UXP/media/libpng/pngrutil.c

/* pngrutil.c - utilities to read a PNG file
 *
 * Last changed in libpng 1.6.26 [October 20, 2016]
 * Copyright (c) 1998-2002,2004,2006-2016 Glenn Randers-Pehrson
 * (Version 0.96 Copyright (c) 1996, 1997 Andreas Dilger)
 * (Version 0.88 Copyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc.)
 *
 * This code is released under the libpng license.
 * For conditions of distribution and use, see the disclaimer
 * and license in png.h
 *
 * This file contains routines that are only called from within
 * libpng itself during the course of reading an image.
 */

#include "pngpriv.h"

#ifdef PNG_READ_SUPPORTED

png_uint_32 PNGAPI
png_get_uint_31(png_const_structrp png_ptr, png_const_bytep buf)
{
   png_uint_32 uval = png_get_uint_32(buf);

   if (uval > PNG_UINT_31_MAX)
      png_error(png_ptr, "PNG unsigned integer out of range");

   return (uval);
}

#if defined(PNG_READ_gAMA_SUPPORTED) || defined(PNG_READ_cHRM_SUPPORTED)
/* The following is a variation on the above for use with the fixed
 * point values used for gAMA and cHRM.  Instead of png_error it
 * issues a warning and returns (-1) - an invalid value because both
 * gAMA and cHRM use *unsigned* integers for fixed point values.
 */
#define PNG_FIXED_ERROR (-1)

static png_fixed_point /* PRIVATE */
png_get_fixed_point(png_structrp png_ptr, png_const_bytep buf)
{
   png_uint_32 uval = png_get_uint_32(buf);

   if (uval <= PNG_UINT_31_MAX)
      return (png_fixed_point)uval; /* known to be in range */

   /* The caller can turn off the warning by passing NULL. */
   if (png_ptr != NULL)
      png_warning(png_ptr, "PNG fixed point integer out of range");

   return PNG_FIXED_ERROR;
}
#endif

#ifdef PNG_READ_INT_FUNCTIONS_SUPPORTED
/* NOTE: the read macros will obscure these definitions, so that if
 * PNG_USE_READ_MACROS is set the library will not use them internally,
 * but the APIs will still be available externally.
 *
 * The parentheses around "PNGAPI function_name" in the following three
 * functions are necessary because they allow the macros to co-exist with
 * these (unused but exported) functions.
 */

/* Grab an unsigned 32-bit integer from a buffer in big-endian format. */
png_uint_32 (PNGAPI
png_get_uint_32)(png_const_bytep buf)
{
   png_uint_32 uval =
       ((png_uint_32)(*(buf    )) << 24) +
       ((png_uint_32)(*(buf + 1)) << 16) +
       ((png_uint_32)(*(buf + 2)) <<  8) +
       ((png_uint_32)(*(buf + 3))      ) ;

   return uval;
}

/* Grab a signed 32-bit integer from a buffer in big-endian format.  The
 * data is stored in the PNG file in two's complement format and there
 * is no guarantee that a 'png_int_32' is exactly 32 bits, therefore
 * the following code does a two's complement to native conversion.
 */
png_int_32 (PNGAPI
png_get_int_32)(png_const_bytep buf)
{
   png_uint_32 uval = png_get_uint_32(buf);
   if ((uval & 0x80000000) == 0) /* non-negative */
      return (png_int_32)uval;

   uval = (uval ^ 0xffffffff) + 1;  /* 2's complement: -x = ~x+1 */
   if ((uval & 0x80000000) == 0) /* no overflow */
      return -(png_int_32)uval;
   /* The following has to be safe; this function only gets called on PNG data
    * and if we get here that data is invalid.  0 is the most safe value and
    * if not then an attacker would surely just generate a PNG with 0 instead.
    */
   return 0;
}

/* Grab an unsigned 16-bit integer from a buffer in big-endian format. */
png_uint_16 (PNGAPI
png_get_uint_16)(png_const_bytep buf)
{
   /* ANSI-C requires an int value to accomodate at least 16 bits so this
    * works and allows the compiler not to worry about possible narrowing
    * on 32-bit systems.  (Pre-ANSI systems did not make integers smaller
    * than 16 bits either.)
    */
   unsigned int val =
       ((unsigned int)(*buf) << 8) +
       ((unsigned int)(*(buf + 1)));

   return (png_uint_16)val;
}

#endif /* READ_INT_FUNCTIONS */

/* Read and check the PNG file signature */
void /* PRIVATE */
png_read_sig(png_structrp png_ptr, png_inforp info_ptr)
{
   png_size_t num_checked, num_to_check;

   /* Exit if the user application does not expect a signature. */
   if (png_ptr->sig_bytes >= 8)
      return;

   num_checked = png_ptr->sig_bytes;
   num_to_check = 8 - num_checked;

#ifdef PNG_IO_STATE_SUPPORTED
   png_ptr->io_state = PNG_IO_READING | PNG_IO_SIGNATURE;
#endif

