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

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Message-ID: <317b9482-d750-9093-e891-21f73feeac0c@hust.edu.cn>
Date:   Fri, 1 Sep 2023 18:59:44 +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 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);
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.

I think this is unexpected.

Let me know if I make any mistakes

>
> -Toke
>