linux-kernel - [PATCH net] net: sched: act_api: size RTM

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Message-ID: <20260130134220.305757-1-p@1g4.org>
Date: Fri, 30 Jan 2026 13:43:29 +0000
From: Paul Moses <p@....org>
To: netdev@...r.kernel.org
Cc: jhs@...atatu.com, xiyou.wangcong@...il.com, jiri@...nulli.us, davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org, pabeni@...hat.com, horms@...nel.org, linux-kernel@...r.kernel.org, Paul Moses <p@....org>, stable@...r.kernel.org
Subject: [PATCH net] net: sched: act_api: size RTM_GETACTION reply by fill size

tcf_action_fill_size() already computes the required dump size, but
RTM_GETACTION replies always allocate NLMSG_GOODSIZE. Large action
state can overrun that skb and make dumps fail.

Use the computed reply size for RTM_GETACTION replies so large actions
can be dumped, while still keeping NLMSG_GOODSIZE as a floor.

Fixes: 4e76e75d6aba ("net sched actions: calculate add/delete event message size")
Cc: stable@...r.kernel.org
Signed-off-by: Paul Moses <p@....org>
---
 net/sched/act_api.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/net/sched/act_api.c b/net/sched/act_api.c
index e1ab0faeb8113..8ab016d352850 100644
--- a/net/sched/act_api.c
+++ b/net/sched/act_api.c
@@ -1685,12 +1685,12 @@ static int tca_get_fill(struct sk_buff *skb, struct tc_action *actions[],
 
 static int
 tcf_get_notify(struct net *net, u32 portid, struct nlmsghdr *n,
-	       struct tc_action *actions[], int event,
+	       struct tc_action *actions[], int event, size_t attr_size,
 	       struct netlink_ext_ack *extack)
 {
 	struct sk_buff *skb;
 
-	skb = alloc_skb(NLMSG_GOODSIZE, GFP_KERNEL);
+	skb = alloc_skb(max_t(size_t, attr_size, NLMSG_GOODSIZE), GFP_KERNEL);
 	if (!skb)
 		return -ENOBUFS;
 	if (tca_get_fill(skb, actions, portid, n->nlmsg_seq, 0, event,
@@ -2041,7 +2041,8 @@ tca_action_gd(struct net *net, struct nlattr *nla, struct nlmsghdr *n,
 	attr_size = tcf_action_full_attrs_size(attr_size);
 
 	if (event == RTM_GETACTION)
-		ret = tcf_get_notify(net, portid, n, actions, event, extack);
+		ret = tcf_get_notify(net, portid, n, actions, event,
+				     attr_size, extack);
 	else { /* delete */
 		ret = tcf_del_notify(net, n, actions, portid, attr_size, extack);
 		if (ret)
-- 
2.52.GIT