Re: [PATCH 5.10 047/126] ath10k: hold RCU lock when calling ieee80211_find_sta_by_ifaddr()

[Shuah Khan]

On 4/5/21 9:34 AM, Pavel Machek wrote:
> Hi!
>
> > Fix ath10k_wmi_tlv_op_pull_peer_stats_info() to hold RCU lock before it
> > calls ieee80211_find_sta_by_ifaddr() and release it when the resulting
> > pointer is no longer needed.
>
> It does that. But is also does the unlock even if it did not take the
> lock:

There is only one path after it takes the lock.

> > +++ b/drivers/net/wireless/ath/ath10k/wmi-tlv.c
> > @@ -576,13 +576,13 @@ static void ath10k_wmi_event_tdls_peer(struct ath10k *ar, struct sk_buff *skb)
> >   	case WMI_TDLS_TEARDOWN_REASON_TX:
> >   	case WMI_TDLS_TEARDOWN_REASON_RSSI:
> >   	case WMI_TDLS_TEARDOWN_REASON_PTR_TIMEOUT:
> > +		rcu_read_lock();

Takes the lock here:

> >   		station = ieee80211_find_sta_by_ifaddr(ar->hw,
> >   						       ev->peer_macaddr.addr,
> >   						       NULL);
> >   		if (!station) {
> >   			ath10k_warn(ar, "did not find station from tdls peer event");
> > -			kfree(tb);
> > -			return;
> > +			goto exit;

Releases it if something fails

> >   		}
> >   		arvif = ath10k_get_arvif(ar, __le32_to_cpu(ev->vdev_id));
> >   		ieee80211_tdls_oper_request(
> > @@ -593,6 +593,9 @@ static void ath10k_wmi_event_tdls_peer(struct ath10k *ar, struct sk_buff *skb)
> >   					);
> >   		break;
> >   	}
> > +

falls through here.

> > +exit:
> > +	rcu_read_unlock();
> >   	kfree(tb);
> >   }
>
> The switch only takes the lock in 3 branches, but it is released
> unconditionally at the end.

I don't see any other switch cases. However, default is missing:

It could be done this way perhaps: (simpler than what you proposed)

diff --git a/drivers/net/wireless/ath/ath10k/wmi-tlv.c 
b/drivers/net/wireless/ath/ath10k/wmi-tlv.c
index d97b33f789e4..7efbe03fbca8 100644
--- a/drivers/net/wireless/ath/ath10k/wmi-tlv.c
+++ b/drivers/net/wireless/ath/ath10k/wmi-tlv.c
@@ -592,6 +592,9 @@ static void ath10k_wmi_event_tdls_peer(struct ath10k 
*ar, struct sk_buff *skb)
                                        GFP_ATOMIC
                                        );
                break;
+       default:
+               kfree(tb);
+               return;
        }

 exit:

thanks,
-- Shuah