linux-kernel - Re: [PATCH 5.10 047/126] ath10k: hold RCU lock when calling ieee80211_find_sta_by

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Date:   Mon, 5 Apr 2021 18:27:15 -0600
From:   Shuah Khan <skhan@...uxfoundation.org>
To:     Pavel Machek <pavel@....cz>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Kalle Valo <kvalo@...eaurora.org>,
        Sasha Levin <sashal@...nel.org>,
        Shuah Khan <skhan@...uxfoundation.org>
Subject: Re: [PATCH 5.10 047/126] ath10k: hold RCU lock when calling
 ieee80211_find_sta_by_ifaddr()

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