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stunmessage.cpp

/*
 * Copyright (C) 2009  Barracuda Networks, Inc.
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
 * 02110-1301  USA
 *
 */

#include "stunmessage.h"

#include <QSharedData>
#include <QtCrypto>
#include "stunutil.h"

#define ENSURE_D { if(!d) d = new Private; }

namespace XMPP {

using namespace StunUtil;

// some attribute types we need to explicitly support
enum
{
      AttribMessageIntegrity = 0x0008,
      AttribFingerprint      = 0x8028
};

// adapted from public domain source by Ross Williams and Eric Durbin
unsigned long crctable[256] =
{
      0x00000000L, 0x77073096L, 0xEE0E612CL, 0x990951BAL,
      0x076DC419L, 0x706AF48FL, 0xE963A535L, 0x9E6495A3L,
      0x0EDB8832L, 0x79DCB8A4L, 0xE0D5E91EL, 0x97D2D988L,
      0x09B64C2BL, 0x7EB17CBDL, 0xE7B82D07L, 0x90BF1D91L,
      0x1DB71064L, 0x6AB020F2L, 0xF3B97148L, 0x84BE41DEL,
      0x1ADAD47DL, 0x6DDDE4EBL, 0xF4D4B551L, 0x83D385C7L,
      0x136C9856L, 0x646BA8C0L, 0xFD62F97AL, 0x8A65C9ECL,
      0x14015C4FL, 0x63066CD9L, 0xFA0F3D63L, 0x8D080DF5L,
      0x3B6E20C8L, 0x4C69105EL, 0xD56041E4L, 0xA2677172L,
      0x3C03E4D1L, 0x4B04D447L, 0xD20D85FDL, 0xA50AB56BL,
      0x35B5A8FAL, 0x42B2986CL, 0xDBBBC9D6L, 0xACBCF940L,
      0x32D86CE3L, 0x45DF5C75L, 0xDCD60DCFL, 0xABD13D59L,
      0x26D930ACL, 0x51DE003AL, 0xC8D75180L, 0xBFD06116L,
      0x21B4F4B5L, 0x56B3C423L, 0xCFBA9599L, 0xB8BDA50FL,
      0x2802B89EL, 0x5F058808L, 0xC60CD9B2L, 0xB10BE924L,
      0x2F6F7C87L, 0x58684C11L, 0xC1611DABL, 0xB6662D3DL,
      0x76DC4190L, 0x01DB7106L, 0x98D220BCL, 0xEFD5102AL,
      0x71B18589L, 0x06B6B51FL, 0x9FBFE4A5L, 0xE8B8D433L,
      0x7807C9A2L, 0x0F00F934L, 0x9609A88EL, 0xE10E9818L,
      0x7F6A0DBBL, 0x086D3D2DL, 0x91646C97L, 0xE6635C01L,
      0x6B6B51F4L, 0x1C6C6162L, 0x856530D8L, 0xF262004EL,
      0x6C0695EDL, 0x1B01A57BL, 0x8208F4C1L, 0xF50FC457L,
      0x65B0D9C6L, 0x12B7E950L, 0x8BBEB8EAL, 0xFCB9887CL,
      0x62DD1DDFL, 0x15DA2D49L, 0x8CD37CF3L, 0xFBD44C65L,
      0x4DB26158L, 0x3AB551CEL, 0xA3BC0074L, 0xD4BB30E2L,
      0x4ADFA541L, 0x3DD895D7L, 0xA4D1C46DL, 0xD3D6F4FBL,
      0x4369E96AL, 0x346ED9FCL, 0xAD678846L, 0xDA60B8D0L,
      0x44042D73L, 0x33031DE5L, 0xAA0A4C5FL, 0xDD0D7CC9L,
      0x5005713CL, 0x270241AAL, 0xBE0B1010L, 0xC90C2086L,
      0x5768B525L, 0x206F85B3L, 0xB966D409L, 0xCE61E49FL,
      0x5EDEF90EL, 0x29D9C998L, 0xB0D09822L, 0xC7D7A8B4L,
      0x59B33D17L, 0x2EB40D81L, 0xB7BD5C3BL, 0xC0BA6CADL,
