2 files changed, 46 insertions, 12 deletions

diff --git a/include/linux/netlink.h b/include/linux/netlink.h
index b971ddd24090..83d8239f0cce 100644
--- a/include/linux/netlink.h
+++ b/include/linux/netlink.h
@@ -162,6 +162,7 @@ extern struct sock *netlink_kernel_create(int unit, unsigned int groups,
                                           struct mutex *cb_mutex,
                                           struct module *module);
 extern int netlink_change_ngroups(struct sock *sk, unsigned int groups);
+extern void netlink_clear_multicast_users(struct sock *sk, unsigned int group);
 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);
diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
index c386eaf6ad5b..5681ce3aebca 100644
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -1027,6 +1027,23 @@ void netlink_set_err(struct sock *ssk, u32 pid, u32 group, int code)
         read_unlock(&nl_table_lock);
 }
 
+/* must be called with netlink table grabbed */
+static void netlink_update_socket_mc(struct netlink_sock *nlk,
+                                     unsigned int group,
+                                     int is_new)
+{
+        int old, new = !!is_new, subscriptions;
+
+        old = test_bit(group - 1, nlk->groups);
+        subscriptions = nlk->subscriptions - old + new;
+        if (new)
+                __set_bit(group - 1, nlk->groups);
+        else
+                __clear_bit(group - 1, nlk->groups);
+        netlink_update_subscriptions(&nlk->sk, subscriptions);
+        netlink_update_listeners(&nlk->sk);
+}
+
 static int netlink_setsockopt(struct socket *sock, int level, int optname,
                               char __user *optval, int optlen)
 {
@@ -1052,9 +1069,6 @@ static int netlink_setsockopt(struct socket *sock, int level, int optname,
                 break;
         case NETLINK_ADD_MEMBERSHIP:
         case NETLINK_DROP_MEMBERSHIP: {
-                unsigned int subscriptions;
-                int old, new = optname == NETLINK_ADD_MEMBERSHIP ? 1 : 0;
-
                 if (!netlink_capable(sock, NL_NONROOT_RECV))
                         return -EPERM;
                 err = netlink_realloc_groups(sk);
@@ -1063,14 +1077,8 @@ static int netlink_setsockopt(struct socket *sock, int level, int optname,
                 if (!val || val - 1 >= nlk->ngroups)
                         return -EINVAL;
                 netlink_table_grab();
-                old = test_bit(val - 1, nlk->groups);
-                subscriptions = nlk->subscriptions - old + new;
-                if (new)
-                        __set_bit(val - 1, nlk->groups);
-                else
-                        __clear_bit(val - 1, nlk->groups);
-                netlink_update_subscriptions(sk, subscriptions);
-                netlink_update_listeners(sk);
+                netlink_update_socket_mc(nlk, val,
+                                         optname == NETLINK_ADD_MEMBERSHIP);
                 netlink_table_ungrab();
                 err = 0;
                 break;
@@ -1351,7 +1359,9 @@ out_sock_release:
  *
  * This changes the number of multicast groups that are available
  * on a certain netlink family. Note that it is not possible to
- * change the number of groups to below 32.
+ * change the number of groups to below 32. Also note that it does
+ * not implicitly call netlink_clear_multicast_users() when the
+ * number of groups is reduced.
  *
  * @sk: The kernel netlink socket, as returned by netlink_kernel_create().
  * @groups: The new number of groups.
@@ -1386,6 +1396,29 @@ int netlink_change_ngroups(struct sock *sk, unsigned int groups)
 }
 EXPORT_SYMBOL(netlink_change_ngroups);
 
+/**
+ * netlink_clear_multicast_users - kick off multicast listeners
+ *
+ * This function removes all listeners from the given group.
+ * @ksk: The kernel netlink socket, as returned by
+ *      netlink_kernel_create().
+ * @group: The multicast group to clear.
+ */
+void netlink_clear_multicast_users(struct sock *ksk, unsigned int group)
+{
+        struct sock *sk;
+        struct hlist_node *node;
+        struct netlink_table *tbl = &nl_table[ksk->sk_protocol];
+
+        netlink_table_grab();
+
+        sk_for_each_bound(sk, node, &tbl->mc_list)
+                netlink_update_socket_mc(nlk_sk(sk), group, 0);
+
+        netlink_table_ungrab();
+}
+EXPORT_SYMBOL(netlink_clear_multicast_users);
+
 void netlink_set_nonroot(int protocol, unsigned int flags)
 {
         if ((unsigned int)protocol < MAX_LINKS)