Reviewed by: Bill fenner

Submitted by:	Archie Cobbs (Archie@whistle.com)

Changes to allow inted to control the number of servers to
start on each service. This is a defence against a denial of service attack
in which the system is made unusable by
an external party. It also allows the behaviour of
small memory systems to be more accuratly predicted, by
bounding the extent to which processes can multiply.

usr.sbin/inetd/Makefile

@@ -4,6 +4,9 @@ PROG=	inetd
 MAN8=	inetd.8
 MLINKS=	inetd.8 inetd.conf.5
 
+COPTS+=	-Wall
+#COPTS+=	-DSANITY_CHECK
+
 DPADD+=	${LIBUTIL}
 LDADD+=	-lutil
 

usr.sbin/inetd/inetd.8

@@ -30,7 +30,7 @@
 .\" SUCH DAMAGE.
 .\"
 .\"     from: @(#)inetd.8	8.3 (Berkeley) 4/13/94
-.\"	$Id: inetd.8,v 1.8 1996/02/07 17:15:00 wollman Exp $
+.\"	$Id: inetd.8,v 1.9 1996/08/09 22:20:23 julian Exp $
 .\"
 .Dd February 7, 1996
 .Dt INETD 8
@@ -101,7 +101,7 @@ fields of the configuration file are as follows:
 service name
 socket type
 protocol
-wait/nowait
+{wait|nowait}[/max-child]
 user
 server program
 server program arguments
@@ -261,6 +261,15 @@ requests until a timeout.
 TCPMUX services must use 
 .Dq nowait .
 .Pp
+The maximum number of outstanding child processes (or ``threads'')
+for a ``nowait'' service may be explicitly specified by appending a
+``/'' followed by the number to the ``nowait'' keyword. Normally
+(or if a value of zero is specified) there is no maximum. Otherwise,
+once the maximum is reached, further connection attempts will be
+queued up until an existing child process exits. This also works
+in the case of ``wait'' mode, although a value other than one (the
+default) might not make sense in some cases.
+.Pp
 The
 .Em user
 entry should contain the user name of the user as whom the server

usr.sbin/inetd/inetd.c

@@ -40,7 +40,7 @@ static char copyright[] __attribute__ ((unused)) =
 #ifndef lint
 /* from: @(#)inetd.c	8.4 (Berkeley) 4/13/94"; */
 static char inetd_c_rcsid[] __attribute__ ((unused)) =
-	"$Id: inetd.c,v 1.15 1996/11/01 01:42:08 alex Exp $";
+	"$Id: inetd.c,v 1.16 1996/11/10 21:07:27 julian Exp $";
 #endif /* not lint */
 
 /*
@@ -132,10 +132,10 @@ static char inetd_c_rcsid[] __attribute__ ((unused)) =
 #define	TOOMANY		256		/* don't start more than TOOMANY */
 #define	CNT_INTVL	60		/* servers in CNT_INTVL sec. */
 #define	RETRYTIME	(60*10)		/* retry after bind or server fail */
+#define MAX_MAXCHLD	32767		/* max allowable max children */
 
 #define	SIGBLOCK	(sigmask(SIGCHLD)|sigmask(SIGHUP)|sigmask(SIGALRM))
 
