Re: [PATCH net-next v3 5/6] netlink: specs: rt-route: describe lwt BPF program options

[Hangbin Liu <hangbin.liu@linux.dev>]

On Thu, Oct 01, 2026 at 01:51:34AM +0000, sashiko-bot@kernel.org wrote:
> Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
> - [Low] netlink: missing max-len validation constraint for string attribute
> --
> 
> commit f56da32d0f53d2458e2f20c65435e7f6e11b64a4
> Author: Hangbin Liu <liuhangbin@kylinos.cn>
> 
> netlink: specs: rt-route: describe lwt BPF program options
> 
> This patch replaces binary BPF attributes with a nested lwt-bpf-prog to
> support lwt bpf prog options in the rt-route netlink specification.
> 
> > diff --git a/Documentation/netlink/specs/rt-route.yaml b/Documentation/netlink/specs/rt-route.yaml
> > index 7649797602eb7..afec0375661f5 100644
> > --- a/Documentation/netlink/specs/rt-route.yaml
> > +++ b/Documentation/netlink/specs/rt-route.yaml
> [ ... ]
> > @@ -621,6 +624,16 @@ attribute-sets:
> >        -
> >          name: hwid
> >          type: u8
> > +  -
> > +    name: lwt-bpf-prog
> > +    name-prefix: lwt-bpf-prog-
> > +    attributes:
> > +      -
> > +        name: fd
> > +        type: u32
> > +      -
> > +        name: name
> > +        type: string
> 
> [Severity: Low]
> Does this string attribute need a maximum length validation constraint?
> 
> The kernel's LWT_BPF_PROG_NAME policy restricts the length to MAX_PROG_NAME
> (which is 256). For netlink string specifications, this usually means adding
> a checks section with max-len: 255.

Why we should use 255 here? The bpf_encap_nlsize() alloc size
nla_total_size(MAX_PROG_NAME).

Hangbin
> 
> Without this declarative constraint, the generated userspace tooling will not
> restrict the string length prior to constructing the netlink message, forcing
> the kernel to reject over-sized strings. This bypasses client-side validation.
> 
> -- 
> Sashiko AI review · https://sashiko.dev/#/patchset/20260930-ynl_rt_encap-v3-0-4106c21b9ee7@kylinos.cn?part=5