   /* The signature must be serialized in a single I/O call. */
   png_read_data(png_ptr, &(info_ptr->signature[num_checked]), num_to_check);
   png_ptr->sig_bytes = 8;

   if (png_sig_cmp(info_ptr->signature, num_checked, num_to_check) != 0)
   {
      if (num_checked < 4 &&
          png_sig_cmp(info_ptr->signature, num_checked, num_to_check - 4))
         png_error(png_ptr, "Not a PNG file");
      else
         png_error(png_ptr, "PNG file corrupted by ASCII conversion");
   }
   if (num_checked < 3)
      png_ptr->mode |= PNG_HAVE_PNG_SIGNATURE;
}

/* Read the chunk header (length + type name).
 * Put the type name into png_ptr->chunk_name, and return the length.
 */
png_uint_32 /* PRIVATE */
png_read_chunk_header(png_structrp png_ptr)
{
   png_byte buf[8];
   png_uint_32 length;

#ifdef PNG_IO_STATE_SUPPORTED
   png_ptr->io_state = PNG_IO_READING | PNG_IO_CHUNK_HDR;
#endif

   /* Read the length and the chunk name.
    * This must be performed in a single I/O call.
    */
   png_read_data(png_ptr, buf, 8);
   length = png_get_uint_31(png_ptr, buf);

   /* Put the chunk name into png_ptr->chunk_name. */
   png_ptr->chunk_name = PNG_CHUNK_FROM_STRING(buf+4);

   png_debug2(0, "Reading %lx chunk, length = %lu",
       (unsigned long)png_ptr->chunk_name, (unsigned long)length);

   /* Reset the crc and run it over the chunk name. */
   png_reset_crc(png_ptr);
   png_calculate_crc(png_ptr, buf + 4, 4);

   /* Check to see if chunk name is valid. */
   png_check_chunk_name(png_ptr, png_ptr->chunk_name);

#ifdef PNG_IO_STATE_SUPPORTED
   png_ptr->io_state = PNG_IO_READING | PNG_IO_CHUNK_DATA;
#endif

   return length;
}

/* Read data, and (optionally) run it through the CRC. */
void /* PRIVATE */
png_crc_read(png_structrp png_ptr, png_bytep buf, png_uint_32 length)
{
   if (png_ptr == NULL)
      return;

   png_read_data(png_ptr, buf, length);
   png_calculate_crc(png_ptr, buf, length);
}

/* Optionally skip data and then check the CRC.  Depending on whether we
 * are reading an ancillary or critical chunk, and how the program has set
 * things up, we may calculate the CRC on the data and print a message.
 * Returns '1' if there was a CRC error, '0' otherwise.
 */
int /* PRIVATE */
png_crc_finish(png_structrp png_ptr, png_uint_32 skip)
{
   /* The size of the local buffer for inflate is a good guess as to a
    * reasonable size to use for buffering reads from the application.
    */
   while (skip > 0)
   {
      png_uint_32 len;
      png_byte tmpbuf[PNG_INFLATE_BUF_SIZE];

      len = (sizeof tmpbuf);
      if (len > skip)
         len = skip;
      skip -= len;

      png_crc_read(png_ptr, tmpbuf, len);
   }

   if (png_crc_error(png_ptr) != 0)
   {
      if (PNG_CHUNK_ANCILLARY(png_ptr->chunk_name) != 0 ?
          (png_ptr->flags & PNG_FLAG_CRC_ANCILLARY_NOWARN) == 0 :
          (png_ptr->flags & PNG_FLAG_CRC_CRITICAL_USE) != 0)
      {
         png_chunk_warning(png_ptr, "CRC error");
      }

      else
         png_chunk_error(png_ptr, "CRC error");

      return (1);
   }

   return (0);
}

/* Compare the CRC stored in the PNG file with that calculated by libpng from
 * the data it has read thus far.
 */
int /* PRIVATE */
png_crc_error(png_structrp png_ptr)
{
   png_byte crc_bytes[4];
   png_uint_32 crc;
   int need_crc = 1;

   if (PNG_CHUNK_ANCILLARY(png_ptr->chunk_name) != 0)
   {
      if ((png_ptr->flags & PNG_FLAG_CRC_ANCILLARY_MASK) ==
          (PNG_FLAG_CRC_ANCILLARY_USE | PNG_FLAG_CRC_ANCILLARY_NOWARN))
         need_crc = 0;
   }

   else /* critical */
   {
      if ((png_ptr->flags & PNG_FLAG_CRC_CRITICAL_IGNORE) != 0)
         need_crc = 0;
   }

#ifdef PNG_IO_STATE_SUPPORTED
   png_ptr->io_state = PNG_IO_READING | PNG_IO_CHUNK_CRC;
#endif

