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Miller" , Eric Dumazet , Paolo Abeni , Simon Horman , Yi-Hung Wei , netdev@vger.kernel.org, dev@openvswitch.org, linux-kernel@vger.kernel.org, Vega , Nan Li , Ren Wei Subject: [PATCH net v6 1/1] openvswitch: Fix CT limit teardown use-after-free Date: Wed, 12 Aug 2026 17:59:56 +0800 Message-ID: X-Mailer: git-send-email 2.54.0 In-Reply-To: References: Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Packet processing uses CT limit state under RCU, while netns teardown frees that state under ovs_mutex. The CT limit pointer was neither removed from readers nor protected by a grace period, allowing packet processing to dereference the freed state. An unprivileged user can trigger this bug from a user and network namespace, causing a slab-use-after-free in ovs_ct_execute() when the netns is torn down. Publish the CT limit pointer through RCU, remove it before teardown, and wait for readers before freeing its contents. Keep ovs_mutex around individual CT limit updates, and use the RCU read-side lock while GET traverses the RCU-protected limit lists. The netlink command handlers do not need NULL checks because the userspace netlink socket holds an active reference to its network namespace while a request is processed. The per-netns exit path therefore cannot run concurrently with SET, DEL, or GET for that socket's namespace. The teardown path currently waits for the RCU grace period while holding ovs_mutex. Moving synchronize_rcu() outside the mutex would require restructuring the teardown path and is left for a separate change. Fixes: 11efd5cb04a1 ("openvswitch: Support conntrack zone limit") Cc: stable@vger.kernel.org Reported-by: Vega Link: https://lore.kernel.org/all/cover.1784711445.git.xuyuqiabc@gmail.com Assisted-by: Codex:GPT-5.4 Co-developed-by: Nan Li Signed-off-by: Nan Li Signed-off-by: Yuqi Xu Reviewed-by: Ren Wei --- Changes in v6: - Explain why netlink command handlers do not need NULL checks. - Document that teardown currently waits for the RCU grace period while holding ovs_mutex, leaving lock-scope optimization for a separate change. - v5 Link: https://lore.kernel.org/all/cover.1786441097.git.xuyuqiabc@gmail.com/ Changes in v5: - Remove unreachable command-path NULL handling because netlink sockets keep their network namespaces alive while requests are processed. - Restore the previous SET, DEL, and GET command semantics. - Document the ct_limit_info RCU and ovs_mutex locking contract. - v4 Link: https://lore.kernel.org/all/cover.1785908366.git.xuyuqiabc@gmail.com/ Changes in v4: - Restore per-entry ovs_mutex locking for CT limit SET and DEL. - Treat CT limit updates racing with netns teardown as successful no-ops. - Free an uninstalled CT limit allocation and document GET helpers' RCU contract. - v3 Link: https://lore.kernel.org/all/cover.1784866791.git.xuyuqiabc@gmail.com/ Changes in v3: - Use RCU dereference and a NULL check for CT limit GET requests. - Limit ovs_mutex to CT limit updates; do not hold it while preparing replies. - Use ovsl_dereference() for update paths and clarify the RCU grace-period comment. - v2 Link: https://lore.kernel.org/all/cover.1784711445.git.xuyuqiabc@gmail.com Changes in v2: - Sort local