Commit message: CVE-2017-13033/VTP: Add more bound and length checks.

This fixes a buffer over-read discovered by Bhargava Shastry.

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.

Update another VTP test's .out file for this change.

Don't treate a TLV type or length of 0 as invalid; a type of 0 should
just be reported as illegal if that type isn't used, and the length is
the length of the *value*, not the length of the entire TLV, so if it's
zero there won't be an infinite loop.  (It's still not *legal*, as the
values of all the TLVs we handle are 1 16-bit word long; we added a
check for that.)

Update some comments while we're at it, to give a new URL for one Cisco
page and a non-Cisco URL for another former Cisco page (Cisco's UniverCD
pages don't seem to be available any more, and Cisco's robots.txt file
didn't allow the Wayback Machine to archive it).
CVE: CVE-2017-13033
CWE: CWE-125
Vulnerability description: The VTP parser in tcpdump before 4.9.2 has a buffer over-read in print-vtp.c:vtp_print().

Project: tcpdump
File: print-vtp.c

vtp_print (netdissect_options *ndo,
           const u_char *pptr, u_int length)
{
    int type, len, tlv_len, tlv_value, mgmtd_len;
    const u_char *tptr;
    const struct vtp_vlan_ *vtp_vlan;

    if (length < VTP_HEADER_LEN)
        goto trunc;

    tptr = pptr;

    ND_TCHECK2(*tptr, VTP_HEADER_LEN);

    type = *(tptr+1);
    ND_PRINT((ndo, "VTPv%u, Message %s (0x%02x), length %u",
	   *tptr,
	   tok2str(vtp_message_type_values,"Unknown message type", type),
	   type,
	   length));

    /* In non-verbose mode, just print version and message type */
    if (ndo->ndo_vflag < 1) {
        return;
    }

    /* verbose mode print all fields */
    ND_PRINT((ndo, "\n\tDomain name: "));
    mgmtd_len = *(tptr + 3);
    if (mgmtd_len < 1 ||  mgmtd_len > 32) {
	ND_PRINT((ndo, " [invalid MgmtD Len %d]", mgmtd_len));
	return;
    }
    fn_printzp(ndo, tptr + 4, mgmtd_len, NULL);
    ND_PRINT((ndo, ", %s: %u",
	   tok2str(vtp_header_values, "Unknown", type),
	   *(tptr+2)));

    tptr += VTP_HEADER_LEN;

    switch (type) {

    case VTP_SUMMARY_ADV:

	/*
	 *  SUMMARY ADVERTISEMENT
	 *
	 *  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
	 *  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	 *  |     Version   |     Code      |    Followers  |    MgmtD Len  |
	 *  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	 *  |       Management Domain Name  (zero-padded to 32 bytes)       |
	 *  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	 *  |                    Configuration revision number              |
	 *  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	 *  |                  Updater Identity IP address                  |
	 *  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	 *  |                    Update Timestamp (12 bytes)                |
	 *  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	 *  |                        MD5 digest (16 bytes)                  |
	 *  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	 *
	 */

	ND_TCHECK2(*tptr, 8);
	ND_PRINT((ndo, "\n\t  Config Rev %x, Updater %s",
	       EXTRACT_32BITS(tptr),
	       ipaddr_string(ndo, tptr+4)));
	tptr += 8;
	ND_TCHECK2(*tptr, VTP_UPDATE_TIMESTAMP_LEN);
	ND_PRINT((ndo, ", Timestamp 0x%08x 0x%08x 0x%08x",
	       EXTRACT_32BITS(tptr),
	       EXTRACT_32BITS(tptr + 4),
	       EXTRACT_32BITS(tptr + 8)));
	tptr += VTP_UPDATE_TIMESTAMP_LEN;
	ND_TCHECK2(*tptr, VTP_MD5_DIGEST_LEN);
	ND_PRINT((ndo, ", MD5 digest: %08x%08x%08x%08x",
	       EXTRACT_32BITS(tptr),
	       EXTRACT_32BITS(tptr + 4),
	       EXTRACT_32BITS(tptr + 8),
	       EXTRACT_32BITS(tptr + 12)));
	tptr += VTP_MD5_DIGEST_LEN;
	break;

    case VTP_SUBSET_ADV:

	/*
	 *  SUBSET ADVERTISEMENT
	 *
	 *  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
	 *  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	 *  |     Version   |     Code      |   Seq number  |    MgmtD Len  |
	 *  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	 *  |       Management Domain Name  (zero-padded to 32 bytes)       |
	 *  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	 *  |                    Configuration revision number              |
	 *  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	 *  |                         VLAN info field 1                     |
	 *  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	 *  |                         ................                      |
	 *  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	 *  |                         VLAN info field N                     |
	 *  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	 *
	 */

	ND_TCHECK_32BITS(tptr);
	ND_PRINT((ndo, ", Config Rev %x", EXTRACT_32BITS(tptr)));

