[PATCH] bridge: relax BR_GROUPFWD_RESTRICTED to forward LLDP frames

Bernhard Thaler
2015-03-29T22:06:58Z

BR_GROUPFWD_RESTRICTED bitmask restricts users from setting values to
/sys/class/net/brX/bridge/group_fwd_mask that allow forwarding of
some IEEE 802.1D Table 7-10 Reserved addresses:

(MAC Control) 802.3 01-80-C2-00-00-01
(Link Aggregation) 802.3 01-80-C2-00-00-02
802.1AB LLDP 01-80-C2-00-00-0E

Relax BR_GROUPFWD_RESTRICTED to at least forward LLDP frames and document
group_fwd_mask.

e.g.
echo 16384 > /sys/class/net/brX/bridge/group_fwd_mask
allows to forward LLDP frames.

Tested on a simple bridge setup with two interfaces. Setting group_fwd_mask
as described above lets crafted LLDP frames traverse bridge.

Signed-off-by: Bernhard Thaler <bernhard.thaler@wvnet.at>
---
v1
* this version only removes LLDP restriction from BR_GROUPFWD_RESTRICTED
* adds documentation of /sys/class/net/brX/bridge/group_fwd_mask

(v0)
* initial version "bridge: remove BR_GROUPFWD_RESTRICTED for arbitrary
forwarding of reserved addresses"

Documentation/ABI/testing/sysfs-class-net | 19 +++++++++++++++++++
net/bridge/br_private.h | 4 ++--
2 files changed, 21 insertions(+), 2 deletions(-)

diff --git a/Documentation/ABI/testing/sysfs-class-net b/Documentation/ABI/testing/sysfs-class-net
index 5ecfd72..668604f 100644
--- a/Documentation/ABI/testing/sysfs-class-net
+++ b/Documentation/ABI/testing/sysfs-class-net
@@ -39,6 +39,25 @@ Description:
Format is a string, e.g: 00:11:22:33:44:55 for an Ethernet MAC
address.

+What: /sys/class/net/<bridge iface>/bridge/group_fwd_mask
+Date: January 2012
+KernelVersion: 3.2
+Contact: netdev@vger.kernel.org
+Description:
+ Bitmask to allow forwarding of link local frames with address
+ 01-80-C2-00-00-0X on a bridge device. Only values that set bits
+ not matching BR_GROUPFWD_RESTRICTED in net/bridge/br_private.h
+ allowed.
+ Default value 0 does not forward any link local frames.
+
+ Restricted bits:
+ 0: 01-80-C2-00-00-00 Bridge Group Address used for STP
+ 1: 01-80-C2-00-00-01 (MAC Control) 802.3 used for MAC PAUSE
+ 2: 01-80-C2-00-00-02 (Link Aggregation) 802.3ad
+
+ Any values not setting these bits can be used. Take special
+ care when forwarding control frames e.g. 802.1X-PAE or LLDP.
+
What: /sys/class/net/<iface>/broadcast
Date: April 2005
KernelVersion: 2.6.12
diff --git a/net/bridge/br_private.h b/net/bridge/br_private.h
index b46fa0c..ef8ef3f 100644
--- a/net/bridge/br_private.h
+++ b/net/bridge/br_private.h
@@ -33,8 +33,8 @@

/* Control of forwarding link local multicast */
#define BR_GROUPFWD_DEFAULT 0
-/* Don't allow forwarding control protocols like STP and LLDP */
-#define BR_GROUPFWD_RESTRICTED 0x4007u
+/* Don't allow forwarding of control protocols like STP, MAC PAUSE and LACP */
+#define BR_GROUPFWD_RESTRICTED 0x0007u
/* The Nearest Customer Bridge Group Address, 01-80-C2-00-00-[00,0B,0C,0D,0F] */
#define BR_GROUPFWD_8021AD 0xB801u

--
1.7.10.4