Re: module loading with CAP_NET_ADMIN

From: Ben Hutchings
Date: Thu Feb 24 2011 - 11:34:35 EST

On Thu, 2011-02-24 at 18:12 +0300, Vasiliy Kulikov wrote:
> Hi netdev folks,
> I'd like to discuss the ability to load any modules from /lib/modules/
> by a process with CAP_NET_ADMIN. Since Linux 2.6.32 [1] there is such
> possibility:
> root@albatros:~# grep Cap /proc/$$/status
> CapInh: 0000000000000000
> CapPrm: fffffffc00001000
> CapEff: fffffffc00001000
> CapBnd: fffffffc00001000
> root@albatros:~# lsmod | grep xfs
> root@albatros:~# ifconfig xfs
> xfs: error fetching interface information: Device not found
> root@albatros:~# lsmod | grep xfs
> xfs 767011 0
> exportfs 4226 2 xfs,nfsd


> Ability of CAP_NET_ADMIN to load the driver to work with a particular
> network device is rational; however, one may load any module not even
> related to network this way. Hopefully, this is not equal to
> CAP_SYS_MODULE since the module set is restricted to /lib/modules
> (additionally may be disabled with /proc/sys/kernel/modules_disabled),
> but the idea of non-netdev module loading is weird.
> My proposal is changing request_module("%s", name) to something like
> request_module("netdev-%s", name) inside of dev_load() and adding
> aliases to related drivers.

AFAIK these interface-name aliases are usually defined by distribution
configuration files rather than within the modules themselves. And that
behaviour is pretty much obsolete now that we have hotplug and udev.

> This would allow to load only netdev
> modules via these ioctls. I'm not sure what modules should be patches -
> at least real physical netdevices have names different from drivers'
> names, so they don't need patching. I suppose the list is not big.

The only modules I can see that declare aliases like this are:



Ben Hutchings, Senior Software Engineer, Solarflare Communications
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.

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