On Tue, Apr 16, 2019 at 10:19:40PM +0200, Arnd Bergmann wrote: > diff --git a/drivers/net/ppp/ppp_generic.c b/drivers/net/ppp/ppp_generic.c > index c708400fff4a..04252c3492ee 100644 > --- a/drivers/net/ppp/ppp_generic.c > +++ b/drivers/net/ppp/ppp_generic.c > @@ -899,6 +899,7 @@ static const struct file_operations ppp_device_fops = { > .write = ppp_write, > .poll = ppp_poll, > .unlocked_ioctl = ppp_ioctl, > + .compat_ioctl = ppp_ioctl, Oh? What happens on e.g. s390 with something like PPPIOCNEWUNIT? Current kernel: * no ->compat_ioctl() * ->unlock_ioctl() is present * found by compat_ioctl_check_table() * pass (unsigned long)compat_ptr(arg) to do_vfs_ioctl() * pass that to ppp_ioctl() * pass that to ppp_unattached_ioctl() * fetch int from (int __user *)compat_ptr(arg) With your patch: * call ppp_ioctl() * pass arg to ppp_unattached_ioctl() * fetch int from (int __user *)arg AFAICS, that's broken... Looking at that ppp_ioctl(), pointer to arch-independent type or ignored: PPPIOCNEWUNIT PPPIOCATTACH PPPIOCATTCHAN PPPIOCSMRU PPPIOCSFLAGS PPPIOCGFLAGS PPPIOCGUNIT PPPIOCSDEBUG PPPIOCSMAXCID PPPIOCCONNECT PPPIOCGDEBUG PPPIOCSMAXCID PPPIOCSMRRU PPPIOCDETACH PPPIOCDISCONN PPPIOCGASYNCMAP PPPIOCSASYNCMAP PPPIOCGRASYNCMAP PPPIOCSRASYNCMAP PPPIOCGXASYNCMAP PPPIOCSXASYNCMAP PPPIOCGNPMODE PPPIOCSNPMODE pointer to struct ppp_option_data (with further pointer-chasing in it): PPPIOCSCOMPRESS pointer to struct ppp_idle: PPPIOCGIDLE pointer to struct sock_filter (with hidden pointer-chasing, AFAICS): PPPIOCSPASS PPPIOCSACTIVE Pretty much all of them take pointers. What's more, reaction to unknown is -ENOTTY, not -ENOIOCTLCM, so that patch will have prevent the translated ones from reaching do_ioctl_trans() What am I missing here? Why not simply do compat_ppp_ioctl() { PPPIOCSCOMPRESS32 => deal with it PPPIOCGIDLE32 => deal with it PPPIOCSPASS32 / PPPIOCSACTIVE32 => deal with it default: pass compat_ptr(arg) to ppp_ioctl() and be done with that } with BPF-related bits (both compat and native) taken to e.g. net/core/bpf-ppp.c, picked by both generic and isdn? IDGI...