/src/wireshark/epan/tap.c

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/* tap.c
 * packet tap interface   2002 Ronnie Sahlberg
 *
 * Wireshark - Network traffic analyzer
 * By Gerald Combs <gerald@wireshark.org>
 * Copyright 1998 Gerald Combs
 *
 * SPDX-License-Identifier: GPL-2.0-or-later
 */

#include <config.h>
#define WS_LOG_DOMAIN LOG_DOMAIN_EPAN

#include <stdio.h>

#include <sys/types.h>

#ifdef HAVE_NETINET_IN_H
# include <netinet/in.h>
#endif

#include <string.h>

#include <glib.h>

#include <epan/packet_info.h>
#include <epan/dfilter/dfilter.h>
#include <epan/tap.h>
#include <wsutil/wslog.h>

static bool tapping_is_active=false;
static dfilter_t *main_filter;

typedef struct _tap_dissector_t {
  struct _tap_dissector_t *next;
  char *name;
} tap_dissector_t;
static tap_dissector_t *tap_dissector_list;

/*
 * This is the list of free and used packets queued for a tap.
 * It is implemented here explicitly instead of using GLib objects
 * in order to be as fast as possible as we need to build and tear down the
 * queued list at least once for each packet we see and thus we must be able
 * to build and tear it down as fast as possible.
 *
 * XXX - some fields in packet_info get overwritten in the dissection
 * process, such as the addresses and the "this is an error packet" flag.
 * A packet may be queued at multiple protocol layers, but the packet_info
 * structure will, when the tap listeners are run, contain the values as
 * set by the topmost protocol layers.
 *
 * This means that the tap listener code can't rely on pinfo->flags.in_error_pkt
 * to determine whether the packet should be handed to the listener, as, for
 * a protocol with error report packets that include a copy of the
 * packet in error (ICMP, ICMPv6, CLNP), that flag changes during the
 * processing of the packet depending on whether we're currently dissecting
 * the packet in error or not.
 *
 * It also means that a tap listener can't depend on the source and destination
 * addresses being the correct ones for the packet being processed if, for
 * example, you have some tunneling that causes multiple layers of the same
 * protocol.
 *
 * For now, we handle the error packet flag by setting a bit in the flags
 * field of the tap_packet_t structure.  We may ultimately want stacks of
 * addresses for this and other reasons.
 */
typedef struct _tap_packet_t {
  int tap_id;
  uint32_t flags;
  packet_info *pinfo;
  const void *tap_specific_data;
} tap_packet_t;

#define TAP_PACKET_IS_ERROR_PACKET  0x00000001  /* packet being queued is an error packet */

#define TAP_PACKET_QUEUE_LEN 5000
static tap_packet_t tap_packet_array[TAP_PACKET_QUEUE_LEN];
static unsigned tap_packet_index;

typedef struct _tap_listener_t {
  struct _tap_listener_t *next;
  int tap_id;
  bool needs_redraw;
  bool failed;
  unsigned flags;
  char *fstring;
  dfilter_t *code;
  void *tapdata;
  tap_reset_cb reset;
  tap_packet_cb packet;
  tap_draw_cb draw;
  tap_finish_cb finish;
} tap_listener_t;

static tap_listener_t *tap_listener_queue;

static GSList *tap_plugins;

#ifdef HAVE_PLUGINS
void
tap_register_plugin(const tap_plugin *plug)
{
  tap_plugins = g_slist_prepend(tap_plugins, (tap_plugin *)plug);
}
#else /* HAVE_PLUGINS */
void
tap_register_plugin(const tap_plugin *plug _U_)
{
  ws_warning("built without support for binary plugins");
}
#endif /* HAVE_PLUGINS */

static void
call_plugin_register_tap_listener(void *data, void *user_data _U_)
{
  tap_plugin *plug = (tap_plugin *)data;

  if (plug->register_tap_listener) {
    plug->register_tap_listener();
  }
}

/*
 * For all taps, call their register routines.
 *
 * The table of register routines is part of the main program, not
 * part of libwireshark, so it must be passed to us as an argument.
 */
void
register_all_tap_listeners(tap_reg_t const *tap_reg_listeners)
{
  /* we register the plugin taps before the other taps because
         * stats_tree taps plugins will be registered as tap listeners
         * by stats_tree_stat.c and need to registered before that */
  g_slist_foreach(tap_plugins, call_plugin_register_tap_listener, NULL);

