Re: [PATCH net 2/2] netdev: Enforce index cap in netdev_get_tx_queue

[Nick Child <nnac123@linux.ibm.com>]

On 3/17/23 13:45, Piotr Raczynski wrote:
> On Fri, Mar 17, 2023 at 01:19:41PM -0500, Nick Child wrote:
>> When requesting a TX queue at a given index, prevent out-of-bounds
>> referencing by ensuring that the index is within the allocated number
>> of queues.
>>
>> If there is an out-of-bounds reference then inform the user and return
>> a reference to the first tx queue instead.
>>
>> Fixes: e8a0464cc950 ("netdev: Allocate multiple queues for TX.")
>> Signed-off-by: Nick Child <nnac123@linux.ibm.com>
>> ---
>>   include/linux/netdevice.h | 7 +++++++
>>   1 file changed, 7 insertions(+)
>>
>> diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
>> index 23b0d7eaaadd..fe88b1a7393d 100644
>> --- a/include/linux/netdevice.h
>> +++ b/include/linux/netdevice.h
>> @@ -2482,6 +2482,13 @@ static inline
>>   struct netdev_queue *netdev_get_tx_queue(const struct net_device *dev,
>>   					 unsigned int index)
>>   {
>> +	if (unlikely(index >= dev->num_tx_queues)) {
>> +		net_warn_ratelimited("%s selects TX queue %d, but number of TX queues is %d\n",
>> +				     dev->name, index,
>> +				     dev->num_tx_queues);
>> +		return &dev->_tx[0];
> 
> Why return first queue here instead of NULL, wouldn't that confuse the
> caller instead of return proper (NULL) value?
> 

Thanks for reviewing Piotr.
netdev_get_tx_queue has over 300 callers, most of these calls
use the returned queue immediately without any checking on
the returned value. I don't expect all of these callers
to go and add conditionals to handle this case either.

So I opted for the warning message and a valid return value.
That being said, I am open to more opinions.


> Piotr.
>> +	}
>> +
>>   	return &dev->_tx[index];
>>   }
>>   
>> -- 
>> 2.31.1
>>