netdev - [PATCH net v2 7/7] net/sched: fix idr leak in the error path of tcf_skbmod

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Message-Id: <fc7d37ebfd766f18a8ea3c925b02c253bfbab7e0.1521465261.git.dcaratti@redhat.com>
Date:   Mon, 19 Mar 2018 15:31:28 +0100
From:   Davide Caratti <dcaratti@...hat.com>
To:     Cong Wang <xiyou.wangcong@...il.com>,
        Jiri Pirko <jiri@...nulli.us>,
        Jamal Hadi Salim <jhs@...atatu.com>,
        "David S. Miller" <davem@...emloft.net>
Cc:     netdev@...r.kernel.org
Subject: [PATCH net v2 7/7] net/sched: fix idr leak in the error path of tcf_skbmod_init()

tcf_skbmod_init() can fail after the idr has been successfully reserved.
When this happens, every subsequent attempt to configure skbmod rules
using the same idr value will systematically fail with -ENOSPC, unless
the first attempt was done using the 'replace' keyword:

 # tc action add action skbmod swap mac index 100
 RTNETLINK answers: Cannot allocate memory
 We have an error talking to the kernel
 # tc action add action skbmod swap mac index 100
 RTNETLINK answers: No space left on device
 We have an error talking to the kernel
 # tc action add action skbmod swap mac index 100
 RTNETLINK answers: No space left on device
 We have an error talking to the kernel
 ...

Fix this in tcf_skbmod_init(), ensuring that tcf_idr_release() is called
on the error path when the idr has been reserved, but not yet inserted.
Also, don't test 'ovr' in the error path, to avoid a 'replace' failure
implicitly become a 'delete' that leaks refcount in act_skbmod module:

 # rmmod act_skbmod; modprobe act_skbmod
 # tc action add action skbmod swap mac index 100
 # tc action add action skbmod swap mac continue index 100
 RTNETLINK answers: File exists
 We have an error talking to the kernel
 # tc action replace action skbmod swap mac continue index 100
 RTNETLINK answers: Cannot allocate memory
 We have an error talking to the kernel
 # tc action list action skbmod
 #
 # rmmod  act_skbmod
 rmmod: ERROR: Module act_skbmod is in use

Fixes: 65a206c01e8e ("net/sched: Change act_api and act_xxx modules to use IDR")
Acked-by: Jamal Hadi Salim <jhs@...atatu.com>
Signed-off-by: Davide Caratti <dcaratti@...hat.com>
---
 net/sched/act_skbmod.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/sched/act_skbmod.c b/net/sched/act_skbmod.c
index d09565d6433e..7b0700f52b50 100644
--- a/net/sched/act_skbmod.c
+++ b/net/sched/act_skbmod.c
@@ -152,7 +152,7 @@ static int tcf_skbmod_init(struct net *net, struct nlattr *nla,
 	ASSERT_RTNL();
 	p = kzalloc(sizeof(struct tcf_skbmod_params), GFP_KERNEL);
 	if (unlikely(!p)) {
-		if (ovr)
+		if (ret == ACT_P_CREATED)
 			tcf_idr_release(*a, bind);
 		return -ENOMEM;
 	}
-- 
2.14.3