  /* Register all builtin listeners. */
  for (tap_reg_t const *t = &tap_reg_listeners[0]; t->cb_func != NULL; t++) {
    t->cb_func();
  }
}

/* **********************************************************************
 * Init routine only called from epan at application startup
 * ********************************************************************** */
/* This function is called once when wireshark starts up and is used
   to init any data structures we may need later.
*/
void
tap_init(void)
{
  tap_packet_index=0;
}

/* **********************************************************************
 * Functions called from dissector when made tappable
 * ********************************************************************** */
/* the following two functions are used from dissectors to
   1. register the ability to tap packets from this subdissector
   2. push packets encountered by the subdissector to anyone tapping
*/

/* This function registers that a dissector has the packet tap ability
   available.  The name parameter is the name of this tap and extensions can
   use open_tap(char *name,... to specify that it wants to receive packets/
   events from this tap.

   This function is only to be called once, when the dissector initializes.

   The return value from this call is later used as a parameter to the
   tap_packet(unsigned int *tap_id,...
   call so that the tap subsystem knows to which tap point this tapped
   packet is associated.
*/
int
register_tap(const char *name)
{
  tap_dissector_t *td, *tdl = NULL, *tdl_prev = NULL;
  int i=0;

  if(tap_dissector_list){
    /* Check if we already have the name registered, if it is return the tap_id of that tap.
     * After the for loop tdl_prev will point to the last element of the list, add the new one there.
     */
    for (i = 1, tdl = tap_dissector_list; tdl; i++, tdl_prev = tdl, tdl = tdl->next) {
      if (!strcmp(tdl->name, name)) {
        return i;
      }
    }
    tdl = tdl_prev;
  }

  td=g_new(tap_dissector_t, 1);
  td->next=NULL;
  td->name = g_strdup(name);

  if(!tap_dissector_list){
    tap_dissector_list=td;
    i=1;
  } else {
    tdl->next=td;
  }
  return i;
}


/* Every time the dissector has finished dissecting a packet (and all
   subdissectors have returned) and if the dissector has been made "tappable"
   it will push some data to everyone tapping this layer by a call
   to tap_queue_packet().
   The first parameter is the tap_id returned by the register_tap()
   call for this dissector (so the tap system can keep track of who it came
   from and who is listening to it)
   The second is the packet_info structure which many tap readers will find
   interesting.
   The third argument is specific to each tap point or NULL if no additional
   data is available to this tap.  A tap point in say IP will probably want to
   push the IP header structure here. Same thing for TCP and ONCRPC.

   The pinfo and the specific pointer are what is supplied to every listener
   in the read_callback() call made to every one currently listening to this
   tap.

   The tap reader is responsible to know how to parse any structure pointed
   to by the tap specific data pointer.
*/
void
tap_queue_packet(int tap_id, packet_info *pinfo, const void *tap_specific_data)
{
  tap_packet_t *tpt;

  if(!tapping_is_active){
    return;
  }
  /*
   * XXX - should we allocate this with an ep_allocator,
   * rather than having a fixed maximum number of entries?
   */
  if(tap_packet_index >= TAP_PACKET_QUEUE_LEN){
    ws_warning("Too many taps queued");
    return;
  }

  tpt=&tap_packet_array[tap_packet_index];
  tpt->tap_id=tap_id;
  tpt->flags = 0;
  if (pinfo->flags.in_error_pkt)
    tpt->flags |= TAP_PACKET_IS_ERROR_PACKET;
  tpt->pinfo=pinfo;
  tpt->tap_specific_data=tap_specific_data;
  tap_packet_index++;
}





/* **********************************************************************
 * Functions used by file.c to drive the tap subsystem
 * ********************************************************************** */

void tap_build_interesting (epan_dissect_t *edt)
{
  tap_listener_t *tl;
  bool need_protocols = false;
  bool need_main_filter = false;

