bridge: don't allow setting hello time to zero

Dushan Tcholich reports that on his system ksoftirqd can consume
between %6 to %10 of cpu time, and cause ~200 context switches per
second.

He then correlated this with a report by bdupree@techfinesse.com:

	http://marc.info/?l=linux-kernel&m=119613299024398&w=2

and the culprit cause seems to be starting the bridge interface.
In particular, when starting the bridge interface, his scripts
are specifying a hello timer interval of "0".

The bridge hello time can't be safely set to values less than 1
second, otherwise it is possible to end up with a runaway timer.

Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 7 insertions, 1 deletions

diff --git a/net/bridge/br_ioctl.c b/net/bridge/br_ioctl.c
index eeee218eed80..5bbf07362172 100644
--- a/net/bridge/br_ioctl.c
+++ b/net/bridge/br_ioctl.c
@@ -188,15 +188,21 @@ static int old_dev_ioctl(struct net_device *dev, struct ifreq *rq, int cmd)
                 return 0;
 
         case BRCTL_SET_BRIDGE_HELLO_TIME:
+        {
+                unsigned long t = clock_t_to_jiffies(args[1]);
                 if (!capable(CAP_NET_ADMIN))
                         return -EPERM;
 
+                if (t < HZ)
+                        return -EINVAL;
+
                 spin_lock_bh(&br->lock);
-                br->bridge_hello_time = clock_t_to_jiffies(args[1]);
+                br->bridge_hello_time = t;
                 if (br_is_root_bridge(br))
                         br->hello_time = br->bridge_hello_time;
                 spin_unlock_bh(&br->lock);
                 return 0;
+        }
 
         case BRCTL_SET_BRIDGE_MAX_AGE:
                 if (!capable(CAP_NET_ADMIN))