3.16.70-rc1 review patch. If anyone has any objections, please let me know.
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From: Xin Long lucien.xin@gmail.com
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@gmail.com Signed-off-by: Xin Long lucien.xin@gmail.com Reviewed-by: David Ahern dsahern@gmail.com Signed-off-by: David S. Miller davem@davemloft.net Signed-off-by: Ben Hutchings ben@decadent.org.uk --- 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;