> On Jun 25, 2018, at 6:32 PM, Tycho Andersen <tycho@xxxxxxxx> wrote: > >> On Sat, Jun 23, 2018 at 12:27:43AM +0200, Jann Horn wrote: >>> On Fri, Jun 22, 2018 at 11:51 PM Kees Cook <keescook@xxxxxxxxxxxx> wrote: >>> >>>> On Fri, Jun 22, 2018 at 11:09 AM, Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote: >>>> One possible extra issue: IIRC /proc/.../mem uses FOLL_FORCE, which is not what we want here. >> >> Uuugh, I forgot about that. >> >>>> 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/$pid/mem, since it's >>> FOLL_FORCE. Is there any other kind of process context id we can use >>> for this instead of pid? There was once an idea of pid-fd but it never >>> landed... This would let us get rid of the "id" in the structure too. >>> And if that existed, we could make process_vm_*v() safer too (taking a >>> pid-fd instead of a pid). >> >> Or make a duplicate of /proc/$pid/mem that only differs in whether it >> sets FOLL_FORCE? The code is basically already there... something like >> this: > > But we want more than just memory access, I think. rootfs access, ns > fds, etc. all seem like they might be useful, and racy to open. > > I guess I see two options: use the existing id and add something to > seccomp() to ask if it's still valid or independent of this patchset > add some kind of pid id :\ > I think we use the existing id / cookie / whatever and ask seccomp, or new syscalls, to do the requested operation. This is because we know the target task is in a very special stopping point. As a result, a seccomp-specific mechanism can do RCU-less fd modifications against a single-threaded target, can muck with things like struct cred, etc, while a more general interface can’t. It might be nice to add a syscall with flags such that it could be used on ptrace-stopped targets later on. Something like: access_remote_task(int fd, u64 id, u32 type, ...) Where type is 16 bits of “id and fd is from seccomp” and 16 bits of “write memory” or such.-- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
