pg_kaboom.c

/*
 Copyright 2022-2024 Crunchy Data Solutions, Inc.
 Licensed under the Apache License, Version 2.0 (the "License");
 you may not use this file except in compliance with the License.
 You may obtain a copy of the License at
      http://www.apache.org/licenses/LICENSE-2.0
 Unless required by applicable law or agreed to in writing, software
 distributed under the License is distributed on an "AS IS" BASIS,
 WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 See the License for the specific language governing permissions and
 limitations under the License.
*/

#include "postgres.h"
#include "fmgr.h"
#include "funcapi.h"
#include "miscadmin.h"
#include "utils/guc.h"
#include "utils/numeric.h"
#include "utils/jsonb.h"
#include "tcop/tcopprot.h"
#include "utils/builtins.h"
#include "storage/ipc.h"
#include "pgstat.h"

#include <signal.h>
#include <unistd.h>
#include <sys/stat.h>

#define PG_KABOOM_DISCLAIMER "I can afford to lose this data and server"

#define PG_MAJOR_VERSION (PG_VERSION_NUM / 100)

/* compatibility macros */
#if PG_MAJOR_VERSION < 1600
#define GET_BEENTRY(i) pgstat_fetch_stat_beentry(i);
#else
#define GET_BEENTRY(i) pgstat_get_beentry_by_backend_id(i);
#endif


#define WPN_ARGS Jsonb *payload, char *arg

/* function signature for the weapon implementation; "payload" is for weapon customization; "arg" is
   static so can expose multiple weapons with same function implementation */

typedef void (*wpn_impl)(WPN_ARGS);

typedef struct Weapon {
	char *wpn_name;
	wpn_impl wpn_impl;
	char *wpn_arg;
	char *wpn_desc;
} Weapon;

/* weapon prototypes */
static void wpn_special(WPN_ARGS);
static void wpn_break_archive(WPN_ARGS);
static void wpn_fill_log(WPN_ARGS);
static void wpn_fill_pgdata(WPN_ARGS);
static void wpn_fill_pgwal(WPN_ARGS);
static void wpn_mem(WPN_ARGS);
static void wpn_restart(WPN_ARGS);
static void wpn_segfault(WPN_ARGS);
static void wpn_signal(WPN_ARGS);
static void wpn_rm_pgdata(WPN_ARGS);
static void wpn_xact_wrap(WPN_ARGS);

Weapon weapons[] = {
	/* "special" weapons */
	{ "random"			, &wpn_special			, "random" , "select a random non-special weapon" },
	{ "null"			, &wpn_special			, "null"   , "noop" },

	{ "break-archive"	, &wpn_break_archive	, NULL, "force archive failures" },
	{ "fill-log"		, &wpn_fill_log			, NULL, "use all the space in the log directory" },
	{ "fill-pgdata"		, &wpn_fill_pgdata		, NULL, "use all the space in the pgdata directory" },
	{ "fill-pgwal"		, &wpn_fill_pgwal		, NULL, "use all the space in the pg_wal directory" },
	{ "mem"				, &wpn_mem				, NULL, "allocate memory in different contexts" },
	{ "restart"			, &wpn_restart			, NULL, "force an immediate restart" },
	{ "segfault"		, &wpn_segfault			, NULL, "segfault inside a backend process" },
	{ "signal"			, &wpn_signal			, NULL, "send a signal to the postmaster (KILL by default)" },
	{ "rm-pgdata"		, &wpn_rm_pgdata		, NULL, "remove the pgdata directory" },
	{ "xact-wrap"		, &wpn_xact_wrap		, NULL, "force wraparound autovacuum" },
	{ NULL, NULL, NULL, NULL }
};

#define NUM_WEAPONS (sizeof(weapons)/sizeof(Weapon) - 1)

/* global variables */
static char *disclaimer;
static char *pgdata_path = NULL;
static bool execute = false;

