Re: [PATCH] fork: Allow init to become a session leader.

[Oleg Nesterov <oleg@tv-sign.ru>]

"Eric W. Biederman" wrote:
> 
> With the bug fixes from killing session == 0 and pgrp == 0 we
> have essentially made pid == 1 a session leader.  However reading
> through the code I can see nothing, that sets the session->leader
> flag.  In fact we actively clear it in all cases during clone.
> And setsid will fail to set it because the session == 1 and
> process group == 1 already exist.
> 
> So this patch forces the session leader flag and for good measure
> the pgrp, session and tty of init as well.
> 
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -1179,9 +1179,16 @@ static task_t *copy_process(unsigned lon
>                 attach_pid(p, PIDTYPE_PID, p->pid);
>                 attach_pid(p, PIDTYPE_TGID, p->tgid);
>                 if (thread_group_leader(p)) {
> -                       p->signal->tty = current->signal->tty;
> -                       p->signal->pgrp = process_group(current);
> -                       p->signal->session = current->signal->session;
> +                       if (unlikely(p->pid == 1)) {
> +                               p->signal->tty = NULL;
> +                               p->signal->leader = 1;
> +                               p->signal->pgrp = 1;
> +                               p->signal->session = 1;

Isn't it enough to just set current->signal->leader = 1
in init/main.c:init() ? This process was already forked
with (1,1) special pids and ->tty == NULL.

Oleg.