linux-kernel - Re: [PATCH] net: mdiobus: Fix memory leak in __mdiobus

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Date:   Tue, 28 Sep 2021 12:26:57 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     Yanfei Xu <yanfei.xu@...driver.com>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>
Cc:     andrew@...n.ch, hkallweit1@...il.com, linux@...linux.org.uk,
        davem@...emloft.net, kuba@...nel.org, p.zabel@...gutronix.de,
        syzbot+398e7dc692ddbbb4cfec@...kaller.appspotmail.com,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
        Pavel Skripkin <paskripkin@...il.com>,
        Dongliang Mu <mudongliangabcd@...il.com>
Subject: Re: [PATCH] net: mdiobus: Fix memory leak in __mdiobus_register

On Tue, Sep 28, 2021 at 11:55:49AM +0300, Dan Carpenter wrote:
> I don't have a solution.  I have commented before that I hate kobjects
> for this reason because they lead to unfixable memory leaks during
> probe.  But this leak will only happen with fault injection and so it
> doesn't affect real life.  And even if it did, a leak it preferable to a
> crash.

The fix for this should have gone in devm_of_mdiobus_register() but it's
quite tricky.

drivers/net/phy/mdio_devres.c
   106  int devm_of_mdiobus_register(struct device *dev, struct mii_bus *mdio,
   107                               struct device_node *np)
   108  {
   109          struct mdiobus_devres *dr;
   110          int ret;
   111  
   112          if (WARN_ON(!devres_find(dev, devm_mdiobus_free,
   113                                   mdiobus_devres_match, mdio)))
   114                  return -EINVAL;

This leaks the bus.  Fix this leak by calling mdiobus_release(mdio);

   115  
   116          dr = devres_alloc(devm_mdiobus_unregister, sizeof(*dr), GFP_KERNEL);
   117          if (!dr)
   118                  return -ENOMEM;

Fix this path by calling mdiobus_release(mdio);

   119  
   120          ret = of_mdiobus_register(mdio, np);
   121          if (ret) {

Ideally here we can could call device_put(mdio), but that won't work for
the one error path that occurs before device_initialize(). /* Do not
continue if the node is disabled */.

Maybe the code could be modified to call device_initialize() on the
error path?  Sort of ugly but it would work.

   122                  devres_free(dr);
   123                  return ret;
   124          }
   125  
   126          dr->mii = mdio;
   127          devres_add(dev, dr);
   128          return 0;
   129  }

Then audit the callers, and there is only one which references the
mdio_bus after devm_of_mdiobus_register() fails.  It's
realtek_smi_setup_mdio().  Modify that debug statement.

regards,
dan carpenter