      0xEDB88320L, 0x9ABFB3B6L, 0x03B6E20CL, 0x74B1D29AL,
      0xEAD54739L, 0x9DD277AFL, 0x04DB2615L, 0x73DC1683L,
      0xE3630B12L, 0x94643B84L, 0x0D6D6A3EL, 0x7A6A5AA8L,
      0xE40ECF0BL, 0x9309FF9DL, 0x0A00AE27L, 0x7D079EB1L,
      0xF00F9344L, 0x8708A3D2L, 0x1E01F268L, 0x6906C2FEL,
      0xF762575DL, 0x806567CBL, 0x196C3671L, 0x6E6B06E7L,
      0xFED41B76L, 0x89D32BE0L, 0x10DA7A5AL, 0x67DD4ACCL,
      0xF9B9DF6FL, 0x8EBEEFF9L, 0x17B7BE43L, 0x60B08ED5L,
      0xD6D6A3E8L, 0xA1D1937EL, 0x38D8C2C4L, 0x4FDFF252L,
      0xD1BB67F1L, 0xA6BC5767L, 0x3FB506DDL, 0x48B2364BL,
      0xD80D2BDAL, 0xAF0A1B4CL, 0x36034AF6L, 0x41047A60L,
      0xDF60EFC3L, 0xA867DF55L, 0x316E8EEFL, 0x4669BE79L,
      0xCB61B38CL, 0xBC66831AL, 0x256FD2A0L, 0x5268E236L,
      0xCC0C7795L, 0xBB0B4703L, 0x220216B9L, 0x5505262FL,
      0xC5BA3BBEL, 0xB2BD0B28L, 0x2BB45A92L, 0x5CB36A04L,
      0xC2D7FFA7L, 0xB5D0CF31L, 0x2CD99E8BL, 0x5BDEAE1DL,
      0x9B64C2B0L, 0xEC63F226L, 0x756AA39CL, 0x026D930AL,
      0x9C0906A9L, 0xEB0E363FL, 0x72076785L, 0x05005713L,
      0x95BF4A82L, 0xE2B87A14L, 0x7BB12BAEL, 0x0CB61B38L,
      0x92D28E9BL, 0xE5D5BE0DL, 0x7CDCEFB7L, 0x0BDBDF21L,
      0x86D3D2D4L, 0xF1D4E242L, 0x68DDB3F8L, 0x1FDA836EL,
      0x81BE16CDL, 0xF6B9265BL, 0x6FB077E1L, 0x18B74777L,
      0x88085AE6L, 0xFF0F6A70L, 0x66063BCAL, 0x11010B5CL,
      0x8F659EFFL, 0xF862AE69L, 0x616BFFD3L, 0x166CCF45L,
      0xA00AE278L, 0xD70DD2EEL, 0x4E048354L, 0x3903B3C2L,
      0xA7672661L, 0xD06016F7L, 0x4969474DL, 0x3E6E77DBL,
      0xAED16A4AL, 0xD9D65ADCL, 0x40DF0B66L, 0x37D83BF0L,
      0xA9BCAE53L, 0xDEBB9EC5L, 0x47B2CF7FL, 0x30B5FFE9L,
      0xBDBDF21CL, 0xCABAC28AL, 0x53B39330L, 0x24B4A3A6L,
      0xBAD03605L, 0xCDD70693L, 0x54DE5729L, 0x23D967BFL,
      0xB3667A2EL, 0xC4614AB8L, 0x5D681B02L, 0x2A6F2B94L,
      0xB40BBE37L, 0xC30C8EA1L, 0x5A05DF1BL, 0x2D02EF8DL
};

00109 class Crc32
{
private:
      quint32 result;

public:
      Crc32()
      {
            clear();
      }

      void clear()
      {
            result = 0xffffffff;
      }

      void update(const QByteArray &in)
      {
            for(int n = 0; n < in.size(); ++n)
                  result = (result >> 8) ^ (crctable[(result & 0xff) ^ (quint8)in[n]]);
      }

      quint32 final()
      {
            return result ^= 0xffffffff;
      }

      static quint32 process(const QByteArray &in)
      {
            Crc32 c;
            c.update(in);
            return c.final();
      }
};

static quint8 magic_cookie[4] = { 0x21, 0x12, 0xA4, 0x42 };

