Re: [PATCH] seccomp: Add group_leader pid to seccomp_notif

Christian Brauner
2020-05-18T12:53:31Z

On Sun, May 17, 2020 at 09:02:15AM -0600, Tycho Andersen wrote:
> On Sun, May 17, 2020 at 08:46:03AM -0600, Tycho Andersen wrote:
> > On Sun, May 17, 2020 at 04:33:11PM +0200, Christian Brauner wrote:
> > > struct seccomp_notif2 {
> > > __u32 notif_size;
> > > __u64 id;
> > > __u32 pid;
> > > __u32 flags;
> > > struct seccomp_data data;
> > > __u32 data_size;
> > > };
> >
> > I guess you need to put data_size before data, otherwise old userspace
> > with a smaller struct seccomp_data will look in the wrong place.
> >
> > But yes, that'll work if you put two sizes in, which is probably
> > reasonable since we're talking about two structs.
>
> Well, no, it doesn't either. Suppose we add a new field first to
> struct seccomp_notif2:
>
> struct seccomp_notif2 {
> __u32 notif_size;
> __u64 id;
> __u32 pid;
> __u32 flags;
> struct seccomp_data data;
> __u32 data_size;
> __u32 new_field;
> };
>
> And next we add a new field to struct secccomp_data. When a userspace
> compiled with just the new seccomp_notif2 field does:
>
> seccomp_notif2.new_field = ...;
>
> the compiler will put it in the wrong place for the kernel with the
> new seccomp_data field too.
>
> Sort of feels like we should do:
>
> struct seccomp_notif2 {
> struct seccomp_notif *notif;
> struct seccomp_data *data;
> };
>
> ?

Oh yes of course, sorry that was my stupid typo. I meant:

struct seccomp_notif2 {
__u32 notif_size;
__u64 id;
__u32 pid;
__u32 flags;
struct seccomp_data *data;
__u32 data_size;
__u32 new_field;
}

at which point things should just work imho. This is similar to how the
set_tid array works. The kernel doesn't need to allocate any more too.
The kernel can just always use the currently know seccomp_data size.
If the kernel supports _less_ than what the caller expects, it can
report the supported size in data_size to userspace returning EINVAL. If
it supports more then it can just copy the known fields, I guess.

This way we don't need to add yet another ioctl...

Christian