   /* The chunk CRC must be serialized in a single I/O call. */
   png_read_data(png_ptr, crc_bytes, 4);

   if (need_crc != 0)
   {
      crc = png_get_uint_32(crc_bytes);
      return ((int)(crc != png_ptr->crc));
   }

   else
      return (0);
}

#if defined(PNG_READ_iCCP_SUPPORTED) || defined(PNG_READ_iTXt_SUPPORTED) ||\
    defined(PNG_READ_pCAL_SUPPORTED) || defined(PNG_READ_sCAL_SUPPORTED) ||\
    defined(PNG_READ_sPLT_SUPPORTED) || defined(PNG_READ_tEXt_SUPPORTED) ||\
    defined(PNG_READ_zTXt_SUPPORTED) || defined(PNG_SEQUENTIAL_READ_SUPPORTED)
/* Manage the read buffer; this simply reallocates the buffer if it is not small
 * enough (or if it is not allocated).  The routine returns a pointer to the
 * buffer; if an error occurs and 'warn' is set the routine returns NULL, else
 * it will call png_error (via png_malloc) on failure.  (warn == 2 means
 * 'silent').
 */
static png_bytep
png_read_buffer(png_structrp png_ptr, png_alloc_size_t new_size, int warn)
{
   png_bytep buffer = png_ptr->read_buffer;

   if (buffer != NULL && new_size > png_ptr->read_buffer_size)
   {
      png_ptr->read_buffer = NULL;
      png_ptr->read_buffer = NULL;
      png_ptr->read_buffer_size = 0;
      png_free(png_ptr, buffer);
      buffer = NULL;
   }

   if (buffer == NULL)
   {
      buffer = png_voidcast(png_bytep, png_malloc_base(png_ptr, new_size));

      if (buffer != NULL)
      {
         png_ptr->read_buffer = buffer;
         png_ptr->read_buffer_size = new_size;
      }

      else if (warn < 2) /* else silent */
      {
         if (warn != 0)
             png_chunk_warning(png_ptr, "insufficient memory to read chunk");

         else
             png_chunk_error(png_ptr, "insufficient memory to read chunk");
      }
   }

   return buffer;
}
#endif /* READ_iCCP|iTXt|pCAL|sCAL|sPLT|tEXt|zTXt|SEQUENTIAL_READ */

/* png_inflate_claim: claim the zstream for some nefarious purpose that involves
 * decompression.  Returns Z_OK on success, else a zlib error code.  It checks
 * the owner but, in final release builds, just issues a warning if some other
 * chunk apparently owns the stream.  Prior to release it does a png_error.
 */
static int
png_inflate_claim(png_structrp png_ptr, png_uint_32 owner)
{
   if (png_ptr->zowner != 0)
   {
      char msg[64];

      PNG_STRING_FROM_CHUNK(msg, png_ptr->zowner);
      /* So the message that results is "<chunk> using zstream"; this is an
       * internal error, but is very useful for debugging.  i18n requirements
       * are minimal.
       */
      (void)png_safecat(msg, (sizeof msg), 4, " using zstream");
#if PNG_RELEASE_BUILD
      png_chunk_warning(png_ptr, msg);
      png_ptr->zowner = 0;
#else
      png_chunk_error(png_ptr, msg);
#endif
   }

   /* Implementation note: unlike 'png_deflate_claim' this internal function
    * does not take the size of the data as an argument.  Some efficiency could
    * be gained by using this when it is known *if* the zlib stream itself does
    * not record the number; however, this is an illusion: the original writer
    * of the PNG may have selected a lower window size, and we really must
    * follow that because, for systems with with limited capabilities, we
    * would otherwise reject the application's attempts to use a smaller window
    * size (zlib doesn't have an interface to say "this or lower"!).
    *
    * inflateReset2 was added to zlib 1.2.4; before this the window could not be
    * reset, therefore it is necessary to always allocate the maximum window
    * size with earlier zlibs just in case later compressed chunks need it.
    */
   {
      int ret; /* zlib return code */
#if ZLIB_VERNUM >= 0x1240
      int window_bits = 0;

# if defined(PNG_SET_OPTION_SUPPORTED) && defined(PNG_MAXIMUM_INFLATE_WINDOW)
      if (((png_ptr->options >> PNG_MAXIMUM_INFLATE_WINDOW) & 3) ==
          PNG_OPTION_ON)
      {
         window_bits = 15;
         png_ptr->zstream_start = 0; /* fixed window size */
      }

      else
      {
         png_ptr->zstream_start = 1;
      }
# endif

#endif /* ZLIB_VERNUM >= 0x1240 */

      /* Set this for safety, just in case the previous owner left pointers to
       * memory allocations.
       */
      png_ptr->zstream.next_in = NULL;
      png_ptr->zstream.avail_in = 0;
      png_ptr->zstream.next_out = NULL;
      png_ptr->zstream.avail_out = 0;

      if ((png_ptr->flags & PNG_FLAG_ZSTREAM_INITIALIZED) != 0)
      {
#if ZLIB_VERNUM >= 0x1240
         ret = inflateReset2(&png_ptr->zstream, window_bits);
#else
         ret = inflateReset(&png_ptr->zstream);
#endif
      }

      else
      {
#if ZLIB_VERNUM >= 0x1240
         ret = inflateInit2(&png_ptr->zstream, window_bits);
#else
         ret = inflateInit(&png_ptr->zstream);
#endif

         if (ret == Z_OK)
            png_ptr->flags |= PNG_FLAG_ZSTREAM_INITIALIZED;
      }

