netlink: add nlk->netlink_bind hook for module auto-loading

This patch adds a hook in the binding path of netlink.

This is used by ctnetlink to allow module autoloading for the case
in which one user executes:

 conntrack -E

So far, this resulted in nfnetlink loaded, but not
nf_conntrack_netlink.

I have received in the past many complains on this behaviour.

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 48 insertions, 0 deletions

diff --git a/net/netfilter/nfnetlink.c b/net/netfilter/nfnetlink.c
index 700e4616a098..5a2132b97fe9 100644
--- a/net/netfilter/nfnetlink.c
+++ b/net/netfilter/nfnetlink.c
@@ -39,6 +39,15 @@ static char __initdata nfversion[] = "0.30";
 static const struct nfnetlink_subsystem __rcu *subsys_table[NFNL_SUBSYS_COUNT];
 static DEFINE_MUTEX(nfnl_mutex);
 
+static const int nfnl_group2type[NFNLGRP_MAX+1] = {
+        [NFNLGRP_CONNTRACK_NEW]         = NFNL_SUBSYS_CTNETLINK,
+        [NFNLGRP_CONNTRACK_UPDATE]      = NFNL_SUBSYS_CTNETLINK,
+        [NFNLGRP_CONNTRACK_DESTROY]     = NFNL_SUBSYS_CTNETLINK,
+        [NFNLGRP_CONNTRACK_EXP_NEW]     = NFNL_SUBSYS_CTNETLINK_EXP,
+        [NFNLGRP_CONNTRACK_EXP_UPDATE]  = NFNL_SUBSYS_CTNETLINK_EXP,
+        [NFNLGRP_CONNTRACK_EXP_DESTROY] = NFNL_SUBSYS_CTNETLINK_EXP,
+};
+
 void nfnl_lock(void)
 {
         mutex_lock(&nfnl_mutex);
@@ -200,12 +209,32 @@ static void nfnetlink_rcv(struct sk_buff *skb)
         netlink_rcv_skb(skb, &nfnetlink_rcv_msg);
 }
 
+#ifdef CONFIG_MODULES
+static void nfnetlink_bind(int group)
+{
+        const struct nfnetlink_subsystem *ss;
+        int type = nfnl_group2type[group];
+
+        rcu_read_lock();
+        ss = nfnetlink_get_subsys(type);
+        if (!ss) {
+                rcu_read_unlock();
+                request_module("nfnetlink-subsys-%d", type);
+                return;
+        }
+        rcu_read_unlock();
+}
+#endif
+
 static int __net_init nfnetlink_net_init(struct net *net)
 {
         struct sock *nfnl;
         struct netlink_kernel_cfg cfg = {
                 .groups = NFNLGRP_MAX,
                 .input  = nfnetlink_rcv,
+#ifdef CONFIG_MODULES
+                .bind   = nfnetlink_bind,
+#endif
         };
 
         nfnl = netlink_kernel_create(net, NETLINK_NETFILTER, THIS_MODULE, &cfg);
diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
index 43a124feaad8..5463969da45b 100644
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -80,6 +80,7 @@ struct netlink_sock {
         struct mutex            *cb_mutex;
         struct mutex            cb_def_mutex;
         void                    (*netlink_rcv)(struct sk_buff *skb);
+        void                    (*netlink_bind)(int group);
         struct module           *module;
 };
 
@@ -124,6 +125,7 @@ struct netlink_table {
         unsigned int            groups;
         struct mutex            *cb_mutex;
         struct module           *module;
+        void                    (*bind)(int group);
         int                     registered;
 };
 
@@ -444,6 +446,7 @@ static int netlink_create(struct net *net, struct socket *sock, int protocol,
         struct module *module = NULL;
         struct mutex *cb_mutex;
         struct netlink_sock *nlk;
+        void (*bind)(int group);
         int err = 0;
 
         sock->state = SS_UNCONNECTED;
@@ -468,6 +471,7 @@ static int netlink_create(struct net *net, struct socket *sock, int protocol,
         else
                 err = -EPROTONOSUPPORT;
         cb_mutex = nl_table[protocol].cb_mutex;
+        bind = nl_table[protocol].bind;
         netlink_unlock_table();
 
         if (err < 0)
@@ -483,6 +487,7 @@ static int netlink_create(struct net *net, struct socket *sock, int protocol,
 
         nlk = nlk_sk(sock->sk);
         nlk->module = module;
+        nlk->netlink_bind = bind;
 out:
         return err;
 
@@ -683,6 +688,15 @@ static int netlink_bind(struct socket *sock, struct sockaddr *addr,
         netlink_update_listeners(sk);
         netlink_table_ungrab();
 
+        if (nlk->netlink_bind && nlk->groups[0]) {
+                int i;
+
+                for (i=0; i<nlk->ngroups; i++) {
+                        if (test_bit(i, nlk->groups))
+                                nlk->netlink_bind(i);
+                }
+        }
+
         return 0;
 }
 
@@ -1239,6 +1253,10 @@ static int netlink_setsockopt(struct socket *sock, int level, int optname,
                 netlink_update_socket_mc(nlk, val,
                                          optname == NETLINK_ADD_MEMBERSHIP);
                 netlink_table_ungrab();
+
+                if (nlk->netlink_bind)
+                        nlk->netlink_bind(val);
+
                 err = 0;
                 break;
         }
@@ -1559,6 +1577,7 @@ netlink_kernel_create(struct net *net, int unit,
                 rcu_assign_pointer(nl_table[unit].listeners, listeners);
                 nl_table[unit].cb_mutex = cb_mutex;
                 nl_table[unit].module = module;
+                nl_table[unit].bind = cfg ? cfg->bind : NULL;
                 nl_table[unit].registered = 1;
         } else {
                 kfree(listeners);