[PATCH] mac80211: Fix race between ieee80211_rx_bss_put and lookup routines.

[PATCH] mac80211: Fix race between ieee80211_rx_bss_put and lookup routines.

[Pavel Emelyanov]

The put routine first decrements the users counter and then
(if it is zero) locks the sta_bss_lock and removes one from
the list and the hash.

Thus, any of ieee80211_sta_config_auth, ieee80211_rx_bss_get
or ieee80211_rx_mesh_bss_get can race with it by finding a
bss that is about to get kfree-ed.

Using atomic_dec_and_lock in ieee80211_rx_bss_put takes care
of this race.

Signed-off-by: Pavel Emelyanov <xemul@openvz.org>

---

diff --git a/net/mac80211/mlme.c b/net/mac80211/mlme.c
index 6b75cb6..dac3c2a 100644
--- a/net/mac80211/mlme.c
+++ b/net/mac80211/mlme.c
@@ -2248,10 +2248,13 @@ static void ieee80211_rx_bss_put(struct net_device *dev,
 				 struct ieee80211_sta_bss *bss)
 {
 	struct ieee80211_local *local = wdev_priv(dev->ieee80211_ptr);
-	if (!atomic_dec_and_test(&bss->users))
+
+	local_bh_disable();
+	if (!atomic_dec_and_lock(&bss->users, &local->sta_bss_lock)) {
+		local_bh_enable();
 		return;
+	}
 
-	spin_lock_bh(&local->sta_bss_lock);
 	__ieee80211_rx_bss_hash_del(dev, bss);
 	list_del(&bss->list);
 	spin_unlock_bh(&local->sta_bss_lock);

Re: [PATCH] mac80211: Fix race between ieee80211_rx_bss_put and lookup routines.

[Johannes Berg]

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On Wed, 2008-04-23 at 11:47 +0400, Pavel Emelyanov wrote:
> The put routine first decrements the users counter and then
> (if it is zero) locks the sta_bss_lock and removes one from
> the list and the hash.
> 
> Thus, any of ieee80211_sta_config_auth, ieee80211_rx_bss_get
> or ieee80211_rx_mesh_bss_get can race with it by finding a
> bss that is about to get kfree-ed.
> 
> Using atomic_dec_and_lock in ieee80211_rx_bss_put takes care
> of this race.

Good catch, thanks.

> Signed-off-by: Pavel Emelyanov <xemul-GEFAQzZX7r8dnm+yROfE0A@public.gmane.org>

Acked-by: Johannes Berg <johannes-cdvu00un1VgdHxzADdlk8Q@public.gmane.org>

I think we will need this in -stable (different file, same contents)

> ---
> 
> diff --git a/net/mac80211/mlme.c b/net/mac80211/mlme.c
> index 6b75cb6..dac3c2a 100644
> --- a/net/mac80211/mlme.c
> +++ b/net/mac80211/mlme.c
> @@ -2248,10 +2248,13 @@ static void ieee80211_rx_bss_put(struct net_device *dev,
>  				 struct ieee80211_sta_bss *bss)
>  {
>  	struct ieee80211_local *local = wdev_priv(dev->ieee80211_ptr);
> -	if (!atomic_dec_and_test(&bss->users))
> +
> +	local_bh_disable();
> +	if (!atomic_dec_and_lock(&bss->users, &local->sta_bss_lock)) {
> +		local_bh_enable();
>  		return;
> +	}
>  
> -	spin_lock_bh(&local->sta_bss_lock);
>  	__ieee80211_rx_bss_hash_del(dev, bss);
>  	list_del(&bss->list);
>  	spin_unlock_bh(&local->sta_bss_lock);
> 

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