[PATCH 01/11] netlink: add reference of module in netlink_dump_start

[Gao feng <gaofeng@cn.fujitsu.com>]

I get a panic when I use ss -a and rmmod inet_diag at the
same time.

it's because netlink_dump use inet_diag_dump witch function
belongs to module inet_diag.

I search the codes and find many modules have the same problem.
We need add reference of the module witch the cb->dump belongs
to.

since CONFIG_NET is bool,so netlink_dump_start in rtnetlink.c
and genetlink.c will never trigger this problem.

Thanks for all help from Stephen,Jan and Eric.

Signed-off-by: Gao feng <gaofeng@cn.fujitsu.com>
---
 include/linux/netlink.h  |    4 ++++
 net/netlink/af_netlink.c |   25 +++++++++++++++++++++----
 2 files changed, 25 insertions(+), 4 deletions(-)

diff --git a/include/linux/netlink.h b/include/linux/netlink.h
index f74dd13..a3641e3 100644
--- a/include/linux/netlink.h
+++ b/include/linux/netlink.h
@@ -232,6 +232,8 @@ struct netlink_callback {
 					struct netlink_callback *cb);
 	int			(*done)(struct netlink_callback *cb);
 	void			*data;
+	/* the module that dump function belong to */
+	struct module		*module;
 	u16			family;
 	u16			min_dump_alloc;
 	unsigned int		prev_seq, seq;
@@ -251,9 +253,11 @@ struct netlink_dump_control {
 	int (*dump)(struct sk_buff *skb, struct netlink_callback *);
 	int (*done)(struct netlink_callback*);
 	void *data;
+	struct module *module;
 	u16 min_dump_alloc;
 };
 
+extern int netlink_dump_done(struct netlink_callback *cb);
 extern int netlink_dump_start(struct sock *ssk, struct sk_buff *skb,
 			      const struct nlmsghdr *nlh,
 			      struct netlink_dump_control *control);
diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
index 5270238..011091c 100644
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -1769,6 +1769,14 @@ errout_skb:
 	return err;
 }
 
+int netlink_dump_done(struct netlink_callback *cb)
+{
+	if (cb->module)
+		module_put(cb->module);
+	return 0;
+}
+EXPORT_SYMBOL(netlink_dump_done);
+
 int netlink_dump_start(struct sock *ssk, struct sk_buff *skb,
 		       const struct nlmsghdr *nlh,
 		       struct netlink_dump_control *control)
@@ -1786,6 +1794,7 @@ int netlink_dump_start(struct sock *ssk, struct sk_buff *skb,
 	cb->done = control->done;
 	cb->nlh = nlh;
 	cb->data = control->data;
+	cb->module = control->module;
 	cb->min_dump_alloc = control->min_dump_alloc;
 	atomic_inc(&skb->users);
 	cb->skb = skb;
@@ -1796,19 +1805,27 @@ int netlink_dump_start(struct sock *ssk, struct sk_buff *skb,
 		return -ECONNREFUSED;
 	}
 	nlk = nlk_sk(sk);
-	/* A dump is in progress... */
+
 	mutex_lock(nlk->cb_mutex);
+	/* A dump is in progress... */
 	if (nlk->cb) {
 		mutex_unlock(nlk->cb_mutex);
 		netlink_destroy_callback(cb);
-		sock_put(sk);
-		return -EBUSY;
+		ret = -EBUSY;
+		goto out;
+	}
+	/* add reference of module witch cb->dump belone to */
+	if (cb->module && !try_module_get(cb->module)) {
+		mutex_unlock(nlk->cb_mutex);
+		ret = -EPROTONOSUPPORT;
+		goto out;
 	}
+
 	nlk->cb = cb;
 	mutex_unlock(nlk->cb_mutex);
 
 	ret = netlink_dump(sk);
-
+out:
 	sock_put(sk);
 
 	if (ret)
-- 
1.7.7.6