On Tue, Jan 08, 2019 at 11:20:23AM -0700, Tycho Andersen wrote:
> On Tue, Jan 08, 2019 at 12:17:42PM -0600, Serge E. Hallyn wrote:
> > On Tue, Jan 08, 2019 at 10:58:43AM -0700, Tycho Andersen wrote:
> > > On Tue, Jan 08, 2019 at 11:54:15AM -0600, Serge E. Hallyn wrote:
> > > > On Tue, Jan 08, 2019 at 10:53:06AM -0700, Tycho Andersen wrote:
> > > > > On Wed, Jan 02, 2019 at 05:16:54PM +0100, Christian Brauner wrote:
> > > > > > + /*
> > > > > > + * Stop the child so we can inspect whether we have
> > > > > > + * recycled pid PID_RECYCLE.
> > > > > > + */
> > > > > > + close(pipe_fds[0]);
> > > > > > + ret = kill(recycled_pid, SIGSTOP);
> > > > > > + close(pipe_fds[1]);
> > > > > > + if (ret) {
> > > > > > + (void)wait_for_pid(recycled_pid);
> > > > > > + _exit(PIDFD_ERROR);
> > > > > > + }
> > > > >
> > > > > Sorry for being late to the party, but I wonder if this whole thing
> > > > > couldn't be simplified with /proc/sys/kenrel/ns_last_pid?
> > > >
> > > > no, bc it's not namespaced :)
> > >
> > > Huh? It looks like it is...
> > >
> > > static int pid_ns_ctl_handler(struct ctl_table *table, int write,
> > > void __user *buffer, size_t *lenp, loff_t *ppos)
> > > {
> > > struct pid_namespace *pid_ns = task_active_pid_ns(current);
> > > struct ctl_table tmp = *table;
> > > int ret, next;
> > >
> > > if (write && !ns_capable(pid_ns->user_ns, CAP_SYS_ADMIN))
> > > return -EPERM;
> > >
> > > ...
> >
> > Oh - hah, but that's ns_last_pid. You'd want pid_max. And that one
> > is not namespaced.
>
> Perhaps I'm misunderstanding, but isn't the point of all this code to
> get the same pid again? So can't we just fork(), kill(), then set
> ns_last_pid to pid-1, and fork() again to re-use?
Oh yeah that would work :)
I was stuck on the idea of just limiting the range of pids.
