linux-kernel - Re: [PATCH v5] wifi: brcmfmac: Fix use-after-free bug in brcmf_cfg80211

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Date:   Mon, 13 Nov 2023 10:18:06 +0100
From:   Arend van Spriel <arend.vanspriel@...adcom.com>
To:     Zheng Hacker <hackerzheng666@...il.com>
Cc:     Kalle Valo <kvalo@...nel.org>, Zheng Wang <zyytlz.wz@....com>,
        aspriel@...il.com, franky.lin@...adcom.com,
        hante.meuleman@...adcom.com, johannes.berg@...el.com,
        marcan@...can.st, linus.walleij@...aro.org,
        jisoo.jang@...sei.ac.kr, linuxlovemin@...sei.ac.kr,
        wataru.gohda@...ress.com, linux-wireless@...r.kernel.org,
        brcm80211-dev-list.pdl@...adcom.com,
        SHA-cyfmac-dev-list@...ineon.com, linux-kernel@...r.kernel.org,
        security@...nel.org, stable@...r.kernel.org
Subject: Re: [PATCH v5] wifi: brcmfmac: Fix use-after-free bug in
 brcmf_cfg80211_detach

On November 8, 2023 4:03:26 AM Zheng Hacker <hackerzheng666@...il.com> 
wrote:

> Arend Van Spriel <arend.vanspriel@...adcom.com> 于2023年11月6日周一 23:48写道：
>>
>> On November 6, 2023 3:44:53 PM Zheng Hacker <hackerzheng666@...il.com> wrote:
>>
>>> Thanks! I didn't test it for I don't have a device. Very appreciated
>>> if anyone could help with that.
>>
>> I would volunteer, but it made me dig deep and not sure if there is a
>> problem to solve here.
>>
>> brcmf_cfg80211_detach() calls wl_deinit_priv() -> brcmf_abort_scanning() ->
>> brcmf_notify_escan_complete() which does delete the timer.
>>
>> What am I missing here?
>
> Thanks four your detailed review. I did see the code and not sure if
> brcmf_notify_escan_complete
> would be triggered for sure. So in the first version I want to delete
> the pending timer ahead of time.

Why requesting a CVE when you are not sure? Seems a bit hasty to put it 
mildly.

> As I'm not very familiar with the logic here. I'm still not sure if we
> should delete the timer_shutdown_sync.
> Looking forward to your reply :)

Reading the kerneldoc of timer_shutdown_sync() has the advantage that 
the timer can not be rearmed by another thread. However, that will only 
happen when a new scan is initiated in firmware, but the bus is already 
down so that can not happen. The only improvement (no bug fix!) I see 
here is to replace timer handling code in brcmf_notify_escan_complete():

-	if (timer_pending(&cfg->escan_timeout))
-		del_timer_sync(&cfg->escan_timeout);
+	timer_delete_sync(&cfg->escan_timeout);

Regards,
Arend

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