/* sanity/utility routines */
static void validate_we_can_blow_up_things();
static void validate_we_can_restart();
static void restart_database();
static void load_pgdata_path();
static void fill_disk_at_path(char *path, char *subpath);
static void command_with_path(char *command, char *path, bool detach);
static void command_with_path_internal(char *command, char *arg1, char *arg2, bool detach);
static void force_settings_and_restart(char **setting, char **value);
static char *quoted_string(char * setting);
static char *missing_weapon_hint();
static char *simple_get_json_str(Jsonb *in, char *key);
static int simple_get_json_int(Jsonb *in, char *key);
static pid_t find_random_pid_of_type(char *type);

/* constants snarfed from postmaster.c; no include */
#define BACKEND_TYPE_NORMAL		0x0001	/* normal backend */
#define BACKEND_TYPE_AUTOVAC	0x0002	/* autovacuum worker process */
#define BACKEND_TYPE_WALSND		0x0004	/* walsender process */
#define BACKEND_TYPE_BGWORKER	0x0008	/* bgworker process */
#define BACKEND_TYPE_ALL		0x000F	/* OR of all the above */


PG_MODULE_MAGIC;

void _PG_init(void);
void _PG_fini(void);

Datum pg_kaboom(PG_FUNCTION_ARGS);
Datum pg_kaboom_arsenal(PG_FUNCTION_ARGS);

PG_FUNCTION_INFO_V1(pg_kaboom);
PG_FUNCTION_INFO_V1(pg_kaboom_arsenal);

void _PG_init(void)
{
	/* ... C code here at time of extension loading ... */
	DefineCustomStringVariable("pg_kaboom.disclaimer",
							   gettext_noop("Disclaimer variable you must set for the pg_kaboom extension to work. Required value is: '"
											PG_KABOOM_DISCLAIMER "'"),
							   NULL,
							   &disclaimer,
							   "",
							   PGC_USERSET, 0,
							   NULL, NULL, NULL);

	DefineCustomStringVariable("pg_kaboom.saved_archive_command",
							   gettext_noop("Storage for the old archive_command if we have replaced this one"),
							   NULL,
							   &disclaimer,
							   "",
							   PGC_USERSET, 0,
							   NULL, NULL, NULL);

	DefineCustomBoolVariable("pg_kaboom.execute",
							   gettext_noop("Whether to actually run the commands that are generated"),
							   NULL,
							   &execute,
							   0,
							   PGC_USERSET, 0,
							   NULL, NULL, NULL);

	load_pgdata_path();
}

void _PG_fini(void)
{
	/* ... C code here at time of extension unloading ... */
}

#define UNKNOWN_HINT_MESSAGE_PREFIX "must be one of: "

Datum pg_kaboom(PG_FUNCTION_ARGS)
{
	char *op = TextDatumGetCString(PG_GETARG_DATUM(0));
	Jsonb *payload = NULL;
	Weapon *weapon = weapons;

	/* special gating function check; will abort if everything isn't allowed */
	validate_we_can_blow_up_things();

	/* check for payload */
	if (!PG_ARGISNULL(1))
		payload = PG_GETARG_JSONB_P(1);

	/* now check how we want to blow things up; linear search for matching name ... */
	while (weapon->wpn_name && pg_strcasecmp(weapon->wpn_name, op) != 0)
		weapon++;

	if (weapon->wpn_name) {
		/* we matched a weapon name */
		weapon->wpn_impl(payload, weapon->wpn_arg);
		PG_RETURN_BOOL(1);
	} else {
		ereport(NOTICE, errmsg("unrecognized operation: '%s'", op), errhint("%s", missing_weapon_hint()));
		PG_RETURN_BOOL(0);
	}
}

static char *missing_weapon_hint() {
	char *hint, *p;
	int i;
	size_t weapon_size = 0;
	Weapon *weapon;

	/* calculate the sum of all of the weapon names */
	weapon = weapons;
	while (weapon->wpn_name) {
		weapon_size += strlen(weapon->wpn_name);
		weapon++;
	}

	/* leading text, the word "or " and trailing newline,
	   additional padding for formatting - 4 bytes per, quote quote comma space */
	weapon_size += sizeof(UNKNOWN_HINT_MESSAGE_PREFIX) + 4 + NUM_WEAPONS * 4;

	/* now allocate the message buffer */
	p = hint = palloc(weapon_size);

