2 files changed, 49 insertions, 4 deletions

diff --git a/include/linux/netlink.h b/include/linux/netlink.h
index c256ebe2a7b4..f8f3d1c927f8 100644
--- a/include/linux/netlink.h
+++ b/include/linux/netlink.h
@@ -151,6 +151,7 @@ struct netlink_skb_parms
 
 extern struct sock *netlink_kernel_create(int unit, unsigned int groups, void (*input)(struct sock *sk, int len), struct module *module);
 extern void netlink_ack(struct sk_buff *in_skb, struct nlmsghdr *nlh, int err);
+extern int netlink_has_listeners(struct sock *sk, unsigned int group);
 extern int netlink_unicast(struct sock *ssk, struct sk_buff *skb, __u32 pid, int nonblock);
 extern int netlink_broadcast(struct sock *ssk, struct sk_buff *skb, __u32 pid,
                              __u32 group, gfp_t allocation);
diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
index 59dc7d140600..d00a9034cb5f 100644
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -106,6 +106,7 @@ struct nl_pid_hash {
 struct netlink_table {
         struct nl_pid_hash hash;
         struct hlist_head mc_list;
+        unsigned long *listeners;
         unsigned int nl_nonroot;
         unsigned int groups;
         struct module *module;
@@ -296,6 +297,24 @@ static inline int nl_pid_hash_dilute(struct nl_pid_hash *hash, int len)
 
 static const struct proto_ops netlink_ops;
 
+static void
+netlink_update_listeners(struct sock *sk)
+{
+        struct netlink_table *tbl = &nl_table[sk->sk_protocol];
+        struct hlist_node *node;
+        unsigned long mask;
+        unsigned int i;
+
+        for (i = 0; i < NLGRPSZ(tbl->groups)/sizeof(unsigned long); i++) {
+                mask = 0;
+                sk_for_each_bound(sk, node, &tbl->mc_list)
+                        mask |= nlk_sk(sk)->groups[i];
+                tbl->listeners[i] = mask;
+        }
+        /* this function is only called with the netlink table "grabbed", which
+         * makes sure updates are visible before bind or setsockopt return. */
+}
+
 static int netlink_insert(struct sock *sk, u32 pid)
 {
         struct nl_pid_hash *hash = &nl_table[sk->sk_protocol].hash;
@@ -456,12 +475,14 @@ static int netlink_release(struct socket *sock)
         if (nlk->module)
                 module_put(nlk->module);
 
+        netlink_table_grab();
         if (nlk->flags & NETLINK_KERNEL_SOCKET) {
-                netlink_table_grab();
+                kfree(nl_table[sk->sk_protocol].listeners);
                 nl_table[sk->sk_protocol].module = NULL;
                 nl_table[sk->sk_protocol].registered = 0;
-                netlink_table_ungrab();
-        }
+        } else if (nlk->subscriptions)
+                netlink_update_listeners(sk);
+        netlink_table_ungrab();
 
         kfree(nlk->groups);
         nlk->groups = NULL;
@@ -589,6 +610,7 @@ static int netlink_bind(struct socket *sock, struct sockaddr *addr, int addr_len
                                          hweight32(nladdr->nl_groups) -
                                          hweight32(nlk->groups[0]));
         nlk->groups[0] = (nlk->groups[0] & ~0xffffffffUL) | nladdr->nl_groups; 
+        netlink_update_listeners(sk);
         netlink_table_ungrab();
 
         return 0;
@@ -807,6 +829,17 @@ retry:
         return netlink_sendskb(sk, skb, ssk->sk_protocol);
 }
 
+int netlink_has_listeners(struct sock *sk, unsigned int group)
+{
+        int res = 0;
+
+        BUG_ON(!(nlk_sk(sk)->flags & NETLINK_KERNEL_SOCKET));
+        if (group - 1 < nl_table[sk->sk_protocol].groups)
+                res = test_bit(group - 1, nl_table[sk->sk_protocol].listeners);
+        return res;
+}
+EXPORT_SYMBOL_GPL(netlink_has_listeners);
+
 static __inline__ int netlink_broadcast_deliver(struct sock *sk, struct sk_buff *skb)
 {
         struct netlink_sock *nlk = nlk_sk(sk);
@@ -1011,6 +1044,7 @@ static int netlink_setsockopt(struct socket *sock, int level, int optname,
                 else
                         __clear_bit(val - 1, nlk->groups);
                 netlink_update_subscriptions(sk, subscriptions);
+                netlink_update_listeners(sk);
                 netlink_table_ungrab();
                 err = 0;
                 break;
@@ -1237,6 +1271,7 @@ netlink_kernel_create(int unit, unsigned int groups,
         struct socket *sock;
         struct sock *sk;
         struct netlink_sock *nlk;
+        unsigned long *listeners = NULL;
 
         if (!nl_table)
                 return NULL;
@@ -1250,6 +1285,13 @@ netlink_kernel_create(int unit, unsigned int groups,
         if (__netlink_create(sock, unit) < 0)
                 goto out_sock_release;
 
+        if (groups < 32)
+                groups = 32;
+
+        listeners = kzalloc(NLGRPSZ(groups), GFP_KERNEL);
+        if (!listeners)
+                goto out_sock_release;
+
         sk = sock->sk;
         sk->sk_data_ready = netlink_data_ready;
         if (input)
@@ -1262,7 +1304,8 @@ netlink_kernel_create(int unit, unsigned int groups,
         nlk->flags |= NETLINK_KERNEL_SOCKET;
 
         netlink_table_grab();
-        nl_table[unit].groups = groups < 32 ? 32 : groups;
+        nl_table[unit].groups = groups;
+        nl_table[unit].listeners = listeners;
         nl_table[unit].module = module;
         nl_table[unit].registered = 1;
         netlink_table_ungrab();
@@ -1270,6 +1313,7 @@ netlink_kernel_create(int unit, unsigned int groups,
         return sk;
 
 out_sock_release:
+        kfree(listeners);
         sock_release(sock);
         return NULL;
 }