2008-04-23 08:31:21

by Pavel Emelyanov

[permalink] [raw]

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

---

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 <[email protected]>

---

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);

2008-04-23 07:54:31

by Johannes Berg

[permalink] [raw]

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

---

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 <[email protected]>

Acked-by: Johannes Berg <[email protected]>

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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