declarations modified by this patch in reverse Christmas-tree order. - v1 Link: https://lore.kernel.org/all/aa8a1d8dcbac8a13dbdf077a642a66f4c5d81e4b.1784355642.git.xuyuqiabc@gmail.com/ net/openvswitch/conntrack.c | 87 +++++++++++++++++++++---------------- net/openvswitch/datapath.h | 6 ++- 2 files changed, 54 insertions(+), 39 deletions(-) diff --git a/net/openvswitch/conntrack.c b/net/openvswitch/conntrack.c index 95697d4e16e6..cc6ea4014c16 100644 --- a/net/openvswitch/conntrack.c +++ b/net/openvswitch/conntrack.c @@ -933,10 +933,14 @@ static int ovs_ct_check_limit(struct net *net, const struct ovs_conntrack_info *info) { struct ovs_net *ovs_net = net_generic(net, ovs_net_id); - const struct ovs_ct_limit_info *ct_limit_info = ovs_net->ct_limit_info; + const struct ovs_ct_limit_info *ct_limit_info; u32 per_zone_limit, connections; u32 conncount_key; + ct_limit_info = rcu_dereference(ovs_net->ct_limit_info); + if (!ct_limit_info) + return 0; + conncount_key = info->zone.id; per_zone_limit = ct_limit_get(ct_limit_info, info->zone.id); @@ -1585,40 +1589,47 @@ static void __ovs_ct_free_action(struct ovs_conntrack_info *ct_info) #if IS_ENABLED(CONFIG_NETFILTER_CONNCOUNT) static int ovs_ct_limit_init(struct net *net, struct ovs_net *ovs_net) { + struct ovs_ct_limit_info *info; int i, err; - ovs_net->ct_limit_info = kmalloc_obj(*ovs_net->ct_limit_info); - if (!ovs_net->ct_limit_info) + info = kmalloc_obj(*info); + if (!info) return -ENOMEM; - ovs_net->ct_limit_info->default_limit = OVS_CT_LIMIT_DEFAULT; - ovs_net->ct_limit_info->limits = + info->default_limit = OVS_CT_LIMIT_DEFAULT; + info->limits = kmalloc_objs(struct hlist_head, CT_LIMIT_HASH_BUCKETS); - if (!ovs_net->ct_limit_info->limits) { - kfree(ovs_net->ct_limit_info); + if (!info->limits) { + kfree(info); return -ENOMEM; } for (i = 0; i < CT_LIMIT_HASH_BUCKETS; i++) - INIT_HLIST_HEAD(&ovs_net->ct_limit_info->limits[i]); + INIT_HLIST_HEAD(&info->limits[i]); - ovs_net->ct_limit_info->data = nf_conncount_init(net, sizeof(u32)); + info->data = nf_conncount_init(net, sizeof(u32)); - if (IS_ERR(ovs_net->ct_limit_info->data)) { - err = PTR_ERR(ovs_net->ct_limit_info->data); - kfree(ovs_net->ct_limit_info->limits); - kfree(ovs_net->ct_limit_info); + if (IS_ERR(info->data)) { + err = PTR_ERR(info->data); + kfree(info->limits); + kfree(info); pr_err("openvswitch: failed to init nf_conncount %d\n", err); return err; } + rcu_assign_pointer(ovs_net->ct_limit_info, info); return 0; } static void ovs_ct_limit_exit(struct net *net, struct ovs_net *ovs_net) { - const struct ovs_ct_limit_info *info = ovs_net->ct_limit_info; + const struct ovs_ct_limit_info *info; int i; + info = rcu_replace_pointer(ovs_net->ct_limit_info, NULL, + lockdep_ovsl_is_held()); + /* Wait for RCU readers to stop using the CT limits. */ + synchronize_rcu(); + nf_conncount_destroy(net, info->data); for (i = 0; i < CT_LIMIT_HASH_BUCKETS; ++i) { struct hlist_head *head = &info->limits[i]; @@ -1665,12 +1676,13 @@ static bool check_zone_id(int zone_id, u16 *pzone) return false; } -static int ovs_ct_limit_set_zone_limit(struct nlattr *nla_zone_limit, - struct ovs_ct_limit_info *info) +static int ovs_ct_limit_set_zone_limit(struct ovs_net *ovs_net, + struct nlattr *nla_zone_limit) { struct