#if ZLIB_VERNUM >= 0x1281
      /* Turn off validation of the ADLER32 checksum */
      if ((png_ptr->flags & PNG_FLAG_CRC_CRITICAL_IGNORE) != 0)
         ret = inflateValidate(&png_ptr->zstream, 0);
#endif

      if (ret == Z_OK)
         png_ptr->zowner = owner;

      else
         png_zstream_error(png_ptr, ret);

      return ret;
   }

#ifdef window_bits
# undef window_bits
#endif
}

#if ZLIB_VERNUM >= 0x1240
/* Handle the start of the inflate stream if we called inflateInit2(strm,0);
 * in this case some zlib versions skip validation of the CINFO field and, in
 * certain circumstances, libpng may end up displaying an invalid image, in
 * contrast to implementations that call zlib in the normal way (e.g. libpng
 * 1.5).
 */
int /* PRIVATE */
png_zlib_inflate(png_structrp png_ptr, int flush)
{
   if (png_ptr->zstream_start && png_ptr->zstream.avail_in > 0)
   {
      if ((*png_ptr->zstream.next_in >> 4) > 7)
      {
         png_ptr->zstream.msg = "invalid window size (libpng)";
         return Z_DATA_ERROR;
      }

      png_ptr->zstream_start = 0;
   }

   return inflate(&png_ptr->zstream, flush);
}
#endif /* Zlib >= 1.2.4 */

#ifdef PNG_READ_COMPRESSED_TEXT_SUPPORTED
#if defined(PNG_READ_zTXt_SUPPORTED) || defined (PNG_READ_iTXt_SUPPORTED)
/* png_inflate now returns zlib error codes including Z_OK and Z_STREAM_END to
 * allow the caller to do multiple calls if required.  If the 'finish' flag is
 * set Z_FINISH will be passed to the final inflate() call and Z_STREAM_END must
 * be returned or there has been a problem, otherwise Z_SYNC_FLUSH is used and
 * Z_OK or Z_STREAM_END will be returned on success.
 *
 * The input and output sizes are updated to the actual amounts of data consumed
 * or written, not the amount available (as in a z_stream).  The data pointers
 * are not changed, so the next input is (data+input_size) and the next
 * available output is (output+output_size).
 */
static int
png_inflate(png_structrp png_ptr, png_uint_32 owner, int finish,
    /* INPUT: */ png_const_bytep input, png_uint_32p input_size_ptr,
    /* OUTPUT: */ png_bytep output, png_alloc_size_t *output_size_ptr)
{
   if (png_ptr->zowner == owner) /* Else not claimed */
   {
      int ret;
      png_alloc_size_t avail_out = *output_size_ptr;
      png_uint_32 avail_in = *input_size_ptr;

      /* zlib can't necessarily handle more than 65535 bytes at once (i.e. it
       * can't even necessarily handle 65536 bytes) because the type uInt is
       * "16 bits or more".  Consequently it is necessary to chunk the input to
       * zlib.  This code uses ZLIB_IO_MAX, from pngpriv.h, as the maximum (the
       * maximum value that can be stored in a uInt.)  It is possible to set
       * ZLIB_IO_MAX to a lower value in pngpriv.h and this may sometimes have
       * a performance advantage, because it reduces the amount of data accessed
       * at each step and that may give the OS more time to page it in.
       */
      png_ptr->zstream.next_in = PNGZ_INPUT_CAST(input);
      /* avail_in and avail_out are set below from 'size' */
      png_ptr->zstream.avail_in = 0;
      png_ptr->zstream.avail_out = 0;

      /* Read directly into the output if it is available (this is set to
       * a local buffer below if output is NULL).
       */
      if (output != NULL)
         png_ptr->zstream.next_out = output;

      do
      {
         uInt avail;
         Byte local_buffer[PNG_INFLATE_BUF_SIZE];

         /* zlib INPUT BUFFER */
         /* The setting of 'avail_in' used to be outside the loop; by setting it
          * inside it is possible to chunk the input to zlib and simply rely on
          * zlib to advance the 'next_in' pointer.  This allows arbitrary
          * amounts of data to be passed through zlib at the unavoidable cost of
          * requiring a window save (memcpy of up to 32768 output bytes)
          * every ZLIB_IO_MAX input bytes.
          */
         avail_in += png_ptr->zstream.avail_in; /* not consumed last time */

         avail = ZLIB_IO_MAX;

         if (avail_in < avail)
            avail = (uInt)avail_in; /* safe: < than ZLIB_IO_MAX */

         avail_in -= avail;
         png_ptr->zstream.avail_in = avail;

         /* zlib OUTPUT BUFFER */
         avail_out += png_ptr->zstream.avail_out; /* not written last time */

         avail = ZLIB_IO_MAX; /* maximum zlib can process */

         if (output == NULL)
         {
            /* Reset the output buffer each time round if output is NULL and
             * make available the full buffer, up to 'remaining_space'
             */
            png_ptr->zstream.next_out = local_buffer;
            if ((sizeof local_buffer) < avail)
               avail = (sizeof local_buffer);
         }

         if (avail_out < avail)
            avail = (uInt)avail_out; /* safe: < ZLIB_IO_MAX */

         png_ptr->zstream.avail_out = avail;
         avail_out -= avail;

