path: root/drivers/net/slip
diff options
authorDavid S. Miller <davem@davemloft.net>2017-05-08 12:52:56 -0400
committerDavid S. Miller <davem@davemloft.net>2017-06-07 15:53:24 -0400
commitcf124db566e6b036b8bcbe8decbed740bdfac8c6 (patch)
treeebe7dd29c461575ec091583da4ec5dd75ffcd5d2 /drivers/net/slip
parentbpf, arm64: use separate register for state in stxr (diff)
net: Fix inconsistent teardown and release of private netdev state.
Network devices can allocate reasources and private memory using netdev_ops->ndo_init(). However, the release of these resources can occur in one of two different places. Either netdev_ops->ndo_uninit() or netdev->destructor(). The decision of which operation frees the resources depends upon whether it is necessary for all netdev refs to be released before it is safe to perform the freeing. netdev_ops->ndo_uninit() presumably can occur right after the NETDEV_UNREGISTER notifier completes and the unicast and multicast address lists are flushed. netdev->destructor(), on the other hand, does not run until the netdev references all go away. Further complicating the situation is that netdev->destructor() almost universally does also a free_netdev(). This creates a problem for the logic in register_netdevice(). Because all callers of register_netdevice() manage the freeing of the netdev, and invoke free_netdev(dev) if register_netdevice() fails. If netdev_ops->ndo_init() succeeds, but something else fails inside of register_netdevice(), it does call ndo_ops->ndo_uninit(). But it is not able to invoke netdev->destructor(). This is because netdev->destructor() will do a free_netdev() and then the caller of register_netdevice() will do the same. However, this means that the resources that would normally be released by netdev->destructor() will not be. Over the years drivers have added local hacks to deal with this, by invoking their destructor parts by hand when register_netdevice() fails. Many drivers do not try to deal with this, and instead we have leaks. Let's close this hole by formalizing the distinction between what private things need to be freed up by netdev->destructor() and whether the driver needs unregister_netdevice() to perform the free_netdev(). netdev->priv_destructor() performs all actions to free up the private resources that used to be freed by netdev->destructor(), except for free_netdev(). netdev->needs_free_netdev is a boolean that indicates whether free_netdev() should be done at the end of unregister_netdevice(). Now, register_netdevice() can sanely release all resources after ndo_ops->ndo_init() succeeds, by invoking both ndo_ops->ndo_uninit() and netdev->priv_destructor(). And at the end of unregister_netdevice(), we invoke netdev->priv_destructor() and optionally call free_netdev(). Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'drivers/net/slip')
1 files changed, 3 insertions, 4 deletions
diff --git a/drivers/net/slip/slip.c b/drivers/net/slip/slip.c
index 1da31dc47f86..74b907206aa7 100644
--- a/drivers/net/slip/slip.c
+++ b/drivers/net/slip/slip.c
@@ -629,7 +629,7 @@ static void sl_uninit(struct net_device *dev)
static void sl_free_netdev(struct net_device *dev)
int i = dev->base_addr;
- free_netdev(dev);
slip_devs[i] = NULL;
@@ -651,7 +651,8 @@ static const struct net_device_ops sl_netdev_ops = {
static void sl_setup(struct net_device *dev)
dev->netdev_ops = &sl_netdev_ops;
- dev->destructor = sl_free_netdev;
+ dev->needs_free_netdev = true;
+ dev->priv_destructor = sl_free_netdev;
dev->hard_header_len = 0;
dev->addr_len = 0;
@@ -1369,8 +1370,6 @@ static void __exit slip_exit(void)
if (sl->tty) {
printk(KERN_ERR "%s: tty discipline still running\n",
- /* Intentionally leak the control block. */
- dev->destructor = NULL;