Re: [PATCH net-next v3 12/15] ibmveth: Expose per-queue buffer pool details via sysfs

[Simon Horman <horms@kernel.org>]

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---
ibmveth: Expose per-queue buffer pool details via sysfs

This commit adds a read-only sysfs attribute buffer_pools to the VIO device
to expose per-queue buffer pool details dynamically. It outputs runtime per-queue
buffer pressure metrics like size, active, and available buffers.

> diff --git a/drivers/net/ethernet/ibm/ibmveth.c b/drivers/net/ethernet/ibm/ibmveth.c
> index 4e3f49b6346fd..ecc472ee8f71f 100644
> --- a/drivers/net/ethernet/ibm/ibmveth.c
> +++ b/drivers/net/ethernet/ibm/ibmveth.c
> @@ -2896,6 +2896,52 @@ static const struct net_device_ops ibmveth_netdev_ops = {
[ ... ]
> +static ssize_t buffer_pools_show(struct device *dev,
> +				 struct device_attribute *attr,
> +				 char *buf)
> +{
> +	struct net_device *netdev = dev_get_drvdata(dev);
> +	struct ibmveth_adapter *adapter = netdev_priv(netdev);
> +	int len = 0;
> +	int i, j;
> +
> +	len += scnprintf(buf + len, PAGE_SIZE - len,
> +			 "Queue  Pool  Size  BuffSize  Active  Available\n");
> +	len += scnprintf(buf + len, PAGE_SIZE - len,
> +			 "-----  ----  ----  --------  ------  ---------\n");

[Severity: Medium]
Does this buffer_pools_show() implementation violate the sysfs "one value
per file" design rule? 

The attribute appears to dump a complex, multi-line ASCII table with headers
and columns rather than exposing a single value per sysfs file.

[ ... ]
> @@ -3056,6 +3102,14 @@ static int ibmveth_probe(struct vio_dev *dev, const struct vio_device_id *id)
>  
>  	netdev_dbg(netdev, "registered\n");
>  
> +	rc = sysfs_create_group(&dev->dev.kobj, &ibmveth_attr_group);
> +	if (rc) {
> +		netdev_err(netdev, "failed to create sysfs attributes rc=%d\n", rc);
> +		unregister_netdev(netdev);
> +		free_netdev(netdev);
> +		return rc;
> +	}

[Severity: High]
If userspace brings up the interface immediately after register_netdev()
succeeds, could adapter->work be scheduled before sysfs_create_group() fails?

If this race occurs, unregister_netdev() does not synchronously cancel the
work. 

Could the global workqueue execute the pending adapter->work item on freed
memory after free_netdev() is called in this ibmveth_probe() error path?

[Severity: High]
This is a pre-existing issue in older error paths of ibmveth_probe(), but it
is duplicated here: does this error path leak the adapter->rx_buff_pool
kobjects?

Since kobject_put() is not called on the pool kobjects before free_netdev()
is executed, the kobjects remain attached to the VIO device with dangling
pointers to the freed adapter memory. 

Could subsequent sysfs accesses to those pool kobjects trigger a
use-after-free?