tor/src/common/torgzip.c

/* Copyright (c) 2004, Roger Dingledine.
 * Copyright (c) 2004-2006, Roger Dingledine, Nick Mathewson.
 * Copyright (c) 2007-2011, The Tor Project, Inc. */
/* See LICENSE for licensing information */

/**
 * \file torgzip.c
 * \brief A simple in-memory gzip implementation.
 **/

#include "orconfig.h"

#include <stdlib.h>
#include <stdio.h>
#include <assert.h>
#ifdef _MSC_VER
#include "..\..\contrib\zlib\zlib.h"
#else
#include <zlib.h>
#endif
#include <string.h>
#ifdef HAVE_NETINET_IN_H
#include <netinet/in.h>
#endif

#include "util.h"
#include "log.h"
#include "torgzip.h"

/** Set to 1 if zlib is a version that supports gzip; set to 0 if it doesn't;
 * set to -1 if we haven't checked yet. */
static int gzip_is_supported = -1;

/** Return true iff we support gzip-based compression.  Otherwise, we need to
 * use zlib. */
int
is_gzip_supported(void)
{
  if (gzip_is_supported >= 0)
    return gzip_is_supported;

  if (!strcmpstart(ZLIB_VERSION, "0.") ||
      !strcmpstart(ZLIB_VERSION, "1.0") ||
      !strcmpstart(ZLIB_VERSION, "1.1"))
    gzip_is_supported = 0;
  else
    gzip_is_supported = 1;

  return gzip_is_supported;
}

/** Return the 'bits' value to tell zlib to use <b>method</b>.*/
static INLINE int
method_bits(compress_method_t method)
{
  /* Bits+16 means "use gzip" in zlib >= 1.2 */
  return method == GZIP_METHOD ? 15+16 : 15;
}

/* These macros define the maximum allowable compression factor.  Anything of
 * size greater than CHECK_FOR_COMPRESSION_BOMB_AFTER is not allowed to
 * have an uncompression factor (uncompressed size:compressed size ratio) of
 * any greater than MAX_UNCOMPRESSION_FACTOR.
 *
 * Picking a value for MAX_UNCOMPRESSION_FACTOR is a trade-off: we want it to
 * be small to limit the attack multiplier, but we also want it to be large
 * enough so that no legitimate document --even ones we might invent in the
 * future -- ever compresses by a factor of greater than
 * MAX_UNCOMPRESSION_FACTOR. Within those parameters, there's a reasonably
 * large range of possible values. IMO, anything over 8 is probably safe; IMO
 * anything under 50 is probably sufficient.
 */
#define MAX_UNCOMPRESSION_FACTOR 25
#define CHECK_FOR_COMPRESSION_BOMB_AFTER (1024*64)

/** Return true if uncompressing an input of size <b>in_size</b> to an input
 * of size at least <b>size_out</b> looks like a compression bomb. */
static int
is_compression_bomb(size_t size_in, size_t size_out)
{
  if (size_in == 0 || size_out < CHECK_FOR_COMPRESSION_BOMB_AFTER)
    return 0;

  return (size_out / size_in > MAX_UNCOMPRESSION_FACTOR);
}

/** Given <b>in_len</b> bytes at <b>in</b>, compress them into a newly
 * allocated buffer, using the method described in <b>method</b>.  Store the
 * compressed string in *<b>out</b>, and its length in *<b>out_len</b>.
 * Return 0 on success, -1 on failure.
 */
int
tor_gzip_compress(char **out, size_t *out_len,
                  const char *in, size_t in_len,
                  compress_method_t method)
{
  struct z_stream_s *stream = NULL;
  size_t out_size, old_size;
  off_t offset;

  tor_assert(out);
  tor_assert(out_len);
  tor_assert(in);
  tor_assert(in_len < UINT_MAX);

  *out = NULL;

  if (method == GZIP_METHOD && !is_gzip_supported()) {
    /* Old zlib version don't support gzip in deflateInit2 */
    log_warn(LD_BUG, "Gzip not supported with zlib %s", ZLIB_VERSION);
    goto err;
  }

  stream = tor_malloc_zero(sizeof(struct z_stream_s));
  stream->zalloc = Z_NULL;
  stream->zfree = Z_NULL;
  stream->opaque = NULL;
  stream->next_in = (unsigned char*) in;
  stream->avail_in = (unsigned int)in_len;

  if (deflateInit2(stream, Z_BEST_COMPRESSION, Z_DEFLATED,
                   method_bits(method),
                   8, Z_DEFAULT_STRATEGY) != Z_OK) {
    log_warn(LD_GENERAL, "Error from deflateInit2: %s",
             stream->msg?stream->msg:"<no message>");
    goto err;
  }