-
 int	debug = 0;
 int	log = 0;
 int	nsock, maxsock;
@@ -151,17 +151,20 @@ struct	servtab {
 	char	*se_service;		/* name of service */
 	int	se_socktype;		/* type of socket to use */
 	char	*se_proto;		/* protocol used */
-	short	se_wait;		/* single threaded server */
+	short	se_maxchild;		/* max number of children */
-	short	se_checked;		/* looked at during merge */
+	short	se_numchild;		/* current number of children */
+	pid_t	*se_pids;		/* array of child pids */
 	char	*se_user;		/* user name to run as */
 	struct	biltin *se_bi;		/* if built-in, description */
 	char	*se_server;		/* server program */
 #define	MAXARGV 20
 	char	*se_argv[MAXARGV+1];	/* program arguments */
 	int	se_fd;			/* open descriptor */
-	int	se_type;		/* type */
 	struct	sockaddr_in se_ctrladdr;/* bound address */
-	int	se_rpc;			/* ==1 if RPC service */
+	u_char	se_type;		/* type: normal, mux, or mux+ */
+	u_char	se_checked;		/* looked at during merge */
+	u_char	se_accept;		/* i.e., wait/nowait mode */
+	u_char	se_rpc;			/* ==1 if RPC service */
 	int	se_rpc_prog;		/* RPC program number */
 	u_int	se_rpc_lowvers;		/* RPC low version */
 	u_int	se_rpc_highvers;	/* RPC high version */
@@ -197,7 +200,10 @@ void		machtime_stream __P((int, struct servtab *));
 char	       *newstr __P((char *));
 char	       *nextline __P((FILE *));
 void		print_service __P((char *, struct servtab *));
+void		addchild __P((struct servtab *, int));
 void		reapchild __P((int));
+void		enable __P((struct servtab *));
+void		disable __P((struct servtab *));
 void		retry __P((int));
 int		setconfig __P((void));
 void		setup __P((struct servtab *));
@@ -211,7 +217,7 @@ struct biltin {
 	char	*bi_service;		/* internally provided service name */
 	int	bi_socktype;		/* type of socket supported */
 	short	bi_fork;		/* 1 if should fork before call */
-	short	bi_wait;		/* 1 if should wait for child */
+	short	bi_maxchild;		/* max number of children (default) */
 	void	(*bi_fn)();		/* function which performs it */
 } biltins[] = {
 	/* Echo received data */
@@ -385,7 +391,7 @@ main(argc, argv, envp)
 		    if (debug)
 			    fprintf(stderr, "someone wants %s\n",
 				sep->se_service);
-		    if (!sep->se_wait && sep->se_socktype == SOCK_STREAM) {
+		    if (sep->se_accept && sep->se_socktype == SOCK_STREAM) {
 			    ctrl = accept(sep->se_fd, (struct sockaddr *)0,
 				(int *)0);
 			    if (debug)
@@ -458,20 +464,15 @@ main(argc, argv, envp)
 		    }
 		    if (pid < 0) {
 			    syslog(LOG_ERR, "fork: %m");
-			    if (!sep->se_wait &&
+			    if (sep->se_accept &&
 				sep->se_socktype == SOCK_STREAM)
 				    close(ctrl);
 			    sigsetmask(0L);
 			    sleep(1);
 			    continue;
 		    }
-		    if (pid && sep->se_wait) {
+		    if (pid)
-			    sep->se_wait = pid;
+			addchild(sep, pid);
-			    if (sep->se_fd >= 0) {
-				FD_CLR(sep->se_fd, &allsock);
-			        nsock--;
-			    }
-		    }
 		    sigsetmask(0L);
 		    if (pid == 0) {
 			    if (dofork) {
@@ -538,17 +539,43 @@ main(argc, argv, envp)
 				_exit(EX_OSERR);
 			    }
 		    }
-		    if (!sep->se_wait && sep->se_socktype == SOCK_STREAM)
+		    if (sep->se_accept && sep->se_socktype == SOCK_STREAM)
 			    close(ctrl);
 		}
 	}
 }
 
+/*
+ * Record a new child pid for this service. If we've reached the
+ * limit on children, then stop accepting incoming requests.
+ */
+
+void
+addchild(struct servtab *sep, pid_t pid)
+{
+#ifdef SANITY_CHECK
+	if (sep->se_numchild >= sep->se_maxchild) {
+		syslog(LOG_ERR, "%s: %d >= %d",
+		    __FUNCTION__, sep->se_numchild, sep->se_maxchild);
+		exit(EX_SOFTWARE);
+	}
+#endif
+	if (sep->se_maxchild == 0)
+		return;
+	sep->se_pids[sep->se_numchild++] = pid;
+	if (sep->se_numchild == sep->se_maxchild)
+		disable(sep);
+}
+
+/*
+ * Some child process has exited. See if it's on somebody's list.
+ */
+
 void
 reapchild(signo)
 	int signo;
 {
-	int status;
+	int k, status;
 	pid_t pid;
 	struct servtab *sep;
 
