path: root/fuzz/fuzzshark.c

/* fuzzshark.c
 *
 * Fuzzer variant of Wireshark for oss-fuzz
 *
 * 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_MAIN

#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <limits.h>

#include <glib.h>

#include <epan/epan.h>

#include <wsutil/cmdarg_err.h>
#include <ui/failure_message.h>
#include <wsutil/filesystem.h>
#include <wsutil/privileges.h>
#include <wsutil/report_message.h>
#include <wsutil/wslog.h>
#include <wsutil/version_info.h>

#include <wiretap/wtap.h>

#include <epan/color_filters.h>
#include <epan/timestamp.h>
#include <epan/prefs.h>
#include <epan/column.h>
#include <epan/column-info.h>
#include <epan/print.h>
#include <epan/epan_dissect.h>
#include <epan/disabled_protos.h>

#ifdef HAVE_PLUGINS
#include <wsutil/plugins.h>
#endif

#include "FuzzerInterface.h"

#define EPAN_INIT_FAIL 2

static column_info fuzz_cinfo;
static epan_t *fuzz_epan;
static epan_dissect_t *fuzz_edt;

/*
 * Report an error in command-line arguments.
 */
static void
fuzzshark_cmdarg_err(const char *msg_format, va_list ap)
{
	fprintf(stderr, "oss-fuzzshark: ");
	vfprintf(stderr, msg_format, ap);
	fprintf(stderr, "\n");
}

/*
 * Report additional information for an error in command-line arguments.
 */
static void
fuzzshark_cmdarg_err_cont(const char *msg_format, va_list ap)
{
	vfprintf(stderr, msg_format, ap);
	fprintf(stderr, "\n");
}

static int
fuzzshark_pref_set(const char *name, const char *value)
{
	char pref[4096];
	char *errmsg = NULL;

	prefs_set_pref_e ret;

	snprintf(pref, sizeof(pref), "%s:%s", name, value);

	ret = prefs_set_pref(pref, &errmsg);
	g_free(errmsg);

	return (ret == PREFS_SET_OK);
}

static const nstime_t *
fuzzshark_get_frame_ts(struct packet_provider_data *prov _U_, uint32_t frame_num _U_)
{
	static nstime_t empty;

	return &empty;
}

static epan_t *
fuzzshark_epan_new(void)
{
	static const struct packet_provider_funcs funcs = {
		fuzzshark_get_frame_ts,
		NULL,
		NULL,
		NULL
	};

	return epan_new(NULL, &funcs);
}

static dissector_handle_t
get_dissector_handle(const char *table, const char *target)
{
	dissector_handle_t fuzz_handle = NULL;

	if (table != NULL && target != NULL)
	{
		/* search for handle, cannot use dissector_table_get_dissector_handle() cause it's using short-name, and I already used filter name in samples ;/ */
		GSList *handle_list = dissector_table_get_dissector_handles(find_dissector_table(table));
		while (handle_list)
		{
			dissector_handle_t handle = (dissector_handle_t) handle_list->data;
			const char *handle_filter_name = proto_get_protocol_filter_name(dissector_handle_get_protocol_index(handle));

			if (!strcmp(handle_filter_name, target))
				fuzz_handle = handle;
			handle_list = handle_list->next;
		}
	}
	else if (target != NULL)
	{
		fuzz_handle = find_dissector(target);
	}

	return fuzz_handle;
}

static void
fuzz_prefs_apply(void)
{
	/* Turn off fragmentation for some protocols */
	fuzzshark_pref_set("ip.defragment", "FALSE");
	fuzzshark_pref_set("ipv6.defragment", "FALSE");
	fuzzshark_pref_set("wlan.defragment", "FALSE");
	fuzzshark_pref_set("tcp.desegment_tcp_streams", "FALSE");

	/* Notify all registered modules that have had any of their preferences changed. */
	prefs_apply_all();
}

static int
fuzz_init(int argc _U_, char **argv)
{
	char                *configuration_init_error;

	static const struct report_message_routines fuzzshark_report_routines = {
		failure_message,
		failure_message,
		open_failure_message,
		read_failure_message,
		write_failure_message,
		cfile_open_failure_message,
		cfile_dump_open_failure_message,
		cfile_read_failure_message,
		cfile_write_failure_message,
		cfile_close_failure_message
	};

	char                *err_msg = NULL;
	e_prefs             *prefs_p;
	int                  ret = EXIT_SUCCESS;
	size_t               i;

	const char *fuzz_target =
#if defined(FUZZ_DISSECTOR_TARGET)
		FUZZ_DISSECTOR_TARGET;
#else
		getenv("FUZZSHARK_TARGET");
#endif

	const char *disabled_dissector_list[] =
	{
#ifdef FUZZ_DISSECTOR_LIST
		FUZZ_DISSECTOR_LIST ,
#endif
		"snort"
	};

