[34-longterm 200/209] net: don't allow CAP_NET_ADMIN to load non-netdev kernel modules

From: Paul Gortmaker
Date: Thu Apr 14 2011 - 14:01:30 EST

From: Vasiliy Kulikov <segoon@xxxxxxxxxxxx>

| This is a commit scheduled for the next v2.6.34 longterm release. |
| If you see a problem with using this for longterm, please comment.|

commit 8909c9ad8ff03611c9c96c9a92656213e4bb495b upstream.

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]

Signed-off-by: Vasiliy Kulikov <segoon@xxxxxxxxxxxx>
Signed-off-by: Michael Tokarev <mjt@xxxxxxxxxx>
Acked-by: David S. Miller <davem@xxxxxxxxxxxxx>
Acked-by: Kees Cook <kees.cook@xxxxxxxxxxxxx>
Signed-off-by: James Morris <jmorris@xxxxxxxxx>
Signed-off-by: Paul Gortmaker <paul.gortmaker@xxxxxxxxxxxxx>
include/linux/netdevice.h | 3 +++
net/core/dev.c | 12 ++++++++++--
net/ipv4/ip_gre.c | 1 +
net/ipv4/ipip.c | 1 +
net/ipv6/sit.c | 2 +-
5 files changed, 16 insertions(+), 3 deletions(-)

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 4737996..0af14f2 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -2214,6 +2214,9 @@ do { \
#define netif_info(priv, type, dev, fmt, args...) \
netif_printk(priv, type, KERN_INFO, (dev), fmt, ##args)

+#define MODULE_ALIAS_NETDEV(device) \
+ MODULE_ALIAS("netdev-" device)
#if defined(DEBUG)
#define netif_dbg(priv, type, dev, format, args...) \
netif_printk(priv, type, KERN_DEBUG, dev, format, ##args)
diff --git a/net/core/dev.c b/net/core/dev.c
index f664177..3095934 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -1104,13 +1104,21 @@ EXPORT_SYMBOL(netdev_bonding_change);
void dev_load(struct net *net, const char *name)
struct net_device *dev;
+ int no_module;

dev = dev_get_by_name_rcu(net, name);

- if (!dev && capable(CAP_NET_ADMIN))
- request_module("%s", name);
+ no_module = !dev;
+ if (no_module && capable(CAP_NET_ADMIN))
+ no_module = request_module("netdev-%s", name);
+ if (no_module && capable(CAP_SYS_MODULE)) {
+ if (!request_module("%s", name))
+ pr_err("Loading kernel module for a network device "
+"with CAP_SYS_MODULE (deprecated). Use CAP_NET_ADMIN and alias netdev-%s "
+"instead\n", name);
+ }

diff --git a/net/ipv4/ip_gre.c b/net/ipv4/ip_gre.c
index fe381d1..6be6fe7 100644
--- a/net/ipv4/ip_gre.c
+++ b/net/ipv4/ip_gre.c
@@ -1709,3 +1709,4 @@ module_exit(ipgre_fini);
diff --git a/net/ipv4/ipip.c b/net/ipv4/ipip.c
index 0b27b14..8900fde 100644
--- a/net/ipv4/ipip.c
+++ b/net/ipv4/ipip.c
@@ -853,3 +853,4 @@ static void __exit ipip_fini(void)
diff --git a/net/ipv6/sit.c b/net/ipv6/sit.c
index 5abae10..5316ce5 100644
--- a/net/ipv6/sit.c
+++ b/net/ipv6/sit.c
@@ -1241,4 +1241,4 @@ static int __init sit_init(void)

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