Received-SPF: pass (google.com: domain of linux-wireless-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Subject: Re: [PATCH] mt76: hold RCU lock when calling
 ieee80211_find_sta_by_ifaddr()
To:     Shuah Khan <skhan@linuxfoundation.org>,
        lorenzo.bianconi83@gmail.com, ryder.lee@mediatek.com,
        kvalo@codeaurora.org, davem@davemloft.net, kuba@kernel.org,
        matthias.bgg@gmail.com
Cc:     linux-wireless@vger.kernel.org, netdev@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org,
        linux-mediatek@lists.infradead.org, linux-kernel@vger.kernel.org
References: <cover.1613090339.git.skhan@linuxfoundation.org>
 <1cfa036227cfa9fdd04316c01e1d754f13a70d9e.1613090339.git.skhan@linuxfoundation.org>
 <20210212021312.40486-1-skhan@linuxfoundation.org>
From:   Felix Fietkau <nbd@nbd.name>
Message-ID: <3949e1fc-c050-73e0-d02f-63a25c4821ef@nbd.name>
Date:   Fri, 12 Feb 2021 06:36:26 +0100
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.14; rv:78.0)
 Gecko/20100101 Thunderbird/78.7.0
MIME-Version: 1.0
In-Reply-To: <20210212021312.40486-1-skhan@linuxfoundation.org>
Content-Type: text/plain; charset=utf-8
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Precedence: bulk


On 2021-02-12 03:13, Shuah Khan wrote:
> ieee80211_find_sta_by_ifaddr() must be called under the RCU lock and
> the resulting pointer is only valid under RCU lock as well.
> 
> Fix mt76_check_sta() to hold RCU read lock before it calls
> ieee80211_find_sta_by_ifaddr() and release it when the resulting
> pointer is no longer needed.
> 
> This problem was found while reviewing code to debug RCU warn from
> ath10k_wmi_tlv_parse_peer_stats_info() and a subsequent manual audit
> of other callers of ieee80211_find_sta_by_ifaddr() that don't hold
> RCU read lock.
> 
> Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>
If I'm not mistaken, this patch is unnecessary. mt76_check_sta is only
called from mt76_rx_poll_complete, which itself is only called under RCU
lock.

- Felix