[PATCH net v5 1/1] openvswitch: Fix CT limit teardown use-after-free
From: Yuqi Xu
Date: Tue Aug 11 2026 - 05:58:08 EST
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.
Fixes: 11efd5cb04a1 ("openvswitch: Support conntrack zone limit")
Cc: stable@xxxxxxxxxxxxxxx
Reported-by: Vega <vega@xxxxxxxxxx>
Link: https://lore.kernel.org/all/cover.1784711445.git.xuyuqiabc@xxxxxxxxx
Assisted-by: Codex:GPT-5.4
Co-developed-by: Nan Li <tonanli66@xxxxxxxxx>
Signed-off-by: Nan Li <tonanli66@xxxxxxxxx>
Signed-off-by: Yuqi Xu <xuyuqiabc@xxxxxxxxx>
Reviewed-by: Ren Wei <enjou1224z@xxxxxxxxx>
---
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@xxxxxxxxx/
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@xxxxxxxxx/
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@xxxxxxxxx
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@xxxxxxxxx/
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