Comment 0 for bug 804366

Since a8f80e8ff94ecba629542d9b4b5f5a8ee3eb565c any process with
CAP_NET_ADMIN may load any module from /lib/modules/. This doesn't mean
that CAP_NET_ADMIN is a superset of CAP_SYS_MODULE as modules are
limited to /lib/modules/**. However, CAP_NET_ADMIN capability shouldn't
allow anybody load any module not related to networking.

This patch restricts an ability of autoloading modules to netdev modules
with explicit aliases. This fixes CVE-2011-1019.

Arnd Bergmann suggested to leave untouched the old pre-v2.6.32 behavior
of loading netdev modules by name (without any prefix) for processes
with CAP_SYS_MODULE to maintain the compatibility with network scripts
that use autoloading netdev modules by aliases like "eth0", "wlan0".

Currently there are only three users of the feature in the upstream
kernel: ipip, ip_gre and sit.

    root@albatros:~# capsh --drop=$(seq -s, 0 11),$(seq -s, 13 34) --
    root@albatros:~# grep Cap /proc/$$/status
    CapInh: 0000000000000000
    CapPrm: fffffff800001000
    CapEff: fffffff800001000
    CapBnd: fffffff800001000
    root@albatros:~# modprobe xfs
    FATAL: Error inserting xfs
    (/lib/modules/2.6.38-rc6-00001-g2bf4ca3/kernel/fs/xfs/xfs.ko): Operation
not permitted
    root@albatros:~# lsmod | grep xfs
    root@albatros:~# ifconfig xfs
    xfs: error fetching interface information: Device not found
    root@albatros:~# lsmod | grep xfs
    root@albatros:~# lsmod | grep sit
    root@albatros:~# ifconfig sit
    sit: error fetching interface information: Device not found
    root@albatros:~# lsmod | grep sit
    root@albatros:~# ifconfig sit0
    sit0 Link encap:IPv6-in-IPv4
       NOARP MTU:1480 Metric:1

    root@albatros:~# lsmod | grep sit
    sit 10457 0
    tunnel4 2957 1 sit

For CAP_SYS_MODULE module loading is still relaxed:

        root@albatros:~# grep Cap /proc/$$/status
        CapInh: 0000000000000000
        CapPrm: ffffffffffffffff
        CapEff: ffffffffffffffff
        CapBnd: ffffffffffffffff
        root@albatros:~# ifconfig xfs
        xfs: error fetching interface information: Device not found
        root@albatros:~# lsmod | grep xfs
        xfs 745319 0

    Reference: https://lkml.org/lkml/2011/2/24/203

    [PG: in 2.6.34, the bare MODULE_ALIAS for ipip/tunl0 and ip_gre/gre0
    didn't exist, but this adds the limited scope MODULE_ALIAS_NETDEV ones]