@@ -559,19 +586,21 @@ reapchild(signo)
 		if (debug)
 			fprintf(stderr, "%d reaped, status %#x\n",
 				pid, status);
-		for (sep = servtab; sep; sep = sep->se_next)
+		for (sep = servtab; sep; sep = sep->se_next) {
-			if (sep->se_wait == pid) {
+			for (k = 0; k < sep->se_numchild; k++)
-				if (status)
+				if (sep->se_pids[k] == pid)
-					syslog(LOG_WARNING,
+					break;
-					    "%s: exit status 0x%x",
+			if (k == sep->se_numchild)
-					    sep->se_server, status);
+				continue;
-				if (debug)
+			if (sep->se_numchild == sep->se_maxchild)
-					fprintf(stderr, "restored %s, fd %d\n",
+				enable(sep);
-					    sep->se_service, sep->se_fd);
+			sep->se_pids[k] = sep->se_pids[--sep->se_numchild];
-				FD_SET(sep->se_fd, &allsock);
+			if (status)
-				nsock++;
+				syslog(LOG_WARNING,
-				sep->se_wait = 1;
+				    "%s[%d]: exit status 0x%x",
-			}
+				    sep->se_server, pid, status);
+			break;
+		}
 	}
 }
 
@@ -579,7 +608,7 @@ void
 config(signo)
 	int signo;
 {
-	struct servtab *sep, *cp, **sepp;
+	struct servtab *sep, *new, **sepp;
 	struct passwd *pwd;
 	long omask;
 
@@ -589,43 +618,57 @@ config(signo)
 	}
 	for (sep = servtab; sep; sep = sep->se_next)
 		sep->se_checked = 0;
-	while (cp = getconfigent()) {
+	while ((new = getconfigent())) {
-		if ((pwd = getpwnam(cp->se_user)) == NULL) {
+		if ((pwd = getpwnam(new->se_user)) == NULL) {
 			syslog(LOG_ERR,
 				"%s/%s: No such user '%s', service ignored",
-				cp->se_service, cp->se_proto, cp->se_user);
+				new->se_service, new->se_proto, new->se_user);
 			continue;
 		}
 		for (sep = servtab; sep; sep = sep->se_next)
-			if (strcmp(sep->se_service, cp->se_service) == 0 &&
+			if (strcmp(sep->se_service, new->se_service) == 0 &&
-			    strcmp(sep->se_proto, cp->se_proto) == 0)
+			    strcmp(sep->se_proto, new->se_proto) == 0)
 				break;
 		if (sep != 0) {
 			int i;
 
