netdev - Re: [PATCH] ipv6: icmp: Add protection from concurrent users in the function icmpv6_echo

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Date:	Tue, 5 Apr 2016 23:36:28 +0200
From:	Hannes Frederic Sowa <hannes@...essinduktion.org>
To:	Bastien Philbert <bastienphilbert@...il.com>, davem@...emloft.net
Cc:	kuznet@....inr.ac.ru, jmorris@...ei.org, yoshfuji@...ux-ipv6.org,
	kaber@...sh.net, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ipv6: icmp: Add protection from concurrent users in the
 function icmpv6_echo_reply

On 05.04.2016 23:27, Bastien Philbert wrote:
> This adds protection from concurrenct users in the function
> icmpv6_echo_reply around the call to the function __in6_dev_get
> by locking/unlocking around this call with calls to the functions
> rtnl_lock and rtnl_unlock to protect against concurrent users
> when calling this function in icmpv6_echo_reply as stated in the
> comments for locking requirements for the function, __in6_dev_get.
>
> Signed-off-by: Bastien Philbert <bastienphilbert@...il.com>
> ---
>   net/ipv6/icmp.c | 2 ++
>   1 file changed, 2 insertions(+)
>
> diff --git a/net/ipv6/icmp.c b/net/ipv6/icmp.c
> index 0a37ddc..798434f 100644
> --- a/net/ipv6/icmp.c
> +++ b/net/ipv6/icmp.c
> @@ -607,7 +607,9 @@ static void icmpv6_echo_reply(struct sk_buff *skb)
>
>   	hlimit = ip6_sk_dst_hoplimit(np, &fl6, dst);
>
> +	rtnl_lock();
>   	idev = __in6_dev_get(skb->dev);
> +	rtnl_unlock();
>
>   	msg.skb = skb;
>   	msg.offset = 0;
>

We can't hold rtnl_lock in bh context. Have you seen a rcu verifier 
report? I am sure we hold rcu read lock at this point.

Bye,
Hannes