// do 3-field check of stun packet
// returns length of packet not counting the header, or -1 on error
static int check_and_get_length(const QByteArray &buf)
{
      // stun packets are at least 20 bytes
      if(buf.size() < 20)
            return -1;

      // minimal 3-field check

      // top 2 bits of packet must be 0
      if(buf[0] & 0xC0)
            return -1;

      const quint8 *p = (const quint8 *)buf.data();
      quint16 mlen = read16(p + 2);

      // bottom 2 bits of message length field must be 0
      if(mlen & 0x03)
            return -1;

      // (also, the message length should be a reasonable size)
      if(mlen + 20 > buf.size())
            return -1;

      // magic cookie must be set
      if(memcmp(p + 4, magic_cookie, 4) != 0)
            return -1;

      return mlen;
}

#define ATTRIBUTE_AREA_START  20
#define ATTRIBUTE_AREA_MAX    65535
#define ATTRIBUTE_VALUE_MAX   65531

// note: because the attribute area of the packet has a maximum size of
//   2^16-1, and each attribute itself has a 4 byte header, it follows that
//   the maximum size of an attribute's value is 2^16-5.  this means that,
//   even if padded with up to 3 bytes, the physical size of an attribute's
//   value will not overflow a 16-bit unsigned integer.
static quint16 round_up_length(quint16 in)
{
      Q_ASSERT(in <= ATTRIBUTE_VALUE_MAX);
      quint16 out = in;
      quint16 remainder = out % 4;
      if(remainder != 0)
            out += (4 - remainder);
      return out;
}

// buf    = entire stun packet
// offset = byte index of current attribute (first is offset=20)
// type   = take attribute type
// len    = take attribute value length (value is at offset + 4)
// returns offset of next attribute, -1 if no more
static int get_attribute_props(const QByteArray &buf, int offset, quint16 *type, int *len)
{
      Q_ASSERT(offset >= ATTRIBUTE_AREA_START);

      const quint8 *p = (const quint8 *)buf.data();

      // need at least 4 bytes for an attribute
      if(offset + 4 > buf.size())
            return -1;

      quint16 _type = read16(p + offset);
      offset += 2;
      quint16 _alen = read16(p + offset);
      offset += 2;

      // get physical length.  stun attributes are 4-byte aligned, and may
      //   contain 0-3 bytes of padding.
      quint16 plen = round_up_length(_alen);
      if(offset + plen > buf.size())
            return -1;

      *type = _type;
      *len = _alen;
      return offset + plen;
}

// buf    = entire stun packet
// type   = attribute type to find
// len    = take attribute value length (value is at offset + 4)
// next   = take offset of next attribute
// returns offset of found attribute, -1 if not found
static int find_attribute(const QByteArray &buf, quint16 type, int *len, int *next = 0)
{
      int at = ATTRIBUTE_AREA_START;
      quint16 _type;
      int _len;
      int _next;

      while(1)
      {
            _next = get_attribute_props(buf, at, &_type, &_len);
            if(_next == -1)
                  break;
            if(_type == type)
            {
                  *len = _len;
                  if(next)
                        *next = _next;
                  return at;
            }
            at = _next;
      }

      return -1;
}

// buf  = stun packet to append attribute to
// type = type of attribute
// len  = length of value
// returns offset of new attribute, or -1 if it can't fit
// note: attribute value is located at offset + 4 and is uninitialized
// note: padding following attribute is zeroed out
static int append_attribute_uninitialized(QByteArray *buf, quint16 type, int len)
{
      if(len > ATTRIBUTE_VALUE_MAX)
            return -1;

      quint16 alen = (quint16)len;
      quint16 plen = round_up_length(alen);

      if((buf->size() - ATTRIBUTE_AREA_START) + 4 + plen > ATTRIBUTE_AREA_MAX)
            return -1;

      int at = buf->size();
      buf->resize(buf->size() + 4 + plen);
      quint8 *p = (quint8 *)buf->data();

      write16(p + at, type);
      write16(p + at + 2, alen);