#if !defined(FUZZ_DISSECTOR_TABLE) && !defined(FUZZ_DISSECTOR_TARGET)
	const char *fuzz_table = getenv("FUZZSHARK_TABLE");

	if (!fuzz_table && !fuzz_target) {
		fprintf(stderr,
"Missing environment variables!\n"
"\n"
"Modes of operation:\n"
"\n"
" 1. Call a dissector directly by its name:\n"
"      FUZZSHARK_TARGET=dns %s input-file\n"
"    Calls dissect_x from register_dissector(NAME, dissect_x, proto_x)\n"
"\n"
" 2. Call a dissector by its filter name in a dissector table:\n"
"      FUZZSHARK_TABLE=ip.proto FUZZSHARK_TARGET=ospf %s input-file\n"
"    The filter name is from proto_register_protocol(., ., FILTER_NAME)\n"
"    Selects dissectors from dissector_add_uint* or dissector_add_for_decode_as.\n"
"\n"
"Either mode runs the selected dissector once and can hopefully reproduce a\n"
"crash. Mode (2) can be used if a dissector (such as 'ospf') is not available\n"
"through (1).\n"
"\n"
"For best results, build dedicated fuzzshark_* targets with:\n"
"    cmake -GNinja -DCMAKE_C_COMPILER=clang -DCMAKE_CXX_COMPILER=clang++\\\n"
"      -DENABLE_FUZZER=1 -DENABLE_ASAN=1 -DENABLE_UBSAN=1\n"
"    ninja all-fuzzers\n"
"These options enable LibFuzzer which makes fuzzing possible as opposed to\n"
"running dissectors only once with a sample (as is the case with this fuzzshark"
"binary). These fuzzshark_* targets are also used by oss-fuzz.\n",
			argv[0], argv[0]);
		return 1;
	}
#endif

	dissector_handle_t fuzz_handle = NULL;

	/* In oss-fuzz running environment g_get_home_dir() fails:
	 * (process:1): GLib-WARNING **: getpwuid_r(): failed due to unknown user id (0)
	 * (process:1): GLib-CRITICAL **: g_once_init_leave: assertion 'result != 0' failed
	 *
	 * Avoid GLib-CRITICAL by setting some XDG environment variables.
	 */
	g_setenv("XDG_CACHE_HOME", "/not/existing/directory", 0);  /* g_get_user_cache_dir() */
	g_setenv("XDG_CONFIG_HOME", "/not/existing/directory", 0); /* g_get_user_config_dir() */
	g_setenv("XDG_DATA_HOME", "/not/existing/directory", 0);   /* g_get_user_data_dir() */

	g_setenv("WIRESHARK_DEBUG_WMEM_OVERRIDE", "simple", 0);
	g_setenv("G_SLICE", "always-malloc", 0);

	cmdarg_err_init(fuzzshark_cmdarg_err, fuzzshark_cmdarg_err_cont);

	/* Initialize log handler early so we can have proper logging during startup. */
	ws_log_init("fuzzshark", vcmdarg_err);

	/* Early logging command-line initialization. */
	ws_log_parse_args(&argc, argv, vcmdarg_err, LOG_ARGS_NOEXIT);

	ws_noisy("Finished log init and parsing command line log arguments");

	/*
	 * Get credential information for later use, and drop privileges
	 * before doing anything else.
	 * Let the user know if anything happened.
	 */
	init_process_policies();
#if 0 /* disable setresgid(), it fails with -EINVAL https://github.com/google/oss-fuzz/pull/532#issuecomment-294515463 */
	relinquish_special_privs_perm();
#endif

	/*
	 * Attempt to get the pathname of the executable file.
	 */
	configuration_init_error = configuration_init(argv[0], NULL);
	if (configuration_init_error != NULL) {
		fprintf(stderr, "fuzzshark: Can't get pathname of oss-fuzzshark program: %s.\n", configuration_init_error);
		g_free(configuration_init_error);
	}

	/* Initialize the version information. */
	ws_init_version_info("OSS Fuzzshark",
	    epan_gather_compile_info, epan_gather_runtime_info);

	init_report_message("fuzzshark", &fuzzshark_report_routines);

	timestamp_set_type(TS_RELATIVE);
	timestamp_set_precision(TS_PREC_AUTO);
	timestamp_set_seconds_type(TS_SECONDS_DEFAULT);

