linux-kernel - Re: [PATCH next] tee: qcom: prevent potential off by one read

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Message-ID: <6a0477dc-2f4a-4a72-85b3-9de42759cdb5@oss.qualcomm.com>
Date: Thu, 25 Sep 2025 11:46:19 +1000
From: Amirreza Zarrabi <amirreza.zarrabi@....qualcomm.com>
To: Dan Carpenter <dan.carpenter@...aro.org>,
        Jens Wiklander <jens.wiklander@...aro.org>
Cc: Sumit Garg <sumit.garg@...nel.org>, linux-arm-msm@...r.kernel.org,
        op-tee@...ts.trustedfirmware.org, linux-kernel@...r.kernel.org,
        kernel-janitors@...r.kernel.org
Subject: Re: [PATCH next] tee: qcom: prevent potential off by one read



On 9/24/2025 7:56 PM, Dan Carpenter wrote:
> On Wed, Sep 24, 2025 at 11:21:34AM +0200, Jens Wiklander wrote:
>> On Wed, Sep 24, 2025 at 9:36 AM Dan Carpenter <dan.carpenter@...aro.org> wrote:
>>>
>>> On Wed, Sep 24, 2025 at 08:58:45AM +1000, Amirreza Zarrabi wrote:
>>>>
>>>>
>>>> On 9/24/2025 8:48 AM, Amirreza Zarrabi wrote:
>>>>> On 9/18/2025 7:50 PM, Dan Carpenter wrote:
>>>>>> Re-order these checks to check if "i" is a valid array index before using
>>>>>> it.  This prevents a potential off by one read access.
>>>>>>
>>>>>> Fixes: d6e290837e50 ("tee: add Qualcomm TEE driver")
>>>>>> Signed-off-by: Dan Carpenter <dan.carpenter@...aro.org>
>>>>>> ---
>>>>>>  drivers/tee/qcomtee/call.c | 2 +-
>>>>>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>>>>>
>>>>>> diff --git a/drivers/tee/qcomtee/call.c b/drivers/tee/qcomtee/call.c
>>>>>> index cc17a48d0ab7..ac134452cc9c 100644
>>>>>> --- a/drivers/tee/qcomtee/call.c
>>>>>> +++ b/drivers/tee/qcomtee/call.c
>>>>>> @@ -308,7 +308,7 @@ static int qcomtee_params_from_args(struct tee_param *params,
>>>>>>    }
>>>>>>
>>>>>>    /* Release any IO and OO objects not processed. */
>>>>>> -  for (; u[i].type && i < num_params; i++) {
>>>>>> +  for (; i < num_params && u[i].type; i++) {
>>>>>>            if (u[i].type == QCOMTEE_ARG_TYPE_OO ||
>>>>>>                u[i].type == QCOMTEE_ARG_TYPE_IO)
>>>>>>                    qcomtee_object_put(u[i].o);
>>>>>
>>>>> This is not required, considering the sequence of clean up, this
>>>>> would never happen. `i` at least have been accessed once in the
>>>>> switch above.
>>>>>
>>>>> Regards,
>>>>> Amir
>>>>>
>>>>>
>>>>
>>>> Also, size of u is always num_params + 1 for the ending 0.
>>>> (basically means `i < num_params` can be removed).
>>>>
>>>
>>> Yes.  This is true.
>>
>> So this patch isn't needed. I'll drop it if no one objects.
> 
> The patch makes the code better though...  It never really makes sense
> to use a variable first and then check if it's valid later.  In this
> case the check isn't required.
> 
> Ideally the code would only have one limit.  We could either do:
> 
> 	for (; i < num_params; i++) {
> Or:
> 	for (; u[i].type != QCOMTEE_ARG_TYPE_INV; i++) {
> 
> Either way works...
> 
> regards,
> dan carpenter
> 

Originally, it was written as

	for (; u[i].type != QCOMTEE_ARG_TYPE_INV; i++) { ...

but changed trough out the review process.	
I do not have any preference. But if having it as

	for (; i < num_params && u[i].type; i++) { ...

is more readable, let's keep it.

Regards,
Amir