  /* Guess 50% compression. */
  out_size = in_len / 2;
  if (out_size < 1024) out_size = 1024;
  *out = tor_malloc(out_size);
  stream->next_out = (unsigned char*)*out;
  stream->avail_out = (unsigned int)out_size;

  while (1) {
    switch (deflate(stream, Z_FINISH))
      {
      case Z_STREAM_END:
        goto done;
      case Z_OK:
        /* In case zlib doesn't work as I think .... */
        if (stream->avail_out >= stream->avail_in+16)
          break;
      case Z_BUF_ERROR:
        offset = stream->next_out - ((unsigned char*)*out);
        old_size = out_size;
        out_size *= 2;
        if (out_size < old_size) {
          log_warn(LD_GENERAL, "Size overflow in compression.");
          goto err;
        }
        *out = tor_realloc(*out, out_size);
        stream->next_out = (unsigned char*)(*out + offset);
        if (out_size - offset > UINT_MAX) {
          log_warn(LD_BUG,  "Ran over unsigned int limit of zlib while "
                   "uncompressing.");
          goto err;
        }
        stream->avail_out = (unsigned int)(out_size - offset);
        break;
      default:
        log_warn(LD_GENERAL, "Gzip compression didn't finish: %s",
                 stream->msg ? stream->msg : "<no message>");
        goto err;
      }
  }
 done:
  *out_len = stream->total_out;
#ifdef OPENBSD
  /* "Hey Rocky!  Watch me change an unsigned field to a signed field in a
   *    third-party API!"
   * "Oh, that trick will just make people do unsafe casts to the unsigned
   *    type in their cross-platform code!"
   * "Don't be foolish.  I'm _sure_ they'll have the good sense to make sure
   *    the newly unsigned field isn't negative." */
  tor_assert(stream->total_out >= 0);
#endif
  if (((size_t)stream->total_out) > out_size + 4097) {
    /* If we're wasting more than 4k, don't. */
    *out = tor_realloc(*out, stream->total_out + 1);
  }
  if (deflateEnd(stream)!=Z_OK) {
    log_warn(LD_BUG, "Error freeing gzip structures");
    goto err;
  }
  tor_free(stream);

  if (is_compression_bomb(*out_len, in_len)) {
    log_warn(LD_BUG, "We compressed something and got an insanely high "
          "compression factor; other Tors would think this was a zlib bomb.");
    goto err;
  }

  return 0;
 err:
  if (stream) {
    deflateEnd(stream);
    tor_free(stream);
  }
  if (*out) {
    tor_free(*out);
  }
  return -1;
}

/** Given zero or more zlib-compressed or gzip-compressed strings of
 * total length
 * <b>in_len</b> bytes at <b>in</b>, uncompress them into a newly allocated
 * buffer, using the method described in <b>method</b>.  Store the uncompressed
 * string in *<b>out</b>, and its length in *<b>out_len</b>.  Return 0 on
 * success, -1 on failure.
 *
 * If <b>complete_only</b> is true, we consider a truncated input as a
 * failure; otherwise we decompress as much as we can.  Warn about truncated
 * or corrupt inputs at <b>protocol_warn_level</b>.
 */
int
tor_gzip_uncompress(char **out, size_t *out_len,
                    const char *in, size_t in_len,
                    compress_method_t method,
                    int complete_only,
                    int protocol_warn_level)
{
  struct z_stream_s *stream = NULL;
  size_t out_size, old_size;
  off_t offset;
  int r;

  tor_assert(out);
  tor_assert(out_len);
  tor_assert(in);
  tor_assert(in_len < UINT_MAX);

  if (method == GZIP_METHOD && !is_gzip_supported()) {
    /* Old zlib version don't support gzip in inflateInit2 */
    log_warn(LD_BUG, "Gzip not supported with zlib %s", ZLIB_VERSION);
    return -1;
  }