	/* start with the hint prefix */
	p = stpcpy(p, UNKNOWN_HINT_MESSAGE_PREFIX);

	/* do our individual copy now of each weapon name, stopping before the last one for the "OR" */
	for (i = 0; i < NUM_WEAPONS - 1; i++) {
		*p++ = '\'';
		p = stpcpy(p, weapons[i].wpn_name);
		*p++ = '\'';
		if (i != NUM_WEAPONS - 2)
			*p++ = ',';
		*p++ = ' ';
	}

	/* final item; only do the " or " if we have more than one */
	if (NUM_WEAPONS > 1) {
		p = stpcpy(p, "or ");
	}

	*p++ = '\'';
	p = stpcpy(p, weapons[NUM_WEAPONS - 1].wpn_name);
	*p++ = '\'';
	*p++ = '.';
	*p++ = '\0';

	return hint;
}

static void validate_we_can_blow_up_things() {
#ifdef WIN32
	/* bail out on windows */
	ereport(ERROR, (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
					errmsg("function not supported on Windows (aren't things already broken enough?)")));
#endif

	/* check that we are running as a superuser */
	if (!session_auth_is_superuser)
		ereport(ERROR,
				(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
				 errmsg("must run this function as a superuser")));

	/* check disclaimer for matching value */
	if (!disclaimer || strcmp(disclaimer, PG_KABOOM_DISCLAIMER))
		ereport(ERROR,
				(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
				 errmsg("for safety, pg_kaboom.disclaimer must be explicitly set to '%s'",
						PG_KABOOM_DISCLAIMER)));
}

static void load_pgdata_path() {
	if (!pgdata_path) {
		MemoryContext oldcontext = MemoryContextSwitchTo(TopMemoryContext);
		pgdata_path = pstrdup(GetConfigOptionByName("data_directory", NULL, false));
		MemoryContextSwitchTo(oldcontext);

		if (!pgdata_path || !strlen(pgdata_path))
			ereport(ERROR,
					(errcode_for_file_access(),
					 errmsg("data directory not found")));
	}
}

#define fill_disk_format "/bin/dd if=/dev/zero of=%s/pg_kaboom_space_filler bs=1m"
static void fill_disk_at_path(char *path, char *subpath) {
	/* we control the callers, so path will always be non-null */
	struct stat buf;

	/* if subpath is set, append to original path */
	if (subpath && *subpath) {
		int len = strlen(path);
		char *p = palloc(len + strlen(subpath) + 2); /* separator + newline */
		strcpy(p, path);
		p[len] = '/';
		strcpy(p + len + 1, subpath);
		path = p;
	}

	/* ensure path is an actual directory */
	if (stat(path, &buf) < 0 || !S_ISDIR(buf.st_mode) || access(path, W_OK) < 0)
        ereport(ERROR,
				(errcode_for_file_access(),
				 errmsg("'%s' is not a writable directory", path)));

	command_with_path(fill_disk_format, path, false);
}

/* helper to run a command with a path substitute */
static void command_with_path(char *template, char *path, bool detach) {
	/* sanity-check our path here ... */
	if (!path || !*path)
		ereport(ERROR, errmsg("can't run with empty path"));

	if (path[0] != '/')
		ereport(ERROR, errmsg("cowardly not running with relative path"));

	command_with_path_internal(template, path, "", detach);
}

static void command_with_path_internal(char *template, char *arg1, char *arg2, bool detach) {
	/* even when crashing things, proper memory offsets are still classy; note we do waste a byte or
	   two (with '%s'), which when filling up entire disks is a venial sin at best */

	char *command = palloc(strlen(template) + strlen(arg1) + strlen(arg2));
	sprintf(command, template, arg1, arg2);
	ereport(NOTICE, errmsg("%srunning command: '%s'", (execute ? "" : "(dry-run) "), command));
	if (execute) {
		if (detach) {
			/* this is yucky, and probably not that good, however it appears to work */
			daemon(0,0);		/* deprecated warnings, but appears to function */

			if (fork())			/* extra fork needed due to only one level of fork() + setsid() */
				proc_exit(0);	/* exit cleanly for pg -- such that it matters */
			setsid();
			system(command);
		} else
			system(command);
	}
}

static void validate_we_can_restart() {
	/* check and error out early if it looks like we can't force a restart */

