[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>

2 files changed, 83 insertions, 24 deletions

diff --git a/include/linux/netlink.h b/include/linux/netlink.h
index 2e23353c28a5..b971ddd24090 100644
--- 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 641cfbc278d8..c386eaf6ad5b 100644
--- 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)