  /* nothing to do, just return */
  if(!tap_listener_queue){
    return;
  }

  /* loop over all tap listeners and build the list of all
     interesting hf_fields */
  for(tl=tap_listener_queue;tl;tl=tl->next){
    if(tl->code){
      epan_dissect_prime_with_dfilter(edt, tl->code);
    }
    if(tl->flags & TL_REQUIRES_PROTOCOLS){
      need_protocols = true;
    }
    if(tl->flags & TL_LIMIT_TO_DISPLAY_FILTER){
      need_main_filter = true;
    }
  }
  if (need_main_filter && main_filter) {
    epan_dissect_prime_with_dfilter(edt, main_filter);
  }
  if (need_protocols) {
    epan_dissect_fake_protocols(edt, false);
  }
}

/* This function is used to delete/initialize the tap queue and prime an
   epan_dissect_t with all the filters for tap listeners.
   To free the tap queue, we just prepend the used queue to the free queue.
*/
void
tap_queue_init(epan_dissect_t *edt)
{
  /* nothing to do, just return */
  if(!tap_listener_queue){
    return;
  }

  tapping_is_active=true;

  tap_packet_index=0;

  tap_build_interesting (edt);
}

/* this function is called after a packet has been fully dissected to push the tapped
   data to all extensions that has callbacks registered.
*/
void
tap_push_tapped_queue(epan_dissect_t *edt)
{
  tap_packet_t *tp;
  tap_listener_t *tl;
  unsigned i;

  /* nothing to do, just return */
  if(!tapping_is_active){
    return;
  }

  tapping_is_active=false;

  /* nothing to do, just return */
  if(!tap_packet_index){
    return;
  }

  /* loop over all tap listeners and call the listener callback
     for all packets that match the filter. */
  for(i=0;i<tap_packet_index;i++){
    for(tl=tap_listener_queue;tl;tl=tl->next){
      tp=&tap_packet_array[i];
      /* Don't tap the packet if it's an "error packet"
       * unless the listener has requested that we do so.
       */
      if (!(tp->flags & TAP_PACKET_IS_ERROR_PACKET) || (tl->flags & TL_REQUIRES_ERROR_PACKETS))
      {
        if(tp->tap_id==tl->tap_id){
          if(!tl->packet){
            /* There isn't a per-packet
             * routine for this tap.
             */
            continue;
          }
          if(tl->failed){
            /* A previous call failed,
             * meaning "stop running this
             * tap", so don't call the
             * packet routine.
             */
            continue;
          }

          /* If we have a filter, see if the
           * packet passes.
           */
          unsigned flags = tl->flags;
          if((tl->flags & TL_LIMIT_TO_DISPLAY_FILTER) && main_filter) {

            if (!dfilter_apply_edt(main_filter, edt)){
              /* The packet didn't
               * pass the filter. */
              if (tl->flags & TL_IGNORE_DISPLAY_FILTER)
                flags |= TL_DISPLAY_FILTER_IGNORED;
              else
                continue;
            }
          }
          if(tl->code){
            if (!dfilter_apply_edt(tl->code, edt)){
              /* The packet didn't
               * pass the filter. */
              if (tl->flags & TL_IGNORE_DISPLAY_FILTER)
                flags |= TL_DISPLAY_FILTER_IGNORED;
              else
                continue;
            }
          }

          /* So call the per-packet routine. */
          tap_packet_status status;

          status = tl->packet(tl->tapdata, tp->pinfo, edt, tp->tap_specific_data, flags);

          switch (status) {

          case TAP_PACKET_DONT_REDRAW:
            break;

          case TAP_PACKET_REDRAW:
            tl->needs_redraw=true;
            break;

          case TAP_PACKET_FAILED:
            tl->failed=true;
            break;
          }
        }
      }
    }
  }
}