         /* zlib inflate call */
         /* In fact 'avail_out' may be 0 at this point, that happens at the end
          * of the read when the final LZ end code was not passed at the end of
          * the previous chunk of input data.  Tell zlib if we have reached the
          * end of the output buffer.
          */
         ret = PNG_INFLATE(png_ptr, avail_out > 0 ? Z_NO_FLUSH :
             (finish ? Z_FINISH : Z_SYNC_FLUSH));
      } while (ret == Z_OK);

      /* For safety kill the local buffer pointer now */
      if (output == NULL)
         png_ptr->zstream.next_out = NULL;

      /* Claw back the 'size' and 'remaining_space' byte counts. */
      avail_in += png_ptr->zstream.avail_in;
      avail_out += png_ptr->zstream.avail_out;

      /* Update the input and output sizes; the updated values are the amount
       * consumed or written, effectively the inverse of what zlib uses.
       */
      if (avail_out > 0)
         *output_size_ptr -= avail_out;

      if (avail_in > 0)
         *input_size_ptr -= avail_in;

      /* Ensure png_ptr->zstream.msg is set (even in the success case!) */
      png_zstream_error(png_ptr, ret);
      return ret;
   }

   else
   {
      /* This is a bad internal error.  The recovery assigns to the zstream msg
       * pointer, which is not owned by the caller, but this is safe; it's only
       * used on errors!
       */
      png_ptr->zstream.msg = PNGZ_MSG_CAST("zstream unclaimed");
      return Z_STREAM_ERROR;
   }
}

/*
 * Decompress trailing data in a chunk.  The assumption is that read_buffer
 * points at an allocated area holding the contents of a chunk with a
 * trailing compressed part.  What we get back is an allocated area
 * holding the original prefix part and an uncompressed version of the
 * trailing part (the malloc area passed in is freed).
 */
static int
png_decompress_chunk(png_structrp png_ptr,
    png_uint_32 chunklength, png_uint_32 prefix_size,
    png_alloc_size_t *newlength /* must be initialized to the maximum! */,
    int terminate /*add a '\0' to the end of the uncompressed data*/)
{
   /* TODO: implement different limits for different types of chunk.
    *
    * The caller supplies *newlength set to the maximum length of the
    * uncompressed data, but this routine allocates space for the prefix and
    * maybe a '\0' terminator too.  We have to assume that 'prefix_size' is
    * limited only by the maximum chunk size.
    */
   png_alloc_size_t limit = PNG_SIZE_MAX;

# ifdef PNG_SET_USER_LIMITS_SUPPORTED
   if (png_ptr->user_chunk_malloc_max > 0 &&
       png_ptr->user_chunk_malloc_max < limit)
      limit = png_ptr->user_chunk_malloc_max;
# elif PNG_USER_CHUNK_MALLOC_MAX > 0
   if (PNG_USER_CHUNK_MALLOC_MAX < limit)
      limit = PNG_USER_CHUNK_MALLOC_MAX;
# endif

   if (limit >= prefix_size + (terminate != 0))
   {
      int ret;

      limit -= prefix_size + (terminate != 0);

      if (limit < *newlength)
         *newlength = limit;

      /* Now try to claim the stream. */
      ret = png_inflate_claim(png_ptr, png_ptr->chunk_name);

      if (ret == Z_OK)
      {
         png_uint_32 lzsize = chunklength - prefix_size;

         ret = png_inflate(png_ptr, png_ptr->chunk_name, 1/*finish*/,
             /* input: */ png_ptr->read_buffer + prefix_size, &lzsize,
             /* output: */ NULL, newlength);

         if (ret == Z_STREAM_END)
         {
            /* Use 'inflateReset' here, not 'inflateReset2' because this
             * preserves the previously decided window size (otherwise it would
             * be necessary to store the previous window size.)  In practice
             * this doesn't matter anyway, because png_inflate will call inflate
             * with Z_FINISH in almost all cases, so the window will not be
             * maintained.
             */
            if (inflateReset(&png_ptr->zstream) == Z_OK)
            {
               /* Because of the limit checks above we know that the new,
                * expanded, size will fit in a size_t (let alone an
                * png_alloc_size_t).  Use png_malloc_base here to avoid an
                * extra OOM message.
                */
               png_alloc_size_t new_size = *newlength;
               png_alloc_size_t buffer_size = prefix_size + new_size +
                   (terminate != 0);
               png_bytep text = png_voidcast(png_bytep, png_malloc_base(png_ptr,
                   buffer_size));

               if (text != NULL)
               {
                  ret = png_inflate(png_ptr, png_ptr->chunk_name, 1/*finish*/,
                      png_ptr->read_buffer + prefix_size, &lzsize,
                      text + prefix_size, newlength);

                  if (ret == Z_STREAM_END)
                  {
                     if (new_size == *newlength)
                     {
                        if (terminate != 0)
                           text[prefix_size + *newlength] = 0;