      // padding
      for(int n = 0; n < plen - alen; ++n)
            p[at + alen + n] = 0;

      return at;
}

static quint32 fingerprint_calc(const quint8 *buf, int size)
{
      QByteArray region = QByteArray::fromRawData((const char *)buf, size);
      return Crc32::process(region) ^ 0x5354554e;
}

static QByteArray message_integrity_calc(const quint8 *buf, int size, const QByteArray &key)
{
      QCA::MessageAuthenticationCode hmac("hmac(sha1)", key);
      QByteArray region = QByteArray::fromRawData((const char *)buf, size);
      QByteArray result = hmac.process(region).toByteArray();
      Q_ASSERT(result.size() == 20);
      return result;
}

// look for fingerprint attribute and confirm it
// buf = entire stun packet
// returns true if fingerprint attribute exists and is correct
static bool fingerprint_check(const QByteArray &buf)
{
      int at, len;
      at = find_attribute(buf, AttribFingerprint, &len);
      if(at == -1 || len != 4) // value must be 4 bytes
            return false;

      const quint8 *p = (const quint8 *)buf.data();
      quint32 fpval = read32(p + at + 4);
      quint32 fpcalc = fingerprint_calc(p, at);
      if(fpval == fpcalc)
            return true;
      else
            return false;
}

// copy the input buffer and prepare for message integrity checking.  the
//   packet is truncated after the message-integrity attribute (since nothing
//   after it is protected), and the packet length is adjusted in the header
//   accordingly.
// buf    = input stun packet
// out    = take output stun packet
// offset = take offset of message-integrity attribute
// returns true if message-integrity attribute exists and packet is prepared
// note: message-integrity value is at offset + 4 and is exactly 20 bytes
static bool message_integrity_prep(const QByteArray &buf, QByteArray *out, int *offset)
{
      int at, len, next;
      at = find_attribute(buf, AttribMessageIntegrity, &len, &next);
      if(at == -1 || len != 20) // value must be 20 bytes
            return false;

      // prepare new attribute area size
      int i = next - ATTRIBUTE_AREA_START;

      // new value must be divisible by 4
      if(i % 4 != 0)
            return false;

      // copy truncated packet
      *out = buf.mid(0, next);

      // set new length in header
      quint16 newlen = (quint16)i;
      write16((quint8 *)out->data() + 2, newlen);

      *offset = at;
      return true;
}

// confirm message integrity
// buf    = prepared stun packet (from message_integrity_prep())
// offset = offset of message-integrity attribute
// key    = the HMAC key
// returns true if correct
static bool message_integrity_check(const QByteArray &buf, int offset, const QByteArray &key)
{
      QByteArray mival = QByteArray::fromRawData(buf.data() + offset + 4, 20);
      QByteArray micalc = message_integrity_calc((const quint8 *)buf.data(), offset, key);
      if(mival == micalc)
            return true;
      else
            return false;
}

00372 class StunMessage::Private : public QSharedData
{
public:
      StunMessage::Class mclass;
      quint16 method;
      quint8 magic[4];
      quint8 id[12];
      QList<Attribute> attribs;

      Private()
      {
            mclass = (StunMessage::Class)-1;
            method = 0;
            memcpy(magic, magic_cookie, 4);
            memset(id, 0, 12);
      }
};

StunMessage::StunMessage() :
      d(0)
{
}

StunMessage::StunMessage(const StunMessage &from) :
      d(from.d)
{
}

StunMessage::~StunMessage()
{
}

StunMessage & StunMessage::operator=(const StunMessage &from)
{
      d = from.d;
      return *this;
}

bool StunMessage::isNull() const
{
      return (d ? false : true);
}

StunMessage::Class StunMessage::mclass() const
{
      Q_ASSERT(d);
      return d->mclass;
}

quint16 StunMessage::method() const
{
      Q_ASSERT(d);
      return d->method;
}

const quint8 *StunMessage::magic() const
{
      Q_ASSERT(d);
      return d->magic;
}

const quint8 *StunMessage::id() const
{
      Q_ASSERT(d);
      return d->id;
}

QList<StunMessage::Attribute> StunMessage::attributes() const
{
      Q_ASSERT(d);
      return d->attribs;
}

