Re: [Linux-kernel-mentees] [PATCH v3] media/v4l2-core: Fix kernel-infoleak in video_put_user()

Arnd Bergmann
2020-07-30T08:15:52Z

On Thu, Jul 30, 2020 at 10:07 AM Bartosz Golaszewski <brgl@bgdev.pl> wrote:
>
> On Tue, Jul 28, 2020 at 3:58 PM Arnd Bergmann <arnd@arndb.de> wrote:
> >
> > On Tue, Jul 28, 2020 at 3:06 PM Dan Carpenter <dan.carpenter@oracle.com> wrote:
> > Something like
> >
> > static int lineevent_put_data(void __user *uptr, struct gpioevent_data *ge)
> > {
> > #ifdef __x86_64__
> > /* i386 has no padding after 'id' */
> > if (in_ia32_syscall()) {
> > struct {
> > compat_u64 timestamp __packed;
> > u32 id;
> > } compat_ge = { ge->timestamp, ge->id };
> >
> > if (copy_to_user(uptr, &compat_ge, sizeof(compat_ge)))
> > return -EFAULT;
> >
> > return sizeof(compat_ge);
> > }
> > #endif
> >
> > if (copy_to_user(uptr, ge, sizeof(*ge))
> > return -EFAULT;
> >
> > return sizeof(*ge);
> > }
> >
> > Arnd
>
> Hi Arnd,
>
> Andy actually had a patch for that but since this isn't a regression
> (it never worked), we decided to leave it as it is and get it right in
> v2 API.

I would argue that it needs to be fixed anyway, unless you also want
to remove the v1 interface for native mode. If this works on 32-bit
kernels, on 64-bit kernels with 64-bit user space and on compat
32-bit user space on 64-bit non-x86 architectures, I see no reason
to leave it broken specifically on x86 compat user space. There are
still reasons to use 32-bit x86 user space for low-memory machines
even though native i386 kernels are getting increasingly silly.

Arnd