6.18-stable review patch. If anyone has any objections, please let me know. ------------------ From: Ilya Maximets [ Upstream commit f85009dfcd65e5969526b0db7a49b5413746e630 ] In a case where skb with an unconfirmed ct entry gets cloned, we may end up processing both again but with different sets of extensions. The series of events: 1. The first clone wants to commit and runs the helpers wiring up the extension pointer into the expectation list. 2. Then it looses the confirmation keeping the entry unconfirmed. 3. Second clone now wants to commit labels or run NAT and adds the new extension for that breaking the pointer in the expectation list causing UAF on the destruction path later. While this is possible to trigger, there should be no practical network pipeline where we need to process both clones without modifications in the same zone. So, let's just reset the entry in case for some reason we got an skb with a shared one. This doesn't affect any known use cases, but avoids any potential problems with sharing and modification of the unconfirmed ct entry. Unlike openvswitch module, act_ct allows for NAT without commit. Changing that would be a uAPI break. So, act_ct needs to reset on NAT regardless of the commit flag to avoid reallocation of the extension space. This, however, doesn't really change the picture for sensible networking cases as there should be no need to run the same packet twice (before and after the clone) through conntrack without packet header or zone changes and without commit. The fixes tag points to the introduction of helpers, since that's the main UAF trigger for the sharing. Fixes: a21b06e73191 ("net: sched: add helper support in act_ct") Cc: stable@vger.kernel.org Reported-by: Axel Mierczuk Signed-off-by: Ilya Maximets Reviewed-by: Aaron Conole Reviewed-by: Xin Long Reviewed-by: Jamal Hadi Salim Link: https://patch.msgid.link/20260921145655.3167436-5-i.maximets@ovn.org Signed-off-by: Jakub Kicinski Signed-off-by: Sasha Levin Signed-off-by: Greg Kroah-Hartman --- net/sched/act_ct.c | 18 ++++++++++++++++-- 1 file changed, 16 insertions(+), 2 deletions(-) --- a/net/sched/act_ct.c +++ b/net/sched/act_ct.c @@ -977,11 +977,11 @@ TC_INDIRECT_SCOPE int tcf_ct_act(struct struct tcf_result *res) { struct net *net = dev_net(skb->dev); + bool cached, commit, clear, nat; enum ip_conntrack_info ctinfo; struct tcf_ct *c = to_ct(a); struct nf_conn *tmpl = NULL; struct nf_hook_state state; - bool cached, commit, clear; int nh_ofs, err, retval; struct tcf_ct_params *p; bool add_helper = false; @@ -996,6 +996,7 @@ TC_INDIRECT_SCOPE int tcf_ct_act(struct retval = p->action; commit = p->ct_action & TCA_CT_ACT_COMMIT; clear = p->ct_action & TCA_CT_ACT_CLEAR; + nat = p->ct_action & TCA_CT_ACT_NAT; tmpl = p->tmpl; tcf_lastuse_update(&c->tcf_tm); @@ -1044,6 +1045,19 @@ TC_INDIRECT_SCOPE int tcf_ct_act(struct * different zone. */ cached = tcf_ct_skb_nfct_cached(net, skb, p); + + /* If the ct entry is not confirmed and shared with some other skb, + * e.g., a cloned one, we can't just modify it with a commit or nat + * as we must not modify the extension set. Reset. + */ + if (cached && (commit || nat)) { + ct = nf_ct_get(skb, &ctinfo); + if (ct && !nf_ct_is_confirmed(ct) && nf_ct_shared(ct)) { + nf_reset_ct(skb); + cached = false; + } + } + if (!cached) { if (tcf_ct_flow_table_lookup(p, skb, family)) { skip_add = true; @@ -1081,7 +1095,7 @@ do_nat: if (err) goto drop; add_helper = true; - if (p->ct_action & TCA_CT_ACT_NAT && !nfct_seqadj(ct)) { + if (nat && !nfct_seqadj(ct)) { if (!nfct_seqadj_ext_add(ct)) goto drop; }