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Date:   Fri, 22 Mar 2019 08:35:24 +0000
From:   Fabien DESSENNE <fabien.dessenne@...com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
CC:     Jiri Slaby <jslaby@...e.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Benjamin GAIGNARD <benjamin.gaignard@...com>
Subject: Re: [PATCH] tty: fix NULL pointer issue when tty_port ops is not set

Hi Greg,

I do not think that any driver faces this problem.

Nevertheless I found 2 drivers declaring an 'empty' struct (wasted) to 
solve this issue:

drivers/char/ttyprintk:
static const struct tty_port_operations null_ops = { };

drivers/tty/vcc.c:
static struct tty_port_operations vcc_port_ops = { 0 };


Please let me know if you prefer I abandon this patch and use an 'empty' 
struct in the new code I add.

Or if you think that this patch is safe, feel free to ask me to update 
the two drivers listed above.


BR


Fabien



On 21/03/2019 6:38 PM, Greg Kroah-Hartman wrote:
> On Thu, Mar 21, 2019 at 04:43:26PM +0100, Fabien Dessenne wrote:
>> Unlike 'client_ops' which is initialized to 'default_client_ops', the
>> port operations 'ops' may be left to NULL.
>> Check the 'ops' value before checking the 'ops->x' value.
>>
>> Signed-off-by: Fabien Dessenne <fabien.dessenne@...com>
>> ---
>>   drivers/tty/tty_port.c | 10 +++++-----
>>   1 file changed, 5 insertions(+), 5 deletions(-)
>>
>> diff --git a/drivers/tty/tty_port.c b/drivers/tty/tty_port.c
>> index 044c3cb..a9e12b3 100644
>> --- a/drivers/tty/tty_port.c
>> +++ b/drivers/tty/tty_port.c
>> @@ -325,7 +325,7 @@ static void tty_port_shutdown(struct tty_port *port, struct tty_struct *tty)
>>   		if (tty && C_HUPCL(tty))
>>   			tty_port_lower_dtr_rts(port);
>>   
>> -		if (port->ops->shutdown)
>> +		if (port->ops && port->ops->shutdown)
>>   			port->ops->shutdown(port);
>>   	}
>>   out:
>> @@ -398,7 +398,7 @@ EXPORT_SYMBOL_GPL(tty_port_tty_wakeup);
>>    */
>>   int tty_port_carrier_raised(struct tty_port *port)
>>   {
>> -	if (port->ops->carrier_raised == NULL)
>> +	if (!port->ops || !port->ops->carrier_raised)
>>   		return 1;
>>   	return port->ops->carrier_raised(port);
>>   }
>> @@ -414,7 +414,7 @@ EXPORT_SYMBOL(tty_port_carrier_raised);
>>    */
>>   void tty_port_raise_dtr_rts(struct tty_port *port)
>>   {
>> -	if (port->ops->dtr_rts)
>> +	if (port->ops && port->ops->dtr_rts)
>>   		port->ops->dtr_rts(port, 1);
>>   }
>>   EXPORT_SYMBOL(tty_port_raise_dtr_rts);
>> @@ -429,7 +429,7 @@ EXPORT_SYMBOL(tty_port_raise_dtr_rts);
>>    */
>>   void tty_port_lower_dtr_rts(struct tty_port *port)
>>   {
>> -	if (port->ops->dtr_rts)
>> +	if (port->ops && port->ops->dtr_rts)
>>   		port->ops->dtr_rts(port, 0);
>>   }
>>   EXPORT_SYMBOL(tty_port_lower_dtr_rts);
>> @@ -684,7 +684,7 @@ int tty_port_open(struct tty_port *port, struct tty_struct *tty,
>>   
>>   	if (!tty_port_initialized(port)) {
>>   		clear_bit(TTY_IO_ERROR, &tty->flags);
>> -		if (port->ops->activate) {
>> +		if (port->ops && port->ops->activate) {
>>   			int retval = port->ops->activate(port, tty);
>>   			if (retval) {
>>   				mutex_unlock(&port->mutex);
>> -- 
>> 2.7.4
>>
> Can you hit this today with any in-kernel drivers?  Or is this only for
> your new code you are adding?
>
> thanks,
>
> greg k-h

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