Commit message: None
CVE: CVE-2014-9656
CWE: CWE-119
Vulnerability description: The tt_sbit_decoder_load_image function in sfnt/ttsbit.c in FreeType before 2.5.4 does not properly check for an integer overflow, which allows remote attackers to cause a denial of service (out-of-bounds read) or possibly have unspecified other impact via a crafted OpenType font.

Project: savannah

  tt_sbit_decoder_load_image( TT_SBitDecoder  decoder,
                              FT_UInt         glyph_index,
                              FT_Int          x_pos,
                              FT_Int          y_pos )
  {
    /*
     *  First, we find the correct strike range that applies to this
     *  glyph index.
     */

    FT_Byte*  p          = decoder->eblc_base + decoder->strike_index_array;
    FT_Byte*  p_limit    = decoder->eblc_limit;
    FT_ULong  num_ranges = decoder->strike_index_count;
    FT_UInt   start, end, index_format, image_format;
    FT_ULong  image_start = 0, image_end = 0, image_offset;


    for ( ; num_ranges > 0; num_ranges-- )
    {
      start = FT_NEXT_USHORT( p );
      end   = FT_NEXT_USHORT( p );

      if ( glyph_index >= start && glyph_index <= end )
        goto FoundRange;

      p += 4;  /* ignore index offset */
    }
    goto NoBitmap;

  FoundRange:
    image_offset = FT_NEXT_ULONG( p );

    /* overflow check */
    p = decoder->eblc_base + decoder->strike_index_array;
    if ( image_offset > (FT_ULong)( p_limit - p ) )
      goto Failure;

    p += image_offset;
    if ( p + 8 > p_limit )
      goto NoBitmap;

    /* now find the glyph's location and extend within the ebdt table */
    index_format = FT_NEXT_USHORT( p );
    image_format = FT_NEXT_USHORT( p );
    image_offset = FT_NEXT_ULONG ( p );

    switch ( index_format )
    {
    case 1: /* 4-byte offsets relative to `image_offset' */
      p += 4 * ( glyph_index - start );
      if ( p + 8 > p_limit )
        goto NoBitmap;

      image_start = FT_NEXT_ULONG( p );
      image_end   = FT_NEXT_ULONG( p );

      if ( image_start == image_end )  /* missing glyph */
        goto NoBitmap;
      break;

    case 2: /* big metrics, constant image size */
      {
        FT_ULong  image_size;


        if ( p + 12 > p_limit )
          goto NoBitmap;

        image_size = FT_NEXT_ULONG( p );

        if ( tt_sbit_decoder_load_metrics( decoder, &p, p_limit, 1 ) )
          goto NoBitmap;

        image_start = image_size * ( glyph_index - start );
        image_end   = image_start + image_size;
      }
      break;

    case 3: /* 2-byte offsets relative to 'image_offset' */
      p += 2 * ( glyph_index - start );
      if ( p + 4 > p_limit )
        goto NoBitmap;

      image_start = FT_NEXT_USHORT( p );
      image_end   = FT_NEXT_USHORT( p );

      if ( image_start == image_end )  /* missing glyph */
        goto NoBitmap;
      break;

    case 4: /* sparse glyph array with (glyph,offset) pairs */
      {
        FT_ULong  mm, num_glyphs;


        if ( p + 4 > p_limit )
          goto NoBitmap;

         num_glyphs = FT_NEXT_ULONG( p );
 
         /* overflow check for p + ( num_glyphs + 1 ) * 4 */
        if ( p + 4 > p_limit                                         ||
             num_glyphs > (FT_ULong)( ( ( p_limit - p ) >> 2 ) - 1 ) )
           goto NoBitmap;
 
         for ( mm = 0; mm < num_glyphs; mm++ )
          FT_UInt  gindex = FT_NEXT_USHORT( p );


          if ( gindex == glyph_index )
          {
            image_start = FT_NEXT_USHORT( p );
            p          += 2;
            image_end   = FT_PEEK_USHORT( p );
            break;
          }
          p += 2;
        }

        if ( mm >= num_glyphs )
          goto NoBitmap;
      }
      break;

    case 5: /* constant metrics with sparse glyph codes */
    case 19:
      {
        FT_ULong  image_size, mm, num_glyphs;


        if ( p + 16 > p_limit )
          goto NoBitmap;

        image_size = FT_NEXT_ULONG( p );

        if ( tt_sbit_decoder_load_metrics( decoder, &p, p_limit, 1 ) )
          goto NoBitmap;

        num_glyphs = FT_NEXT_ULONG( p );

        /* overflow check for p + 2 * num_glyphs */
        if ( num_glyphs > (FT_ULong)( ( p_limit - p ) >> 1 ) )
          goto NoBitmap;

        for ( mm = 0; mm < num_glyphs; mm++ )
        {
          FT_UInt  gindex = FT_NEXT_USHORT( p );


          if ( gindex == glyph_index )
            break;
        }

        if ( mm >= num_glyphs )
          goto NoBitmap;

        image_start = image_size * mm;
        image_end   = image_start + image_size;
      }
      break;

    default:
      goto NoBitmap;
    }