[NETLINK]: Switch cb_lock spinlock to mutex and allow to override it

Switch cb_lock to mutex and allow netlink kernel users to override it
with a subsystem specific mutex for consistent locking in dump callbacks.
All netlink_dump_start users have been audited not to rely on any
side-effects of the previously used spinlock.

Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 24 insertions, 16 deletions

diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
index 2cbf1682f63..ec16c9b7b3b 100644
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -56,6 +56,7 @@
 #include <linux/types.h>
 #include <linux/audit.h>
 #include <linux/selinux.h>
+#include <linux/mutex.h>
 
 #include <net/sock.h>
 #include <net/scm.h>
@@ -76,7 +77,8 @@ struct netlink_sock {
 	unsigned long		state;
 	wait_queue_head_t	wait;
 	struct netlink_callback	*cb;
-	spinlock_t		cb_lock;
+	struct mutex		*cb_mutex;
+	struct mutex		cb_def_mutex;
 	void			(*data_ready)(struct sock *sk, int bytes);
 	struct module		*module;
 };
@@ -108,6 +110,7 @@ struct netlink_table {
 	unsigned long *listeners;
 	unsigned int nl_nonroot;
 	unsigned int groups;
+	struct mutex *cb_mutex;
 	struct module *module;
 	int registered;
 };
@@ -370,7 +373,8 @@ static struct proto netlink_proto = {
 	.obj_size = sizeof(struct netlink_sock),
 };
 
-static int __netlink_create(struct socket *sock, int protocol)
+static int __netlink_create(struct socket *sock, struct mutex *cb_mutex,
+			    int protocol)
 {
 	struct sock *sk;
 	struct netlink_sock *nlk;
@@ -384,7 +388,8 @@ static int __netlink_create(struct socket *sock, int protocol)
 	sock_init_data(sock, sk);
 
 	nlk = nlk_sk(sk);
-	spin_lock_init(&nlk->cb_lock);
+	nlk->cb_mutex = cb_mutex ? : &nlk->cb_def_mutex;
+	mutex_init(nlk->cb_mutex);
 	init_waitqueue_head(&nlk->wait);
 
 	sk->sk_destruct = netlink_sock_destruct;
@@ -395,6 +400,7 @@ static int __netlink_create(struct socket *sock, int protocol)
 static int netlink_create(struct socket *sock, int protocol)
 {
 	struct module *module = NULL;
+	struct mutex *cb_mutex;
 	struct netlink_sock *nlk;
 	int err = 0;
 
@@ -417,9 +423,10 @@ static int netlink_create(struct socket *sock, int protocol)
 	if (nl_table[protocol].registered &&
 	    try_module_get(nl_table[protocol].module))
 		module = nl_table[protocol].module;
+	cb_mutex = nl_table[protocol].cb_mutex;
 	netlink_unlock_table();
 
-	if ((err = __netlink_create(sock, protocol)) < 0)
+	if ((err = __netlink_create(sock, cb_mutex, protocol)) < 0)
 		goto out_module;
 
 	nlk = nlk_sk(sock->sk);
@@ -444,14 +451,14 @@ static int netlink_release(struct socket *sock)
 	sock_orphan(sk);
 	nlk = nlk_sk(sk);
 
-	spin_lock(&nlk->cb_lock);
+	mutex_lock(nlk->cb_mutex);
 	if (nlk->cb) {
 		if (nlk->cb->done)
 			nlk->cb->done(nlk->cb);
 		netlink_destroy_callback(nlk->cb);
 		nlk->cb = NULL;
 	}
-	spin_unlock(&nlk->cb_lock);
+	mutex_unlock(nlk->cb_mutex);
 