	/*
	 * Libwiretap must be initialized before libwireshark is, so that
	 * dissection-time handlers for file-type-dependent blocks can
	 * register using the file type/subtype value for the file type.
	 */
	wtap_init(true);

	/* Register all dissectors; we must do this before checking for the
	   "-G" flag, as the "-G" flag dumps information registered by the
	   dissectors, and we must do it before we read the preferences, in
	   case any dissectors register preferences. */
	if (!epan_init(NULL, NULL, false))
	{
		ret = EPAN_INIT_FAIL;
		goto clean_exit;
	}

	/* Load libwireshark settings from the current profile. */
	prefs_p = epan_load_settings();

	if (!color_filters_init(&err_msg, NULL))
	{
		fprintf(stderr, "%s\n", err_msg);
		g_free(err_msg);
	}

	for (i = 0; i < G_N_ELEMENTS(disabled_dissector_list); i++)
	{
		const char *item = disabled_dissector_list[i];

		/* XXX, need to think how to disallow chains like: IP -> .... -> IP,
		 * best would be to disable dissector always, but allow it during initial call. */
		if (fuzz_target == NULL || strcmp(fuzz_target, item))
		{
			fprintf(stderr, "oss-fuzzshark: disabling: %s\n", item);
			proto_disable_proto_by_name(item);
		}
	}

	fuzz_prefs_apply();

	/* Build the column format array */
	build_column_format_array(&fuzz_cinfo, prefs_p->num_cols, true);

#if defined(FUZZ_DISSECTOR_TABLE) && defined(FUZZ_DISSECTOR_TARGET)
# define FUZZ_EPAN 1
	fprintf(stderr, "oss-fuzzshark: configured for dissector: %s in table: %s\n", fuzz_target, FUZZ_DISSECTOR_TABLE);
	fuzz_handle = get_dissector_handle(FUZZ_DISSECTOR_TABLE, fuzz_target);

#elif defined(FUZZ_DISSECTOR_TARGET)
# define FUZZ_EPAN 2
	fprintf(stderr, "oss-fuzzshark: configured for dissector: %s\n", fuzz_target);
	fuzz_handle = get_dissector_handle(NULL, fuzz_target);

#else
# define FUZZ_EPAN 3
	if (fuzz_table) {
		fprintf(stderr, "oss-fuzzshark: requested dissector: %s in table %s\n", fuzz_target, fuzz_table);
	} else {
		fprintf(stderr, "oss-fuzzshark: requested dissector: %s\n", fuzz_target);
	}
	fuzz_handle = get_dissector_handle(fuzz_table, fuzz_target);
#endif

#ifdef FUZZ_EPAN
	g_assert(fuzz_handle != NULL && "Requested dissector is not found!");
	register_postdissector(fuzz_handle);
#endif

	fuzz_epan = fuzzshark_epan_new();
	fuzz_edt = epan_dissect_new(fuzz_epan, true, false);

	return 0;
clean_exit:
	wtap_cleanup();
	free_progdirs();
	return ret;
}

#ifdef FUZZ_EPAN
int
LLVMFuzzerTestOneInput(const uint8_t *buf, size_t real_len)
{
	static uint32_t framenum = 0;
	epan_dissect_t *edt = fuzz_edt;

	uint32_t len = (uint32_t) real_len;

	wtap_rec rec;
	frame_data fdlocal;

	memset(&rec, 0, sizeof(rec));

	rec.rec_type = REC_TYPE_PACKET;
	rec.rec_header.packet_header.caplen = len;
	rec.rec_header.packet_header.len = len;

	/* whdr.pkt_encap = WTAP_ENCAP_ETHERNET; */
	rec.rec_header.packet_header.pkt_encap = INT16_MAX;
	rec.presence_flags = WTAP_HAS_TS | WTAP_HAS_CAP_LEN; /* most common flags... */

	frame_data_init(&fdlocal, ++framenum, &rec, /* offset */ 0, /* cum_bytes */ 0);
	/* frame_data_set_before_dissect() not needed */
	epan_dissect_run(edt, WTAP_FILE_TYPE_SUBTYPE_UNKNOWN, &rec, tvb_new_real_data(buf, len, len), &fdlocal, NULL /* &fuzz_cinfo */);
	frame_data_destroy(&fdlocal);

	epan_dissect_reset(edt);
	return 0;
}

#else
# error "Missing fuzz target."
#endif

int
LLVMFuzzerInitialize(int *argc, char ***argv)
{
	int ret;

	ret = fuzz_init(*argc, *argv);
	if (ret != 0)
		exit(ret);

	return 0;
}

/*
 * 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:
 */