Re: [PATCH] seccomp: passthrough uretprobe systemcall without filtering

Kees Cook
2025-01-27T19:43:10Z

On Mon, Jan 27, 2025 at 11:39:44AM -0800, Eyal Birger wrote:
> On Mon, Jan 27, 2025 at 11:33 AM Kees Cook <kees@kernel.org> wrote:
> >
> > On Mon, Jan 27, 2025 at 11:24:02AM -0800, Eyal Birger wrote:
> > > Hi Kees,
> > >
> > > On Mon, Jan 20, 2025 at 1:34 PM Kees Cook <kees@kernel.org> wrote:
> > > >
> > > > On Sat, Jan 18, 2025 at 07:39:25PM -0800, Eyal Birger wrote:
> > > > > Alternatively, maybe this syscall implementation should be reverted?
> > > >
> > > > Honestly, that seems the best choice. I don't think any thought was
> > > > given to how it would interact with syscall interposers (including
> > > > ptrace, strict mode seccomp, etc).
> > >
> > > I don't know if you noticed Andrii's and others' comments on this [1].
> > >
> > > Given that:
> > > - this issue requires immediate remediation
> > > - there seems to be pushback for reverting the syscall implementation
> > > - filtering uretprobe is not within the capabilities of seccomp without this
> > > syscall (so reverting the syscall is equivalent to just passing it through
> > > seccomp)
> > >
> > > is it possible to consider applying this current fix, with the possibility of
> > > extending seccomp in the future to support filtering uretprobe if deemed
> > > necessary (for example by allowing userspace to define a stricter policy)?
> >
> > I still think this is a Docker problem, but I agree that uretprobe
> > without syscall is just as unfilterable as seccomp ignoring the syscall.
> >
> > Can you please update the patch to use the existing action_cache bitmaps
> > instead of adding an open-coded check? We can consider adding
> > syscall_restart to this as well in the future...
>
> I can. The main difference as far as I can tell is that it would not
> apply to strict mode. Is that OK? it means that existing binaries using
> strict mode would still crash if uretprobe is attached to them.

Ah, good point. Please also add it to mode1_syscalls for strict. :)

--
Kees Cook