p, prot_ipv6, 8) == 0 && al == 16) {
                        /*


@@ -302,41 +351,44 @@ cdp_print_addr(const u_char * p, int l)
                         * Ethertype, address length = 16
                         */
                        p += 10;
                         * Ethertype, address length = 16
                         */
                        p += 10;

-                       TCHECK2(*p, al);
+                       ND_TCHECK_LEN(p, al);

                        if (p + al > endp)
                                goto trunc;
 
                        if (p + al > endp)
                                goto trunc;
 

-                       printf("IPv6 (%u) %s",
-                               num,
-                               ip6addr_string(p));
+                       ND_PRINT("IPv6 (%u) %s", num, GET_IP6ADDR_STRING(p));

                        p += al;
                }
                        p += al;
                }

-#endif

                else {
                        /*
                         * Generic case: just print raw data
                         */
                else {
                        /*
                         * Generic case: just print raw data
                         */

-                       TCHECK2(*p, pl);
+                       ND_TCHECK_LEN(p, pl);

                        if (p + pl > endp)
                                goto trunc;
                        if (p + pl > endp)
                                goto trunc;

-                       printf("pt=0x%02x, pl=%d, pb=", *(p - 2), pl);
-                       while (pl-- > 0)
-                               printf(" %02x", *p++);
-                       TCHECK2(*p, 2);
+                       ND_PRINT("pt=0x%02x, pl=%u, pb=", GET_U_1((p - 2)),
+                                pl);
+                       while (pl != 0) {
+                               ND_PRINT(" %02x", GET_U_1(p));
+                               p++;
+                               pl--;
+                       }
+                       ND_TCHECK_2(p);

                        if (p + 2 > endp)
                                goto trunc;
                        if (p + 2 > endp)
                                goto trunc;

-                       al = (*p << 8) + *(p + 1);
-                       printf(", al=%d, a=", al);
+                       ND_PRINT(", al=%u, a=", al);

                        p += 2;
                        p += 2;

-                       TCHECK2(*p, al);
+                       ND_TCHECK_LEN(p, al);

                        if (p + al > endp)
                                goto trunc;
                        if (p + al > endp)
                                goto trunc;

-                       while (al-- > 0)
-                               printf(" %02x", *p++);
+                       while (al != 0) {
+                               ND_PRINT(" %02x", GET_U_1(p));
+                               p++;
+                               al--;
+                       }

                }
                num--;
                if (num)
                }
                num--;
                if (num)

-                       printf(" ");
+                       ND_PRINT(" ");

        }
 
        return 0;
        }
 
        return 0;


@@ -347,15 +399,18 @@ trunc:
 
 
 static int
 
 
 static int

-cdp_print_prefixes(const u_char * p, int l)
+cdp_print_prefixes(netdissect_options *ndo,
+                  const u_char * p, u_int l)

 {
        if (l % 5)
                goto trunc;
 
 {
        if (l % 5)
                goto trunc;
 

-       printf(" IPv4 Prefixes (%d):", l / 5);
+       ND_PRINT(" IPv4 Prefixes (%u):", l / 5);

 
        while (l > 0) {
 
        while (l > 0) {

-               printf(" %u.%u.%u.%u/%u", p[0], p[1], p[2], p[3], p[4]);
+               ND_PRINT(" %u.%u.%u.%u/%u",
+                         GET_U_1(p), GET_U_1(p + 1), GET_U_1(p + 2),
+                         GET_U_1(p + 3), GET_U_1(p + 4));

                l -= 5;
                p += 5;
        }
                l -= 5;
                p += 5;
        }


@@ -367,14 +422,15 @@ trunc:
 }
 
 /* read in a <n>-byte number, MSB first
 }
 
 /* read in a <n>-byte number, MSB first

- * (of course this can handle max sizeof(long))
+ * (of course this can handle max sizeof(int))

  */
  */

-static unsigned long cdp_get_number(const u_char * p, int l)
+static unsigned int
+cdp_get_number(netdissect_options *ndo, const u_char * p, u_int l)

 {
 {

-    unsigned long res=0;
+    unsigned int res=0;

     while( l>0 )
     {
     while( l>0 )
     {

-       res = (res<<8) + *p;
+       res = (res<<8) + GET_U_1(p);

        p++; l--;
     }
     return res;
        p++; l--;
     }
     return res;