Re: [PATCH v4 3/3] IB/ipoib: Log sysfs 'dev_id' accesses from userspace

[Jason Gunthorpe <jgg@ziepe.ca>]

On Fri, Sep 07, 2018 at 01:14:51PM -0400, Doug Ledford wrote:
> On Fri, 2018-09-07 at 09:43 -0600, Jason Gunthorpe wrote:
> > On Thu, Sep 06, 2018 at 05:51:12PM +0300, Arseny Maslennikov wrote:
> > > Some tools may currently be using only the deprecated attribute;
> > > let's print an elaborate and clear deprecation notice to kmsg.
> > > 
> > > To do that, we have to replace the whole sysfs file, since we inherit
> > > the original one from netdev.
> > > 
> > > Signed-off-by: Arseny Maslennikov <ar@cs.msu.ru>
> > >  drivers/infiniband/ulp/ipoib/ipoib_main.c | 31 +++++++++++++++++++++++
> > >  1 file changed, 31 insertions(+)
> > > 
> > > diff --git a/drivers/infiniband/ulp/ipoib/ipoib_main.c b/drivers/infiniband/ulp/ipoib/ipoib_main.c
> > > index 30f840f874b3..74732726ec6f 100644
> > > +++ b/drivers/infiniband/ulp/ipoib/ipoib_main.c
> > > @@ -2386,6 +2386,35 @@ 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);
> > > +
> > > +	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? See Documentation/ABI/testing/sysfs-class-net for more info.\n",
> > > +			current->comm);
> > > +
> > > +	return sprintf(buf, "%#x\n", ndev->dev_id);
> > > +}
> > > +static DEVICE_ATTR_RO(dev_id);
> > > +
> > > +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);
> > > +}
> > 
> > Isn't this racey with userspace? Ie what happens if udev is querying
> > the dev_id right here?
> > 
> > Do we know there is no userspace doing this?
> 
> I don't think that it can race (or reasonably can).  The intercept
> function is done as part of ipoib_add_port() so the port itself isn't
> live yet.

The above code is after register_netdev, so the port itself is
certainly live as far as userspace is concerned..

All the other sysfs stuff in add_port is already wrong/racy.. See
Parav's recent series fixing this for the main devices..

Jason