From 52643cdf01a25deb17d41f9439442bba7bbafad4 Mon Sep 17 00:00:00 2001 From: Hongbo Li Date: Tue, 5 Nov 2019 18:59:12 +0800 Subject: [PATCH] route: set the deleted fnhe fnhe_daddr to 0 upstream: ee60ad219f5c ("route: set the deleted fnhe fnhe_daddr to 0 ") 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: Hongbo Li --- net/ipv4/route.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/net/ipv4/route.c b/net/ipv4/route.c index cb30f4e4e..cd67b6881 100644 --- a/net/ipv4/route.c +++ b/net/ipv4/route.c @@ -1315,6 +1315,10 @@ static void ip_del_fnhe(struct fib_nh *nh, __be32 daddr) 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;