thr3ads.net - Linux Ethernet Bridging - [Bridge] [RFC 1/1] bridge: relax BR_GROUPFWD_RESTRICTED to forward LLDP frames [Mar 2015]

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Bernhard Thaler

2015-Mar-22 22:24 UTC

[Bridge] [RFC 1/1] bridge: relax BR_GROUPFWD_RESTRICTED to forward LLDP frames

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 at 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 at 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

Bernhard Thaler

2015-Mar-29 22:06 UTC

head link

[Bridge] [PATCH] bridge: relax BR_GROUPFWD_RESTRICTED to forward LLDP frames

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 at 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 at 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

David Miller

2015-Apr-01 19:28 UTC

head link

[Bridge] [PATCH] bridge: relax BR_GROUPFWD_RESTRICTED to forward LLDP frames

From: Bernhard Thaler <bernhard.thaler at wvnet.at>
Date: Mon, 30 Mar 2015 00:06:02 +0200
> 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 at wvnet.at>
I don't understand why we want to allow forwarding LLDP by default, it
specifically is the case that an 802.1D bridge is only compliant if it
does not forward LLDP packets.

We've blocked forwarding of LLDP by default for such a long time, so I
argue against this change from the perspective of users expecting LLDP
to be not forwarded by the Linux bridge by default.

Linux Ethernet Bridging - Mar 2015 - [Bridge] [RFC 1/1] bridge: relax BR_GROUPFWD_RESTRICTED to forward LLDP frames

[Bridge] [RFC 1/1] bridge: relax BR_GROUPFWD_RESTRICTED to forward LLDP frames

[Bridge] [PATCH] bridge: relax BR_GROUPFWD_RESTRICTED to forward LLDP frames

[Bridge] [PATCH] bridge: relax BR_GROUPFWD_RESTRICTED to forward LLDP frames