Subject: Re: [PATCH] connector: Fix sid connector (was: Badness at kernel/softirq.c:143...)

From: Oleg Nesterov <[email-masked]>
Date: Tue, 29 Sep 2009 16:45:54 +0200

On 09/29, Oleg Nesterov wrote:
>
> On 09/29, Evgeniy Polyakov wrote:
> >
> > On Tue, Sep 29, 2009 at 03:47:21PM +0200, Christian Borntraeger ([email-masked]) wrote:
> > > Ok,  can confirm that this patch fixes my problem, but I am not sure if the
> > > intended behaviour is still working as expected.
> >
> > Your patch breaks assumption that task_session(current->group_leader) is
> > not equal to new session id,
>
> Afaics, no.
>
> > --- a/kernel/sys.c
> > +++ b/kernel/sys.c
> > @@ -1090,6 +1090,7 @@ SYSCALL_DEFINE0(setsid)
> >  	struct pid *sid = task_pid(group_leader);
> >  	pid_t session = pid_vnr(sid);
> >  	int err = -EPERM;
> > +	int send_cn = 0;
> >
> >  	write_lock_irq(&tasklist_lock);
> >  	/* Fail if I am already a session leader */
> > @@ -1104,12 +1105,18 @@ SYSCALL_DEFINE0(setsid)
> >
> >  	group_leader->signal->leader = 1;
> >  	__set_special_pids(sid);
> > +	if (task_session(group_leader) != sid)
> > +		send_cn = 1;
>
> This is not right, task_session(group_leader) must be == sid after
> __set_special_pids().
>
> And I don't think "int send_cn" is needed. sys_setsid() must not
> succeed if the caller lived in session == task_pid(group_leader).

IOW, if sys_setsid() succeeds, we know it creates the new unique session,
we should report this change.

Note this check

	if (pid_task(sid, PIDTYPE_PGID))
		goto out;

before we actually change pids.

I think Christian's patch only needs the small fixup.

Oleg.