linux-kernel - Re: rionet: NULL pointer dereference

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Date:	Thu, 16 Jun 2011 15:53:24 -0700
From:	Connor Hansen <cmdkhh@...il.com>
To:	Jesper Juhl <jj@...osbits.net>
Cc:	linux-kernel@...r.kernel.org,
	Matt Porter <mporter@...nel.crashing.org>,
	netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>
Subject: Re: rionet: NULL pointer dereference

On Thu, Jun 16, 2011 at 3:06 PM, Jesper Juhl <jj@...osbits.net> wrote:
> Hi
>
> Just noticed that drivers/net/rionet.c::rionet_remove() can cause a NULL
> deref when it calls unregister_netdev().
> It initializes local variable 'ndev' to NULL and nothing changes this
> before the call to unregister_netdev(ndev) - that functions then calls:
> unregister_netdevice > unregister_netdevice_queue > list_move_tail >
> __list_del_entry  which dereferences the pointer (which, being NULL, will
> end in tears).

unregister_netdevice(struct net_device *dev)
{
        unregister_netdevice_queue(dev, NULL);
}

 so unregister_netdevice_queue is being called with NULL,NULL

void unregister_netdevice_queue(struct net_device *dev, struct list_head *head)
{
        ASSERT_RTNL();

        if (head) {
                list_move_tail(&dev->unreg_list, head);
        } else {
                rollback_registered(dev);
                /* Finish processing unregister after unlock */
                net_set_todo(dev);
        }
}

if head is null, which it is from the call, then we call
rollback_registered, and not list_move_tail()

the else calls rollback_registered(NULL) then net_set_todo(NULL)

both of which dereference null when passed, so yes there is a null
dereference, just not in the code branch you thought.

static void rollback_registered(struct net_device *dev)
{
        LIST_HEAD(single);

        list_add(&dev->unreg_list, &single);    null dereference
        rollback_registered_many(&single);
        list_del(&single);
}

static void net_set_todo(struct net_device *dev)
{
        list_add_tail(&dev->todo_list, &net_todo_list);  null dereference
}

Connor

>
> I won't claim to know this code nor what the proper fix is; just thought
> i'd report it so someone else with more knowledge of this could perhaps
> come up with a fix.
>
> Have a nice day.
>
> --
> Jesper Juhl <jj@...osbits.net>       http://www.chaosbits.net/
> Don't top-post http://www.catb.org/jargon/html/T/top-post.html
> Plain text mails only, please.
>
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