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Date:   Mon, 25 Feb 2019 13:05:51 -0800
From:   "Paul E. McKenney" <paulmck@...ux.ibm.com>
To:     "Joel Fernandes (Google)" <joel@...lfernandes.org>
Cc:     linux-kernel@...r.kernel.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>,
        Ingo Molnar <mingo@...hat.com>,
        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,
        kernel-hardening@...ts.openwall.com, kernel-team@...roid.com,
        Kirill Tkhai <ktkhai@...tuozzo.com>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Martin KaFai Lau <kafai@...com>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        netdev@...r.kernel.org, Peter Zijlstra <peterz@...radead.org>,
        Quentin Perret <quentin.perret@....com>, rcu@...r.kernel.org,
        Song Liu <songliubraving@...com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        xdp-newbies@...r.kernel.org, Yonghong Song <yhs@...com>
Subject: Re: [PATCH v2 1/6] net: rtnetlink: Fix incorrect RCU API usage

On Sat, Feb 23, 2019 at 01:34:29AM -0500, Joel Fernandes (Google) wrote:
> 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>

>From an RCU perspective:

Reviewed-by: Paul E. McKenney <paulmck@...ux.ibm.com>

> ---
>  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
> 

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