  *out = NULL;

  stream = tor_malloc_zero(sizeof(struct z_stream_s));
  stream->zalloc = Z_NULL;
  stream->zfree = Z_NULL;
  stream->opaque = NULL;
  stream->next_in = (unsigned char*) in;
  stream->avail_in = (unsigned int)in_len;

  if (inflateInit2(stream,
                   method_bits(method)) != Z_OK) {
    log_warn(LD_GENERAL, "Error from inflateInit2: %s",
             stream->msg?stream->msg:"<no message>");
    goto err;
  }

  out_size = in_len * 2;  /* guess 50% compression. */
  if (out_size < 1024) out_size = 1024;
  if (out_size >= SIZE_T_CEILING || out_size > UINT_MAX)
    goto err;

  *out = tor_malloc(out_size);
  stream->next_out = (unsigned char*)*out;
  stream->avail_out = (unsigned int)out_size;

  while (1) {
    switch (inflate(stream, complete_only ? Z_FINISH : Z_SYNC_FLUSH))
      {
      case Z_STREAM_END:
        if (stream->avail_in == 0)
          goto done;
        /* There may be more compressed data here. */
        if ((r = inflateEnd(stream)) != Z_OK) {
          log_warn(LD_BUG, "Error freeing gzip structures");
          goto err;
        }
        if (inflateInit2(stream, method_bits(method)) != Z_OK) {
          log_warn(LD_GENERAL, "Error from second inflateInit2: %s",
                   stream->msg?stream->msg:"<no message>");
          goto err;
        }
        break;
      case Z_OK:
        if (!complete_only && stream->avail_in == 0)
          goto done;
        /* In case zlib doesn't work as I think.... */
        if (stream->avail_out >= stream->avail_in+16)
          break;
      case Z_BUF_ERROR:
        if (stream->avail_out > 0) {
          log_fn(protocol_warn_level, LD_PROTOCOL,
                 "possible truncated or corrupt zlib data");
          goto err;
        }
        offset = stream->next_out - (unsigned char*)*out;
        old_size = out_size;
        out_size *= 2;
        if (out_size < old_size) {
          log_warn(LD_GENERAL, "Size overflow in uncompression.");
          goto err;
        }
        if (is_compression_bomb(in_len, out_size)) {
          log_warn(LD_GENERAL, "Input looks like a possible zlib bomb; "
                   "not proceeding.");
          goto err;
        }
        if (out_size >= SIZE_T_CEILING) {
          log_warn(LD_BUG, "Hit SIZE_T_CEILING limit while uncompressing.");
          goto err;
        }
        *out = tor_realloc(*out, out_size);
        stream->next_out = (unsigned char*)(*out + offset);
        if (out_size - offset > UINT_MAX) {
          log_warn(LD_BUG,  "Ran over unsigned int limit of zlib while "
                   "uncompressing.");
          goto err;
        }
        stream->avail_out = (unsigned int)(out_size - offset);
        break;
      default:
        log_warn(LD_GENERAL, "Gzip decompression returned an error: %s",
                 stream->msg ? stream->msg : "<no message>");
        goto err;
      }
  }
 done:
  *out_len = stream->next_out - (unsigned char*)*out;
  r = inflateEnd(stream);
  tor_free(stream);
  if (r != Z_OK) {
    log_warn(LD_BUG, "Error freeing gzip structures");
    goto err;
  }

  /* NUL-terminate output. */
  if (out_size == *out_len)
    *out = tor_realloc(*out, out_size + 1);
  (*out)[*out_len] = '\0';

  return 0;
 err:
  if (stream) {
    inflateEnd(stream);
    tor_free(stream);
  }
  if (*out) {
    tor_free(*out);
  }
  return -1;
}

/** Try to tell whether the <b>in_len</b>-byte string in <b>in</b> is likely
 * to be compressed or not.  If it is, return the likeliest compression method.
 * Otherwise, return UNKNOWN_METHOD.
 */
compress_method_t
detect_compression_method(const char *in, size_t in_len)
{
  if (in_len > 2 && !memcmp(in, "\x1f\x8b", 2)) {
    return GZIP_METHOD;
  } else if (in_len > 2 && (in[0] & 0x0f) == 8 &&
             (ntohs(get_uint16(in)) % 31) == 0) {
    return ZLIB_METHOD;
  } else {
    return UNKNOWN_METHOD;
  }
}

/** Internal state for an incremental zlib compression/decompression.  The
 * body of this struct is not exposed. */
struct tor_zlib_state_t {
  struct z_stream_s stream;
  int compress;

