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

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Message-Id: <20190221054942.132388-2-joel@joelfernandes.org>
Date:   Thu, 21 Feb 2019 00:49:38 -0500
From:   "Joel Fernandes (Google)" <joel@...lfernandes.org>
To:     linux-kernel@...r.kernel.org
Cc:     "Joel Fernandes (Google)" <joel@...lfernandes.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Christian Brauner <christian@...uner.io>,
        Daniel Borkmann <daniel@...earbox.net>,
        David Ahern <dsahern@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Ido Schimmel <idosch@...lanox.com>,
        Ingo Molnar <mingo@...hat.com>,
        intel-wired-lan@...ts.osuosl.org (moderated list:INTEL ETHERNET DRIVERS),
        Jakub Kicinski <jakub.kicinski@...ronome.com>,
        Jeff Kirsher <jeffrey.t.kirsher@...el.com>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        John Fastabend <john.fastabend@...il.com>,
        Josh Triplett <josh@...htriplett.org>, keescook@...omium.org,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Martin KaFai Lau <kafai@...com>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        netdev@...r.kernel.org, "Paul E. McKenney" <paulmck@...ux.ibm.com>,
        Peter Zijlstra <peterz@...radead.org>, rcu@...r.kernel.org,
        Song Liu <songliubraving@...com>,
        Steven Rostedt <rostedt@...dmis.org>,
        xdp-newbies@...r.kernel.org, Yonghong Song <yhs@...com>
Subject: [PATCH RFC 1/5] net: rtnetlink: Fix incorrect RCU API usage

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 (Google) <joel@...lfernandes.org>
---
 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