+#define SWAP(a, b) { typeof(a) c = a; a = b; b = c; }
 			omask = sigblock(SIGBLOCK);
-			/*
+			/* copy over outstanding child pids */
-			 * sep->se_wait may be holding the pid of a daemon
+			if (sep->se_maxchild && new->se_maxchild) {
-			 * that we're waiting for.  If so, don't overwrite
+				new->se_numchild = sep->se_numchild;
-			 * it unless the config file explicitly says don't
+				if (new->se_numchild > new->se_maxchild)
-			 * wait.
+					new->se_numchild = new->se_maxchild;
-			 */
+				memcpy(new->se_pids, sep->se_pids,
-			if (cp->se_bi == 0 &&
+				    new->se_numchild * sizeof(*new->se_pids));
-			    (sep->se_wait == 1 || cp->se_wait == 0))
+			}
-				sep->se_wait = cp->se_wait;
+			SWAP(sep->se_pids, new->se_pids);
-#define SWAP(a, b) { char *c = a; a = b; b = c; }
+			sep->se_maxchild = new->se_maxchild;
-			if (cp->se_user)
+			sep->se_numchild = new->se_numchild;
-				SWAP(sep->se_user, cp->se_user);
+			/* might need to turn on or off service now */
-			if (cp->se_server)
+			if (sep->se_fd >= 0) {
-				SWAP(sep->se_server, cp->se_server);
+			      if (sep->se_maxchild
+				  && sep->se_numchild == sep->se_maxchild) {
+				      if (FD_ISSET(sep->se_fd, &allsock))
+					  disable(sep);
+			      } else {
+				      if (!FD_ISSET(sep->se_fd, &allsock))
+					  enable(sep);
+			      }
+			}
+			sep->se_accept = new->se_accept;
+			if (new->se_user)
+				SWAP(sep->se_user, new->se_user);
+			if (new->se_server)
+				SWAP(sep->se_server, new->se_server);
 			for (i = 0; i < MAXARGV; i++)
-				SWAP(sep->se_argv[i], cp->se_argv[i]);
+				SWAP(sep->se_argv[i], new->se_argv[i]);
 			sigsetmask(omask);
-			freeconfig(cp);
+			freeconfig(new);
 			if (debug)
 				print_service("REDO", sep);
 		} else {
-			sep = enter(cp);
+			sep = enter(new);
 			if (debug)
 				print_service("ADD ", sep);
 		}
@@ -799,10 +842,7 @@ setsockopt(fd, SOL_SOCKET, opt, (char *)&on, sizeof (on))
         }
 	if (sep->se_socktype == SOCK_STREAM)
 		listen(sep->se_fd, 64);
-	FD_SET(sep->se_fd, &allsock);
+	enable(sep);
-	nsock++;
-	if (sep->se_fd > maxsock)
-		maxsock = sep->se_fd;
 	if (debug) {
 		fprintf(stderr, "registered %s on %d\n",
 			sep->se_server, sep->se_fd);
@@ -817,18 +857,13 @@ close_sep(sep)
 	struct servtab *sep;
 {
 	if (sep->se_fd >= 0) {
-		nsock--;
+		if (FD_ISSET(sep->se_fd, &allsock))
-		FD_CLR(sep->se_fd, &allsock);
+			disable(sep);
 		(void) close(sep->se_fd);
 		sep->se_fd = -1;
 	}
 	sep->se_count = 0;
-	/*
+	sep->se_numchild = 0;	/* forget about any existing children */
-	 * Don't keep the pid of this running deamon: when reapchild()
-	 * reaps this pid, it would erroneously increment nsock.
-	 */
-	if (sep->se_wait > 1)
-		sep->se_wait = 1;
 }
 
