Re: [PATCH 1/3] fix setsid() for sub-namespace /sbin/init

[Pavel Emelyanov <xemul@openvz.org>]

Oleg Nesterov wrote:
> sys_setsid() still deals with pid_t's from the global namespace. This means
> that the "session > 1" check can't help for sub-namespace init, setsid() can't
> succeed because copy_process(CLONE_NEWPID) populates PIDTYPE_PGID/SID links.
> 
> Remove the usage of task_struct->pid and convert the code to use "struct pid".
> This also simplifies and speedups the code, saves one find_pid().
> 
> Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>

Acked-by: Pavel Emelyanov <xemul@openvz.org>

> --- PT/kernel/sys.c~1_setsid	2007-11-26 15:52:15.000000000 +0300
> +++ PT/kernel/sys.c	2007-11-26 16:10:43.000000000 +0300
> @@ -1045,35 +1045,33 @@ asmlinkage long sys_getsid(pid_t pid)
>  asmlinkage long sys_setsid(void)
>  {
>  	struct task_struct *group_leader = current->group_leader;
> -	pid_t session;
> +	struct pid *sid = task_pid(group_leader);
> +	pid_t session = pid_vnr(sid);
>  	int err = -EPERM;
>  
>  	write_lock_irq(&tasklist_lock);
> -
>  	/* Fail if I am already a session leader */
>  	if (group_leader->signal->leader)
>  		goto out;
>  
> -	session = group_leader->pid;
> -	/* Fail if a process group id already exists that equals the
> -	 * proposed session id.
> +	/* Fail if a process group id already exists that equals the proposed
> +	 * session id.
>  	 *
> -	 * Don't check if session id == 1 because kernel threads use this
> -	 * session id and so the check will always fail and make it so
> -	 * init cannot successfully call setsid.
> +	 * Don't check if session == 1 because kernel threads and CLONE_NEWPID
> +	 * tasks use this session id and so the check will always fail and make
> +	 * it so init cannot successfully call setsid.
>  	 */
> -	if (session > 1 && find_task_by_pid_type_ns(PIDTYPE_PGID,
> -				session, &init_pid_ns))
> +	if (session != 1 && pid_task(sid, PIDTYPE_PGID))
>  		goto out;
>  
>  	group_leader->signal->leader = 1;
> -	__set_special_pids(session, session);
> +	__set_special_pids(pid_nr(sid), pid_nr(sid));
>  
>  	spin_lock(&group_leader->sighand->siglock);
>  	group_leader->signal->tty = NULL;
>  	spin_unlock(&group_leader->sighand->siglock);
>  
> -	err = task_pgrp_vnr(group_leader);
> +	err = session;
>  out:
>  	write_unlock_irq(&tasklist_lock);
>  	return err;
> 
>