[commits] [batman-adv] maint: batman-adv: Fix inconsistent teardown and release of private netdev state. (33e9de0c)

postmaster at open-mesh.org postmaster at open-mesh.org
Tue Jun 13 12:14:51 CEST 2017

Repository : ssh://git@open-mesh.org/batman-adv

On branch  : maint


commit 33e9de0c769c7b0c5e615a5788b0f09655304720
Author: David S. Miller <davem at davemloft.net>
Date:   Fri Jun 9 18:42:34 2017 +0200

    batman-adv: 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()
    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()
    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
    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 at davemloft.net>
    [sven at narfation.org: Add compat code]
    Signed-off-by: Sven Eckelmann <sven at narfation.org>
    [sw: pimped the compat code]
    Signed-off-by: Simon Wunderlich <sw at simonwunderlich.de>


 compat-include/linux/netdevice.h | 19 +++++++++++++++++++
 net/batman-adv/soft-interface.c  |  5 ++---
 2 files changed, 21 insertions(+), 3 deletions(-)

diff --git a/compat-include/linux/netdevice.h b/compat-include/linux/netdevice.h
index 1a37952c..1b36e529 100644
--- a/compat-include/linux/netdevice.h
+++ b/compat-include/linux/netdevice.h
@@ -86,4 +86,23 @@ static inline void batadv_netif_trans_update(struct net_device *dev)
 #endif /* < KERNEL_VERSION(4, 7, 0) */
+/* work around missing attribute needs_free_netdev and priv_destructor in
+ * net_device
+ */
+#define ether_setup(dev) \
+	void batadv_softif_free2(struct net_device *dev) \
+	{ \
+		batadv_softif_free(dev); \
+		free_netdev(dev); \
+	} \
+	void (*t1)(struct net_device *dev) __attribute__((unused)); \
+	bool t2 __attribute__((unused)); \
+	ether_setup(dev)
+#define needs_free_netdev destructor = batadv_softif_free2; t2
+#define priv_destructor destructor = batadv_softif_free2; t1
+#endif /* < KERNEL_VERSION(4, 12, 0) */
diff --git a/net/batman-adv/soft-interface.c b/net/batman-adv/soft-interface.c
index b25789ab..10f7edfb 100644
--- a/net/batman-adv/soft-interface.c
+++ b/net/batman-adv/soft-interface.c
@@ -1034,8 +1034,6 @@ static void batadv_softif_free(struct net_device *dev)
 	 * netdev and its private data (bat_priv)
-	free_netdev(dev);
@@ -1047,7 +1045,8 @@ static void batadv_softif_init_early(struct net_device *dev)
 	dev->netdev_ops = &batadv_netdev_ops;
-	dev->destructor = batadv_softif_free;
+	dev->needs_free_netdev = true;
+	dev->priv_destructor = batadv_softif_free;
 	dev->priv_flags |= IFF_NO_QUEUE;

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