Re: [PATCH net-next 2/4] tools: ynl: reject zero-length attributes instead of looping forever

[Jakub Kicinski]

On Tue, 08 Sep 2026 19:45:08 -0400 Taylor Bates wrote:
> The BRIDGE_VLANDB_GOPTS_MCAST_ROUTER_PORTS payload the kernel then sends:
> 
>   34 00 02 00   MDBA_ROUTER, len 52
>   30 00 01 00   MDBA_ROUTER_PORT, len 48
>   08 00 00 00   bare ifindex 8, written by nla_put_nohdr()
>   08 00 01 00   MDBA_ROUTER_PATTR_TIMER, len 8
>   00 00 00 00   timer value, 0 for a permanent router

Sounds like the family outputs garbage and should not be supported.

>          while offset < len(msg):
>              attr = NlAttr(msg, offset)
> +            if attr.full_len < 4:
> +                raise YnlException(
> +                    f'Malformed attribute at offset {offset}: '
> +                    f'length {attr.payload_len} is shorter than the header')
>              offset += attr.full_len
>              self.attrs.append(attr)

Not sure i follow you logic. If anything I'd have written:

	if len(msg) - offset < 4:
		raise ...short, not overly verbose msg")

? But again, if the kernel is not outputting valid attrs that's not
YNL's problem.