Re: [PATCH v4 1/4] seccomp: add a return code to trap to userspace

Kees Cook
2018-06-22T21:51:28Z

On Fri, Jun 22, 2018 at 11:09 AM, Andy Lutomirski <luto@amacapital.net> wrote:
> One possible extra issue: IIRC /proc/.../mem uses FOLL_FORCE, which is not what we want here.
>
> How about just adding an explicit “read/write the seccomp-trapped task’s memory” primitive? That should be easier than a “open mem fd” primitive.

Uuugh. Can we avoid adding another "read/write remote process memory"
interface? The point of this series was to provide a lightweight
approach to what should normally be possible via the existing
seccomp+ptrace interface. I do like Jann's context idea, but I agree
with Andy: it can't be a handle to /proc/$pid/mem, since it's
FOLL_FORCE. Is there any other kind of process context id we can use
for this instead of pid? There was once an idea of pid-fd but it never
landed... This would let us get rid of the "id" in the structure too.
And if that existed, we could make process_vm_*v() safer too (taking a
pid-fd instead of a pid).

-Kees

--
Kees Cook
Pixel Security