Commit 10e4ea75 authored Aug 05, 2015 by Tom Herbert Committed by David S. Miller Aug 07, 2015

net: Fix race condition in store_rps_map



There is a race condition in store_rps_map that allows jump label
count in rps_needed to go below zero. This can happen when
concurrently attempting to set and a clear map.

Scenario:

1. rps_needed count is zero
2. New map is assigned by setting thread, but rps_needed count _not_ yet
   incremented (rps_needed count still zero)
2. Map is cleared by second thread, old_map set to that just assigned
3. Second thread performs static_key_slow_dec, rps_needed count now goes
   negative

Fix is to increment or decrement rps_needed under the spinlock.

Signed-off-by: Tom Herbert <tom@herbertland.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent e05176a3

net/core/net-sysfs.c

+7 −4

Original line number	Diff line number	Diff line
		@@ -726,14 +726,17 @@ static ssize_t store_rps_map(struct netdev_rx_queue *queue,
		old_map = rcu_dereference_protected(queue->rps_map,
		lockdep_is_held(&rps_map_lock));
		rcu_assign_pointer(queue->rps_map, map);
		spin_unlock(&rps_map_lock);

		if (map)
		static_key_slow_inc(&rps_needed);
		if (old_map) {
		kfree_rcu(old_map, rcu);
		if (old_map)
		static_key_slow_dec(&rps_needed);
		}

		spin_unlock(&rps_map_lock);

		if (old_map)
		kfree_rcu(old_map, rcu);

		free_cpumask_var(mask);
		return len;
		}

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