[ 3.5.y.z extended stable ] Patch "bridge: Clamp forward_delay when enabling STP" has been added to staging queue

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

    bridge: Clamp forward_delay when enabling STP

to the linux-3.5.y-queue branch of the 3.5.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.5.y-queue

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.5.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From 5da346ff617272367e706c45a31d43b1e8ea1eeb Mon Sep 17 00:00:00 2001
From: Herbert Xu <herbert at gondor.apana.org.au>
Date: Thu, 12 Sep 2013 17:12:05 +1000
Subject: [PATCH] bridge: Clamp forward_delay when enabling STP

commit be4f154d5ef0ca147ab6bcd38857a774133f5450 upstream.

At some point limits were added to forward_delay.  However, the
limits are only enforced when STP is enabled.  This created a
scenario where you could have a value outside the allowed range
while STP is disabled, which then stuck around even after STP
is enabled.

This patch fixes this by clamping the value when we enable STP.

I had to move the locking around a bit to ensure that there is
no window where someone could insert a value outside the range
while we're in the middle of enabling STP.

Signed-off-by: Herbert Xu <herbert at gondor.apana.org.au>
Signed-off-by: David S. Miller <davem at davemloft.net>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 net/bridge/br_private.h |  1 +
 net/bridge/br_stp.c     | 21 +++++++++++++++------
 net/bridge/br_stp_if.c  | 12 ++++++++++--
 3 files changed, 26 insertions(+), 8 deletions(-)

diff --git a/net/bridge/br_private.h b/net/bridge/br_private.h
index a768b24..68d9266 100644
--- a/net/bridge/br_private.h
+++ b/net/bridge/br_private.h
@@ -512,6 +512,7 @@ extern struct net_bridge_port *br_get_port(struct net_bridge *br,
 extern void br_init_port(struct net_bridge_port *p);
 extern void br_become_designated_port(struct net_bridge_port *p);

+extern void __br_set_forward_delay(struct net_bridge *br, unsigned long t);
 extern int br_set_forward_delay(struct net_bridge *br, unsigned long x);
 extern int br_set_hello_time(struct net_bridge *br, unsigned long x);
 extern int br_set_max_age(struct net_bridge *br, unsigned long x);
diff --git a/net/bridge/br_stp.c b/net/bridge/br_stp.c
index 2e46d07..73920c2 100644
--- a/net/bridge/br_stp.c
+++ b/net/bridge/br_stp.c
@@ -517,18 +517,27 @@ int br_set_max_age(struct net_bridge *br, unsigned long val)

 }

+void __br_set_forward_delay(struct net_bridge *br, unsigned long t)
+{
+	br->bridge_forward_delay = t;
+	if (br_is_root_bridge(br))
+		br->forward_delay = br->bridge_forward_delay;
+}
+
 int br_set_forward_delay(struct net_bridge *br, unsigned long val)
 {
 	unsigned long t = clock_t_to_jiffies(val);
+	int err = -ERANGE;

+	spin_lock_bh(&br->lock);
 	if (br->stp_enabled != BR_NO_STP &&
 	    (t < BR_MIN_FORWARD_DELAY || t > BR_MAX_FORWARD_DELAY))
-		return -ERANGE;
+		goto unlock;

-	spin_lock_bh(&br->lock);
-	br->bridge_forward_delay = t;
-	if (br_is_root_bridge(br))
-		br->forward_delay = br->bridge_forward_delay;
+	__br_set_forward_delay(br, t);
+	err = 0;
+
+unlock:
 	spin_unlock_bh(&br->lock);
-	return 0;
+	return err;
 }
diff --git a/net/bridge/br_stp_if.c b/net/bridge/br_stp_if.c
index 9d5a414..7ba2ed5 100644
--- a/net/bridge/br_stp_if.c
+++ b/net/bridge/br_stp_if.c
@@ -129,6 +129,14 @@ static void br_stp_start(struct net_bridge *br)
 	char *envp[] = { NULL };

 	r = call_usermodehelper(BR_STP_PROG, argv, envp, UMH_WAIT_PROC);
+
+	spin_lock_bh(&br->lock);
+
+	if (br->bridge_forward_delay < BR_MIN_FORWARD_DELAY)
+		__br_set_forward_delay(br, BR_MIN_FORWARD_DELAY);
+	else if (br->bridge_forward_delay < BR_MAX_FORWARD_DELAY)
+		__br_set_forward_delay(br, BR_MAX_FORWARD_DELAY);
+
 	if (r == 0) {
 		br->stp_enabled = BR_USER_STP;
 		br_debug(br, "userspace STP started\n");
@@ -137,10 +145,10 @@ static void br_stp_start(struct net_bridge *br)
 		br_debug(br, "using kernel STP\n");

 		/* To start timers on any ports left in blocking */
-		spin_lock_bh(&br->lock);
 		br_port_state_selection(br);
-		spin_unlock_bh(&br->lock);
 	}
+
+	spin_unlock_bh(&br->lock);
 }

 static void br_stp_stop(struct net_bridge *br)
--
1.8.3.2