allocate memory in cb->start(), which means passing 'static' variable
through control->data,
then allocate memory in cb->start() according to cb->data (cb->data is
equal to control->data now),
and set the memory back to cb->data which will be used in cb->dump().
It's a bit complicated， please see nf_tables_getset.
2018-07-23 2:09 GMT+08:00 Florian Westphal <f...@strlen.de>:
> David Miller <da...@davemloft.net> wrote:
> > From: Florian Westphal <f...@strlen.de>
> > Date: Sun, 22 Jul 2018 18:39:25 +0200
> >
> > > 3. change meaning of ->done() so its always called once ->start()
> > > was invoked (and returned 0), this requires audit of all
> > > places that provide .done to make sure they won't trip.
> > >
> > > 3) seems to be what Tom intended when he added .start, so probably
> > > best to investigate that first.
> >
> > Hmmm...
> >
> > Any time ->start() succeeds, we set cb_running to true.
>
> Right.
>
> > From that point forward, ->done() will be called at some point at all
> > of the locations that check if cb_running is true and set it to false.
>
> Also right, thanks for pointing this out, I missed fact that netlink
> core restarts a dump after this.
>
> So 3) is already true which means we should try to see if we can move
> all dump-related extra magic into ->start().
>
> Shaochun, can you see if this is possible?
>
> Something along these lines (totally untested), which makes this
> a netfilter fix:
>
> diff --git a/net/netfilter/nf_tables_api.c b/net/netfilter/nf_tables_api.c
> --- a/net/netfilter/nf_tables_api.c
> +++ b/net/netfilter/nf_tables_api.c
> @@ -5010,6 +5013,22 @@ nft_obj_filter_alloc(const struct nlattr * const
> nla[])
> return filter;
> }
>
> +static int nf_tables_dump_obj_start(struct netlink_callback *cb)
> +{
> + const struct nlattr * const *nla = cb->data;
> + struct nft_obj_filter *filter = NULL;
> +
> + if (nla[NFTA_OBJ_TABLE] ||
> + nla[NFTA_OBJ_TYPE]) {
> + filter = nft_obj_filter_alloc(nla);
> + if (IS_ERR(filter))
> + return -ENOMEM;
> + }
> +
> + cb->data = filter;
> + return 0;
> +}
> +
> /* called with rcu_read_lock held */
> static int nf_tables_getobj(struct net *net, struct sock *nlsk,
> struct sk_buff *skb, const struct nlmsghdr
> *nlh,
> @@ -5028,21 +5047,13 @@ static int nf_tables_getobj(struct net *net,
> struct sock *nlsk,
>
> if (nlh->nlmsg_flags & NLM_F_DUMP) {
> struct netlink_dump_control c = {
> + .start = nf_tables_dump_obj_start,
> .dump = nf_tables_dump_obj,
> .done = nf_tables_dump_obj_done,
> .module = THIS_MODULE,
> + .data = (void *)nla,
> };
>
> - if (nla[NFTA_OBJ_TABLE] ||
> - nla[NFTA_OBJ_TYPE]) {
> - struct nft_obj_filter *filter;
> -
> - filter = nft_obj_filter_alloc(nla);
> - if (IS_ERR(filter))
> - return -ENOMEM;
> -
> - c.data = filter;
> - }
> return nft_netlink_dump_start_rcu(nlsk, skb, nlh, &c);
> }
>
>
