[Bridge] [patch net/stable v2] br: fix use of ->rx_handler_data in code executed on non-rx_handler path

[Stephen Hemminger]

On Thu,  5 Dec 2013 16:27:37 +0100
Jiri Pirko <jiri at resnulli.us> wrote:

> br_stp_rcv() is reached by non-rx_handler path. That means there is no
> guarantee that dev is bridge port and therefore simple NULL check of
> ->rx_handler_data is not enough. There is need to check if dev is really
> bridge port and since only rcu read lock is held here, do it by checking
> ->rx_handler pointer.
> 
> Note that synchronize_net() in netdev_rx_handler_unregister() ensures
> this approach as valid.
> 


I think this patch is simpler/better, it restores the old logic.

Ps. submitting patches to bugzilla is a good way to have them ignored.

From Stephen Hemminger <stephen at networkplumber.org>

Check that incoming STP packet is received on a port assigned to bridge
before processing. It is possible to receive packet on non-bridge port
because they are multicast.

See:
 https://bugzilla.kernel.org/show_bug.cgi?id=64911


Regression introduced by:
commit 716ec052d2280d511e10e90ad54a86f5b5d4dcc2
Author: Hong Zhiguo <zhiguohong at tencent.com>
Date:   Sat Sep 14 22:42:28 2013 +0800

    bridge: fix NULL pointer deref of br_port_get_rcu


Reported-by: Alexander Y. Fomichev
Signed-off-by: Stephen Hemminger <stephen at networkplumber.org>


--- a/net/bridge/br_stp_bpdu.c	2013-06-11 09:50:21.522919061 -0700
+++ b/net/bridge/br_stp_bpdu.c	2013-12-05 08:46:56.090463702 -0800
@@ -153,6 +153,9 @@ void br_stp_rcv(const struct stp_proto *
 	if (buf[0] != 0 || buf[1] != 0 || buf[2] != 0)
 		goto err;
 
+	if (!br_port_exists(dev))
+		goto err;
+
 	p = br_port_get_rcu(dev);
 	if (!p)
 		goto err;