From: Roman Mashak <mrv@mojatatu.com>
Date: Fri, 11 May 2018 14:35:33 -0400
Subject: net sched actions: fix refcnt leak in skbmod
Git-commit: a52956dfc503f8cc5cfe6454959b7049fddb4413
Patch-mainline: v4.17-rc5
References: networking-stable-18_05_15

When application fails to pass flags in netlink TLV when replacing
existing skbmod action, the kernel will leak refcnt:

$ tc actions get action skbmod index 1
total acts 0

        action order 0: skbmod pipe set smac 00:11:22:33:44:55
         index 1 ref 1 bind 0

For example, at this point a buggy application replaces the action with
index 1 with new smac 00:aa:22:33:44:55, it fails because of zero flags,
however refcnt gets bumped:

$ tc actions get actions skbmod index 1
total acts 0

        action order 0: skbmod pipe set smac 00:11:22:33:44:55
         index 1 ref 2 bind 0
$

Tha patch fixes this by calling tcf_idr_release() on existing actions.

Fixes: 86da71b57383d ("net_sched: Introduce skbmod action")
Signed-off-by: Roman Mashak <mrv@mojatatu.com>
Acked-by: Cong Wang <xiyou.wangcong@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
---
 net/sched/act_skbmod.c |    5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

--- a/net/sched/act_skbmod.c
+++ b/net/sched/act_skbmod.c
@@ -131,8 +131,11 @@ static int tcf_skbmod_init(struct net *n
 	if (exists && bind)
 		return 0;
 
-	if (!lflags)
+	if (!lflags) {
+		if (exists)
+			tcf_idr_release(*a, bind);
 		return -EINVAL;
+	}
 
 	if (!exists) {
 		ret = tcf_idr_create(tn, parm->index, est, a,