Hi Florian,
a few questions, comments.
On Fri, Aug 05, 2022 at 04:47:45PM +0200, Florian Westphal wrote:
> To avoid allocation of the conntrack extension area when possible,
> the default behaviour was changed to only allocate the event extension
> if a userspace program is subscribed to a notification group.
>
> Problem is that while 'conntrack -E' does enable the event allocation
> behind the scenes, 'conntrack -E expect' does not: no expectation events
> are delivered unless user sets
> "net.netfilter.nf_conntrack_events" back to 1 (always on).
>
> Fix the autodetection to also consider EXP type group.
>
> We need to track the 6 event groups (3+3, new/update/destroy for events and
> for expectations each) independently, else we'd disable events again
> if an expectation group becomes empty while there is still an active
> event group.
>
> Fixes: 2794cdb0b97b ("netfilter: nfnetlink: allow to detect if ctnetlink listeners exist")
> Reported-by: Yi Chen <yiche@xxxxxxxxxx>
> Signed-off-by: Florian Westphal <fw@xxxxxxxxx>
> ---
> include/net/netns/conntrack.h | 2 +-
> net/netfilter/nfnetlink.c | 83 ++++++++++++++++++++++++++++++-----
> 2 files changed, 72 insertions(+), 13 deletions(-)
>
> diff --git a/include/net/netns/conntrack.h b/include/net/netns/conntrack.h
> index 0677cd3de034..c396a3862e80 100644
> --- a/include/net/netns/conntrack.h
> +++ b/include/net/netns/conntrack.h
> @@ -95,7 +95,7 @@ struct nf_ip_net {
>
> struct netns_ct {
> #ifdef CONFIG_NF_CONNTRACK_EVENTS
> - bool ctnetlink_has_listener;
> + u8 ctnetlink_has_listener;
so now ctnetlink_has_listener is a bitmask, right?
> bool ecache_dwork_pending;
> #endif
> u8 sysctl_log_invalid; /* Log invalid packets */
> diff --git a/net/netfilter/nfnetlink.c b/net/netfilter/nfnetlink.c
> index c24b1240908f..6c268f1c201a 100644
> --- a/net/netfilter/nfnetlink.c
> +++ b/net/netfilter/nfnetlink.c
> @@ -44,6 +44,10 @@ MODULE_DESCRIPTION("Netfilter messages via netlink socket");
>
> static unsigned int nfnetlink_pernet_id __read_mostly;
>
> +#ifdef CONFIG_NF_CONNTRACK_EVENTS
> +static DEFINE_SPINLOCK(nfnl_grp_active_lock);
> +#endif
> +
> struct nfnl_net {
> struct sock *nfnl;
> };
> @@ -654,6 +658,44 @@ static void nfnetlink_rcv(struct sk_buff *skb)
> netlink_rcv_skb(skb, nfnetlink_rcv_msg);
> }
>
> +static void nfnetlink_bind_event(struct net *net, unsigned int group)
> +{
> +#ifdef CONFIG_NF_CONNTRACK_EVENTS
> + int type, group_bit;
> + u8 v;
> +
> + /* ctnetlink_has_listener is u8, all NFNLGRP_CONNTRACK_* groups
> + * coming from userspace are < 8.
Nit. is ctnetlink_has_listener relevant in the comment? It reads a bit
confusing.
> + */
> + if (group >= 8)
Nit.
enum nfnetlink_groups has __NFNLGRP_MAX, which is 9.
This skips NFNLGRP_NFTRACE which is the last one in the array, not a
big deal since the switch (type) results in return; but better fix
this for the future?
> + return;
> +
> + type = nfnl_group2type[group];
> +
> + switch (type) {
> + case NFNL_SUBSYS_CTNETLINK:
> + break;
> + case NFNL_SUBSYS_CTNETLINK_EXP:
> + break;
> + default:
> + return;
> + }
> +
> + group_bit = (1 << group);
> +
> + spin_lock(&nfnl_grp_active_lock);
suggestion: maybe mutex instead?
> + v = READ_ONCE(net->ct.ctnetlink_has_listener);
> + if ((v & group_bit) == 0) {
> + v |= group_bit;
> +
> + /* read concurrently without nfnl_grp_active_lock held. */
> + WRITE_ONCE(net->ct.ctnetlink_has_listener, v);
> + }
> +
> + spin_unlock(&nfnl_grp_active_lock);
> +#endif
> +}
> +
> static int nfnetlink_bind(struct net *net, int group)
> {
> const struct nfnetlink_subsystem *ss;
> @@ -670,28 +712,45 @@ static int nfnetlink_bind(struct net *net, int group)
> if (!ss)
> request_module_nowait("nfnetlink-subsys-%d", type);
>
> -#ifdef CONFIG_NF_CONNTRACK_EVENTS
> - if (type == NFNL_SUBSYS_CTNETLINK) {
> - nfnl_lock(NFNL_SUBSYS_CTNETLINK);
> - WRITE_ONCE(net->ct.ctnetlink_has_listener, true);
> - nfnl_unlock(NFNL_SUBSYS_CTNETLINK);
> - }
> -#endif
> + nfnetlink_bind_event(net, group);
> return 0;
> }
>
> static void nfnetlink_unbind(struct net *net, int group)
> {
> #ifdef CONFIG_NF_CONNTRACK_EVENTS
> + int type, group_bit;
> +
> if (group <= NFNLGRP_NONE || group > NFNLGRP_MAX)
> return;
>
> - if (nfnl_group2type[group] == NFNL_SUBSYS_CTNETLINK) {
> - nfnl_lock(NFNL_SUBSYS_CTNETLINK);
> - if (!nfnetlink_has_listeners(net, group))
> - WRITE_ONCE(net->ct.ctnetlink_has_listener, false);
> - nfnl_unlock(NFNL_SUBSYS_CTNETLINK);
> + type = nfnl_group2type[group];
> +
> + switch (type) {
> + case NFNL_SUBSYS_CTNETLINK:
> + break;
> + case NFNL_SUBSYS_CTNETLINK_EXP:
> + break;
> + default:
> + return;
> + }
> +
> + /* ctnetlink_has_listener is u8 */
> + if (group >= 8)
Same here?
> + return;
> +
> + group_bit = (1 << group);
> +
> + spin_lock(&nfnl_grp_active_lock);
> + if (!nfnetlink_has_listeners(net, group)) {
> + u8 v = READ_ONCE(net->ct.ctnetlink_has_listener);
> +
> + v &= ~group_bit;
> +
> + /* read concurrently without nfnl_grp_active_lock held. */
> + WRITE_ONCE(net->ct.ctnetlink_has_listener, v);
> }
> + spin_unlock(&nfnl_grp_active_lock);
> #endif
> }
>
> --
> 2.35.1
>
