Re: [PATCH net-next 4/4] ethtool: runtime-resume netdev parent in ethnl_ops_begin

On 05.08.2021 13:51, Julian Wiedmann wrote:

On 01.08.21 13:41, Heiner Kallweit wrote:

quoted

If a network device is runtime-suspended then:
- network device may be flagged as detached and all ethtool ops (even if not
  accessing the device) will fail because netif_device_present() returns
  false
- ethtool ops may fail because device is not accessible (e.g. because being
  in D3 in case of a PCI device)

It may not be desirable that userspace can't use even simple ethtool ops
that not access the device if interface or link is down. To be more friendly
to userspace let's ensure that device is runtime-resumed when executing the
respective ethtool op in kernel.

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
---
 net/ethtool/netlink.c | 31 +++++++++++++++++++++++++------
 1 file changed, 25 insertions(+), 6 deletions(-)

[...]

quoted

 
 void ethnl_ops_complete(struct net_device *dev)
 {
 	if (dev && dev->ethtool_ops->complete)
 		dev->ethtool_ops->complete(dev);
+
+	if (dev->dev.parent)
+		pm_runtime_put(dev->dev.parent);
 }
 
 /**

Hello Heiner,

Coverity complains that we checked dev != NULL earlier but now
unconditionally dereference it:

Thanks for the hint. I wonder whether we have any valid case where
dev could be NULL. There are several places where dev is dereferenced
after the call to ethnl_ops_begin(). Just one example:
linkmodes_prepare_data()

Only ethnl_request_ops where allow_nodev_do is true is
ethnl_strset_request_ops. However in strset_prepare_data()
ethnl_ops_begin() is called only if dev isn't NULL.
Supposedly we should return an error from ethnl_ops_begin()
if dev is NULL.

*** CID 1506213:  Null pointer dereferences  (FORWARD_NULL)
/net/ethtool/netlink.c: 67 in ethnl_ops_complete()
61     
62     void ethnl_ops_complete(struct net_device *dev)
63     {
64     	if (dev && dev->ethtool_ops->complete)
65     		dev->ethtool_ops->complete(dev);
66     

quoted

quoted

quoted

    CID 1506213:  Null pointer dereferences  (FORWARD_NULL)
    Dereferencing null pointer "dev".

67     	if (dev->dev.parent)
68     		pm_runtime_put(dev->dev.parent);
69     }
70     
71     /**
72      * ethnl_parse_header_dev_get() - parse request header