[PATCH] netlink: allocate group bitmaps dynamically

Johannes Berg
2007-07-04T11:44:49Z

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>

---
include/linux/netlink.h | 1
net/netlink/af_netlink.c | 86 +++++++++++++++++++++++++++++++++++------------
2 files changed, 66 insertions(+), 21 deletions(-)

--- wireless-dev.orig/net/netlink/af_netlink.c 2007-07-03 12:21:52.161407395 +0200
+++ wireless-dev/net/netlink/af_netlink.c 2007-07-03 18:31:12.371730691 +0200
@@ -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
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();
groups = nl_table[sk->sk_protocol].groups;
if (!nl_table[sk->sk_protocol].registered)
err = -ENOENT;
- netlink_unlock_table();

if (err)
- return err;
+ goto out_unlock;

- nlk->groups = kzalloc(NLGRPSZ(groups), GFP_KERNEL);
- if (nlk->groups == NULL)
- return -ENOMEM;
+ if (nlk->ngroups >= groups)
+ goto out_unlock;
+
+ new_groups = krealloc(nlk->groups, NLGRPSZ(groups), GFP_KERNEL);
+ 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_unlock_table();
+ 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 *s
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 soc

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 +1346,32 @@ out_sock_release:
return NULL;
}

+int netlink_change_ngroups(int unit, unsigned int groups)
+{
+ unsigned long *listeners, old = NULL;
+ int err = 0;
+
+ netlink_table_grab();
+ if (NLGRPSZ(nl_table[unit].groups) < NLGRPSZ(groups)) {
+ listeners = kzalloc(NLGRPSZ(groups), GFP_ATOMIC);
+ if (!listeners) {
+ err = -ENOMEM;
+ goto out_ungrab;
+ }
+ old = nl_table[unit].listeners;
+ memcpy(listeners, old, NLGRPSZ(nl_table[unit].groups));
+ rcu_assign_pointer(nl_table[unit].listeners, listeners);
+ }
+ nl_table[unit].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)
--- wireless-dev.orig/include/linux/netlink.h 2007-07-03 12:21:50.401407395 +0200
+++ wireless-dev/include/linux/netlink.h 2007-07-03 18:30:49.831730691 +0200
@@ -161,6 +161,7 @@ extern struct sock *netlink_kernel_creat
void (*input)(struct sock *sk, int len),
struct mutex *cb_mutex,
struct module *module);
+extern int netlink_change_ngroups(int unit, 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);