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SubjectRe: [PATCH v3 02/26] compat_ioctl: move simple ppp command handling into driver
On Thu, Apr 18, 2019 at 1:53 AM Al Viro <viro@zeniv.linux.org.uk> wrote:
> On Thu, Apr 18, 2019 at 12:03:07AM +0200, Arnd Bergmann wrote:
> > On Wed, Apr 17, 2019 at 11:13 PM Al Viro <viro@zeniv.linux.org.uk> wrote:
> > >
> > > 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
_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...
> >
> > I was trying to unify the native and compat code paths as much
> > as possible here. Handling the four PPPIO*32 commands in
> > compat_ppp_ioctl would either require duplicating large chunks
> > of ppp_ioctl, or keeping the extra compat_alloc_user_space()
> > copy from the existing implementation.
> >
> > I'll try to come up with a different way to structure the patches.
>
> Huh? Instead of
> case PPPIOCSCOMPRESS:
> err = ppp_set_compress(ppp, arg);
> break;
> in native, have
> struct ppp_option_data data;
> ...
> case PPPIOCSCOMPRESS:
> if (copy_from_user(&data, argp, sizeof(data)))
> err = -EFAULT;
> else
> err = ppp_set_compress(ppp, &data);
> break;

Right, I ended up with something similar before I saw your message.

> in native and similar in compat, with get_bpf_ppp() replaced
> with call of compat_get_bpf_ppp() and ioctl numbers obviously
> adjusted. All there is to it... Helpers obviously shared
> with isdn and yes, all crap gone from fs/compat_ioctl.c...

I would still leave the ISDN side alone, aside from adding
the 64-bit time_t support.

> Why would you want to duplicate large chunks of anything?
> The above is not even compile-tested, but... I can put
> together a patch if you wish. Or am I missing something
> here?

I expected that the ppp_compat_ioctl() function would end up
fairly complex, to duplicate the logic before the switch()/case.

What I have now is

static long ppp_compat_ioctl(struct file *file, unsigned int cmd,
unsigned long arg)
{
struct ppp_file *pf;
struct ppp *ppp;
int err = -ENOIOCTLCMD;
struct ppp_option_data32 data32;
struct ppp_option_data data;
void __user *argp = compat_ptr(arg);

mutex_lock(&ppp_mutex);

pf = file->private_data;
if (!pf || pf->kind != INTERFACE)
goto out;

ppp = PF_TO_PPP(pf);
switch (cmd) {
case PPPIOCSCOMPRESS32:
if (copy_from_user(&data32, argp, sizeof(data32))) {
err = -EFAULT;
goto out;
}

data.ptr = compat_ptr(data32.ptr);
data.length = data32.length;
data.transmit = data32.transmit;

err = ppp_set_compress(ppp, &data);
break;

#ifdef CONFIG_PPP_FILTER
case PPPIOCSPASS32:
err = compat_get_sock_fprog(&uprog, argp);
if (err)
break;
err = ppp_set_filter(ppp, &uprog, &ppp->pass_filter);
break;

case PPPIOCSACTIVE32:
err = compat_get_sock_fprog(&uprog, argp);
if (err)
break;
err = ppp_set_filter(ppp, &uprog, &ppp->active_filter);
break;
#endif /* CONFIG_PPP_FILTER */

default:
break;
}

out:
mutex_unlock(&ppp_mutex);

if (err == -ENOIOCTLCMD)
err = ppp_ioctl(file, cmd, (unsigned long)compat_ptr(arg));

return err;
}

Which doesn't look nearly as bad as I had feared, but still is
a larger change to the existing code than what I had before,
so there is a bigger risk that I screwed up somewhere new.

Arnd

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