[PATCH 3/4] net: don't allow CAP_NET_ADMIN to load non-netdev kernel modules CVE-2011-1019

[paolo.pisati at canonical.com]

From: Vasiliy Kulikov <segoon at openwall.com>

BugLink: http://bugs.launchpad.net/bugs/804366

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

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

For CAP_SYS_MODULE module loading is still relaxed:

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

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

CVE-2011-1019

Signed-off-by: Vasiliy Kulikov <segoon at openwall.com>
Signed-off-by: Michael Tokarev <mjt at tls.msk.ru>
Acked-by: David S. Miller <davem at davemloft.net>
Acked-by: Kees Cook <kees.cook at canonical.com>
Signed-off-by: James Morris <jmorris at namei.org>
Signed-off-by: Greg Kroah-Hartman <gregkh at suse.de>
Signed-off-by: Andi Kleen <ak at linux.intel.com>
Signed-off-by: Tim Gardner <tim.gardner at canonical.com>
Signed-off-by: Paolo Pisati <paolo.pisati at canonical.com>
---
 include/linux/netdevice.h |    4 ++++
 net/core/dev.c            |   13 ++++++++++---
 net/ipv4/ip_gre.c         |    1 +
 net/ipv4/ipip.c           |    1 +
 net/ipv6/sit.c            |    2 +-
 5 files changed, 17 insertions(+), 4 deletions(-)

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 142bf18..e857c94 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -2344,6 +2344,10 @@ do {								\
 })
 #endif
 
+#define MODULE_ALIAS_NETDEV(device) \
+	MODULE_ALIAS("netdev-" device)
+
+
 #endif /* __KERNEL__ */
 
 #endif	/* _LINUX_NETDEVICE_H */
diff --git a/net/core/dev.c b/net/core/dev.c
index 4c8f36d..d11a74d 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -1121,13 +1121,20 @@ EXPORT_SYMBOL(netdev_bonding_change);
 void dev_load(struct net *net, const char *name)
 {
 	struct net_device *dev;
+	int no_module;
 
 	rcu_read_lock();
 	dev = dev_get_by_name_rcu(net, name);
 	rcu_read_unlock();
-
-	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);
+	}
 }
 EXPORT_SYMBOL(dev_load);
 
diff --git a/net/ipv4/ip_gre.c b/net/ipv4/ip_gre.c
index 32618e1..cd527c4 100644
--- a/net/ipv4/ip_gre.c
+++ b/net/ipv4/ip_gre.c
@@ -1701,3 +1701,4 @@ module_exit(ipgre_fini);
 MODULE_LICENSE("GPL");
 MODULE_ALIAS_RTNL_LINK("gre");
 MODULE_ALIAS_RTNL_LINK("gretap");
+MODULE_ALIAS_NETDEV("gre0");
diff --git a/net/ipv4/ipip.c b/net/ipv4/ipip.c
index 7fd6367..5d8e362 100644
--- a/net/ipv4/ipip.c
+++ b/net/ipv4/ipip.c
@@ -850,3 +850,4 @@ static void __exit ipip_fini(void)
 module_init(ipip_init);
 module_exit(ipip_fini);
 MODULE_LICENSE("GPL");
+MODULE_ALIAS_NETDEV("tunl0");
diff --git a/net/ipv6/sit.c b/net/ipv6/sit.c
index e51e650..2020bea 100644
--- a/net/ipv6/sit.c
+++ b/net/ipv6/sit.c
@@ -1239,4 +1239,4 @@ static int __init sit_init(void)
 module_init(sit_init);
 module_exit(sit_cleanup);
 MODULE_LICENSE("GPL");
-MODULE_ALIAS("sit0");
+MODULE_ALIAS_NETDEV("sit0");
-- 
1.7.4.1