                        if (prefix_size > 0)
                           memcpy(text, png_ptr->read_buffer, prefix_size);

                        {
                           png_bytep old_ptr = png_ptr->read_buffer;

                           png_ptr->read_buffer = text;
                           png_ptr->read_buffer_size = buffer_size;
                           text = old_ptr; /* freed below */
                        }
                     }

                     else
                     {
                        /* The size changed on the second read, there can be no
                         * guarantee that anything is correct at this point.
                         * The 'msg' pointer has been set to "unexpected end of
                         * LZ stream", which is fine, but return an error code
                         * that the caller won't accept.
                         */
                        ret = PNG_UNEXPECTED_ZLIB_RETURN;
                     }
                  }

                  else if (ret == Z_OK)
                     ret = PNG_UNEXPECTED_ZLIB_RETURN; /* for safety */

                  /* Free the text pointer (this is the old read_buffer on
                   * success)
                   */
                  png_free(png_ptr, text);

                  /* This really is very benign, but it's still an error because
                   * the extra space may otherwise be used as a Trojan Horse.
                   */
                  if (ret == Z_STREAM_END &&
                     chunklength - prefix_size != lzsize)
                     png_chunk_benign_error(png_ptr, "extra compressed data");
               }

               else
               {
                  /* Out of memory allocating the buffer */
                  ret = Z_MEM_ERROR;
                  png_zstream_error(png_ptr, Z_MEM_ERROR);
               }
            }

            else
            {
               /* inflateReset failed, store the error message */
               png_zstream_error(png_ptr, ret);

               if (ret == Z_STREAM_END)
                  ret = PNG_UNEXPECTED_ZLIB_RETURN;
            }
         }

         else if (ret == Z_OK)
            ret = PNG_UNEXPECTED_ZLIB_RETURN;

         /* Release the claimed stream */
         png_ptr->zowner = 0;
      }

      else /* the claim failed */ if (ret == Z_STREAM_END) /* impossible! */
         ret = PNG_UNEXPECTED_ZLIB_RETURN;

      return ret;
   }

   else
   {
      /* Application/configuration limits exceeded */
      png_zstream_error(png_ptr, Z_MEM_ERROR);
      return Z_MEM_ERROR;
   }
}
#endif /* READ_zTXt || READ_iTXt */
#endif /* READ_COMPRESSED_TEXT */

#ifdef PNG_READ_iCCP_SUPPORTED
/* Perform a partial read and decompress, producing 'avail_out' bytes and
 * reading from the current chunk as required.
 */
static int
png_inflate_read(png_structrp png_ptr, png_bytep read_buffer, uInt read_size,
    png_uint_32p chunk_bytes, png_bytep next_out, png_alloc_size_t *out_size,
    int finish)
{
   if (png_ptr->zowner == png_ptr->chunk_name)
   {
      int ret;

      /* next_in and avail_in must have been initialized by the caller. */
      png_ptr->zstream.next_out = next_out;
      png_ptr->zstream.avail_out = 0; /* set in the loop */

      do
      {
         if (png_ptr->zstream.avail_in == 0)
         {
            if (read_size > *chunk_bytes)
               read_size = (uInt)*chunk_bytes;
            *chunk_bytes -= read_size;

            if (read_size > 0)
               png_crc_read(png_ptr, read_buffer, read_size);

            png_ptr->zstream.next_in = read_buffer;
            png_ptr->zstream.avail_in = read_size;
         }

         if (png_ptr->zstream.avail_out == 0)
         {
            uInt avail = ZLIB_IO_MAX;
            if (avail > *out_size)
               avail = (uInt)*out_size;
            *out_size -= avail;

            png_ptr->zstream.avail_out = avail;
         }

         /* Use Z_SYNC_FLUSH when there is no more chunk data to ensure that all
          * the available output is produced; this allows reading of truncated
          * streams.
          */
         ret = PNG_INFLATE(png_ptr, *chunk_bytes > 0 ?
             Z_NO_FLUSH : (finish ? Z_FINISH : Z_SYNC_FLUSH));
      }
      while (ret == Z_OK && (*out_size > 0 || png_ptr->zstream.avail_out > 0));

      *out_size += png_ptr->zstream.avail_out;
      png_ptr->zstream.avail_out = 0; /* Should not be required, but is safe */

      /* Ensure the error message pointer is always set: */
      png_zstream_error(png_ptr, ret);
      return ret;
   }

   else
   {
      png_ptr->zstream.msg = PNGZ_MSG_CAST("zstream unclaimed");
      return Z_STREAM_ERROR;
   }
}
#endif

/* Read and check the IDHR chunk */

void /* PRIVATE */
png_handle_IHDR(png_structrp png_ptr, png_inforp info_ptr, png_uint_32 length)
{
   png_byte buf[13];
   png_uint_32 width, height;
   int bit_depth, color_type, compression_type, filter_type;
   int interlace_type;

   png_debug(1, "in png_handle_IHDR");

   if ((png_ptr->mode & PNG_HAVE_IHDR) != 0)
      png_chunk_error(png_ptr, "out of place");

