Subject: Re: [PATCH v3 3/3] IB/ipoib: Log sysfs 'dev_id' accesses from userspace

From: Arseny Maslennikov <[email-masked]>
Date: Thu, 6 Sep 2018 10:04:33 +0300

On Wed, Sep 05, 2018 at 04:50:35PM +0300, Leon Romanovsky wrote:
> On Mon, Sep 03, 2018 at 07:13:16PM +0300, Arseny Maslennikov wrote:
> > Signed-off-by: Arseny Maslennikov <[email-masked]>
> > ---
> >  drivers/infiniband/ulp/ipoib/ipoib_main.c | 38 +++++++++++++++++++++++
> >  1 file changed, 38 insertions(+)
> >
> > diff --git a/drivers/infiniband/ulp/ipoib/ipoib_main.c b/drivers/infiniband/ulp/ipoib/ipoib_main.c
> > index 30f840f874b3..7386e5bde3d3 100644
> > --- a/drivers/infiniband/ulp/ipoib/ipoib_main.c
> > +++ b/drivers/infiniband/ulp/ipoib/ipoib_main.c
> > @@ -2386,6 +2386,42 @@ int ipoib_add_pkey_attr(struct net_device *dev)
> >  	return device_create_file(&dev->dev, &dev_attr_pkey);
> >  }
> >
> > +/*
> > + * We erroneously exposed the iface's port number in the dev_id
> > + * sysfs field long after dev_port was introduced for that purpose[1],
> > + * and we need to stop everyone from relying on that.
> > + * Let's overload the shower routine for the dev_id file here
> > + * to gently bring the issue up.
> > + *
> > + * [1] https://www.spinics.net/lists/netdev/msg272123.html
> > + */
> > +static ssize_t dev_id_show(struct device *dev,
> > +			   struct device_attribute *attr, char *buf)
> > +{
> > +	struct net_device *ndev = to_net_dev(dev);
> > +	ssize_t ret = -EINVAL;
> > +
> > +	if (ndev->dev_id == ndev->dev_port) {
> > +		netdev_info_once(ndev,
> > +			"\"%s\" wants to know my dev_id. "
> > +			"Should it look at dev_port instead?\n",
> > +			current->comm);
> > +		netdev_info_once(ndev,
> > +			"See Documentation/ABI/testing/sysfs-class-net for more info.\n");
> > +	}
> > +
> > +	ret = sprintf(buf, "%#x\n", ndev->dev_id);
> > +
> > +	return ret;
> > +}
> > +static DEVICE_ATTR_RO(dev_id);
> > +
> 
> I don't see this field among exposed by IPoIB, why should we expose it now?
> 

To deviate from standard netdev behaviour, which only prints the
field out. Doug wanted this to also print a deprecation message, and
netdev (obviously) does not do that. See below.

> > +int ipoib_intercept_dev_id_attr(struct net_device *dev)
> > +{
> > +	device_remove_file(&dev->dev, &dev_attr_dev_id);
> > +	return device_create_file(&dev->dev, &dev_attr_dev_id);
> 
> Why isn't enough to rely on netdev code?
> 

Netdev code relies on macros around a *static* function 'netdev_show',
which is defined in net/core/net-sysfs.c; it is not listed in any header
files, and the macros aren't as well. This all leads me to believe it
was not really meant to be used from outside net/core/net-sysfs.

The only way we could use any netdev code here is to set up our own
handler (again), printk() a message, then call netdev_show — but we have
no access to it.

Of course, it also may be that I'm terribly missing a clue.

> > +}
> > +
> >  static struct net_device *ipoib_add_port(const char *format,
> >  					 struct ib_device *hca, u8 port)
> >  {
> > @@ -2427,6 +2463,8 @@ static struct net_device *ipoib_add_port(const char *format,
> >  	 */
> >  	ndev->priv_destructor = ipoib_intf_free;
> >
> > +	if (ipoib_intercept_dev_id_attr(ndev))
> > +		goto sysfs_failed;
> >  	if (ipoib_cm_add_mode_attr(ndev))
> >  		goto sysfs_failed;
> >  	if (ipoib_add_pkey_attr(ndev))
> > --
> > 2.19.0.rc1
> >