From 251367a0a3319fa565daf7468b0afd933b1f5ab1 Mon Sep 17 00:00:00 2001 From: Victor Nogueira Date: Mon, 24 Aug 2026 12:39:02 -0300 Subject: [PATCH] net/sched: act_api: fix skb sizing and action leak on reoffload delete tcf_reoffload_del_notify_msg() sizes the RTM_DELACTION skb with tcf_action_fill_size(action) alone. Unlike every other notification path it never wraps that in tcf_action_full_attrs_size(), so the nlmsg_put() header, struct tcamsg and the TCA_ACT_TAB nest that tca_get_fill() emits - 24 bytes on x86_64 - are not budgeted. As long as the single action stays well under NLMSG_GOODSIZE the floor in alloc_skb() hides this, but once its fill size crosses NLMSG_GOODSIZE the allocation is exactly 24 bytes short and tca_get_fill() runs out of tailroom. That is now easy to reach for an offloadable act_pedit with a large tcfp_nkeys, which commit 8e2efb3f45a5 ("net/sched: add get_fill_size callbacks for actions missing them") started accounting for properly. When that happens tcf_reoffload_del_notify() returns early, before tcf_idr_release_unsafe(), and tcf_action_reoffload_cb() discards the return value: if (tc_act_skip_sw(p->tcfa_flags) && !tc_act_in_hw(p)) tcf_reoffload_del_notify(net, p); The action has just lost its last hardware instance and is skip_sw, so it is left installed while processing no packets, and with no notification to tell userspace about it. An -ENOBUFS from alloc_skb() gets the same treatment. Fix this by budgeting the message header the way the add and delete paths do, and release the action even when the notification cannot be built - dropping the notification is strictly better than leaking a dead action, and there is no caller left to report the error to. Fixes: 13926d19a11e ("flow_offload: add reoffload process to update hw_count") Reported-by: Sashiko Closes: https://netdev-ai.bots.linux.dev/sashiko/#/patchset/20260810164357.1653956-1-victor%40mojatatu.com Acked-by: Jamal Hadi Salim Signed-off-by: Victor Nogueira Reviewed-by: Pedro Tammela Link: https://patch.msgid.link/20260824153903.4143642-4-victor@mojatatu.com Signed-off-by: Jakub Kicinski --- net/sched/act_api.c | 17 +++++++++++------ 1 file changed, 11 insertions(+), 6 deletions(-) diff --git a/net/sched/act_api.c b/net/sched/act_api.c index 20b6501fd33b..37eced84dfa5 100644 --- a/net/sched/act_api.c +++ b/net/sched/act_api.c @@ -1867,11 +1867,13 @@ static int tcf_action_delete(struct net *net, struct tc_action *actions[]) static struct sk_buff *tcf_reoffload_del_notify_msg(struct net *net, struct tc_action *action) { - size_t attr_size = tcf_action_fill_size(action); struct tc_action *actions[TCA_ACT_MAX_PRIO] = { [0] = action, }; struct sk_buff *skb; + size_t attr_size; + + attr_size = tcf_action_full_attrs_size(tcf_action_fill_size(action)); skb = alloc_skb(max(attr_size, NLMSG_GOODSIZE), GFP_KERNEL); if (!skb) @@ -1888,15 +1890,18 @@ static struct sk_buff *tcf_reoffload_del_notify_msg(struct net *net, static int tcf_reoffload_del_notify(struct net *net, struct tc_action *action) { const struct tc_action_ops *ops = action->ops; - struct sk_buff *skb; + struct sk_buff *skb = NULL; int ret; - if (!rtnl_notify_needed(net, 0, RTNLGRP_TC)) { - skb = NULL; - } else { + if (rtnl_notify_needed(net, 0, RTNLGRP_TC)) { skb = tcf_reoffload_del_notify_msg(net, action); + /* The action has already lost its hardware instance and is + * skip_sw, so it must be released whether or not the + * notification can be built. Drop the notification rather + * than leave an action behind that processes no packets. + */ if (IS_ERR(skb)) - return PTR_ERR(skb); + skb = NULL; } ret = tcf_idr_release_unsafe(action);