[PATCH net-next 2/8] rtnetlink: add rtnl_register_module

[Florian Westphal <fw@strlen.de>]

Add yet another rtnl_register function.  It will be used by modules
that can be removed.

The passed module struct is used to take a reference while a netlink
dump is in progress to prevent module unload while netlink core can
invoke registered dumper function again.

Signed-off-by: Florian Westphal <fw@strlen.de>
---
 include/net/rtnetlink.h |   2 +
 net/core/rtnetlink.c    | 103 +++++++++++++++++++++++++++++++++++++-----------
 2 files changed, 83 insertions(+), 22 deletions(-)

diff --git a/include/net/rtnetlink.h b/include/net/rtnetlink.h
index ead018744ff5..e326b3f9eb5f 100644
--- a/include/net/rtnetlink.h
+++ b/include/net/rtnetlink.h
@@ -17,6 +17,8 @@ int __rtnl_register(int protocol, int msgtype,
 		    rtnl_doit_func, rtnl_dumpit_func, unsigned int flags);
 void rtnl_register(int protocol, int msgtype,
 		   rtnl_doit_func, rtnl_dumpit_func, unsigned int flags);
+int rtnl_register_module(struct module *owner, int protocol, int msgtype,
+			 rtnl_doit_func, rtnl_dumpit_func, unsigned int flags);
 int rtnl_unregister(int protocol, int msgtype);
 void rtnl_unregister_all(int protocol);
 
diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
index c70f62137dd8..50b483b24845 100644
--- a/net/core/rtnetlink.c
+++ b/net/core/rtnetlink.c
@@ -62,6 +62,7 @@
 struct rtnl_link {
 	rtnl_doit_func		doit;
 	rtnl_dumpit_func	dumpit;
+	struct module		*owner;
 	unsigned int		flags;
 };
 
@@ -143,27 +144,10 @@ static inline int rtm_msgindex(int msgtype)
 	return msgindex;
 }
 
-/**
- * __rtnl_register - Register a rtnetlink message type
- * @protocol: Protocol family or PF_UNSPEC
- * @msgtype: rtnetlink message type
- * @doit: Function pointer called for each request message
- * @dumpit: Function pointer called for each dump request (NLM_F_DUMP) message
- * @flags: rtnl_link_flags to modifiy behaviour of doit/dumpit functions
- *
- * Registers the specified function pointers (at least one of them has
- * to be non-NULL) to be called whenever a request message for the
- * specified protocol family and message type is received.
- *
- * The special protocol family PF_UNSPEC may be used to define fallback
- * function pointers for the case when no entry for the specific protocol
- * family exists.
- *
- * Returns 0 on success or a negative error code.
- */
-int __rtnl_register(int protocol, int msgtype,
-		    rtnl_doit_func doit, rtnl_dumpit_func dumpit,
-		    unsigned int flags)
+static int rtnl_register_internal(struct module *owner,
+				  int protocol, int msgtype,
+				  rtnl_doit_func doit, rtnl_dumpit_func dumpit,
+				  unsigned int flags)
 {
 	struct rtnl_link *tab;
 	int msgindex;
@@ -180,6 +164,12 @@ int __rtnl_register(int protocol, int msgtype,
 		rcu_assign_pointer(rtnl_msg_handlers[protocol], tab);
 	}
 
+	WARN_ON(tab[msgindex].owner && tab[msgindex].owner != owner);
+
+	tab[msgindex].owner = owner;
+	/* make sure owner is always visible first */
+	smp_wmb();
+
 	if (doit)
 		tab[msgindex].doit = doit;
 	if (dumpit)
@@ -188,6 +178,60 @@ int __rtnl_register(int protocol, int msgtype,
 
