Re: [PATCH v1 RESEND] slimbus: stream: Add null pointer check for client functions

[Viken Dadhaniya <quic_vdadhani@quicinc.com>]

On 4/11/2024 9:26 PM, Bjorn Andersson wrote:
> On Wed, Mar 27, 2024 at 02:02:14PM +0530, Viken Dadhaniya wrote:
>> There is a possible scenario where client driver is calling
> 
> How can we asses the validity or the risk of this problem?
> How would I know if this matches e.g. a bug report reported by a user?
> 
> Describe the problem such that the reviewer can asses the validity and
> severity of your bug fixes.

Ok. Updated commit log in v2

> 
>> slimbus stream APIs in incorrect sequence and it might lead to
>> invalid null access of the stream pointer in slimbus
>> enable/disable/prepare/unprepare/free function.
>>
>> Fix this by checking validity of the stream before accessing in
>> all function API’s exposed to client.
>>
> 
> You use the work "fix" a few time, are you fixing an actual bug? Are you
> just guarding the driver from incorrect usage?
> 
> If it's a fix, then add Fixes and Cc: stable here.

Let me correct myself there. Not a fix but consider an improvement where 
preventing a crash due to client following the incorrect sequence.

> 
>> Signed-off-by: Viken Dadhaniya <quic_vdadhani@quicinc.com>
>> ---
>>   drivers/slimbus/stream.c | 37 +++++++++++++++++++++++++++++++++----
>>   1 file changed, 33 insertions(+), 4 deletions(-)
>>
>> diff --git a/drivers/slimbus/stream.c b/drivers/slimbus/stream.c
>> index 1d6b38657917..c5a436fd0952 100644
>> --- a/drivers/slimbus/stream.c
>> +++ b/drivers/slimbus/stream.c
>> @@ -202,10 +202,16 @@ static int slim_get_prate_code(int rate)
>>   int slim_stream_prepare(struct slim_stream_runtime *rt,
>>   			struct slim_stream_config *cfg)
>>   {
>> -	struct slim_controller *ctrl = rt->dev->ctrl;
>> +	struct slim_controller *ctrl;
>>   	struct slim_port *port;
>>   	int num_ports, i, port_id, prrate;
>>   
>> +	if (!rt || !cfg) {
>> +		pr_err("%s: Stream or cfg is NULL, Check from client side\n", __func__);
> 
> Use dev_err() and write your error messages such that they make sense
> without the use of __func__.

For error scenario, we don't have valid dev to be used in dev_err argument.
this log will help for debug. Please let us know any concern with pr_err

> 
>> +		return -EINVAL;
> 
> Is this expected to happen during normal operation, or is this a sign of
> a bug?
> 

It's a scenario where client doesn't follow the proper sequence and 
slimbus driver can crash if not checked against NULL.

> 
> Neither of the two callers of this function checks the return value, so
> is this really going to result in a good system state?
> 

we expect client to check return value of framework APIs.

> 
> It would make sense to require the client to pass valid rt and cfg
> pointers, and if you have an issue in the client driver in which we
> might end up with invalid points, then those drivers should be fixed -
> rather than relying on chance and swipe it under the rug here.
> 
> Regards,
> Bjorn
> 

Agree. it is sequence mismatch from client driver, and they should take 
care. it is leading to NULL pointer access in slimbus APIs, so prevent 
crash by adding check.

>> +	}
>> +
>> +	ctrl = rt->dev->ctrl;
>>   	if (rt->ports) {
>>   		dev_err(&rt->dev->dev, "Stream already Prepared\n");
>>   		return -EINVAL;
>> @@ -358,9 +364,15 @@ int slim_stream_enable(struct slim_stream_runtime *stream)
>>   {
>>   	DEFINE_SLIM_BCAST_TXN(txn, SLIM_MSG_MC_BEGIN_RECONFIGURATION,
>>   				3, SLIM_LA_MANAGER, NULL);
>> -	struct slim_controller *ctrl = stream->dev->ctrl;
>> +	struct slim_controller *ctrl;
>>   	int ret, i;
>>   
>> +	if (!stream) {
>> +		pr_err("%s: Stream is NULL, Check from client side\n", __func__);
>> +		return -EINVAL;
>> +	}
>> +
>> +	ctrl = stream->dev->ctrl;
>>   	if (ctrl->enable_stream) {
>>   		ret = ctrl->enable_stream(stream);
>>   		if (ret)
>> @@ -411,12 +423,18 @@ int slim_stream_disable(struct slim_stream_runtime *stream)
>>   {
>>   	DEFINE_SLIM_BCAST_TXN(txn, SLIM_MSG_MC_BEGIN_RECONFIGURATION,
>>   				3, SLIM_LA_MANAGER, NULL);
>> -	struct slim_controller *ctrl = stream->dev->ctrl;
>> +	struct slim_controller *ctrl;
>>   	int ret, i;
>>   
>> +	if (!stream) {
>> +		pr_err("%s: Stream is NULL, Check from client side\n", __func__);
>> +		return -EINVAL;
>> +	}
>> +
>>   	if (!stream->ports || !stream->num_ports)
>>   		return -EINVAL;
>>   
>> +	ctrl = stream->dev->ctrl;
>>   	if (ctrl->disable_stream)
>>   		ctrl->disable_stream(stream);
>>   
>> @@ -448,6 +466,11 @@ int slim_stream_unprepare(struct slim_stream_runtime *stream)
>>   {
>>   	int i;
>>   
>> +	if (!stream) {
>> +		pr_err("%s: Stream is NULL, Check from client side\n", __func__);
>> +		return -EINVAL;
>> +	}
>> +
>>   	if (!stream->ports || !stream->num_ports)
>>   		return -EINVAL;
>>   
>> @@ -476,8 +499,14 @@ EXPORT_SYMBOL_GPL(slim_stream_unprepare);
>>    */
>>   int slim_stream_free(struct slim_stream_runtime *stream)
>>   {
>> -	struct slim_device *sdev = stream->dev;
>> +	struct slim_device *sdev;
>> +
>> +	if (!stream) {
>> +		pr_err("%s: Stream is NULL, Check from client side\n", __func__);
>> +		return -EINVAL;
>> +	}
>>   
>> +	sdev = stream->dev;
>>   	spin_lock(&sdev->stream_list_lock);
>>   	list_del(&stream->node);
>>   	spin_unlock(&sdev->stream_list_lock);
>> -- 
>> QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a member
>> of Code Aurora Forum, hosted by The Linux Foundation
>>