/* This function can be used by a dissector to fetch any tapped data before
 * returning.
 * This can be useful if one wants to extract the data inside dissector  BEFORE
 * it exists as an alternative to the callbacks that are all called AFTER the
 * dissection has completed.
 *
 * Example: SMB2 uses this mechanism to extract the data tapped from NTLMSSP
 * containing the account and domain names before exiting.
 * Note that the SMB2 tap listener specifies all three callbacks as NULL.
 *
 * Beware: when using this mechanism to extract the tapped data you can not
 * use "filters" and should specify the "filter" as NULL when registering
 * the tap listener.
 */
const void *
fetch_tapped_data(int tap_id, int idx)
{
  tap_packet_t *tp;
  unsigned i;

  /* nothing to do, just return */
  if(!tapping_is_active){
    return NULL;
  }

  /* nothing to do, just return */
  if(!tap_packet_index){
    return NULL;
  }

  /* loop over all tapped packets and return the one with index idx */
  for(i=0;i<tap_packet_index;i++){
    tp=&tap_packet_array[i];
    if(tp->tap_id==tap_id){
      if(!idx--){
        return tp->tap_specific_data;
      }
    }
  }

  return NULL;
}

/* This function is called when we need to reset all tap listeners, for example
   when we open/start a new capture or if we need to rescan the packet list.
*/
void
reset_tap_listeners(void)
{
  tap_listener_t *tl;

  for(tl=tap_listener_queue;tl;tl=tl->next){
    if(tl->reset){
      tl->reset(tl->tapdata);
    }
    tl->needs_redraw=true;
    tl->failed=false;
  }

}


/* This function is called when we need to redraw all tap listeners, for example
   when we open/start a new capture or if we need to rescan the packet list.
   It should be called from a low priority thread say once every 3 seconds

   If draw_all is true, redraw all applications regardless if they have
   changed or not.
*/
void
draw_tap_listeners(bool draw_all)
{
  tap_listener_t *tl;

  for(tl=tap_listener_queue;tl;tl=tl->next){
    if(tl->needs_redraw || draw_all){
      if(tl->draw){
        tl->draw(tl->tapdata);
      }
    }
    tl->needs_redraw=false;
  }
}

/* Gets a GList of the tap names. The content of the list
   is owned by the tap table and should not be modified or freed.
   Use g_list_free() when done using the list. */
GList*
get_tap_names(void)
{
  GList *list = NULL;
  tap_dissector_t *td;

  for(td=tap_dissector_list; td; td=td->next) {
    list = g_list_prepend(list, td->name);
  }

  return g_list_reverse(list);
}

/* **********************************************************************
 * Functions used by tap to
 * 1. register that a really simple extension is available for use by
 *    Wireshark.
 * 2. start tapping from a subdissector
 * 3. close an already open tap
 * ********************************************************************** */
/* this function will return the tap_id for the specific protocol tap
   or 0 if no such tap was found.
 */
int
find_tap_id(const char *name)
{
  tap_dissector_t *td;
  int i;

  for(i=1,td=tap_dissector_list;td;i++,td=td->next) {
    if(!strcmp(td->name,name)){
      return i;
    }
  }
  return 0;
}

static void
free_tap_listener(tap_listener_t *tl)
{
  /* The free_tap_listener is called in the error path of
   * register_tap_listener (when the dfilter fails to be registered)
   * and the finish callback is set after that.
   * If this is changed make sure the finish callback is not called
   * twice to prevent double-free errors.
   */
  if (tl->finish) {
    tl->finish(tl->tapdata);
  }
  dfilter_free(tl->code);
  g_free(tl->fstring);
  g_free(tl);
}

/* this function attaches the tap_listener to the named tap.
 * function returns :
 *     NULL: ok.
 * non-NULL: error, return value points to GString containing error
 *           message.
 */
GString *
register_tap_listener(const char *tapname, void *tapdata, const char *fstring,
          unsigned flags, tap_reset_cb reset, tap_packet_cb packet,
          tap_draw_cb draw, tap_finish_cb finish)
{
  tap_listener_t *tl;
  int tap_id;
  dfilter_t *code=NULL;
  GString *error_string;
  df_error_t *df_err;

  tap_id=find_tap_id(tapname);
  if(!tap_id){
    error_string = g_string_new("");
    g_string_printf(error_string, "Tap %s not found", tapname);
    return error_string;
  }