 	return 0;
 }
+
+/**
+ * rtnl_register_module - Register a rtnetlink message type
+ *
+ * @owner: module registering the hook (THIS_MODULE)
+ * @protocol: Protocol family or PF_UNSPEC
+ * @msgtype: rtnetlink message type
+ * @doit: Function pointer called for each request message
+ * @dumpit: Function pointer called for each dump request (NLM_F_DUMP) message
+ * @flags: rtnl_link_flags to modifiy behaviour of doit/dumpit functions
+ *
+ * Like rtnl_register, but for use by removable modules.
+ */
+int rtnl_register_module(struct module *owner,
+			 int protocol, int msgtype,
+			 rtnl_doit_func doit, rtnl_dumpit_func dumpit,
+			 unsigned int flags)
+{
+	int ret;
+
+	rtnl_lock();
+	ret = rtnl_register_internal(owner, protocol, msgtype,
+				     doit, dumpit, flags);
+	rtnl_unlock();
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(rtnl_register_module);
+
+/**
+ * __rtnl_register - Register a rtnetlink message type
+ * @protocol: Protocol family or PF_UNSPEC
+ * @msgtype: rtnetlink message type
+ * @doit: Function pointer called for each request message
+ * @dumpit: Function pointer called for each dump request (NLM_F_DUMP) message
+ * @flags: rtnl_link_flags to modifiy behaviour of doit/dumpit functions
+ *
+ * Registers the specified function pointers (at least one of them has
+ * to be non-NULL) to be called whenever a request message for the
+ * specified protocol family and message type is received.
+ *
+ * The special protocol family PF_UNSPEC may be used to define fallback
+ * function pointers for the case when no entry for the specific protocol
+ * family exists.
+ *
+ * Returns 0 on success or a negative error code.
+ */
+int __rtnl_register(int protocol, int msgtype,
+		    rtnl_doit_func doit, rtnl_dumpit_func dumpit,
+		    unsigned int flags)
+{
+	return rtnl_register_internal(NULL, protocol, msgtype,
+				      doit, dumpit, flags);
+}
 EXPORT_SYMBOL_GPL(__rtnl_register);
 
 /**
@@ -235,6 +279,9 @@ int rtnl_unregister(int protocol, int msgtype)
 	handlers[msgindex].doit = NULL;
 	handlers[msgindex].dumpit = NULL;
 	handlers[msgindex].flags = 0;
+	/* make sure we clear owner last */
+	smp_wmb();
+	handlers[msgindex].owner = NULL;
 	rtnl_unlock();
 
 	return 0;
@@ -4346,6 +4393,7 @@ static int rtnetlink_rcv_msg(struct sk_buff *skb, struct nlmsghdr *nlh,
 	}
 
 	if (kind == 2 && nlh->nlmsg_flags&NLM_F_DUMP) {
+		struct module *owner = NULL;
 		struct sock *rtnl;
 		rtnl_dumpit_func dumpit;
 		u16 min_dump_alloc = 0;
@@ -4360,20 +4408,31 @@ static int rtnetlink_rcv_msg(struct sk_buff *skb, struct nlmsghdr *nlh,
 			dumpit = READ_ONCE(handlers[type].dumpit);
 			if (!dumpit)
 				goto err_unlock;
+			owner = READ_ONCE(handlers[type].owner);
 		}
 
 		if (type == RTM_GETLINK - RTM_BASE)
 			min_dump_alloc = rtnl_calcit(skb, nlh);
 
+		err = 0;
+		/* need to do this before rcu_read_unlock() */
+		if (!try_module_get(owner))
+			err = -EPROTONOSUPPORT;
+
 		rcu_read_unlock();
 
 		rtnl = net->rtnl;
-		{
+		if (err == 0) {
 			struct netlink_dump_control c = {
 				.dump		= dumpit,
 				.min_dump_alloc	= min_dump_alloc,
+				.module		= owner,
 			};
 			err = netlink_dump_start(rtnl, skb, nlh, &c);
+			/* netlink_dump_start() will keep a reference on
+			 * module if dump is still in progress.
+			 */
+			module_put(owner);
 		}
 		return err;
 	}
-- 
2.13.6