[RFC 1/5] net: rtnetlink: Fix incorrect RCU API usage

[Joel Fernandes (Google)]

From: Joel Fernandes <joel@xxxxxxxxxxxxxxxxx>

rtnl_register_internal() and rtnl_unregister_all tries to directly
dereference an RCU protected pointed outside RCU read side section.
While this is Ok to do since a lock is held, let us use the correct
API to avoid programmer bugs in the future.

This also fixes sparse warnings arising from not using RCU API.

net/core/rtnetlink.c:332:13: warning: incorrect type in assignment
(different address spaces) net/core/rtnetlink.c:332:13:    expected
struct rtnl_link **tab net/core/rtnetlink.c:332:13:    got struct
rtnl_link *[noderef] <asn:4>*<noident>

Signed-off-by: Joel Fernandes <joel@xxxxxxxxxxxxxxxxx>
---
 net/core/rtnetlink.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
index 5ea1bed08ede..98be4b4818a9 100644
--- a/net/core/rtnetlink.c
+++ b/net/core/rtnetlink.c
@@ -188,7 +188,7 @@ static int rtnl_register_internal(struct module *owner,
 	msgindex = rtm_msgindex(msgtype);
 
 	rtnl_lock();
-	tab = rtnl_msg_handlers[protocol];
+	tab = rtnl_dereference(rtnl_msg_handlers[protocol]);
 	if (tab == NULL) {
 		tab = kcalloc(RTM_NR_MSGTYPES, sizeof(void *), GFP_KERNEL);
 		if (!tab)
@@ -329,7 +329,7 @@ void rtnl_unregister_all(int protocol)
 	BUG_ON(protocol < 0 || protocol > RTNL_FAMILY_MAX);
 
 	rtnl_lock();
-	tab = rtnl_msg_handlers[protocol];
+	tab = rtnl_dereference(rtnl_msg_handlers[protocol]);
 	if (!tab) {
 		rtnl_unlock();
 		return;
-- 
2.21.0.rc0.258.g878e2cd30e-goog