Re: [PATCH 5/6] seccomp: add a way to attach a filter via eBPF fd

[Alexei Starovoitov <alexei.starovoitov@gmail.com>]

On Wed, Sep 09, 2015 at 08:47:24AM -0600, Tycho Andersen wrote:
> On Tue, Sep 08, 2015 at 05:07:03PM -0700, Kees Cook wrote:
> >
> > Yeah, bpf's union looks good. Let's add a "command" flag, though:
> > 
> > seccomp(SECCOMP_MODE_FILTER_EBPF, int cmd, union, size);
> > 
> > And this cmd could be ADD_FD or something?
> > 
> > How's that look?
> 
> I think we can drop the size (using the same strategy as bpf() and
> checking for zeroes at the end), and keep the same signature for
> seccomp(); so:
> 
> seccomp(SECCOMP_MODE_FILTER_EBPF, SECCOMP_ADD_BPF_FD, &union)
> 
> Yes, I'll use this in the next version.

actually bpf() has size as the last argument:
SYSCALL_DEFINE3(bpf, int, cmd, union bpf_attr __user *, uattr, unsigned int, size)
perf_event_open() doesn't and size is embedded as one of the fields.
Both approaches are equivally powerfull from extensitiblity
point of view. My preference was to keep size as an explicit
argument.