Re: [PATCH 18/38] C/R: core stuff

From: Alexey Dobriyan
Date: Wed May 27 2009 - 18:26:05 EST

On Wed, May 27, 2009 at 04:56:27PM -0400, Oren Laadan wrote:
> > Now here goes second version, with prefixes fixed (kstate_") like Ingo
> > suggested and so Linus could look at the code and with C/R code moved
> > close to usual code and with more checks added (which you should have
> > already!) to not restore null selector in %cs for example.
> It is far from perfect. In fact, it's even clearly commented as such,
> and exactly there. It would have been helpful if you pointed that
> out in a review, or even - god forbid - sent a patch to improve it.

This is ridiculous.

First, you declare that restart(2) should be allowed for anyone(!).
and then send patchset for inclusion in -mm which doesn't even check
if selectors are right!

> But it works, and it lets people play with a more-than-a-toy
> implementation and provide us with important feedback. Oh, and by
> the way, it doesn't require that people use containers to try it out.

Setting up container for playing is not hard:


#define _GNU_SOURCE
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sched.h>
#include <sys/mount.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/wait.h>
#include <fcntl.h>

#define CLONE_NEWNS 0x00020000
#define CLONE_NEWUTS 0x04000000
#define CLONE_NEWIPC 0x08000000
#define CLONE_NEWUSER 0x10000000
#define CLONE_NEWPID 0x20000000
#define CLONE_NEWNET 0x40000000

static int fn(void *_argv)
char **argv = (char **)_argv;

setpgid(getpid(), getpid());

execve(argv[0], argv, __environ);
return 1;

int main(int argc, char *argv[])
unsigned long flags = 0;
int status;
pid_t pid;
void *p;

flags |= CLONE_NEWNS;
flags |= CLONE_NEWUTS;
flags |= CLONE_NEWIPC;
flags |= CLONE_NEWPID;
flags |= CLONE_NEWNET;

p = malloc(4 * 4096);
if (!p)
return 1;
pid = clone(fn, p + 4 * 4096, flags, (void *)argv);
fprintf(stderr, "pid = %d\n", pid);
if (pid == -1)
return 1;
waitpid(pid, &status, __WALL);
return 0;
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