	/*
	 *  VLAN INFORMATION
	 *  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
	 *  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	 *  | V info len    |    Status     |  VLAN type    | VLAN name len |
	 *  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	 *  |       ISL vlan id             |            MTU size           |
	 *  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	 *  |                     802.10 index (SAID)                       |
	 *  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	 *  |                         VLAN name                             |
	 *  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	 *
	 */

	tptr += 4;
	while (tptr < (pptr+length)) {

	    ND_TCHECK_8BITS(tptr);
	    len = *tptr;
	    if (len == 0)
		break;

 	    ND_TCHECK2(*tptr, len);
 
 	    vtp_vlan = (const struct vtp_vlan_*)tptr;
 	    ND_TCHECK(*vtp_vlan);
 	    ND_PRINT((ndo, "\n\tVLAN info status %s, type %s, VLAN-id %u, MTU %u, SAID 0x%08x, Name ",
 		   tok2str(vtp_vlan_status,"Unknown",vtp_vlan->status),
 		   tok2str(vtp_vlan_type_values,"Unknown",vtp_vlan->type),
 		   EXTRACT_16BITS(&vtp_vlan->vlanid),
 		   EXTRACT_16BITS(&vtp_vlan->mtu),
 		   EXTRACT_32BITS(&vtp_vlan->index)));
	    fn_printzp(ndo, tptr + VTP_VLAN_INFO_OFFSET, vtp_vlan->name_len, NULL);
            /*
             * Vlan names are aligned to 32-bit boundaries.
             */
            len  -= VTP_VLAN_INFO_OFFSET + 4*((vtp_vlan->name_len + 3)/4);
            tptr += VTP_VLAN_INFO_OFFSET + 4*((vtp_vlan->name_len + 3)/4);
 
             /* TLV information follows */
 
             while (len > 0) {
 
                 /*
                 * Cisco specs says 2 bytes for type + 2 bytes for length, take only 1
                 * See: http://www.cisco.com/univercd/cc/td/doc/product/lan/trsrb/frames.htm
                  */
                 type = *tptr;
                 tlv_len = *(tptr+1);
 
                 ND_PRINT((ndo, "\n\t\t%s (0x%04x) TLV",
                        tok2str(vtp_vlan_tlv_values, "Unknown", type),
                        type));
 
                /*
                 * infinite loop check
                 */
                if (type == 0 || tlv_len == 0) {
                     return;
                 }
                 ND_TCHECK2(*tptr, tlv_len * 2 +2);
 
                tlv_value = EXTRACT_16BITS(tptr+2);
                switch (type) {
                case VTP_VLAN_STE_HOP_COUNT:
                    ND_PRINT((ndo, ", %u", tlv_value));
                    break;
                case VTP_VLAN_PRUNING:
                    ND_PRINT((ndo, ", %s (%u)",
                           tlv_value == 1 ? "Enabled" : "Disabled",
                           tlv_value));
                    break;
                case VTP_VLAN_STP_TYPE:
                    ND_PRINT((ndo, ", %s (%u)",
                           tok2str(vtp_stp_type_values, "Unknown", tlv_value),
                           tlv_value));
                    break;
                case VTP_VLAN_BRIDGE_TYPE:
                    ND_PRINT((ndo, ", %s (%u)",
                           tlv_value == 1 ? "SRB" : "SRT",
                           tlv_value));
                    break;
                case VTP_VLAN_BACKUP_CRF_MODE:
                    ND_PRINT((ndo, ", %s (%u)",
                           tlv_value == 1 ? "Backup" : "Not backup",
                           tlv_value));
                    break;
                    /*
                     * FIXME those are the defined TLVs that lack a decoder
                     * you are welcome to contribute code ;-)
                     */
                case VTP_VLAN_SOURCE_ROUTING_RING_NUMBER:
                case VTP_VLAN_SOURCE_ROUTING_BRIDGE_NUMBER:
                case VTP_VLAN_PARENT_VLAN:
                case VTP_VLAN_TRANS_BRIDGED_VLAN:
                case VTP_VLAN_ARP_HOP_COUNT:
                default:
		    print_unknown_data(ndo, tptr, "\n\t\t  ", 2 + tlv_len*2);
                    break;
                 }
                 len -= 2 + tlv_len*2;
                 tptr += 2 + tlv_len*2;
            }
	}
	break;

    case VTP_ADV_REQUEST:

	/*
	 *  ADVERTISEMENT REQUEST
	 *
	 *  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
	 *  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	 *  |     Version   |     Code      |   Reserved    |    MgmtD Len  |
	 *  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	 *  |       Management Domain Name  (zero-padded to 32 bytes)       |
	 *  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	 *  |                          Start value                          |
	 *  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	 *
	 */

	ND_TCHECK2(*tptr, 4);
	ND_PRINT((ndo, "\n\tStart value: %u", EXTRACT_32BITS(tptr)));
	break;

    case VTP_JOIN_MESSAGE:

	/* FIXME - Could not find message format */
	break;

    default:
	break;
    }

    return;

 trunc:
    ND_PRINT((ndo, "[|vtp]"));
}