linux-kernel - Re: bonding: potential null dereference?

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Date:	Fri, 08 Jan 2010 09:46:00 -0800
From:	Jay Vosburgh <fubar@...ibm.com>
To:	Jiri Slaby <jirislaby@...il.com>
cc:	netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>,
	bonding-devel@...ts.sourceforge.net,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: bonding: potential null dereference?

Jiri Slaby <jirislaby@...il.com> wrote:

>I'm looking at Stanse errors and it detected a suspected behaviour in
>bonding. In bond_slave_netdev_event, bond_dev is passed down to
>netdev_priv, but due to 'if (bond_dev)' test later, it deduced it can be
>also NULL.
>
>I can see, that passing NULL to netdev_priv is OK nowadays, as it just
>returns NULL + some offset. But what if this changes in the future?
>
>I would bake a patch, but I don't know if bond_dev may be NULL at all
>(i.e. superfluous test) or may not (wrong netdev_priv(bond_dev)).
>
>static int (unsigned long event,
>                                   struct net_device *slave_dev)
>{
>        struct net_device *bond_dev = slave_dev->master;
>        struct bonding *bond = netdev_priv(bond_dev);
>
>        switch (event) {
>        case NETDEV_UNREGISTER:
>                if (bond_dev) {
>                        if (bond->setup_by_slave)
>                                bond_release_and_destroy(bond_dev,
>slave_dev);
>                        else
>                                bond_release(bond_dev, slave_dev);
>                }
>                break;

	I don't believe bond_dev will ever actually be NULL here,
because bond_netdev_event (the only caller of bond_slave_netdev_event)
checks that the device is, in fact, a bonding slave before the call.

	Just from looking at the code, I don't see any issues with
removing the "if (bond_dev)" test.

	-J

---
	-Jay Vosburgh, IBM Linux Technology Center, fubar@...ibm.com
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