linux-kernel - Re: [PATCH] ath9k: fix null-ptr-deref in ath_chanctx

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Message-ID: <f183e79c-692e-54b0-2018-bf63424d7908@hust.edu.cn>
Date:   Fri, 1 Sep 2023 19:21:31 +0800
From:   Dongliang Mu <dzm91@...t.edu.cn>
To:     Toke Høiland-Jørgensen <toke@...e.dk>,
        Kalle Valo <kvalo@...nel.org>,
        Sujith Manoharan <c_manoha@....qualcomm.com>,
        "John W. Linville" <linville@...driver.com>
Cc:     hust-os-kernel-patches@...glegroups.com,
        linux-wireless@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ath9k: fix null-ptr-deref in ath_chanctx_event


On 2023/9/1 19:16, Toke Høiland-Jørgensen wrote:
> Dongliang Mu <dzm91@...t.edu.cn> writes:
>
>> On 2023/9/1 18:41, 'Toke Høiland-Jørgensen' via HUST OS Kernel
>> Contribution wrote:
>>> Dongliang Mu <dzm91@...t.edu.cn> writes:
>>>
>>>> Smatch reports:
>>>>
>>>> ath_chanctx_event() error: we previously assumed 'vif' could be null
>>>>
>>>> The function ath_chanctx_event can be called with vif argument as NULL.
>>>> If vif is NULL, ath_dbg can trigger a null pointer dereference.
>>>>
>>>> Fix this by adding a null pointer check.
>>>>
>>>> Fixes: 878066e745b5 ("ath9k: Add more debug statements for channel context")
>>>> Signed-off-by: Dongliang Mu <dzm91@...t.edu.cn>
>>>> ---
>>>>    drivers/net/wireless/ath/ath9k/channel.c | 4 +++-
>>>>    1 file changed, 3 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/drivers/net/wireless/ath/ath9k/channel.c b/drivers/net/wireless/ath/ath9k/channel.c
>>>> index 571062f2e82a..e343c8962d14 100644
>>>> --- a/drivers/net/wireless/ath/ath9k/channel.c
>>>> +++ b/drivers/net/wireless/ath/ath9k/channel.c
>>>> @@ -576,7 +576,9 @@ void ath_chanctx_event(struct ath_softc *sc, struct ieee80211_vif *vif,
>>>>    		if (sc->sched.state != ATH_CHANCTX_STATE_WAIT_FOR_BEACON)
>>>>    			break;
>>>>    
>>>> -		ath_dbg(common, CHAN_CTX, "Preparing beacon for vif: %pM\n", vif->addr);
>>>> +		if (vif)
>>>> +			ath_dbg(common, CHAN_CTX,
>>>> +				"Preparing beacon for vif: %pM\n", vif->addr);
>>> Please don't send patches for static checker errors without actually
>>> checking if there is a valid bug. Which there isn't in this case.
>> Before sending this patch, I searched in the code, there are many call
>> sites of ath_chanctx_event with argument vif as NULL.
>>
>> Functions calling this function: ath_chanctx_event
>>
>>     File      Function                   Line
>> 0 beacon.c  ath9k_beacon_tasklet        459 ath_chanctx_event(sc, vif,
>> ATH_CHANCTX_EVENT_BEACON_PREPARE);
> But only this one has ATH_CHANCTX_EVENT_BEACON_PREPARE as an argument,
> which is required to hit the code path you are changing.
>
>> 1 channel.c ath_chanctx_check_active    321 ath_chanctx_event(sc, NULL,
>> 2 channel.c ath_chanctx_beacon_sent_ev  781 ath_chanctx_event(sc, NULL, ev);
>> 3 channel.c ath_chanctx_beacon_recv_ev  787 ath_chanctx_event(sc, NULL, ev);
>> 4 channel.c ath_chanctx_timer          1054 ath_chanctx_event(sc, NULL,
>> ATH_CHANCTX_EVENT_TSF_TIMER);
>> 5 channel.c ath_chanctx_set_next       1321 ath_chanctx_event(sc, NULL,
>> ATH_CHANCTX_EVENT_SWITCH);
>> 6 channel.c ath9k_p2p_ps_timer         1566 ath_chanctx_event(sc, NULL,
>> ATH_CHANCTX_EVENT_TSF_TIMER);
>> 7 main.c    ath9k_sta_state            1671 ath_chanctx_event(sc, vif,
>> 8 main.c    ath9k_remove_chanctx       2577 ath_chanctx_event(sc, NULL,
>> ATH_CHANCTX_EVENT_UNASSIGN);
>> 9 xmit.c    ath_tx_edma_tasklet        2749 ath_chanctx_event(sc, NULL,
>>
>> This NULL parameters would cause some abnormal behaviors.
>>
>>> Specifically, that branch of the switch statement dereferences the avp
>>> pointer, which will be NULL if 'vif' is. Meaning we will have crashed
>>> way before reaching this statement if vif is indeed NULL.
>> Yeah, you are right. However, no matter where or which variable causing
>> the null-ptr-def crash, the crash is there.
> There is no crash, see above.

Yeah, I see where my problem is. Please ignore this patch.

In the future I will check more and think more about the code logic when 
verifying the result of static analyzer.

Thanks for your patience.

>
> -Toke