Messages in this thread | | | Date | Tue, 10 Sep 2019 16:46:15 +0200 | From | Christian Brauner <> | Subject | Re: [PATCH] fork: fail on non-zero higher 32 bits of args.exit_signal |
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On Tue, Sep 10, 2019 at 04:39:44PM +0200, Oleg Nesterov wrote: > On 09/10, Christian Brauner wrote: > > On Tue, Sep 10, 2019 at 03:10:48PM +0200, Christian Brauner wrote: > > > On Tue, Sep 10, 2019 at 03:09:35PM +0200, Christian Brauner wrote: > > > > 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. > > > > So we could do your check in copy_clone_args_from_user(), and then we do > > another valid_signal() check in clone3_args_valid()? We could do the > > latter in copy_clone_args_from_user() too but it's nicer to do it along > > the other checks in clone3_args_valid(). > > I am fine either way. Sure, we can add valid_signal() into clone3_args_valid(), > but then I'd ask to simplify the "overflow" check above. Something like > > if (args.exit_signal > UINT_MAX) > return -EINVAL; > > looks much more readable to me. > > > Or we can simply do > > if (args.exit_signal & ~((u64)CSIGNAL)) > return -EINVAL; > > in copy_clone_args_from_user() and forget about all problems.
Both are fine with me. The latter might have the advantage that we catch both legacy clone and clone3. I think Eugene prefers this as well.
Christian
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