	/* for now do nothing */
}

static void restart_database() {
	/* run pg_ctl to restart this database cluster */

	/* it is definitely possible this will not work in all cases (systemd overrides, etc) */
	/* TODO: read/parse /proc invocation of postmaster and just issue that instead? */

	/* for now, we will just force an immediate shutdown and then run pg_ctl -D $pgdata start */
	#define template_template "bash -c 'kill -9 %d; sleep 1; %s -D %%s start -l /tmp/pg_kaboom_startup.log'"
	char pg_ctl_path[MAXPGPATH];
	char command_template[MAXPGPATH + sizeof(template_template)];
	if (find_other_exec(my_exec_path, "pg_ctl", PG_BACKEND_VERSIONSTR,
						pg_ctl_path) < 0)
		ereport(FATAL,
				(errmsg("%s: could not locate matching pg_ctl executable",
						my_exec_path)));

	snprintf(command_template, MAXPGPATH + sizeof(template_template), template_template, PostmasterPid, pg_ctl_path);
	command_with_path(command_template, pgdata_path, true);
}

static void force_settings_and_restart(char **settings, char **values) {
	char sql[255];
	List *raw_parsetree_list;
	ListCell *lc1;

	validate_we_can_restart();

	while (*settings && *values) {
		char *setting = settings[0];
		char *value = values[0];

		settings++;
		values++;

		/* tried using ALTER SYSTEM directly via SPI, but won't run in a function block */
		/* so we are trying to hack the parser and invoke directly */

		snprintf(sql, 255, "ALTER SYSTEM SET %s = %s", setting, value);

		raw_parsetree_list = pg_parse_query((const char*)sql);

		if (raw_parsetree_list && list_length(raw_parsetree_list) == 1) {
			foreach(lc1, raw_parsetree_list) {
				RawStmt    *parsetree = lfirst_node(RawStmt, lc1);
				AlterSystemSetConfigFile((AlterSystemStmt*)parsetree->stmt);
			}
		} else {
			ereport(ERROR,
					(errcode(ERRCODE_SYNTAX_ERROR),
					 errmsg("error running ALTER SYSTEM")));
		}
	}

	sleep(1);
	restart_database();
}

static char *quoted_string (char *setting) {
	size_t size = strlen(setting) + 3;
	char *qstring = palloc(size); /* start quote, end quote, newline */
	snprintf(qstring, size, "'%s'", setting);

	return qstring;
}

/* simple handlers for pulling expected values from JSON type */
/* returns NULL if missing, or -1 if an int */
static char *simple_get_json_str(Jsonb *in, char *key) {
	JsonbValue *jsonkey, *jsonval;
	char *str = NULL;

	Assert(in != NULL);
	Assert(key != NULL);
	Assert(JB_ROOT_IS_OBJECT(in));

	jsonkey = palloc(sizeof(JsonbValue));
	jsonkey->type = jbvString;
	jsonkey->val.string.len = strlen(key);
	jsonkey->val.string.val = key;

	jsonval = findJsonbValueFromContainer(&in->root, JB_FOBJECT, jsonkey);

	if (!jsonval)
		return NULL;

	/* check if it is a simple scalar value, which it should be */
	if (jsonval->type != jbvString)
		ereport(ERROR, errmsg("expected string type"));

	str = palloc(jsonval->val.string.len + 1);
	strncpy(str, jsonval->val.string.val, jsonval->val.string.len);
	str[jsonval->val.string.len] = '\0';

	pfree(jsonkey);
	pfree(jsonval);

	return str;
}

static int simple_get_json_int(Jsonb *in, char *key) {
	JsonbValue *jsonkey, *jsonval;
	char *str;
	int ret;

	Assert(in != NULL);
	Assert(key != NULL);
	Assert(JB_ROOT_IS_OBJECT(in));

	jsonkey = palloc(sizeof(JsonbValue));
	jsonkey->type = jbvString;
	jsonkey->val.string.len = strlen(key);
	jsonkey->val.string.val = key;

	jsonval = findJsonbValueFromContainer(&in->root, JB_FOBJECT, jsonkey);

	if (!jsonval)
		return -1;

