From 7950ad0b144569f9e5796a4526e92710f3ea94b1 Mon Sep 17 00:00:00 2001 From: Pablo Neira Ayuso Date: Wed, 25 Mar 2026 14:11:04 +0100 Subject: [PATCH] netfilter: ctnetlink: ensure safe access to master conntrack ANBZ: #34871 commit bffcaad9afdfe45d7fc777397d3b83c1e3ebffe5 upstream. Holding reference on the expectation is not sufficient, the master conntrack object can just go away, making exp->master invalid. To access exp->master safely: - Grab the nf_conntrack_expect_lock, this gets serialized with clean_from_lists() which also holds this lock when the master conntrack goes away. - Hold reference on master conntrack via nf_conntrack_find_get(). Not so easy since the master tuple to look up for the master conntrack is not available in the existing problematic paths. This patch goes for extending the nf_conntrack_expect_lock section to address this issue for simplicity, in the cases that are described below this is just slightly extending the lock section. The add expectation command already holds a reference to the master conntrack from ctnetlink_create_expect(). However, the delete expectation command needs to grab the spinlock before looking up for the expectation. Expand the existing spinlock section to address this to cover the expectation lookup. Note that, the nf_ct_expect_iterate_net() calls already grabs the spinlock while iterating over the expectation table, which is correct. The get expectation command needs to grab the spinlock to ensure master conntrack does not go away. This also expands the existing spinlock section to cover the expectation lookup too. I needed to move the netlink skb allocation out of the spinlock to keep it GFP_KERNEL. For the expectation events, the IPEXP_DESTROY event is already delivered under the spinlock, just move the delivery of IPEXP_NEW under the spinlock too because the master conntrack event cache is reached through exp->master. While at it, add lockdep notations to help identify what codepaths need to grab the spinlock. Signed-off-by: Florian Westphal Signed-off-by: Pablo Neira Ayuso Fixes: CVE-2026-43116 Assisted-by: PatchPilot Signed-off-by: D. Wythe --- include/net/netfilter/nf_conntrack_core.h | 5 +++ net/netfilter/nf_conntrack_ecache.c | 2 ++ net/netfilter/nf_conntrack_expect.c | 10 +++++- net/netfilter/nf_conntrack_netlink.c | 37 ++++++++++++++--------- 4 files changed, 39 insertions(+), 15 deletions(-) diff --git a/include/net/netfilter/nf_conntrack_core.h b/include/net/netfilter/nf_conntrack_core.h index 5805fe4947f3..ef9c0cac225b 100644 --- a/include/net/netfilter/nf_conntrack_core.h +++ b/include/net/netfilter/nf_conntrack_core.h @@ -85,4 +85,9 @@ void nf_conntrack_lock(spinlock_t *lock); extern spinlock_t nf_conntrack_expect_lock; +static inline void lockdep_nfct_expect_lock_held(void) +{ + lockdep_assert_held(&nf_conntrack_expect_lock); +} + #endif /* _NF_CONNTRACK_CORE_H */ diff --git a/net/netfilter/nf_conntrack_ecache.c b/net/netfilter/nf_conntrack_ecache.c index 7956c9f19899..aa866d3e519a 100644 --- a/net/netfilter/nf_conntrack_ecache.c +++ b/net/netfilter/nf_conntrack_ecache.c @@ -249,6 +249,8 @@ void nf_ct_expect_event_report(enum ip_conntrack_expect_events event, struct nf_exp_event_notifier *notify; struct nf_conntrack_ecache *e; + lockdep_nfct_expect_lock_held(); + rcu_read_lock(); notify = rcu_dereference(net->ct.nf_expect_event_cb); if (!notify) diff --git a/net/netfilter/nf_conntrack_expect.c b/net/netfilter/nf_conntrack_expect.c index 42557d2b6a90..3462e9710a75 100644 --- a/net/netfilter/nf_conntrack_expect.c +++ b/net/netfilter/nf_conntrack_expect.c @@ -50,6 +50,7 @@ void nf_ct_unlink_expect_report(struct nf_conntrack_expect *exp, struct nf_conn_help *master_help = nfct_help(exp->master); struct net *net = nf_ct_exp_net(exp); + lockdep_nfct_expect_lock_held(); WARN_ON(!master_help); WARN_ON(timer_pending(&exp->timeout)); @@ -104,6 +105,8 @@ nf_ct_exp_equal(const struct nf_conntrack_tuple *tuple, bool nf_ct_remove_expect(struct nf_conntrack_expect *exp) { + lockdep_nfct_expect_lock_held(); + if (del_timer(&exp->timeout)) { nf_ct_unlink_expect(exp); nf_ct_expect_put(exp); @@ -161,6 +164,8 @@ nf_ct_find_expectation(struct net *net, struct nf_conntrack_expect *i, *exp = NULL; unsigned int h; + lockdep_nfct_expect_lock_held(); + if (!net->ct.expect_count) return NULL; @@ -423,6 +428,8 @@ static inline int __nf_ct_expect_check(struct nf_conntrack_expect *expect, unsigned int h; int ret = 0; + lockdep_nfct_expect_lock_held(); + if (!master_help) { ret = -ESHUTDOWN; goto out; @@ -478,8 +485,9 @@ int nf_ct_expect_related_report(struct nf_conntrack_expect *expect, nf_ct_expect_insert(expect); - spin_unlock_bh(&nf_conntrack_expect_lock); nf_ct_expect_event_report(IPEXP_NEW, expect, portid, report); + spin_unlock_bh(&nf_conntrack_expect_lock); + return 0; out: spin_unlock_bh(&nf_conntrack_expect_lock); diff --git a/net/netfilter/nf_conntrack_netlink.c b/net/netfilter/nf_conntrack_netlink.c index 25b352639f5b..79e47f228fc9 100644 --- a/net/netfilter/nf_conntrack_netlink.c +++ b/net/netfilter/nf_conntrack_netlink.c @@ -3355,33 +3355,40 @@ static int ctnetlink_get_expect(struct net *net, struct sock *ctnl, if (err < 0) return err; + skb2 = nlmsg_new(NLMSG_DEFAULT_SIZE, GFP_KERNEL); + if (!skb2) + return -ENOMEM; + + spin_lock_bh(&nf_conntrack_expect_lock); exp = nf_ct_expect_find_get(net, &zone, &tuple); - if (!exp) + if (!exp) { + spin_unlock_bh(&nf_conntrack_expect_lock); + kfree_skb(skb2); return -ENOENT; + } if (cda[CTA_EXPECT_ID]) { __be32 id = nla_get_be32(cda[CTA_EXPECT_ID]); if (id != nf_expect_get_id(exp)) { nf_ct_expect_put(exp); + spin_unlock_bh(&nf_conntrack_expect_lock); + kfree_skb(skb2); return -ENOENT; } } - err = -ENOMEM; - skb2 = nlmsg_new(NLMSG_DEFAULT_SIZE, GFP_KERNEL); - if (skb2 == NULL) { - nf_ct_expect_put(exp); - goto out; - } - rcu_read_lock(); err = ctnetlink_exp_fill_info(skb2, NETLINK_CB(skb).portid, nlh->nlmsg_seq, IPCTNL_MSG_EXP_NEW, exp); rcu_read_unlock(); nf_ct_expect_put(exp); - if (err <= 0) - goto free; + spin_unlock_bh(&nf_conntrack_expect_lock); + + if (err <= 0) { + kfree_skb(skb2); + return -ENOMEM; + } err = netlink_unicast(ctnl, skb2, NETLINK_CB(skb).portid, MSG_DONTWAIT); if (err < 0) @@ -3389,8 +3396,6 @@ static int ctnetlink_get_expect(struct net *net, struct sock *ctnl, return 0; -free: - kfree_skb(skb2); out: /* this avoids a loop in nfnetlink. */ return err == -EAGAIN ? -ENOBUFS : err; @@ -3434,22 +3439,26 @@ static int ctnetlink_del_expect(struct net *net, struct sock *ctnl, if (err < 0) return err; + spin_lock_bh(&nf_conntrack_expect_lock); + /* bump usage count to 2 */ exp = nf_ct_expect_find_get(net, &zone, &tuple); - if (!exp) + if (!exp) { + spin_unlock_bh(&nf_conntrack_expect_lock); return -ENOENT; + } if (cda[CTA_EXPECT_ID]) { __be32 id = nla_get_be32(cda[CTA_EXPECT_ID]); if (id != nf_expect_get_id(exp)) { nf_ct_expect_put(exp); + spin_unlock_bh(&nf_conntrack_expect_lock); return -ENOENT; } } /* after list removal, usage count == 1 */ - spin_lock_bh(&nf_conntrack_expect_lock); if (del_timer(&exp->timeout)) { nf_ct_unlink_expect_report(exp, NETLINK_CB(skb).portid, nlmsg_report(nlh)); -- Gitee