Re: [PATCH] fork: fix copy_process(CLONE_PARENT) race with the exiting ->real_parent

Re: [PATCH] fork: fix copy_process(CLONE_PARENT) race with the exiting ->real_parent

[Linus Torvalds]

.. oh, and I suspect it should have been marked for stable.

I added Oleg's ack (implicit in an earlier thread), but didn't add a stable tag.

It's commit b4e00444cab4 ("fork: fix copy_process(CLONE_PARENT) race
with the exiting ->real_parent") in my tree.

I'm not sure how serious it is. Yeah, the race can cause the wrong
exit signal in theory, but I think you almost have to do it with
cooperating processes, at which point you could have just done it
intentionally in the first place.

But it does look like a real data race, and the fix looks small and
obvious enough that I think it's stable material.

Oleg?

             Linus

On Sun, Nov 8, 2020 at 11:19 AM Linus Torvalds
<torvalds@linux-foundation.org> wrote:
>
> On Fri, Nov 6, 2020 at 10:47 PM Eddy Wu <itseddy0402@gmail.com> wrote:
> >
> > current->group_leader->exit_signal may change during copy_process() if
> > current->real_parent exits, move the assignment inside tasklist_lock to avoid
> > the race.
>
> Applied. Thanks,
>
>            Linus

Re: [PATCH] fork: fix copy_process(CLONE_PARENT) race with the exiting ->real_parent

[Greg KH]

On Sun, Nov 08, 2020 at 11:56:48AM -0800, Linus Torvalds wrote:
> .. oh, and I suspect it should have been marked for stable.
> 
> I added Oleg's ack (implicit in an earlier thread), but didn't add a stable tag.
> 
> It's commit b4e00444cab4 ("fork: fix copy_process(CLONE_PARENT) race
> with the exiting ->real_parent") in my tree.
> 
> I'm not sure how serious it is. Yeah, the race can cause the wrong
> exit signal in theory, but I think you almost have to do it with
> cooperating processes, at which point you could have just done it
> intentionally in the first place.
> 
> But it does look like a real data race, and the fix looks small and
> obvious enough that I think it's stable material.

Now queued up to stable trees, thanks!

greg k-h

Re: [PATCH] fork: fix copy_process(CLONE_PARENT) race with the exiting ->real_parent

[Oleg Nesterov]

On 11/08, Linus Torvalds wrote:
>
> But it does look like a real data race, and the fix looks small and
> obvious enough that I think it's stable material.

Agreed, the patch looks fine for -stable. I don't think that
cgroup_can_fork() could ever use thread_group_leader() or anything
else which checks ->exit_code...

And I see that Greg has already sent the patches with the correct
modifications for the case when we need "clone_flags & CSIGNAL"
rather than args->exit_signal.

Thanks Greg,

Oleg.