linux-kernel - Re: [PATCH] usb: gadget: rndis: Avoid dereference before NULL check

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Date:   Fri, 23 Sep 2022 00:00:14 +0300
From:   Sergei Shtylyov <sergei.shtylyov@...il.com>
To:     Greg KH <gregkh@...uxfoundation.org>, Jim Lin <jilin@...dia.com>
Cc:     balbi@...nel.org, linux-usb@...r.kernel.org,
        linux-kernel@...r.kernel.org, Aniruddha TVS Rao <anrao@...dia.com>
Subject: Re: [PATCH] usb: gadget: rndis: Avoid dereference before NULL check

Hello!

On 9/9/22 8:38 AM, Greg KH wrote:

>> NULL check is performed after params->dev is dereferenced in
>> dev_get_stats.
> 
> I do not understand this statement.
> 
>> Fixed by adding a NULL check before dereferencing params->dev and
>> removing subsequent NULL checks for it.
>>
>> Signed-off-by: Aniruddha TVS Rao <anrao@...dia.com>
>> Signed-off-by: Jim Lin <jilin@...dia.com>
>> ---
>>  drivers/usb/gadget/function/rndis.c | 37 ++++++++++++-----------------
>>  1 file changed, 15 insertions(+), 22 deletions(-)
>>
>> diff --git a/drivers/usb/gadget/function/rndis.c b/drivers/usb/gadget/function/rndis.c
>> index 64de9f1b874c..d2f18f34c8e5 100644
>> --- a/drivers/usb/gadget/function/rndis.c
>> +++ b/drivers/usb/gadget/function/rndis.c
>> @@ -198,6 +198,9 @@ static int gen_ndis_query_resp(struct rndis_params *params, u32 OID, u8 *buf,
>>  	outbuf = (__le32 *)&resp[1];
>>  	resp->InformationBufferOffset = cpu_to_le32(16);
>>  
>> +	if (!params->dev)
>> +		return -ENODEV;
>> +
> 
> As Sergey points out, this check is useless and the ones below should
> also be removed.

   Would you accept this patch modulo the above check then? If not,
I'll just resolve the corresponding SVACE checker as "won't fix" here. :-)

> But, why make this check at all, how did you trigger a problem with the
> current code?

   There's no problem, just the redundant NULL checks...

> Are you using this driver?  If so, why?  It is totally broken (as per
> the specification) and we really really need to just delete it from the
> tree to prevent anyone else from ever using it.

   Well, delete it then... :-)

> thanks,
> 
> greg k-h

MBR, Sergey