Subject: Re: [PATCH v4 net-next 04/10] net/ncsi: Ethtool operation to get NCSI topology

From: Gavin Shan <[email-masked]>
Date: Thu, 4 May 2017 16:15:59 +1000

On Wed, May 03, 2017 at 10:19:44PM -0700, Stephen Hemminger wrote:
>On Wed,  3 May 2017 14:44:35 +1000
>Gavin Shan <[email-masked]> wrote:
>
>> +static int ethtool_get_ncsi_channels(struct net_device *dev,
>> +				     void __user *useraddr)
>
>Please don't use an opaque type for this. See how other ethtool
>operations take a struct.
>

After checking output from below command, all other ethtool operations
uses "void __user *" or "char __user *".

   git grep static.*useraddr net/core/ethtool.c

>> +{
>> +	struct ethtool_ncsi_channels *enc;
>> +	short nr_channels;
>Should be __u16 or unsigned not short.
>

Nope, It's for signed number. User expects to get number of available
channels when negative number is passed in. When it's positive, it's
going to get the channels' information.

>> +	ssize_t size = 0;
>> +	int ret;
>> +
>> +	if (!dev->ethtool_ops->get_ncsi_channels)
>> +		return -EOPNOTSUPP;
>> +
>> +	if (copy_from_user(&nr_channels, useraddr + sizeof(enc->cmd),
>> +			   sizeof(nr_channels)))
>> +		return -EFAULT;
>> +
>> +	size = sizeof(*enc);
>> +	if (nr_channels > 0)
>> +		size += nr_channels * sizeof(enc->id[0]);
>
>You have no upper bound on number of channels, and therefore an incorrectly
>application could grab an excessive amount of kernel memory.
>

Yeah, I'll limit it to 256 in next respin. 256 is the maximal number
of channels for one particular net device.

Cheers,
Gavin