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SubjectRe: [PATCH] don't allow CAP_NET_ADMIN to load non-netdev kernel modules
27.02.2011 23:22, Arnd Bergmann wrote:
> On Friday 25 February 2011, Michał Mirosław wrote:
>>> 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.
>
> The backwards compatibility should mostly be for systems that today don't
> use split capabilities, right?
>
> The fallback could therefore rely on CAP_SYS_MODULE as well:
>
> if (request_module("netdev-%s", name)) {
> if (capable(CAP_SYS_MODULE))
> request_module("%s", name);
> }
>
> Not 100% solution, but should solve the capability escalation nicely without
> causing much pain.

To me this looks like the best solution so far - trivial and
compatible.

Thanks!

/mjt
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