[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 2cbf1682f63d..ec16c9b7b3bd 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 fac2e7a6dbe4..6e31234a4196 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");