[NETLINK]: allocate group bitmaps dynamically

Allow changing the number of groups for a netlink family
after it has been created, use RCU to protect the listeners
bitmap keeping netlink_has_listeners() lock-free.

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Acked-by: Patrick McHardy <kaber@trash.net>
Acked-by: Jamal Hadi Salim <hadi@cyberus.ca>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/include/linux/netlink.h b/include/linux/netlink.h
index 2e23353c28a54c5757269d16b3491076a344134f..b971ddd24090e4c9f496a88ec7eb8419b6416259 100644 (file)
--- a/include/linux/netlink.h
+++ b/include/linux/netlink.h
@@ -161,6 +161,7 @@ extern struct sock *netlink_kernel_create(int unit, unsigned int groups,
                                          void (*input)(struct sock *sk, int len),
                                          struct mutex *cb_mutex,
                                          struct module *module);
+extern int netlink_change_ngroups(struct sock *sk, unsigned int groups);
 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 641cfbc278d8534acbc7514bc4a5d3d31c255fec..c386eaf6ad5b4000e7aab7c8f98333fe6ffc0f0a 100644 (file)
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -62,6 +62,7 @@
 #include <net/netlink.h>
 
 #define NLGRPSZ(x)     (ALIGN(x, sizeof(unsigned long) * 8) / 8)
+#define NLGRPLONGS(x)  (NLGRPSZ(x)/sizeof(unsigned long))
 
 struct netlink_sock {
        /* struct sock has to be the first member of netlink_sock */
@@ -314,10 +315,12 @@ netlink_update_listeners(struct sock *sk)
        unsigned long mask;
        unsigned int i;
 
-       for (i = 0; i < NLGRPSZ(tbl->groups)/sizeof(unsigned long); i++) {
+       for (i = 0; i < NLGRPLONGS(tbl->groups); i++) {
                mask = 0;
-               sk_for_each_bound(sk, node, &tbl->mc_list)
-                       mask |= nlk_sk(sk)->groups[i];
+               sk_for_each_bound(sk, node, &tbl->mc_list) {
+                       if (i < NLGRPLONGS(nlk_sk(sk)->ngroups))
+                               mask |= nlk_sk(sk)->groups[i];
+               }
                tbl->listeners[i] = mask;
        }
        /* this function is only called with the netlink table "grabbed", which
@@ -555,26 +558,37 @@ netlink_update_subscriptions(struct sock *sk, unsigned int subscriptions)
        nlk->subscriptions = subscriptions;
 }
 
-static int netlink_alloc_groups(struct sock *sk)
+static int netlink_realloc_groups(struct sock *sk)
 {
        struct netlink_sock *nlk = nlk_sk(sk);
        unsigned int groups;
+       unsigned long *new_groups;
        int err = 0;
 
-       netlink_lock_table();
+       netlink_table_grab();
+
        groups = nl_table[sk->sk_protocol].groups;
-       if (!nl_table[sk->sk_protocol].registered)
+       if (!nl_table[sk->sk_protocol].registered) {
                err = -ENOENT;
-       netlink_unlock_table();
+               goto out_unlock;
+       }
 
-       if (err)
-               return err;
+       if (nlk->ngroups >= groups)
+               goto out_unlock;
 
-       nlk->groups = kzalloc(NLGRPSZ(groups), GFP_KERNEL);
-       if (nlk->groups == NULL)
-               return -ENOMEM;
+       new_groups = krealloc(nlk->groups, NLGRPSZ(groups), GFP_ATOMIC);
+       if (new_groups == NULL) {
+               err = -ENOMEM;
+               goto out_unlock;
+       }
+       memset((char*)new_groups + NLGRPSZ(nlk->ngroups), 0,
+              NLGRPSZ(groups) - NLGRPSZ(nlk->ngroups));
+
+       nlk->groups = new_groups;
        nlk->ngroups = groups;
-       return 0;
+ out_unlock:
+       netlink_table_ungrab();
+       return err;
 }
 
 static int netlink_bind(struct socket *sock, struct sockaddr *addr, int addr_len)
@@ -591,11 +605,9 @@ static int netlink_bind(struct socket *sock, struct sockaddr *addr, int addr_len
        if (nladdr->nl_groups) {
                if (!netlink_capable(sock, NL_NONROOT_RECV))
                        return -EPERM;
-               if (nlk->groups == NULL) {
-                       err = netlink_alloc_groups(sk);
-                       if (err)
-                               return err;
-               }
+               err = netlink_realloc_groups(sk);
+               if (err)
+                       return err;
        }
 
        if (nlk->pid) {
@@ -839,10 +851,18 @@ retry:
 int netlink_has_listeners(struct sock *sk, unsigned int group)
 {
        int res = 0;
+       unsigned long *listeners;
 
        BUG_ON(!(nlk_sk(sk)->flags & NETLINK_KERNEL_SOCKET));
+
+       rcu_read_lock();
+       listeners = rcu_dereference(nl_table[sk->sk_protocol].listeners);
+
        if (group - 1 < nl_table[sk->sk_protocol].groups)
-               res = test_bit(group - 1, nl_table[sk->sk_protocol].listeners);
+               res = test_bit(group - 1, listeners);
+
+       rcu_read_unlock();
+
        return res;
 }
 EXPORT_SYMBOL_GPL(netlink_has_listeners);
@@ -1037,11 +1057,9 @@ static int netlink_setsockopt(struct socket *sock, int level, int optname,
 
                if (!netlink_capable(sock, NL_NONROOT_RECV))
                        return -EPERM;
-               if (nlk->groups == NULL) {
-                       err = netlink_alloc_groups(sk);
-                       if (err)
-                               return err;
-               }
+               err = netlink_realloc_groups(sk);
+               if (err)
+                       return err;
                if (!val || val - 1 >= nlk->ngroups)
                        return -EINVAL;
                netlink_table_grab();
@@ -1328,6 +1346,46 @@ out_sock_release:
        return NULL;
 }
 
+/**
+ * netlink_change_ngroups - change number of multicast groups
+ *
+ * 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.
+ *
+ * @sk: The kernel netlink socket, as returned by netlink_kernel_create().
+ * @groups: The new number of groups.
+ */
+int netlink_change_ngroups(struct sock *sk, unsigned int groups)
+{
+       unsigned long *listeners, *old = NULL;
+       struct netlink_table *tbl = &nl_table[sk->sk_protocol];
+       int err = 0;
+
+       if (groups < 32)
+               groups = 32;
+
+       netlink_table_grab();
+       if (NLGRPSZ(tbl->groups) < NLGRPSZ(groups)) {
+               listeners = kzalloc(NLGRPSZ(groups), GFP_ATOMIC);
+               if (!listeners) {
+                       err = -ENOMEM;
+                       goto out_ungrab;
+               }
+               old = tbl->listeners;
+               memcpy(listeners, old, NLGRPSZ(tbl->groups));
+               rcu_assign_pointer(tbl->listeners, listeners);
+       }
+       tbl->groups = groups;
+
+ out_ungrab:
+       netlink_table_ungrab();
+       synchronize_rcu();
+       kfree(old);
+       return err;
+}
+EXPORT_SYMBOL(netlink_change_ngroups);
+
 void netlink_set_nonroot(int protocol, unsigned int flags)
 {
        if ((unsigned int)protocol < MAX_LINKS)