ovs_zone_limit *zone_limit; - int rem; + struct ovs_ct_limit_info *info; u16 zone; + int rem; rem = NLA_ALIGN(nla_len(nla_zone_limit)); zone_limit = (struct ovs_zone_limit *)nla_data(nla_zone_limit); @@ -1679,6 +1691,7 @@ static int ovs_ct_limit_set_zone_limit(struct nlattr *nla_zone_limit, if (unlikely(zone_limit->zone_id == OVS_ZONE_LIMIT_DEFAULT_ZONE)) { ovs_lock(); + info = ovsl_dereference(ovs_net->ct_limit_info); info->default_limit = zone_limit->limit; ovs_unlock(); } else if (unlikely(!check_zone_id( @@ -1695,6 +1708,7 @@ static int ovs_ct_limit_set_zone_limit(struct nlattr *nla_zone_limit, ct_limit->limit = zone_limit->limit; ovs_lock(); + info = ovsl_dereference(ovs_net->ct_limit_info); ct_limit_set(info, ct_limit); ovs_unlock(); } @@ -1709,12 +1723,13 @@ static int ovs_ct_limit_set_zone_limit(struct nlattr *nla_zone_limit, return 0; } -static int ovs_ct_limit_del_zone_limit(struct nlattr *nla_zone_limit, - struct ovs_ct_limit_info *info) +static int ovs_ct_limit_del_zone_limit(struct ovs_net *ovs_net, + struct nlattr *nla_zone_limit) { struct ovs_zone_limit *zone_limit; - int rem; + struct ovs_ct_limit_info *info; u16 zone; + int rem; rem = NLA_ALIGN(nla_len(nla_zone_limit)); zone_limit = (struct ovs_zone_limit *)nla_data(nla_zone_limit); @@ -1723,6 +1738,7 @@ static int ovs_ct_limit_del_zone_limit(struct nlattr *nla_zone_limit, if (unlikely(zone_limit->zone_id == OVS_ZONE_LIMIT_DEFAULT_ZONE)) { ovs_lock(); + info = ovsl_dereference(ovs_net->ct_limit_info); info->default_limit = OVS_CT_LIMIT_DEFAULT; ovs_unlock(); } else if (unlikely(!check_zone_id( @@ -1730,6 +1746,7 @@ static int ovs_ct_limit_del_zone_limit(struct nlattr *nla_zone_limit, OVS_NLERR(true, "zone id is out of range"); } else { ovs_lock(); + info = ovsl_dereference(ovs_net->ct_limit_info); ct_limit_del(info, zone); ovs_unlock(); } @@ -1773,6 +1790,7 @@ static int __ovs_ct_limit_get_zone_limit(struct net *net, return nla_put_nohdr(reply, sizeof(zone_limit), &zone_limit); } +/* Called with RCU read lock held. */ static int ovs_ct_limit_get_zone_limit(struct net *net, struct nlattr *nla_zone_limit, struct ovs_ct_limit_info *info, @@ -1796,12 +1814,10 @@ static int ovs_ct_limit_get_zone_limit(struct net *net, &zone))) { OVS_NLERR(true, "zone id is out of range"); } else { - rcu_read_lock(); limit = ct_limit_get(info, zone); err = __ovs_ct_limit_get_zone_limit( net, info->data, zone, limit, reply); - rcu_read_unlock(); if (err) return err; } @@ -1816,6 +1832,7 @@ static int ovs_ct_limit_get_zone_limit(struct net *net, return 0; } +/* Called with RCU read lock held. */ static int ovs_ct_limit_get_all_zone_limit(struct net *net, struct ovs_ct_limit_info *info, struct sk_buff *reply) @@ -1828,19 +1845,16 @@ static int ovs_ct_limit_get_all_zone_limit(struct net *net, if (err) return err; - rcu_read_lock(); for (i = 0; i < CT_LIMIT_HASH_BUCKETS; ++i) { head = &info->limits[i]; hlist_for_each_entry_rcu(ct_limit, head, hlist_node) { err = __ovs_ct_limit_get_zone_limit(net, info->data, ct_limit->zone, ct_limit->limit, reply); if (err) - goto exit_err; + return err; } } -exit_err: - rcu_read_unlock(); return err; } @@ -1850,7 +1864,6 @@ static int ovs_ct_limit_cmd_set(struct sk_buff *skb, struct genl_info *info) struct