 struct servtab *
@@ -852,6 +887,68 @@ enter(cp)
 	return (sep);
 }
 
+void
+enable(struct servtab *sep)
+{
+	if (debug)
+		fprintf(stderr,
+		    "enabling %s, fd %d", sep->se_service, sep->se_fd);
+#ifdef SANITY_CHECK
+	if (sep->se_fd < 0) {
+		syslog(LOG_ERR,
+		    "%s: %s: bad fd", __FUNCTION__, sep->se_service);
+		exit(EX_SOFTWARE);
+	}
+	if (ISMUX(sep)) {
+		syslog(LOG_ERR,
+		    "%s: %s: is mux", __FUNCTION__, sep->se_service);
+		exit(EX_SOFTWARE);
+	}
+	if (FD_ISSET(sep->se_fd, &allsock)) {
+		syslog(LOG_ERR,
+		    "%s: %s: not off", __FUNCTION__, sep->se_service);
+		exit(EX_SOFTWARE);
+	}
+#endif
+	FD_SET(sep->se_fd, &allsock);
+	nsock++;
+	if (sep->se_fd > maxsock)
+		maxsock = sep->se_fd;
+}
+
+void
+disable(struct servtab *sep)
+{
+	if (debug)
+		fprintf(stderr,
+		    "disabling %s, fd %d", sep->se_service, sep->se_fd);
+#ifdef SANITY_CHECK
+	if (sep->se_fd < 0) {
+		syslog(LOG_ERR,
+		    "%s: %s: bad fd", __FUNCTION__, sep->se_service);
+		exit(EX_SOFTWARE);
+	}
+	if (ISMUX(sep)) {
+		syslog(LOG_ERR,
+		    "%s: %s: is mux", __FUNCTION__, sep->se_service);
+		exit(EX_SOFTWARE);
+	}
+	if (!FD_ISSET(sep->se_fd, &allsock)) {
+		syslog(LOG_ERR,
+		    "%s: %s: not on", __FUNCTION__, sep->se_service);
+		exit(EX_SOFTWARE);
+	}
+	if (nsock == 0) {
+		syslog(LOG_ERR, "%s: nsock=0", __FUNCTION__);
+		exit(EX_SOFTWARE);
+	}
+#endif
+	FD_CLR(sep->se_fd, &allsock);
+	nsock--;
+	if (sep->se_fd == maxsock)
+		maxsock--;
+}
+
 FILE	*fconfig = NULL;
 struct	servtab serv;
 char	line[LINE_MAX];
@@ -882,7 +979,7 @@ getconfigent()
 {
 	struct servtab *sep = &serv;
 	int argc;
-	char *cp, *arg;
+	char *cp, *arg, *s;
 	char *versp;
 	static char TCPMUX_TOKEN[] = "tcpmux/";
 #define MUX_LEN		(sizeof(TCPMUX_TOKEN)-1)
@@ -962,14 +1059,36 @@ getconfigent()
                 }
         }
 	arg = sskip(&cp);
-	sep->se_wait = strcmp(arg, "wait") == 0;
+	if (!strncmp(arg, "wait", 4))
+		sep->se_accept = 0;
+	else if (!strncmp(arg, "nowait", 6))
+		sep->se_accept = 1;
+	else {
+		syslog(LOG_ERR,
+			"%s: bad wait/nowait for service %s",
+			CONFIG, sep->se_service);
+		goto more;
+	}
+	sep->se_maxchild = -1;
+	if ((s = strchr(arg, '/')) != NULL) {
+		char *eptr;
+		u_long val;
+
+		val = strtoul(s + 1, &eptr, 10);
+		if (eptr == s + 1 || *eptr || val > MAX_MAXCHLD) {
+			syslog(LOG_ERR,
+				"%s: bad max-child for service %s",
+				CONFIG, sep->se_service);
+			goto more;
+		}
+		sep->se_maxchild = val;
+	}
 	if (ISMUX(sep)) {
 		/*
-		 * Silently enforce "nowait" for TCPMUX services since
+		 * Silently enforce "nowait" mode for TCPMUX services
-		 * they don't have an assigned port to listen on.
+		 * since they don't have an assigned port to listen on.
 		 */
-		sep->se_wait = 0;
+		sep->se_accept = 1;
-
 		if (strcmp(sep->se_proto, "tcp")) {
 			syslog(LOG_ERR,
 				"%s: bad protocol for tcpmux service %s",
@@ -997,14 +1116,32 @@ getconfigent()
 				sep->se_service);
 			goto more;
 		}
+		sep->se_accept = 1;	/* force accept mode for built-ins */
 		sep->se_bi = bi;
-		sep->se_wait = bi->bi_wait;
 	} else
 		sep->se_bi = NULL;
+	if (sep->se_maxchild < 0)	/* apply default max-children */
+		if (sep->se_bi)
+			sep->se_maxchild = sep->se_bi->bi_maxchild;
+		else
+			sep->se_maxchild = sep->se_accept ? 0 : 1;
+	if (sep->se_maxchild) {
+		sep->se_pids = malloc(sep->se_maxchild * sizeof(*sep->se_pids));
+		if (sep->se_pids == NULL) {
+			syslog(LOG_ERR, "Out of memory.");
+			exit(EX_OSERR);
+		}
+	}
 	argc = 0;
 	for (arg = skip(&cp); cp; arg = skip(&cp))
-		if (argc < MAXARGV)
+		if (argc < MAXARGV) {
 			sep->se_argv[argc++] = newstr(arg);
+		} else {
+			syslog(LOG_ERR,
+				"%s: too many arguments for service %s",
+				CONFIG, sep->se_service);
+			goto more;
+		}
 	while (argc <= MAXARGV)
 		sep->se_argv[argc++] = NULL;
 	return (sep);
@@ -1024,6 +1161,8 @@ freeconfig(cp)
 		free(cp->se_user);
 	if (cp->se_server)
 		free(cp->se_server);
+	if (cp->se_pids)
+		free(cp->se_pids);
 	for (i = 0; i < MAXARGV; i++)
 		if (cp->se_argv[i])
 			free(cp->se_argv[i]);