linux-kernel - [PATCH 3.16 169/212] net sched actions: decrement module reference count after table flush.

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Message-ID: <lsq.1496331796.998343451@decadent.org.uk>
Date:   Thu, 01 Jun 2017 16:43:16 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, "Roman Mashak" <mrv@...atatu.com>,
        "David S. Miller" <davem@...emloft.net>,
        "Jamal Hadi Salim" <jhs@...atatu.com>,
        "Cong Wang" <xiyou.wangcong@...il.com>
Subject: [PATCH 3.16 169/212] net sched actions: decrement module
 reference count after table flush.

3.16.44-rc1 review patch.  If anyone has any objections, please let me know.

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

From: Roman Mashak <mrv@...atatu.com>

commit edb9d1bff4bbe19b8ae0e71b1f38732591a9eeb2 upstream.

When tc actions are loaded as a module and no actions have been installed,
flushing them would result in actions removed from the memory, but modules
reference count not being decremented, so that the modules would not be
unloaded.

Following is example with GACT action:

% sudo modprobe act_gact
% lsmod
Module                  Size  Used by
act_gact               16384  0
%
% sudo tc actions ls action gact
%
% sudo tc actions flush action gact
% lsmod
Module                  Size  Used by
act_gact               16384  1
% sudo tc actions flush action gact
% lsmod
Module                  Size  Used by
act_gact               16384  2
% sudo rmmod act_gact
rmmod: ERROR: Module act_gact is in use
....

After the fix:
% lsmod
Module                  Size  Used by
act_gact               16384  0
%
% sudo tc actions add action pass index 1
% sudo tc actions add action pass index 2
% sudo tc actions add action pass index 3
% lsmod
Module                  Size  Used by
act_gact               16384  3
%
% sudo tc actions flush action gact
% lsmod
Module                  Size  Used by
act_gact               16384  0
%
% sudo tc actions flush action gact
% lsmod
Module                  Size  Used by
act_gact               16384  0
% sudo rmmod act_gact
% lsmod
Module                  Size  Used by
%

Fixes: f97017cdefef ("net-sched: Fix actions flushing")
Signed-off-by: Roman Mashak <mrv@...atatu.com>
Signed-off-by: Jamal Hadi Salim <jhs@...atatu.com>
Acked-by: Cong Wang <xiyou.wangcong@...il.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 net/sched/act_api.c | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

--- a/net/sched/act_api.c
+++ b/net/sched/act_api.c
@@ -799,10 +799,8 @@ static int tca_action_flush(struct net *
 		goto out_module_put;
 
 	err = a.ops->walk(skb, &dcb, RTM_DELACTION, &a);
-	if (err < 0)
+	if (err <= 0)
 		goto out_module_put;
-	if (err == 0)
-		goto noflush_out;
 
 	nla_nest_end(skb, nest);
 
@@ -819,7 +817,6 @@ static int tca_action_flush(struct net *
 out_module_put:
 	module_put(a.ops->owner);
 err_out:
-noflush_out:
 	kfree_skb(skb);
 	return err;
 }