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

Shuah Khan
2021-04-06T00:27:21Z

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