On Tue, Sep 10, 2019 at 04:46:15PM +0200, Christian Brauner wrote: > 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.
Unfortunately, it doesn't. I think, the best place for the check is either in _do_fork or copy_process itself; however, it's quite messy as that way it's detached from the other checks, but, at the same time, there are a lot of code paths (like the one in arch/x86/ia32/sys_ia32.c), and it's kinda obscure that the caller of _do_fork has to check that exit_syscall is positive itself. > Christian