QByteArray StunMessage::attribute(quint16 type) const
{
      Q_ASSERT(d);

      foreach(const Attribute &i, d->attribs)
      {
            if(i.type == type)
                  return i.value;
      }
      return QByteArray();
}

void StunMessage::setClass(Class mclass)
{
      ENSURE_D
      d->mclass = mclass;
}

void StunMessage::setMethod(quint16 method)
{
      ENSURE_D
      d->method = method;
}

void StunMessage::setMagic(const quint8 *magic)
{
      ENSURE_D
      memcpy(d->magic, magic, 4);
}

void StunMessage::setId(const quint8 *id)
{
      ENSURE_D
      memcpy(d->id, id, 12);
}

void StunMessage::setAttributes(const QList<Attribute> &attribs)
{
      ENSURE_D
      d->attribs = attribs;
}

QByteArray StunMessage::toBinary(int validationFlags, const QByteArray &key) const
{
      Q_ASSERT(d);

      // header
      QByteArray buf(20, 0);
      quint8 *p = (quint8 *)buf.data();

      quint8 classbits = 0;
      if(d->mclass == Request)
            classbits = 0; // 00
      else if(d->mclass == Indication)
            classbits = 1; // 01
      else if(d->mclass == SuccessResponse)
            classbits = 2; // 10
      else if(d->mclass == ErrorResponse)
            classbits = 3; // 11
      else
            Q_ASSERT(0);

      // method bits are split into 3 sections
      quint16 m1, m2, m3;
      m1 = d->method & 0x0f80; // M7-11
      m1 <<= 2;
      m2 = d->method & 0x0070; // M4-6
      m2 <<= 1;
      m3 = d->method & 0x000f; // M0-3

      // class bits are split into 2 sections
      quint16 c1, c2;
      c1 = classbits & 0x02; // C1
      c1 <<= 7;
      c2 = classbits & 0x01; // C0
      c2 <<= 4;

      quint16 type = m1 | m2 | m3 | c1 | c2;
      write16(p, type);
      write16(p + 2, 0);
      memcpy(p + 4, d->magic, 4);
      memcpy(p + 8, d->id, 12);

      foreach(const Attribute &i, d->attribs)
      {
            int at = append_attribute_uninitialized(&buf, i.type, i.value.size());
            if(at == -1)
                  return QByteArray();

            p = (quint8 *)buf.data(); // follow the resize

            memcpy(buf.data() + at + 4, i.value.data(), i.value.size());
      }

      // set attribute area size
      write16(p + 2, buf.size() - ATTRIBUTE_AREA_START);

      if(validationFlags & MessageIntegrity)
      {
            quint16 alen = 20; // size of hmac(sha1)
            int at = append_attribute_uninitialized(&buf, AttribMessageIntegrity, alen);
            if(at == -1)
                  return QByteArray();

            p = (quint8 *)buf.data(); // follow the resize

            // set attribute area size to include the new attribute
            write16(p + 2, buf.size() - ATTRIBUTE_AREA_START);

            // now calculate the hash and fill in the value
            QByteArray result = message_integrity_calc(p, at, key);
            Q_ASSERT(result.size() == alen);
            memcpy(p + at + 4, result.data(), alen);
      }

      if(validationFlags & Fingerprint)
      {
            quint16 alen = 4; // size of crc32
            int at = append_attribute_uninitialized(&buf, AttribFingerprint, alen);
            if(at == -1)
                  return QByteArray();

            p = (quint8 *)buf.data(); // follow the resize

            // set attribute area size to include the new attribute
            write16(p + 2, buf.size() - ATTRIBUTE_AREA_START);

