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

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Message-ID: <20190910130935.jxqxbt7wop3ostob@wittgenstein>
Date:   Tue, 10 Sep 2019 15:09:36 +0200
From:   Christian Brauner <christian.brauner@...ntu.com>
To:     Oleg Nesterov <oleg@...hat.com>
Cc:     Eugene Syromiatnikov <esyr@...hat.com>,
        linux-kernel@...r.kernel.org,
        Christian Brauner <christian@...uner.io>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        "Dmitry V. Levin" <ldv@...linux.org>,
        Eric Biederman <ebiederm@...ssion.com>
Subject: Re: [PATCH] fork: fail on non-zero higher 32 bits of args.exit_signal

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