Messages in this thread | | | Date | Wed, 21 Oct 2015 23:47:03 +0200 | From | Oleg Nesterov <> | Subject | Re: [PATCH 1/2] wait/ptrace: always assume __WALL if the child is traced |
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On 10/21, Denys Vlasenko wrote: > > On 10/21/2015 09:59 PM, Denys Vlasenko wrote: > > On 10/21/2015 12:31 AM, Andrew Morton wrote: > >> Well, to fix this a distro needs to roll out a new kernel. Or a new > >> init(8). Is there any reason to believe that distributing/deploying a > >> new kernel is significantly easier for everyone? Because fixing init > >> sounds like a much preferable solution to this problem. > > > > People will continue to write new init(8) implementations, > > and they will miss this obscure case. > > > > Before this bug was found, it was considered possible to use > > a shell script as init process. What now, every shell needs to add > > __WALL to its waitpids?
Why not? I think it can safely use __WALL too.
> > The use of PTRACE_TRACEME in this reproducer is clearly pathological: > > PTRACE_TRACEME was never intended to be used to attach to unsuspecting > > processes.
Sure. But people do the things which were never intended to be used all the time. We simply can not know if this "feature" already has a creative user or not.
As for the patch,
> --- a/kernel/ptrace.c > +++ b/kernel/ptrace.c > @@ -385,6 +385,17 @@ static int ptrace_traceme(void) > write_lock_irq(&tasklist_lock); > /* Are we already being traced? */ > if (!current->ptrace) { > + struct pid_namespace *pid_ns; > + > + pid_ns = task_active_pid_ns(current->parent); > + if (current->parent == pid_ns->child_reaper) {
Well, at least this needs same_thread_group(parent, child_reaper).
Plus we have PR_SET_CHILD_SUBREAPER so we also need to traverse the ->real_parent list if has_subreaper.
Finally it is not clear which ->child_reaper we should use after setns(pidns_fd).
This all is fixable (although this again reminds me about a bug with CHILD_SUBREAPER we probably need to fix first). But I didn't even try to consider this option because it can break something.
And honestly, personally I don't like it. If we believe that we can do this because "PTRACE_TRACEME was never intended to be used to attach to unsuspecting processes", then we need a more generic change, imo.
See http://marc.info/?l=linux-kernel&m=144536282305282 . Just in case, it is not that I think "parent_exec_id != self_exec_id" is all we need. This needs more discussion.
Oleg.
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