fix building when ARG_MAX is not defined

patch by Tom-Steve Watzke

http://bugs.gentoo.org/225341

--- netkit-rsh-0.17/rexecd/rexecd.c
+++ netkit-rsh-0.17/rexecd/rexecd.c
@@ -234,7 +234,8 @@
 static void
 doit(struct sockaddr_in *fromp)
 {
-	char cmdbuf[ARG_MAX+1];
+	char *cmdbuf;
+	int cmdbuflen;
 	char user[16], pass[16];
 	struct passwd *pwd;
 	int s = -1;
@@ -253,6 +254,15 @@
 #endif
 #endif /* USE_PAM */
 
+	cmdbuflen = sysconf(_SC_ARG_MAX);
+	if (cmdbuflen < _POSIX_ARG_MAX)
+		cmdbuflen = _POSIX_ARG_MAX;
+	cmdbuf = malloc(cmdbuflen);
+	if (cmdbuf == NULL) {
+		syslog(LOG_ERR, "unable to malloc(%i) for command buffer: %s", cmdbuflen, strerror(errno));
+		fatal("out of memory\n");
+	}
+
 	signal(SIGINT, SIG_DFL);
 	signal(SIGQUIT, SIG_DFL);
 	signal(SIGTERM, SIG_DFL);
@@ -302,7 +312,7 @@
 
 	getstr(user, sizeof(user), "username too long\n");
 	getstr(pass, sizeof(pass), "password too long\n");
-	getstr(cmdbuf, sizeof(cmdbuf), "command too long\n");
+	getstr(cmdbuf, cmdbuflen, "command too long\n");
 #ifdef USE_PAM
        #define PAM_BAIL if (pam_error != PAM_SUCCESS) { \
 	       pam_end(pamh, pam_error); exit(1); \
--- netkit-rsh-0.17/rshd/rshd.c
+++ netkit-rsh-0.17/rshd/rshd.c
@@ -337,7 +337,8 @@
 static void
 doit(struct sockaddr_in *fromp)
 {
-	char cmdbuf[ARG_MAX+1];
+	char *cmdbuf;
+	int cmdbuflen;
 	const char *theshell, *shellname;
 	char locuser[16], remuser[16];
 	struct passwd *pwd;
@@ -346,6 +347,15 @@
 	u_short port;
 	int pv[2], pid, ifd;
 
+	cmdbuflen = sysconf(_SC_ARG_MAX);
+	if (cmdbuflen < _POSIX_ARG_MAX)
+		cmdbuflen = _POSIX_ARG_MAX;
+	cmdbuf = malloc(cmdbuflen);
+	if (cmdbuf == NULL) {
+		syslog(LOG_ERR, "unable to malloc(%i) for command buffer: %s", cmdbuflen, strerror(errno));
+		exit(1);
+	}
+
 	signal(SIGINT, SIG_DFL);
 	signal(SIGQUIT, SIG_DFL);
 	signal(SIGTERM, SIG_DFL);
@@ -382,7 +392,7 @@
 
 	getstr(remuser, sizeof(remuser), "remuser");
 	getstr(locuser, sizeof(locuser), "locuser");
-	getstr(cmdbuf, sizeof(cmdbuf), "command");
+	getstr(cmdbuf, cmdbuflen, "command");
 	if (!strcmp(locuser, "root")) paranoid = 1;
 
 	hostname = findhostname(fromp, remuser, locuser, cmdbuf);