netdev - Re: [PATCH 4/5] batman-adv: Reduce refcnt of removed router when updating route

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Date:	Tue, 26 Apr 2016 17:42:54 +0300
From:	Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
To:	Antonio Quartulli <a@...table.cc>, davem@...emloft.net
Cc:	netdev@...r.kernel.org, b.a.t.m.a.n@...ts.open-mesh.org,
	Sven Eckelmann <sven@...fation.org>,
	Marek Lindner <mareklindner@...mailbox.ch>
Subject: Re: [PATCH 4/5] batman-adv: Reduce refcnt of removed router when
 updating route

Hello.

On 4/26/2016 6:27 AM, Antonio Quartulli wrote:

> From: Sven Eckelmann <sven@...fation.org>
>
> _batadv_update_route rcu_derefences orig_ifinfo->router outside of a
> spinlock protected region to print some information messages to the debug
> log. But this pointer is not checked again when the new pointer is assigned
> in the spinlock protected region. Thus is can happen that the value of

    Thus is can? :-)

> orig_ifinfo->router changed in the meantime and thus the reference counter
> of the wrong router gets reduced after the spinlock protected region.
>
> Just rcu_dereferencing the value of orig_ifinfo->router inside the spinlock
> protected region (which also set the new pointer) is enough to get the
> correct old router object.
>
> Fixes: e1a5382f978b ("batman-adv: Make orig_node->router an rcu protected pointer")
> Signed-off-by: Sven Eckelmann <sven@...fation.org>
> Signed-off-by: Marek Lindner <mareklindner@...mailbox.ch>
> Signed-off-by: Antonio Quartulli <a@...table.cc>
> ---
>  net/batman-adv/routing.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
>
> diff --git a/net/batman-adv/routing.c b/net/batman-adv/routing.c
> index 4dd646a52f1a..b781bf753250 100644
> --- a/net/batman-adv/routing.c
> +++ b/net/batman-adv/routing.c
> @@ -105,6 +105,15 @@ static void _batadv_update_route(struct batadv_priv *bat_priv,
>  		neigh_node = NULL;
>
>  	spin_lock_bh(&orig_node->neigh_list_lock);
> +	/* curr_router used earlier may not be the current orig_ifinfo->router
> +	 * anymore because it was dereferenced outside of the neigh_list_lock
> +	 * protected region. After the new best neighbor has replace the current

    Replaced.

[...]

MBR, Sergei