[PATCH net 1/1] net sched actions: fix GETing actions

From: Jamal Hadi Salim <jhs@mojatatu.com>

Example of what broke:
...add a gact action to drop
sudo $TC actions add action drop index 10
...now retrieve it, looks good
sudo $TC actions get action gact index 10
...retrieve it again and find it is gone!
sudo $TC actions get action gact index 10

Fixes: f07fed82ad79 ("net_sched: remove the leftover cleanup_a())

Signed-off-by: Jamal Hadi Salim <jhs@mojatatu.com>
---
 net/sched/act_api.c | 20 +++++++++++++++++---
 1 file changed, 17 insertions(+), 3 deletions(-)

diff --git a/net/sched/act_api.c b/net/sched/act_api.c
index d09d068..d4b4704 100644
--- a/net/sched/act_api.c
+++ b/net/sched/act_api.c

@@ -612,6 +612,8 @@ int tcf_action_init(struct net *net, struct nlattr *nla,
 			goto err;
 		}
 		act->order = i;
+		if (ovr)
+			act->tcfa_refcnt+=1;
 		list_add_tail(&act->list, actions);
 	}
 	return 0;

@@ -856,6 +858,15 @@ tcf_del_notify(struct net *net, struct nlmsghdr *n, struct list_head *actions,
 	return ret;
 }
 
+static void cleanup_a(struct list_head *actions)
+{
+	struct tc_action *a, *tmp;
+
+	list_for_each_entry_safe(a, tmp, actions, list) {
+		list_del(&a->list);
+	}
+}
+
 static int
 tca_action_gd(struct net *net, struct nlattr *nla, struct nlmsghdr *n,
 	      u32 portid, int event)

@@ -883,6 +894,7 @@ tca_action_gd(struct net *net, struct nlattr *nla, struct nlmsghdr *n,
 			goto err;
 		}
 		act->order = i;
+		act->tcfa_refcnt+=1;
 		list_add_tail(&act->list, &actions);
 	}
 

@@ -892,10 +904,12 @@ tca_action_gd(struct net *net, struct nlattr *nla, struct nlmsghdr *n,
 		ret = tcf_del_notify(net, n, &actions, portid);
 		if (ret)
 			goto err;
+		cleanup_a(&actions);
 		return ret;
 	}
 err:
 	tcf_action_destroy(&actions, 0);
+	cleanup_a(&actions);
 	return ret;
 }
 

@@ -931,10 +945,10 @@ tcf_action_add(struct net *net, struct nlattr *nla, struct nlmsghdr *n,
 	LIST_HEAD(actions);
 
 	ret = tcf_action_init(net, nla, NULL, NULL, ovr, 0, &actions);
-	if (ret)
-		return ret;
 
-	return tcf_add_notify(net, n, &actions, portid);
+	ret = tcf_add_notify(net, n, &actions, portid);
+	cleanup_a(&actions);
+	return ret;
 }
 
 static int tc_ctl_action(struct sk_buff *skb, struct nlmsghdr *n)

-- 
1.9.1

On Thu, Sep 8, 2016 at 5:12 AM, Jamal Hadi Salim [off-list ref] wrote:

From: Jamal Hadi Salim <jhs@mojatatu.com>

Example of what broke:
...add a gact action to drop
sudo $TC actions add action drop index 10
...now retrieve it, looks good
sudo $TC actions get action gact index 10
...retrieve it again and find it is gone!
sudo $TC actions get action gact index 10

This changelog sucks, it only tells the phenomenon of the bug,
never explains what causes the bug, which is crucial for review.

This looks like not relevant to commit f07fed82ad79 at all?

After my patches, all the action lists are now temporary,
you didn't explain why we should remove an action from
a temporary list, they should just come and go, since
we call ist_add() every time.

Did see any list corruption or kernel crash (your changelog
didn't say so)?

Maybe we only need to fixup the refcnt without touching list,
from my quick observation to your bug report (again, you didn't explain).

On 16-09-08 01:12 PM, Cong Wang wrote:

quoted

+}
+
 static int
 tca_action_gd(struct net *net, struct nlattr *nla, struct nlmsghdr *n,
              u32 portid, int event)

@@ -883,6 +894,7 @@ tca_action_gd(struct net *net, struct nlattr *nla, struct nlmsghdr *n,
                        goto err;
                }
                act->order = i;
+               act->tcfa_refcnt+=1;

Maybe we only need to fixup the refcnt without touching list,
from my quick observation to your bug report (again, you didn't explain).

Yes, you are correct. clearing the list is unnecessary since it is
temporary. When i get the chance i will fix it up, test and resubmit.

What do you want the commit message to say? It shows an example because
the functionality broke.

cheers,
jamal

On Sun, Sep 11, 2016 at 9:30 AM, Jamal Hadi Salim [off-list ref] wrote:

What do you want the commit message to say? It shows an example because
the functionality broke.

I expect it to explain why we need to increase that refcnt for GET
and how we missed it. Also need to find a right commit to blame. ;)

Thanks.