	/* check if it is a simple scalar value, which it should be */
	if (jsonval->type != jbvNumeric)
		ereport(ERROR, errmsg("expected integer type"));

	str = numeric_normalize(jsonval->val.numeric);

	pfree(jsonkey);
	pfree(jsonval);

	if (str && parse_int(str, &ret, 0, NULL))
		return ret;

	ereport(ERROR, errmsg("expected integer type"));

	return -1;
}

/* find a backend of the given type randomly; if picking a client backend, excludes this specific
   backend for obvious reasons.  returns the pid of the process or 0 if not found */

static pid_t find_random_pid_of_type(char *type) {
	int i,
		startIdx,
		num_procs = pgstat_fetch_stat_numbackends(),
		backend_type;
	pid_t pid = 0;
	bool is_first = true;

	/* first calculate the backend_type based on "type" param */
	backend_type =
		!pg_strcasecmp("backend", type) ? BACKEND_TYPE_NORMAL :
		!pg_strcasecmp("autovac", type) ? BACKEND_TYPE_AUTOVAC :
		!pg_strcasecmp("walsender", type) ? BACKEND_TYPE_WALSND :
		!pg_strcasecmp("bgworker", type) ? BACKEND_TYPE_BGWORKER :
		0
		;

	/* TODO: add Auxilary Procs handling to allow you to target them too */
	if (!backend_type)
		ereport(ERROR, (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
						errmsg("can't find backend of type %s", type)));

	/* pick a start index based on a random entry point into the ProcArray */
	i = startIdx = random() % num_procs;

	/* do a linear wrapping search through the array starting at the random offset */
	for (i = startIdx; i != startIdx || is_first; i = ((i + 1) >= num_procs ? 0 : i + 1), is_first = false) {
		PgBackendStatus *st = GET_BEENTRY(i);
		if (st && st->st_procpid > 0 && st->st_procpid != MyProcPid) {
			/* check for correct backend type and exit loop if so */
			if (st->st_backendType == backend_type) {
				pid = st->st_procpid;
				break;
			}
		}
	}

	return pid;
}

/* Weapon definitions */

static void wpn_special(WPN_ARGS) {
	/* this is a "special" metaweapon, not a weapon itself */
	if (!pg_strcasecmp(arg, "random")) {
		int wpn_idx;

		do {
			/* doesn't need to be secure, just pseudo-random is fine */
			wpn_idx = rand() % NUM_WEAPONS;

			/* exclude "null" and "random" from random selection */
		} while (!strcmp(weapons[wpn_idx].wpn_name, "null") ||
				 !strcmp(weapons[wpn_idx].wpn_name, "random"));

		ereport(NOTICE, errmsg("deviously selecting the random weapon '%s'",
							   weapons[wpn_idx].wpn_name));

		weapons[wpn_idx].wpn_impl(payload, weapons[wpn_idx].wpn_arg);
	} else if (!pg_strcasecmp(arg, "null")) {
		ereport(NOTICE, errmsg("intentionally doing nothing"));
	}
}

static void wpn_break_archive(WPN_ARGS) {
	char *bad_archive_command = payload ? simple_get_json_str(payload, "archive_command") : "/usr/bin/false";
	char *archive_command = GetConfigOptionByName("archive_command", NULL, false);
	char *settings[] = { "archive_mode", "archive_command", "pg_kaboom.saved_archive_command", NULL };
	char *values[] = { "on", quoted_string(bad_archive_command), quoted_string(archive_command), NULL };

	force_settings_and_restart(settings, values);
}

static void wpn_fill_log(WPN_ARGS) {
	char *log_destination = GetConfigOptionByName("log_destination", NULL, false);
	char *log_directory = GetConfigOptionByName("log_directory", NULL, false);

	if (pg_strcasecmp(log_destination, "stderr") || !*log_directory)
		ereport(ERROR, (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
						errmsg("can only fill up log_directory if stderr and set")));