   /* Check the length */
   if (length != 13)
      png_chunk_error(png_ptr, "invalid");

   png_ptr->mode |= PNG_HAVE_IHDR;

   png_crc_read(png_ptr, buf, 13);
   png_crc_finish(png_ptr, 0);

   width = png_get_uint_31(png_ptr, buf);
   height = png_get_uint_31(png_ptr, buf + 4);
   bit_depth = buf[8];
   color_type = buf[9];
   compression_type = buf[10];
   filter_type = buf[11];
   interlace_type = buf[12];

#ifdef PNG_READ_APNG_SUPPORTED
   png_ptr->first_frame_width = width;
   png_ptr->first_frame_height = height;
#endif

   /* Set internal variables */
   png_ptr->width = width;
   png_ptr->height = height;
   png_ptr->bit_depth = (png_byte)bit_depth;
   png_ptr->interlaced = (png_byte)interlace_type;
   png_ptr->color_type = (png_byte)color_type;
#ifdef PNG_MNG_FEATURES_SUPPORTED
   png_ptr->filter_type = (png_byte)filter_type;
#endif
   png_ptr->compression_type = (png_byte)compression_type;

   /* Find number of channels */
   switch (png_ptr->color_type)
   {
      default: /* invalid, png_set_IHDR calls png_error */
      case PNG_COLOR_TYPE_GRAY:
      case PNG_COLOR_TYPE_PALETTE:
         png_ptr->channels = 1;
         break;

      case PNG_COLOR_TYPE_RGB:
         png_ptr->channels = 3;
         break;

      case PNG_COLOR_TYPE_GRAY_ALPHA:
         png_ptr->channels = 2;
         break;

      case PNG_COLOR_TYPE_RGB_ALPHA:
         png_ptr->channels = 4;
         break;
   }

   /* Set up other useful info */
   png_ptr->pixel_depth = (png_byte)(png_ptr->bit_depth * png_ptr->channels);
   png_ptr->rowbytes = PNG_ROWBYTES(png_ptr->pixel_depth, png_ptr->width);
   png_debug1(3, "bit_depth = %d", png_ptr->bit_depth);
   png_debug1(3, "channels = %d", png_ptr->channels);
   png_debug1(3, "rowbytes = %lu", (unsigned long)png_ptr->rowbytes);
   png_set_IHDR(png_ptr, info_ptr, width, height, bit_depth,
       color_type, interlace_type, compression_type, filter_type);
}

/* Read and check the palette */
void /* PRIVATE */
png_handle_PLTE(png_structrp png_ptr, png_inforp info_ptr, png_uint_32 length)
{
   png_color palette[PNG_MAX_PALETTE_LENGTH];
   int max_palette_length, num, i;
#ifdef PNG_POINTER_INDEXING_SUPPORTED
   png_colorp pal_ptr;
#endif

   png_debug(1, "in png_handle_PLTE");

   if ((png_ptr->mode & PNG_HAVE_IHDR) == 0)
      png_chunk_error(png_ptr, "missing IHDR");

   /* Moved to before the 'after IDAT' check below because otherwise duplicate
    * PLTE chunks are potentially ignored (the spec says there shall not be more
    * than one PLTE, the error is not treated as benign, so this check trumps
    * the requirement that PLTE appears before IDAT.)
    */
   else if ((png_ptr->mode & PNG_HAVE_PLTE) != 0)
      png_chunk_error(png_ptr, "duplicate");

   else if ((png_ptr->mode & PNG_HAVE_IDAT) != 0)
   {
      /* This is benign because the non-benign error happened before, when an
       * IDAT was encountered in a color-mapped image with no PLTE.
       */
      png_crc_finish(png_ptr, length);
      png_chunk_benign_error(png_ptr, "out of place");
      return;
   }

   png_ptr->mode |= PNG_HAVE_PLTE;

   if ((png_ptr->color_type & PNG_COLOR_MASK_COLOR) == 0)
   {
      png_crc_finish(png_ptr, length);
      png_chunk_benign_error(png_ptr, "ignored in grayscale PNG");
      return;
   }

#ifndef PNG_READ_OPT_PLTE_SUPPORTED
   if (png_ptr->color_type != PNG_COLOR_TYPE_PALETTE)
   {
      png_crc_finish(png_ptr, length);
      return;
   }
#endif

   if (length > 3*PNG_MAX_PALETTE_LENGTH || length % 3)
   {
      png_crc_finish(png_ptr, length);

      if (png_ptr->color_type != PNG_COLOR_TYPE_PALETTE)
         png_chunk_benign_error(png_ptr, "invalid");

      else
         png_chunk_error(png_ptr, "invalid");

      return;
   }

   /* The cast is safe because 'length' is less than 3*PNG_MAX_PALETTE_LENGTH */
   num = (int)length / 3;

