Re: [9fans] protection against resource exhaustion

[arisawa <arisawa@ar.aichi-u.ac.jp>]

Hello,

I have been playing the following program.
I tried on official plan9, 9front, and 9atom.
none of them showed messages that come from:
		sysfatal("fork: %r”);
		sysfatal("exec: %r");
I suspect that
	fork()
does not return -1 even if it failed in creating new process.

Be ware this program may cause system panic.

#include <u.h>
#include <libc.h>
#define ERRLEN 256

static int
waitfor(int pid, char *msg)
{
	Waitmsg *w;
	while((w = wait()) != nil){
		if(w->pid == pid){
			strncpy(msg, w->msg, ERRMAX);
			free(w);
			return 0;
		}
		free(w);
	}
	return -1;
}

int
run(char *path, char *cmd)
{
	int pid;
	int status;
	int n;
	char *args[32];
	char msg[ERRLEN];

	n = tokenize(cmd, args, 32);
	args[n] = nil;

	switch(pid = fork()) {/* assign = */
	case -1:
		sysfatal("fork: %r");
	case 0:
		close(0);
		exec(path, args);
		sysfatal("exec: %r");
	default:
		break;
	}
	status = waitfor(pid, msg);
	if(status < 0){
		werrstr("waitfor: %r");
		return -1;
	}
	return 0;
}

void main(int argc, char *argv[])
{	char *e;
	int n;
	int m = 100;
	char buf[32];
	ARGBEGIN{
	case 'm':	m = atoi(ARGF());
		break;
	default: sysfatal("usage");
	}ARGEND

	if(argv[0])
		n = atoi(argv[0]);
	else
		n = 0;
	if(n == m)
		sysfatal("stop");

	print("%d\n",n);
	snprint(buf,sizeof(buf),"8.out -m %d %d",m,n + 1);
	run("./8.out", buf);
	exits(nil);
}