3.16.70-rc1 review patch. If anyone has any objections, please let me know.
------------------
From: Xin Long <lucien.xin@xxxxxxxxx>
commit ee60ad219f5c7c4fb2f047f88037770063ef785f upstream.
The race occurs in __mkroute_output() when 2 threads lookup a dst:
CPU A CPU B
find_exception()
find_exception() [fnhe expires]
ip_del_fnhe() [fnhe is deleted]
rt_bind_exception()
In rt_bind_exception() it will bind a deleted fnhe with the new dst, and
this dst will get no chance to be freed. It causes a dev defcnt leak and
consecutive dmesg warnings:
unregister_netdevice: waiting for ethX to become free. Usage count = 1
Especially thanks Jon to identify the issue.
This patch fixes it by setting fnhe_daddr to 0 in ip_del_fnhe() to stop
binding the deleted fnhe with a new dst when checking fnhe's fnhe_daddr
and daddr in rt_bind_exception().
It works as both ip_del_fnhe() and rt_bind_exception() are protected by
fnhe_lock and the fhne is freed by kfree_rcu().
Fixes: deed49df7390 ("route: check and remove route cache when we get route")
Signed-off-by: Jon Maxwell <jmaxwell37@xxxxxxxxx>
Signed-off-by: Xin Long <lucien.xin@xxxxxxxxx>
Reviewed-by: David Ahern <dsahern@xxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
net/ipv4/route.c | 4 ++++
1 file changed, 4 insertions(+)
--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c
@@ -1279,6 +1279,10 @@ static void ip_del_fnhe(struct fib_nh *n
if (fnhe->fnhe_daddr == daddr) {
rcu_assign_pointer(*fnhe_p, rcu_dereference_protected(
fnhe->fnhe_next, lockdep_is_held(&fnhe_lock)));
+ /* set fnhe_daddr to 0 to ensure it won't bind with
+ * new dsts in rt_bind_exception().
+ */
+ fnhe->fnhe_daddr = 0;
fnhe_flush_routes(fnhe);
kfree_rcu(fnhe, rcu);
break;