  tl=g_new0(tap_listener_t, 1);
  tl->needs_redraw=true;
  tl->failed=false;
  if (flags & TL_REQUIRES_PROTOCOLS) {
    /* Requiring protocols implies needing a protocol tree.
     * XXX - Warn?
     */
    flags |= TL_REQUIRES_PROTO_TREE;
  }
  tl->flags=flags;
  if(fstring && *fstring){
    if(!dfilter_compile(fstring, &code, &df_err)){
      error_string = g_string_new("");
      g_string_printf(error_string,
          "Filter \"%s\" is invalid - %s",
          fstring, df_err->msg);
      df_error_free(&df_err);
      free_tap_listener(tl);
      return error_string;
    }
    tl->fstring=g_strdup(fstring);
    tl->code=code;
  }

  tl->tap_id=tap_id;
  tl->tapdata=tapdata;
  tl->reset=reset;
  tl->packet=packet;
  tl->draw=draw;
  tl->finish=finish;
  tl->next=tap_listener_queue;

  tap_listener_queue=tl;

  return NULL;
}

/* this function sets a new dfilter to a tap listener
 */
GString *
set_tap_dfilter(void *tapdata, const char *fstring)
{
  tap_listener_t *tl=NULL,*tl2;
  dfilter_t *code=NULL;
  GString *error_string;
  df_error_t *df_err;

  if(!tap_listener_queue){
    return NULL;
  }

  if(tap_listener_queue->tapdata==tapdata){
    tl=tap_listener_queue;
  } else {
    for(tl2=tap_listener_queue;tl2->next;tl2=tl2->next){
      if(tl2->next->tapdata==tapdata){
        tl=tl2->next;
        break;
      }

    }
  }

  if(tl){
    if(tl->code){
      dfilter_free(tl->code);
      tl->code=NULL;
    }
    tl->needs_redraw=true;
    g_free(tl->fstring);
    if(fstring){
      if(!dfilter_compile(fstring, &code, &df_err)){
        tl->fstring=NULL;
        error_string = g_string_new("");
        g_string_printf(error_string,
             "Filter \"%s\" is invalid - %s",
             fstring, df_err->msg);
        df_error_free(&df_err);
        return error_string;
      }
    }
    tl->fstring=g_strdup(fstring);
    tl->code=code;
  }

  return NULL;
}

GString *
set_tap_flags(void *tapdata, unsigned flags)
{
  /* This never fails, and hence always returns NULL.
   * It could fail on an unknown flag, but that's a
   * programming error, not a runtime error (a bad filter
   * above can be a runtime error. Also like the above,
   * there's no failure notification on an unknown listener.
   */
  tap_listener_t *tl=NULL,*tl2;

  if(!tap_listener_queue){
    return NULL;
  }

  if(tap_listener_queue->tapdata==tapdata){
    tl=tap_listener_queue;
  } else {
    for(tl2=tap_listener_queue;tl2->next;tl2=tl2->next){
      if(tl2->next->tapdata==tapdata){
        tl=tl2->next;
        break;
      }

    }
  }

  if(tl && tl->flags != flags) {
    tl->needs_redraw=true;
    tl->flags=flags;
  }

  return NULL;
}

/* this function recompiles dfilter for all registered tap listeners
 */
void
tap_listeners_dfilter_recompile(void)
{
  tap_listener_t *tl;
  dfilter_t *code;

  for(tl=tap_listener_queue;tl;tl=tl->next){
    if(tl->code){
      dfilter_free(tl->code);
      tl->code=NULL;
    }
    tl->needs_redraw=true;
    code=NULL;
    if(tl->fstring){
      if(!dfilter_compile(tl->fstring, &code, NULL)){
        /* Not valid, make a dfilter matching no packets */
        dfilter_compile("frame.number == 0", &code, NULL);
      }
    }
    tl->code=code;
  }
}

