Re: [PATCH net v5 1/2] genetlink: Reject joining multicast groups no family owns

[Anil Kaushik <anilkaushikwireless@gmail.com>]

> The commit message says:
>
>     Nothing is ever sent to such a group, so joining it has no use.
>
> Does this hold for the group IDs that genetlink assigns as fixed values?

No, that sentence is too broad. An early join does get the messages once
a family registers. That is the problem this patch fixes.

> Is this regression intended for privileged callers? I couldn't find
> existing userspace that does this; dropwatch appears to resolve the
> family first.

Yes. Before the family registers there are no group flags to check, so
the patch rejects every caller. I don't know of a program that joins
early either. A program that resolves the family first still joins.

> The commit message mentions the getsockname() change and the setsockopt()
> -ENOENT. Could it also say that early subscription to fixed IDs stops
> working for privileged callers, and that NETLINK_LIST_MEMBERSHIPS output
> changes as well?

I can add both, and a comment on the -ENOENT meaning on the bind member,
if a new version is needed. I won't send one only for this unless
someone asks.

Anil