propagate prefork value

otherwise the child processes still believet the prefork value is
3 and can end up reading/writing out of bounds when setting up the
sockets.  Actually, server processes shouldn't create pipes to other
servers, but this is left for a follow-up diff.

Issue reported by la ninpre, thank you!

gmid.c

@@ -54,7 +54,7 @@ static struct privsep_proc procs[] = {
 	{ "logger",	PROC_LOGGER,	main_dispatch_logger, logger },
 };
 
-static const char	*opts = "c:D:fI:hnP:T:U:VvX:";
+static const char	*opts = "c:D:fI:J:hnP:T:U:VvX:";
 
 static const struct option longopts[] = {
 	{"help",	no_argument,		NULL,	'h'},
@@ -240,6 +240,7 @@ main(int argc, char **argv)
 	int ch, conftest = 0;
 	int proc_instance = 0;
 	int proc_id = PROC_PARENT;
+	int nprocs = 0;
 	int argc0 = argc;
 
 	setlocale(LC_CTYPE, "");
@@ -269,6 +270,13 @@ main(int argc, char **argv)
 			if (errstr != NULL)
 				fatalx("invalid process instance");
 			break;
+		case 'J':
+			nprocs = strtonum(optarg, 0, PROC_MAX_INSTANCES,
+			    &errstr);
+			if (errstr != NULL)
+				fatalx("invalid process instance");
+			log_warnx("nprocs is %d", nprocs);
+			break;
 		case 'n':
 			conftest++;
 			break;
@@ -320,6 +328,7 @@ main(int argc, char **argv)
 		if (chroot && strlcpy(conf->chroot, chroot, sizeof(conf->chroot))
 		    >= sizeof(conf->chroot))
 			fatalx("chroot path too long: %s", chroot);
+		conf->prefork = nprocs;
 	}
 
 	if ((ps = calloc(1, sizeof(*ps))) == NULL)

proc.c

@@ -79,14 +79,17 @@ proc_exec(struct privsep *ps, struct privsep_proc *procs, unsigned int nproc,
 	unsigned int		 proc, nargc, i, proc_i, proc_X = 0;
 	const char		**nargv;
 	struct privsep_proc	*p;
-	char			 num[32];
+	char			 num[32], prefork[32];
 	int			 fd;
 
 	/* Prepare the new process argv. */
-	nargv = calloc(argc + 9, sizeof(char *));
+	nargv = calloc(argc + 11, sizeof(char *));
 	if (nargv == NULL)
 		fatal("%s: calloc", __func__);
 
+	/* Update prefork number */
+	snprintf(prefork, sizeof(prefork), "%d", ps->ps_instances[PROC_SERVER]);
+
 	/* Copy call argument first. */
 	nargc = 0;
 	nargv[nargc++] = argv[0];
@@ -106,6 +109,10 @@ proc_exec(struct privsep *ps, struct privsep_proc *procs, unsigned int nproc,
 		nargc++;
 	}
 
+	/* Set server prefork number */ 
+	nargv[nargc++] = "-J";
+	nargv[nargc++] = prefork;
+
 	/* Point process instance arg to stack and copy the original args. */
 	nargv[nargc++] = "-I";
 	nargv[nargc++] = num;
@@ -354,6 +361,8 @@ proc_setup(struct privsep *ps, struct privsep_proc *procs, unsigned int nproc)
 	 */
 	for (src = 0; src < PROC_MAX; src++) {
 		/* Allocate destination array for each process */
+		log_debug("allocating %d for proc %d/%d",
+		    ps->ps_instances[src], src, PROC_MAX);
 		if ((ps->ps_pipes[src] = calloc(ps->ps_instances[src],
 		    sizeof(struct privsep_pipes))) == NULL)
 			fatal("%s: calloc", __func__);

regress/regress

@@ -68,6 +68,7 @@ run_test test_log_file
 run_test test_ipv4_addr
 run_test test_ipv6_addr need_ipv6
 run_test test_ipv6_server need_ipv6
+run_test test_high_prefork
 
 # TODO: add test that uses only a TLSv1.2 or TLSv1.3
 # TODO: add a test that attempt to serve a non-regular file

regress/tests.sh

@@ -521,3 +521,10 @@ test_ipv6_server() {
 	fetch /
 	check_reply "20 text/gemini" "# hello world" || return 1
 }
+
+test_high_prefork() {
+	setup_simple_test 'prefork 12'
+
+	fetch /
+	check_reply "20 text/gemini" "# hello world" || return 1
+}