netdev - Re: [PATCH net] net: Fix null de-reference of device refcount

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Message-Id: <20190912.125632.1276632741198765477.davem@davemloft.net>
Date:   Thu, 12 Sep 2019 12:56:32 +0200 (CEST)
From:   David Miller <davem@...emloft.net>
To:     subashab@...eaurora.org
Cc:     dlezcano@...ibm.com, eric.dumazet@...il.com,
        netdev@...r.kernel.org, stranche@...eaurora.org
Subject: Re: [PATCH net] net: Fix null de-reference of device refcount

From: Subash Abhinov Kasiviswanathan <subashab@...eaurora.org>
Date: Tue, 10 Sep 2019 14:02:57 -0600

> In event of failure during register_netdevice, free_netdev is
> invoked immediately. free_netdev assumes that all the netdevice
> refcounts have been dropped prior to it being called and as a
> result frees and clears out the refcount pointer.
> 
> However, this is not necessarily true as some of the operations
> in the NETDEV_UNREGISTER notifier handlers queue RCU callbacks for
> invocation after a grace period. The IPv4 callback in_dev_rcu_put
> tries to access the refcount after free_netdev is called which
> leads to a null de-reference-
 ...
> Fix this by waiting for the completion of the call_rcu() in
> case of register_netdevice errors.
> 
> Fixes: 93ee31f14f6f ("[NET]: Fix free_netdev on register_netdev failure.")
> Cc: Sean Tranchetti <stranche@...eaurora.org>
> Signed-off-by: Subash Abhinov Kasiviswanathan <subashab@...eaurora.org>

Applied and queued up for -stable.