linux-kernel - Re: [PATCH][next] staging: rtl8188eu: Fix null pointer dereference on free

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Message-ID: <028e75cd-6229-6004-84bb-ca751346420d@canonical.com>
Date:   Wed, 24 Mar 2021 16:12:08 +0000
From:   Colin Ian King <colin.king@...onical.com>
To:     Martin Kaiser <martin@...ser.cx>
Cc:     Larry Finger <Larry.Finger@...inger.net>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-staging@...ts.linux.dev, kernel-janitors@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH][next] staging: rtl8188eu: Fix null pointer dereference on
 free_netdev call

On 24/03/2021 16:11, Martin Kaiser wrote:
> Hello Colin,
> 
> Thus wrote Colin King (colin.king@...onical.com):
> 
>> From: Colin Ian King <colin.king@...onical.com>
> 
>> An unregister_netdev call checks if pnetdev is null, hence a later
>> call to free_netdev can potentially be passing a null pointer, causing
>> a null pointer dereference. Avoid this by adding a null pointer check
>> on pnetdev before calling free_netdev.
> 
>> Fixes: 1665c8fdffbb ("staging: rtl8188eu: use netdev routines for private data")
>> Signed-off-by: Colin Ian King <colin.king@...onical.com>
>> ---
>>  drivers/staging/rtl8188eu/os_dep/usb_intf.c | 3 ++-
>>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
>> diff --git a/drivers/staging/rtl8188eu/os_dep/usb_intf.c b/drivers/staging/rtl8188eu/os_dep/usb_intf.c
>> index 518e9feb3f46..91a3d34a1050 100644
>> --- a/drivers/staging/rtl8188eu/os_dep/usb_intf.c
>> +++ b/drivers/staging/rtl8188eu/os_dep/usb_intf.c
>> @@ -446,7 +446,8 @@ static void rtw_usb_if1_deinit(struct adapter *if1)
>>  	pr_debug("+r871xu_dev_remove, hw_init_completed=%d\n",
>>  		 if1->hw_init_completed);
>>  	rtw_free_drv_sw(if1);
>> -	free_netdev(pnetdev);
>> +	if (pnetdev)
>> +		free_netdev(pnetdev);
>>  }
> 
>>  static int rtw_drv_init(struct usb_interface *pusb_intf, const struct usb_device_id *pdid)
>> -- 
>> 2.30.2
> 
> you're right. I removed the NULL check that was part of rtw_free_netdev.
> Sorry for the mistake and thanks for your fix.

Thank static analysis :-)

> 
> Reviewed-by: Martin Kaiser <martin@...ser.cx>
> 
> Best regards,
> Martin
>