  /* Number of bytes read so far.  Used to detect zlib bombs. */
  size_t input_so_far;
  /* Number of bytes written so far.  Used to detect zlib bombs. */
  size_t output_so_far;
};

/** Construct and return a tor_zlib_state_t object using <b>method</b>.  If
 * <b>compress</b>, it's for compression; otherwise it's for
 * decompression. */
tor_zlib_state_t *
tor_zlib_new(int compress, compress_method_t method)
{
  tor_zlib_state_t *out;

  if (method == GZIP_METHOD && !is_gzip_supported()) {
    /* Old zlib version don't support gzip in inflateInit2 */
    log_warn(LD_BUG, "Gzip not supported with zlib %s", ZLIB_VERSION);
    return NULL;
 }

 out = tor_malloc_zero(sizeof(tor_zlib_state_t));
 out->stream.zalloc = Z_NULL;
 out->stream.zfree = Z_NULL;
 out->stream.opaque = NULL;
 out->compress = compress;
 if (compress) {
   if (deflateInit2(&out->stream, Z_BEST_COMPRESSION, Z_DEFLATED,
                    method_bits(method), 8, Z_DEFAULT_STRATEGY) != Z_OK)
     goto err;
 } else {
   if (inflateInit2(&out->stream, method_bits(method)) != Z_OK)
     goto err;
 }
 return out;

 err:
 tor_free(out);
 return NULL;
}

/** Compress/decompress some bytes using <b>state</b>.  Read up to
 * *<b>in_len</b> bytes from *<b>in</b>, and write up to *<b>out_len</b> bytes
 * to *<b>out</b>, adjusting the values as we go.  If <b>finish</b> is true,
 * we've reached the end of the input.
 *
 * Return TOR_ZLIB_DONE if we've finished the entire compression/decompression.
 * Return TOR_ZLIB_OK if we're processed everything from the input.
 * Return TOR_ZLIB_BUF_FULL if we're out of space on <b>out</b>.
 * Return TOR_ZLIB_ERR if the stream is corrupt.
 */
tor_zlib_output_t
tor_zlib_process(tor_zlib_state_t *state,
                 char **out, size_t *out_len,
                 const char **in, size_t *in_len,
                 int finish)
{
  int err;
  tor_assert(*in_len <= UINT_MAX);
  tor_assert(*out_len <= UINT_MAX);
  state->stream.next_in = (unsigned char*) *in;
  state->stream.avail_in = (unsigned int)*in_len;
  state->stream.next_out = (unsigned char*) *out;
  state->stream.avail_out = (unsigned int)*out_len;

  if (state->compress) {
    err = deflate(&state->stream, finish ? Z_FINISH : Z_SYNC_FLUSH);
  } else {
    err = inflate(&state->stream, finish ? Z_FINISH : Z_SYNC_FLUSH);
  }

  state->input_so_far += state->stream.next_in - ((unsigned char*)*in);
  state->output_so_far += state->stream.next_out - ((unsigned char*)*out);

  *out = (char*) state->stream.next_out;
  *out_len = state->stream.avail_out;
  *in = (const char *) state->stream.next_in;
  *in_len = state->stream.avail_in;

  if (! state->compress &&
      is_compression_bomb(state->input_so_far, state->output_so_far)) {
    log_warn(LD_DIR, "Possible zlib bomb; abandoning stream.");
    return TOR_ZLIB_ERR;
  }

  switch (err)
    {
    case Z_STREAM_END:
      return TOR_ZLIB_DONE;
    case Z_BUF_ERROR:
      if (state->stream.avail_in == 0)
        return TOR_ZLIB_OK;
      return TOR_ZLIB_BUF_FULL;
    case Z_OK:
      if (state->stream.avail_out == 0 || finish)
        return TOR_ZLIB_BUF_FULL;
      return TOR_ZLIB_OK;
    default:
      log_warn(LD_GENERAL, "Gzip returned an error: %s",
               state->stream.msg ? state->stream.msg : "<no message>");
      return TOR_ZLIB_ERR;
    }
}

/** Deallocate <b>state</b>. */
void
tor_zlib_free(tor_zlib_state_t *state)
{
  tor_assert(state);

  if (state->compress)
    deflateEnd(&state->stream);
  else
    inflateEnd(&state->stream);

  tor_free(state);
}