netdev - Re: [PATCH net-next 3/3 v9] drivers: net: ethernet: qualcomm: rmnet: Initial implementation

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Fri, 25 Aug 2017 20:06:23 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     subashab@...eaurora.org
Cc:     netdev@...r.kernel.org, fengguang.wu@...el.com, dcbw@...hat.com,
        jiri@...nulli.us, stephen@...workplumber.org,
        David.Laight@...LAB.COM, marcel@...tmann.org, andrew@...n.ch
Subject: Re: [PATCH net-next 3/3 v9] drivers: net: ethernet: qualcomm:
 rmnet: Initial implementation

From: Subash Abhinov Kasiviswanathan <subashab@...eaurora.org>
Date: Thu, 24 Aug 2017 22:39:26 -0600

> +static void rmnet_force_unassociate_device(struct net_device *dev)
> +{
> +	struct net_device *real_dev = dev;
> +	struct rmnet_walk_data d;
> +	LIST_HEAD(list);
> +
> +	if (!rmnet_is_real_dev_registered(real_dev))
> +		return;
> +
> +	ASSERT_RTNL();
> +
> +	d.real_dev = real_dev;
> +	d.head = &list;
> +
> +	rcu_read_lock();
> +	netdev_walk_all_lower_dev_rcu(real_dev, rmnet_dev_walk_unreg, &d);
> +	synchronize_net();
> +
> +	unregister_netdevice_many(&list);
> +	rcu_read_unlock();
> +
> +	rmnet_unregister_real_device(real_dev);
> +}

In these code paths where you are the writer, you have to rely upon
the RTNL mutex (or some other mutual exclusion mechanism) to protect
the update operation.  RCU locking itself does not provide this.

So you should use something like rcu_dereference_rtnl() or similar.

So this would be rmnet_force_unassociate_device() and rmnet_dellink()

RCU is subtle and the writer paths have the be handled differently
from the reader paths.  Please take some time to study how RCU should
be applied properly in these situations rather than just slapping a
patch together overnight.

Thank you.