[PATCH v3 12/26] compat_ioctl: move more drivers to compat_ptr_ioctl

[Johannes Berg]

On Thu, 2019-04-25 at 17:55 +0200, Arnd Bergmann wrote:
> On Thu, Apr 25, 2019 at 5:35 PM Al Viro <viro at zeniv.linux.org.uk> wrote:
> > 
> > On Thu, Apr 25, 2019 at 12:21:53PM -0300, Mauro Carvalho Chehab wrote:
> > 
> > > If I understand your patch description well, using compat_ptr_ioctl
> > > only works if the driver is not for s390, right?
> > 
> > No; s390 is where "oh, just set ->compat_ioctl same as ->unlocked_ioctl
> > and be done with that; compat_ptr() is a no-op anyway" breaks.  IOW,
> > s390 is the reason for having compat_ptr_ioctl() in the first place;
> > that thing works on all biarch architectures, as long as all stuff
> > handled by ->ioctl() takes pointer to arch-independent object as
> > argument.  IOW,
> >         argument ignored => OK
> >         any arithmetical type => no go, compat_ptr() would bugger it
> >         pointer to int => OK
> >         pointer to string => OK
> >         pointer to u64 => OK
> >         pointer to struct {u64 addr; char s[11];} => OK
> 
> To be extra pedantic, the 'struct {u64 addr; char s[11];} '
> case is also broken on x86, because sizeof (obj) is smaller
> on i386, even though the location of the members are
> the same. i.e. you can copy_from_user() this

Actually, you can't even do that because the struct might sit at the end
of a page and then you'd erroneously fault in this case.

We had this a while ago with struct ifreq, see commit 98406133dd and its
parents.

johannes