On Mon, 05 Oct 2020 22:12:25 +0200 Johannes Berg wrote:
> On Mon, 2020-10-05 at 21:53 +0200, Johannes Berg wrote:
> > Hm. I like that idea.
> >
> > If we have NLMSGERR_ATTR_OFFS we could accompany that with the sub-
> > policy for that particular attribute, something like
> >
> > [NLMSGERR_ATTR_POLICY] = nested {
> > [NL_POLICY_TYPE_ATTR_TYPE] = ...
> > [NL_POLICY_TYPE_ATTR_MASK] = ...
> > }
> >
> > which we could basically do by factoring out the inner portion of
> > netlink_policy_dump_write():
> >
> > attr = nla_nest_start(skb, state->attr_idx);
> > if (!attr)
> > goto nla_put_failure;
> > ...
> > nla_nest_end(skb, attr);
> >
> > from there into a separate function, give it the pt and the nested
> > attribute (what's "state->attr_idx" here) as arguments, and then we call
> > it with NLMSGERR_ATTR_POLICY from here, and with "state->attr_idx" from
> > netlink_policy_dump_write() :-)
> >
> > Nice, easy & useful, maybe I'll code it up tomorrow.
>
> OK I thought about it a bit more and looked at the code, and it's not
> actually possible to do easily right now, because we can't actually
> point to the bad attribute from the general lib/nlattr.c code ...
>
> Why? Because we don't know right now, e.g. for nla_validate(), where in
> the message we started validation, i.e. the offset of the "head" inside
> the particular message.
>
> For nlmsg_parse() and friends that's a bit easier, but it needs more
> rejiggering than I'm willing to do tonight ;)
I thought we'd record the const struct nla_policy *tp for the failing
attr in struct netlink_ext_ack and output based on that.