/* this function removes a tap listener
 */
void
remove_tap_listener(void *tapdata)
{
  tap_listener_t *tl=NULL,*tl2;

  if(!tap_listener_queue){
    return;
  }

  if(tap_listener_queue->tapdata==tapdata){
    tl=tap_listener_queue;
    tap_listener_queue=tap_listener_queue->next;
  } else {
    for(tl2=tap_listener_queue;tl2->next;tl2=tl2->next){
      if(tl2->next->tapdata==tapdata){
        tl=tl2->next;
        tl2->next=tl2->next->next;
        break;
      }

    }
    if(!tl) {
      ws_warning("no listener found with that tap data");
      return;
    }
  }
  free_tap_listener(tl);
}

/*
 * Return true if we have one or more tap listeners that require dissection,
 * false otherwise.
 */
bool
tap_listeners_require_dissection(void)
{
  tap_listener_t *tap_queue = tap_listener_queue;

  while(tap_queue) {
    if(!(tap_queue->flags & TL_IS_DISSECTOR_HELPER))
      return true;

    tap_queue = tap_queue->next;
  }

  return false;

}

/*
 * Return true if we have one or more tap listeners that require the columns,
 * false otherwise.
 */
bool
tap_listeners_require_columns(void)
{
  tap_listener_t *tap_queue = tap_listener_queue;

  while(tap_queue) {
    if(tap_queue->flags & TL_REQUIRES_COLUMNS)
      return true;

    if(dfilter_requires_columns(tap_queue->code))
      return true;

    tap_queue = tap_queue->next;
  }

  return false;

}

/* Returns true there is an active tap listener for the specified tap id. */
bool
have_tap_listener(int tap_id)
{
  tap_listener_t *tap_queue = tap_listener_queue;

  while(tap_queue) {
    if(tap_queue->tap_id == tap_id)
      return true;

    tap_queue = tap_queue->next;
  }

  return false;
}

/*
 * Return true if we have any tap listeners with filters, false otherwise.
 */
bool
have_filtering_tap_listeners(void)
{
  tap_listener_t *tl;

  for(tl=tap_listener_queue;tl;tl=tl->next){
    if(tl->code)
      return true;
    if((tl->flags & TL_LIMIT_TO_DISPLAY_FILTER) && main_filter)
      return true;
  }
  return false;
}

void
tap_listeners_load_field_references(epan_dissect_t *edt)
{
  tap_listener_t *tl;

  for(tl=tap_listener_queue;tl;tl=tl->next){
    if(tl->code)
      dfilter_load_field_references_edt(tl->code, edt);
  }
}

/*
 * Get the union of all the flags for all the tap listeners; that gives
 * an indication of whether the protocol tree, or the columns, are
 * required by any taps.
 */
unsigned
union_of_tap_listener_flags(void)
{
  tap_listener_t *tl;
  unsigned flags = 0;

  for(tl=tap_listener_queue;tl;tl=tl->next){
    flags|=tl->flags;
  }
  return flags;
}

void tap_cleanup(void)
{
  tap_listener_t *elem_lq;
  tap_listener_t *head_lq = tap_listener_queue;
  tap_dissector_t *elem_dl;
  tap_dissector_t *head_dl = tap_dissector_list;

  while(head_lq){
    elem_lq = head_lq;
    head_lq = head_lq->next;
    free_tap_listener(elem_lq);
  }
  tap_listener_queue = NULL;

  while(head_dl){
    elem_dl = head_dl;
    head_dl = head_dl->next;
    g_free(elem_dl->name);
    g_free((void *)elem_dl);
  }
  tap_dissector_list = NULL;

  g_slist_free(tap_plugins);
  tap_plugins = NULL;
}

void tap_load_main_filter(dfilter_t *dfcode)
{
  /* Does not take ownership. This is not const because too
   * much of the dfilter API does not accept a const dfilter_t.
   */
  main_filter = dfcode;
}

/*
 * Editor modelines  -  https://www.wireshark.org/tools/modelines.html
 *
 * Local variables:
 * c-basic-offset: 8
 * tab-width: 8
 * indent-tabs-mode: t
 * End:
 *
 * vi: set shiftwidth=8 tabstop=8 noexpandtab:
 * :indentSize=8:tabSize=8:noTabs=false:
 */

Coverage Report

Created: 2025-04-03 08:43