   /* If the palette has 256 or fewer entries but is too large for the bit
    * depth, we don't issue an error, to preserve the behavior of previous
    * libpng versions. We silently truncate the unused extra palette entries
    * here.
    */
   if (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE)
      max_palette_length = (1 << png_ptr->bit_depth);
   else
      max_palette_length = PNG_MAX_PALETTE_LENGTH;

   if (num > max_palette_length)
      num = max_palette_length;

#ifdef PNG_POINTER_INDEXING_SUPPORTED
   for (i = 0, pal_ptr = palette; i < num; i++, pal_ptr++)
   {
      png_byte buf[3];

      png_crc_read(png_ptr, buf, 3);
      pal_ptr->red = buf[0];
      pal_ptr->green = buf[1];
      pal_ptr->blue = buf[2];
   }
#else
   for (i = 0; i < num; i++)
   {
      png_byte buf[3];

      png_crc_read(png_ptr, buf, 3);
      /* Don't depend upon png_color being any order */
      palette[i].red = buf[0];
      palette[i].green = buf[1];
      palette[i].blue = buf[2];
   }
#endif

   /* If we actually need the PLTE chunk (ie for a paletted image), we do
    * whatever the normal CRC configuration tells us.  However, if we
    * have an RGB image, the PLTE can be considered ancillary, so
    * we will act as though it is.
    */
#ifndef PNG_READ_OPT_PLTE_SUPPORTED
   if (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE)
#endif
   {
      png_crc_finish(png_ptr, (png_uint_32) (length - (unsigned int)num * 3));
   }

#ifndef PNG_READ_OPT_PLTE_SUPPORTED
   else if (png_crc_error(png_ptr) != 0)  /* Only if we have a CRC error */
   {
      /* If we don't want to use the data from an ancillary chunk,
       * we have two options: an error abort, or a warning and we
       * ignore the data in this chunk (which should be OK, since
       * it's considered ancillary for a RGB or RGBA image).
       *
       * IMPLEMENTATION NOTE: this is only here because png_crc_finish uses the
       * chunk type to determine whether to check the ancillary or the critical
       * flags.
       */
      if ((png_ptr->flags & PNG_FLAG_CRC_ANCILLARY_USE) == 0)
      {
         if ((png_ptr->flags & PNG_FLAG_CRC_ANCILLARY_NOWARN) != 0)
            return;

         else
            png_chunk_error(png_ptr, "CRC error");
      }

      /* Otherwise, we (optionally) emit a warning and use the chunk. */
      else if ((png_ptr->flags & PNG_FLAG_CRC_ANCILLARY_NOWARN) == 0)
         png_chunk_warning(png_ptr, "CRC error");
   }
#endif

   /* TODO: png_set_PLTE has the side effect of setting png_ptr->palette to its
    * own copy of the palette.  This has the side effect that when png_start_row
    * is called (this happens after any call to png_read_update_info) the
    * info_ptr palette gets changed.  This is extremely unexpected and
    * confusing.
    *
    * Fix this by not sharing the palette in this way.
    */
   png_set_PLTE(png_ptr, info_ptr, palette, num);

   /* The three chunks, bKGD, hIST and tRNS *must* appear after PLTE and before
    * IDAT.  Prior to 1.6.0 this was not checked; instead the code merely
    * checked the apparent validity of a tRNS chunk inserted before PLTE on a
    * palette PNG.  1.6.0 attempts to rigorously follow the standard and
    * therefore does a benign error if the erroneous condition is detected *and*
    * cancels the tRNS if the benign error returns.  The alternative is to
    * amend the standard since it would be rather hypocritical of the standards
    * maintainers to ignore it.
    */
#ifdef PNG_READ_tRNS_SUPPORTED
   if (png_ptr->num_trans > 0 ||
       (info_ptr != NULL && (info_ptr->valid & PNG_INFO_tRNS) != 0))
   {
      /* Cancel this because otherwise it would be used if the transforms
       * require it.  Don't cancel the 'valid' flag because this would prevent
       * detection of duplicate chunks.
       */
      png_ptr->num_trans = 0;

      if (info_ptr != NULL)
         info_ptr->num_trans = 0;

      png_chunk_benign_error(png_ptr, "tRNS must be after");
   }
#endif

#ifdef PNG_READ_hIST_SUPPORTED
   if (info_ptr != NULL && (info_ptr->valid & PNG_INFO_hIST) != 0)
      png_chunk_benign_error(png_ptr, "hIST must be after");
#endif

#ifdef PNG_READ_bKGD_SUPPORTED
   if (info_ptr != NULL && (info_ptr->valid & PNG_INFO_bKGD) != 0)
      png_chunk_benign_error(png_ptr, "bKGD must be after");
#endif
}

void /* PRIVATE */
png_handle_IEND(png_structrp png_ptr, png_inforp info_ptr, png_uint_32 length)
{
   png_debug(1, "in png_handle_IEND");

   if ((png_ptr->mode & PNG_HAVE_IHDR) == 0 ||
       (png_ptr->mode & PNG_HAVE_IDAT) == 0)
      png_chunk_error(png_ptr, "out of place");

   png_ptr->mode |= (PNG_AFTER_IDAT | PNG_HAVE_IEND);

   png_crc_finish(png_ptr, length);