[PATCH 4.14 284/496] net/sched: fix idr leak in the error path of tcf_skbmod_init()

[Greg Kroah-Hartman]

4.14-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Davide Caratti <dcaratti@xxxxxxxxxx>

[ Upstream commit f29cdfbe33d6915ba8056179b0041279a67e3647 ]

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@xxxxxxxxxxxx>
Signed-off-by: Davide Caratti <dcaratti@xxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <alexander.levin@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 net/sched/act_skbmod.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/net/sched/act_skbmod.c
+++ b/net/sched/act_skbmod.c
@@ -155,7 +155,7 @@ static int tcf_skbmod_init(struct net *n
 	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;
 	}