	/* if an absolute path, just use that, otherwise append to the data directory */
	if (*log_directory == '/')
		fill_disk_at_path(log_directory, NULL);
	else
		fill_disk_at_path(pgdata_path, log_directory);
}

static void wpn_fill_pgdata(WPN_ARGS) {
	fill_disk_at_path(pgdata_path, NULL);
}

static void wpn_fill_pgwal(WPN_ARGS) {
	fill_disk_at_path(pgdata_path, "pg_wal");
}

static void wpn_restart(WPN_ARGS) {
	validate_we_can_restart();
	restart_database();
}

static void wpn_segfault(WPN_ARGS) {
	volatile char *segfault = NULL;
	*segfault = '\0';
}

static void wpn_signal(WPN_ARGS) {
	int sig = SIGKILL;
	pid_t sig_pid = PostmasterPid;

	if (payload) {
		int raw_sig;
		/* maybe pull out a signal and a backend to target */
		char *type = simple_get_json_str(payload, "type");

		/* look for the pid of a random backend of the given type */
		if (type) {
			sig_pid = find_random_pid_of_type(type);
			if (!sig_pid)
				ereport(NOTICE, errmsg("couldn't find pid of type '%s'", type));
		}
		raw_sig = simple_get_json_int(payload, "signal");
		if (raw_sig != -1)
			sig = raw_sig;
	}

	kill(sig_pid, sig);
}

static void wpn_rm_pgdata(WPN_ARGS) {
	command_with_path("/bin/rm -Rf %s", pgdata_path, false);
}

static void wpn_xact_wrap(WPN_ARGS) {
	char *settings[] = { "autovacuum_freeze_max_age", NULL };
	char *values[] = { "100000", NULL };

	force_settings_and_restart(settings, values);
}

static void wpn_mem(WPN_ARGS) {
	char *size = payload ? simple_get_json_str(payload, "size") : "1GB";
	//char *context = payload ? simple_get_json_str(payload, "context") : "Current"; /* TODO */

	int64 alloc_size = DatumGetInt64(DirectFunctionCall1(pg_size_bytes, CStringGetDatum(size)));
	pfree(palloc(alloc_size));
}

/* SRF to return information about the available weapons */
Datum pg_kaboom_arsenal(PG_FUNCTION_ARGS)
{
	ReturnSetInfo *rsinfo = (ReturnSetInfo *) fcinfo->resultinfo;
	TupleDesc	tupdesc;
	Tuplestorestate *tupstore;
	MemoryContext per_query_ctx;
	MemoryContext oldcontext;
	Weapon *weapon = weapons;

	/* check to see if caller supports us returning a tuplestore */
	if (rsinfo == NULL || !IsA(rsinfo, ReturnSetInfo))
		ereport(ERROR,
				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
				 errmsg("set-valued function called in context that cannot accept a set")));
	if (!(rsinfo->allowedModes & SFRM_Materialize))
		ereport(ERROR,
				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
				 errmsg("materialize mode required, but it is not allowed in this context")));

	/* Build a tuple descriptor for our result type */
	if (get_call_result_type(fcinfo, NULL, &tupdesc) != TYPEFUNC_COMPOSITE)
		elog(ERROR, "return type must be a row type");

	per_query_ctx = rsinfo->econtext->ecxt_per_query_memory;
	oldcontext = MemoryContextSwitchTo(per_query_ctx);

	tupstore = tuplestore_begin_heap(true, false, work_mem);
	rsinfo->returnMode = SFRM_Materialize;
	rsinfo->setResult = tupstore;
	rsinfo->setDesc = tupdesc;

	MemoryContextSwitchTo(oldcontext);

	while (weapon->wpn_name)
	{
		/* for each row */
		Datum		values[2];
		bool		nulls[2];

		MemSet(values, 0, sizeof(values));
		MemSet(nulls, 0, sizeof(nulls));

		values[0] = CStringGetTextDatum(weapon->wpn_name);
		values[1] = CStringGetTextDatum(weapon->wpn_desc);

		tuplestore_putvalues(tupstore, tupdesc, values, nulls);
		weapon++;
	}

	/* clean up and return the tuplestore */
	tuplestore_donestoring(tupstore);

	return (Datum) 0;
}