linux-kernel - Re: [PATCH 08/14] net: sched: account for temporary action reference

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Message-ID: <20180516071232.GA1972@nanopsycho>
Date:   Wed, 16 May 2018 09:12:32 +0200
From:   Jiri Pirko <jiri@...nulli.us>
To:     Vlad Buslov <vladbu@...lanox.com>
Cc:     netdev@...r.kernel.org, davem@...emloft.net, jhs@...atatu.com,
        xiyou.wangcong@...il.com, pablo@...filter.org,
        kadlec@...ckhole.kfki.hu, fw@...len.de, ast@...nel.org,
        daniel@...earbox.net, edumazet@...gle.com, keescook@...omium.org,
        linux-kernel@...r.kernel.org, netfilter-devel@...r.kernel.org,
        coreteam@...filter.org, kliteyn@...lanox.com
Subject: Re: [PATCH 08/14] net: sched: account for temporary action reference

Mon, May 14, 2018 at 04:27:09PM CEST, vladbu@...lanox.com wrote:
>tca_get_fill function has 'bind' and 'ref' arguments that get passed
>down to action dump function. These arguments values are subtracted from
>actual reference and bind counter values before writing them to skb.
>
>In order to prevent concurrent action delete, RTM_GETACTION handler
>acquires a reference to action before 'dumping' it and releases it
>afterwards. This reference is temporal and should not be accounted by
>userspace clients. (both logically and to preserver current API
>behavior)
>
>Use existing infrastructure of tca_get_fill arguments to subtract that
>temporary reference and not expose it to userspace.
>
>Signed-off-by: Vlad Buslov <vladbu@...lanox.com>
>---
> net/sched/act_api.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
>diff --git a/net/sched/act_api.c b/net/sched/act_api.c
>index 3f02cd1..2772276e 100644
>--- a/net/sched/act_api.c
>+++ b/net/sched/act_api.c
>@@ -935,7 +935,7 @@ tcf_get_notify(struct net *net, u32 portid, struct nlmsghdr *n,
> 	if (!skb)
> 		return -ENOBUFS;
> 	if (tca_get_fill(skb, actions, portid, n->nlmsg_seq, 0, event,
>-			 0, 0) <= 0) {
>+			 0, 1) <= 0) {
> 		NL_SET_ERR_MSG(extack, "Failed to fill netlink attributes while adding TC action");
> 		kfree_skb(skb);
> 		return -EINVAL;
>@@ -1125,7 +1125,7 @@ tcf_del_notify(struct net *net, struct nlmsghdr *n, struct list_head *actions,
> 		return -ENOBUFS;
> 
> 	if (tca_get_fill(skb, actions, portid, n->nlmsg_seq, 0, RTM_DELACTION,
>-			 0, 1) <= 0) {
>+			 0, 2) <= 0) {

So now you are adjusting dump because of a change in a different patch
right? This also breaks bisect.