 	/* OK. Socket is unlinked, and, therefore,
 	   no new packets will arrive */
@@ -1266,7 +1273,7 @@ static void netlink_data_ready(struct sock *sk, int len)
 struct sock *
 netlink_kernel_create(int unit, unsigned int groups,
 		      void (*input)(struct sock *sk, int len),
-		      struct module *module)
+		      struct mutex *cb_mutex, struct module *module)
 {
 	struct socket *sock;
 	struct sock *sk;
@@ -1281,7 +1288,7 @@ netlink_kernel_create(int unit, unsigned int groups,
 	if (sock_create_lite(PF_NETLINK, SOCK_DGRAM, unit, &sock))
 		return NULL;
 
-	if (__netlink_create(sock, unit) < 0)
+	if (__netlink_create(sock, cb_mutex, unit) < 0)
 		goto out_sock_release;
 
 	if (groups < 32)
@@ -1305,6 +1312,7 @@ netlink_kernel_create(int unit, unsigned int groups,
 	netlink_table_grab();
 	nl_table[unit].groups = groups;
 	nl_table[unit].listeners = listeners;
+	nl_table[unit].cb_mutex = cb_mutex;
 	nl_table[unit].module = module;
 	nl_table[unit].registered = 1;
 	netlink_table_ungrab();
@@ -1347,7 +1355,7 @@ static int netlink_dump(struct sock *sk)
 	if (!skb)
 		goto errout;
 
-	spin_lock(&nlk->cb_lock);
+	mutex_lock(nlk->cb_mutex);
 
 	cb = nlk->cb;
 	if (cb == NULL) {
@@ -1358,7 +1366,7 @@ static int netlink_dump(struct sock *sk)
 	len = cb->dump(skb, cb);
 
 	if (len > 0) {
-		spin_unlock(&nlk->cb_lock);
+		mutex_unlock(nlk->cb_mutex);
 		skb_queue_tail(&sk->sk_receive_queue, skb);
 		sk->sk_data_ready(sk, len);
 		return 0;
@@ -1376,13 +1384,13 @@ static int netlink_dump(struct sock *sk)
 	if (cb->done)
 		cb->done(cb);
 	nlk->cb = NULL;
-	spin_unlock(&nlk->cb_lock);
+	mutex_unlock(nlk->cb_mutex);
 
 	netlink_destroy_callback(cb);
 	return 0;
 
 errout_skb:
-	spin_unlock(&nlk->cb_lock);
+	mutex_unlock(nlk->cb_mutex);
 	kfree_skb(skb);
 errout:
 	return err;
@@ -1414,15 +1422,15 @@ int netlink_dump_start(struct sock *ssk, struct sk_buff *skb,
 	}
 	nlk = nlk_sk(sk);
 	/* A dump or destruction is in progress... */
-	spin_lock(&nlk->cb_lock);
+	mutex_lock(nlk->cb_mutex);
 	if (nlk->cb || sock_flag(sk, SOCK_DEAD)) {
-		spin_unlock(&nlk->cb_lock);
+		mutex_unlock(nlk->cb_mutex);
 		netlink_destroy_callback(cb);
 		sock_put(sk);
 		return -EBUSY;
 	}
 	nlk->cb = cb;
-	spin_unlock(&nlk->cb_lock);
+	mutex_unlock(nlk->cb_mutex);
 
 	netlink_dump(sk);
 	sock_put(sk);
diff --git a/net/netlink/genetlink.c b/net/netlink/genetlink.c
index fac2e7a6dbe..6e31234a419 100644
--- a/net/netlink/genetlink.c
+++ b/net/netlink/genetlink.c
@@ -558,7 +558,7 @@ static int __init genl_init(void)
 
 	netlink_set_nonroot(NETLINK_GENERIC, NL_NONROOT_RECV);
 	genl_sock = netlink_kernel_create(NETLINK_GENERIC, GENL_MAX_ID,
-					  genl_rcv, THIS_MODULE);
+					  genl_rcv, NULL, THIS_MODULE);
 	if (genl_sock == NULL)
 		panic("GENL: Cannot initialize generic netlink\n");