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 <fw@xxxxxxxxx>:
David Miller <davem@xxxxxxxxxxxxx> wrote:
> From: Florian Westphal <fw@xxxxxxxxx>
> 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 = ""> + 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 = "" *)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 = "">- }
return nft_netlink_dump_start_rcu(nlsk, skb, nlh, &c);
}
