Re: [PATCH] fork: fail on non-zero higher 32 bits of args.exit_signal

[Christian Brauner]

On Tue, Sep 10, 2019 at 02:44:41PM +0200, Oleg Nesterov wrote:
> On 09/10, Eugene Syromiatnikov wrote:
> >
> > --- a/kernel/fork.c
> > +++ b/kernel/fork.c
> > @@ -2562,6 +2562,9 @@ noinline static int copy_clone_args_from_user(struct kernel_clone_args *kargs,
> >  	if (copy_from_user(&args, uargs, size))
> >  		return -EFAULT;
> >  
> > +	if (unlikely(((unsigned int)args.exit_signal) != args.exit_signal))
> > +		return -EINVAL;
> 
> Hmm. Unless I am totally confused you found a serious bug...
> 
> Without CLONE_THREAD/CLONE_PARENT copy_process() blindly does
> 
> 	p->exit_signal = args->exit_signal;
> 
> the valid_signal(sig) check in do_notify_parent() mostly saves us, but we
> must not allow child->exit_signal < 0, if nothing else this breaks
> thread_group_leader().
> 
> And afaics this patch doesn't fix this? I think we need the valid_signal()
> check...

Thanks for sending this patch so quickly after our conversation
yesterday, Eugene!
We definitely want valid_signal() to verify the signal is ok.

Eugene, can you please update the patch to use valid signal and keep it
as a separate patch from the cleanup and selftest patches?

Christian