linux-kernel - Re: [PATCH] don't allow CAP_NET_ADMIN to load non-netdev kernel modules

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Date:	Fri, 25 Feb 2011 21:59:50 +0100
From:	Michał Mirosław <mirqus@...il.com>
To:	Ben Hutchings <bhutchings@...arflare.com>
Cc:	David Miller <davem@...emloft.net>, segoon@...nwall.com,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	kuznet@....inr.ac.ru, pekkas@...core.fi, jmorris@...ei.org,
	yoshfuji@...ux-ipv6.org, kaber@...sh.net, eric.dumazet@...il.com,
	therbert@...gle.com, xiaosuo@...il.com, jesse@...ira.com,
	kees.cook@...onical.com, eugene@...hat.com,
	dan.j.rosenberg@...il.com, akpm@...ux-foundation.org
Subject: Re: [PATCH] don't allow CAP_NET_ADMIN to load non-netdev kernel modules

2011/2/25 Ben Hutchings <bhutchings@...arflare.com>:
> I bet something like this (plus Vasiliy's changes to static module
> aliases) would cover 99.9% of legitimate uses of this feature:
>
> diff --git a/net/core/dev.c b/net/core/dev.c
> index 54aaca6..0d09baa 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -1120,8 +1120,20 @@ void dev_load(struct net *net, const char *name)
>        dev = dev_get_by_name_rcu(net, name);
>        rcu_read_unlock();
>
> -       if (!dev && capable(CAP_NET_ADMIN))
> -               request_module("%s", name);
> +       if (!dev && capable(CAP_NET_ADMIN)) {
> +               /* Check whether the name looks like one that a net
> +                * driver will generate initially.  If not, require a
> +                * module alias with a suitable prefix, so that this
> +                * can't be used to load arbitrary modules.
> +                */
> +               if ((strncmp(name, "eth", 3) == 0 &&
> +                    isdigit((unsigned char)name[3])) ||
> +                   (strncmp(name, "wlan", 4) == 0 &&
> +                    isdigit((unsigned char)name[4])))
> +                       request_module("%s", name);
> +               else
> +                       request_module("netdev-%s", name);
> +       }
>  }
>  EXPORT_SYMBOL(dev_load);
>

This might be better as:

if (request_module("netdev-%s", name))
    ... fallback

Then after some years the fallback could be removed if announced properly.

Best Regards,
Michał Mirosław
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