l2tp: initialise l2tp_eth sessions before registering them
commit ee28de6b upstream. Sessions must be initialised before being made externally visible by l2tp_session_register(). Otherwise the session may be concurrently deleted before being initialised, which can confuse the deletion path and eventually lead to kernel oops. Therefore, we need to move l2tp_session_register() down in l2tp_eth_create(), but also handle the intermediate step where only the session or the netdevice has been registered. We can't just call l2tp_session_register() in ->ndo_init() because we'd have no way to properly undo this operation in ->ndo_uninit(). Instead, let's register the session and the netdevice in two different steps and protect the session's device pointer with RCU. And now that we allow the session's .dev field to be NULL, we don't need to prevent the netdevice from being removed anymore. So we can drop the dev_hold() and dev_put() calls in l2tp_eth_create() and l2tp_eth_dev_uninit(). Backporting Notes l2tp_eth.c: In l2tp_eth_create the "out" label was renamed to "err". There was one extra occurrence of "goto out" to update. Fixes: d9e31d17 ("l2tp: Add L2TP ethernet pseudowire support") Signed-off-by:Guillaume Nault <g.nault@alphalink.fr> Signed-off-by:
David S. Miller <davem@davemloft.net> Signed-off-by:
Giuliano Procida <gprocida@google.com> Signed-off-by:
Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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