sk_buff *reply; struct ovs_header *ovs_reply_header; struct ovs_net *ovs_net = net_generic(sock_net(skb->sk), ovs_net_id); - struct ovs_ct_limit_info *ct_limit_info = ovs_net->ct_limit_info; int err; reply = ovs_ct_limit_cmd_reply_start(info, OVS_CT_LIMIT_CMD_SET, @@ -1863,8 +1876,8 @@ static int ovs_ct_limit_cmd_set(struct sk_buff *skb, struct genl_info *info) goto exit_err; } - err = ovs_ct_limit_set_zone_limit(a[OVS_CT_LIMIT_ATTR_ZONE_LIMIT], - ct_limit_info); + err = ovs_ct_limit_set_zone_limit(ovs_net, + a[OVS_CT_LIMIT_ATTR_ZONE_LIMIT]); if (err) goto exit_err; @@ -1884,7 +1897,6 @@ static int ovs_ct_limit_cmd_del(struct sk_buff *skb, struct genl_info *info) struct sk_buff *reply; struct ovs_header *ovs_reply_header; struct ovs_net *ovs_net = net_generic(sock_net(skb->sk), ovs_net_id); - struct ovs_ct_limit_info *ct_limit_info = ovs_net->ct_limit_info; int err; reply = ovs_ct_limit_cmd_reply_start(info, OVS_CT_LIMIT_CMD_DEL, @@ -1897,8 +1909,8 @@ static int ovs_ct_limit_cmd_del(struct sk_buff *skb, struct genl_info *info) goto exit_err; } - err = ovs_ct_limit_del_zone_limit(a[OVS_CT_LIMIT_ATTR_ZONE_LIMIT], - ct_limit_info); + err = ovs_ct_limit_del_zone_limit(ovs_net, + a[OVS_CT_LIMIT_ATTR_ZONE_LIMIT]); if (err) goto exit_err; @@ -1918,7 +1930,7 @@ static int ovs_ct_limit_cmd_get(struct sk_buff *skb, struct genl_info *info) struct ovs_header *ovs_reply_header; struct net *net = sock_net(skb->sk); struct ovs_net *ovs_net = net_generic(net, ovs_net_id); - struct ovs_ct_limit_info *ct_limit_info = ovs_net->ct_limit_info; + struct ovs_ct_limit_info *ct_limit_info; int err; reply = ovs_ct_limit_cmd_reply_start(info, OVS_CT_LIMIT_CMD_GET, @@ -1932,18 +1944,19 @@ static int ovs_ct_limit_cmd_get(struct sk_buff *skb, struct genl_info *info) goto exit_err; } + rcu_read_lock(); + ct_limit_info = rcu_dereference(ovs_net->ct_limit_info); if (a[OVS_CT_LIMIT_ATTR_ZONE_LIMIT]) { err = ovs_ct_limit_get_zone_limit( net, a[OVS_CT_LIMIT_ATTR_ZONE_LIMIT], ct_limit_info, reply); - if (err) - goto exit_err; } else { err = ovs_ct_limit_get_all_zone_limit(net, ct_limit_info, reply); - if (err) - goto exit_err; } + rcu_read_unlock(); + if (err) + goto exit_err; nla_nest_end(reply, nla_reply); genlmsg_end(reply, ovs_reply_header); diff --git a/net/openvswitch/datapath.h b/net/openvswitch/datapath.h index 696640e88fa7..06c6956fb1dc 100644 --- a/net/openvswitch/datapath.h +++ b/net/openvswitch/datapath.h @@ -164,7 +164,9 @@ struct dp_upcall_info { * Protected by genl_mutex. * @dp_notify_work: A work notifier to handle port unregistering. * @masks_rebalance: A work to periodically optimize flow table caches. - * @ct_limit_info: A hash table of conntrack zone connection limits. + * @ct_limit_info: Hash table of conntrack zone connection limits. Protected + * by RCU; updates and teardown are serialized by ovs_mutex. May be NULL during + * netns teardown. * @xt_label: Whether connlables are configured for the network or not. */ struct ovs_net { @@ -172,7 +174,7 @@ struct ovs_net { struct work_struct dp_notify_work; struct delayed_work masks_rebalance; #if IS_ENABLED(CONFIG_NETFILTER_CONNCOUNT) - struct ovs_ct_limit_info *ct_limit_info; + struct ovs_ct_limit_info __rcu *ct_limit_info; #endif bool xt_label; }; -- 2.54.0