            // now calculate the fingerprint and fill in the value
            quint32 fpcalc = fingerprint_calc(p, at);
            write32(p + at + 4, fpcalc);
      }

      return buf;
}

StunMessage StunMessage::fromBinary(const QByteArray &a, ConvertResult *result, int validationFlags, const QByteArray &key)
{
      int mlen = check_and_get_length(a);
      if(mlen == -1)
      {
            if(result)
                  *result = ErrorFormat;
            return StunMessage();
      }

      if(validationFlags & Fingerprint)
      {
            if(!fingerprint_check(a))
            {
                  if(result)
                        *result = ErrorFingerprint;
                  return StunMessage();
            }
      }

      QByteArray in;

      if(validationFlags & MessageIntegrity)
      {
            int offset;
            if(!message_integrity_prep(a, &in, &offset))
            {
                  if(result)
                        *result = ErrorMessageIntegrity;
                  return StunMessage();
            }

            if(!message_integrity_check(in, offset, key))
            {
                  if(result)
                        *result = ErrorMessageIntegrity;
                  return StunMessage();
            }
      }
      else
            in = a;

      // all validating complete, now just parse the packet

      const quint8 *p = (const quint8 *)in.data();

      // method bits are split into 3 sections
      quint16 m1, m2, m3;
      m1 = p[0] & 0x3e; // M7-11
      m1 <<= 6;
      m2 = p[1] & 0xe0; // M4-6
      m2 >>= 1;
      m3 = p[1] & 0x0f; // M0-3

      // class bits are split into 2 sections
      quint8 c1, c2;
      c1 = p[0] & 0x01; // C1
      c1 <<= 1;
      c2 = p[1] & 0x10; // C0
      c2 >>= 4;

      quint16 method = m1 | m2 | m3;
      quint8 classbits = c1 | c2;

      Class mclass;
      if(classbits == 0) // 00
            mclass = Request;
      else if(classbits == 1) // 01
            mclass = Indication;
      else if(classbits == 2) // 10
            mclass = SuccessResponse;
      else // 11
            mclass = ErrorResponse;

      StunMessage out;
      out.setClass(mclass);
      out.setMethod(method);
      out.setMagic(p + 4);
      out.setId(p + 8);

      QList<Attribute> list;
      int at = ATTRIBUTE_AREA_START;
      while(1)
      {
            quint16 type;
            int len;
            int next;

            next = get_attribute_props(in, at, &type, &len);
            if(next == -1)
                  break;

            Attribute attrib;
            attrib.type = type;
            attrib.value = in.mid(at + 4, len);
            list += attrib;

            at = next;
      }
      out.setAttributes(list);

      if(result)
            *result = ConvertGood;
      return out;
}

bool StunMessage::isProbablyStun(const QByteArray &a)
{
      return (check_and_get_length(a) != -1 ? true : false);
}

StunMessage::Class StunMessage::extractClass(const QByteArray &in)
{
      const quint8 *p = (const quint8 *)in.data();

      // class bits are split into 2 sections
      quint8 c1, c2;
      c1 = p[0] & 0x01; // C1
      c1 <<= 1;
      c2 = p[1] & 0x10; // C0
      c2 >>= 4;

      quint8 classbits = c1 | c2;

      Class mclass;
      if(classbits == 0) // 00
            mclass = Request;
      else if(classbits == 1) // 01
            mclass = Indication;
      else if(classbits == 2) // 10
            mclass = SuccessResponse;
      else // 11
            mclass = ErrorResponse;

      return mclass;
}

bool StunMessage::containsStun(const quint8 *data, int size)
{
      // check_and_get_length does a full packet check so it works even on a stream
      return (check_and_get_length(QByteArray::fromRawData((const char *)data, size)) != -1 ? true : false);
}

QByteArray StunMessage::readStun(const quint8 *data, int size)
{
      QByteArray in = QByteArray::fromRawData((const char *)data, size);
      int mlen = check_and_get_length(in);
      if(mlen != -1)
            return QByteArray((const char *)data, mlen + 20);
      else
            return QByteArray();
}

}

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