Re: [BUG] KFENCE: use-after-free read in udp_tunnel_nic_device_sync_work
From: Eric Dumazet
Date: Wed Jun 24 2026 - 10:12:02 EST
On Wed, Jun 24, 2026 at 6:59 AM Eric Dumazet <edumazet@xxxxxxxxxx> wrote:
> Oh well.
>
> u8 need_sync:1;
> u8 need_replay:1;
> u8 work_pending:1;
>
> These bitfields are not safe, obviously :/
>
> Time to convert them to atomic bit operations.
Can you try:
diff --git a/net/ipv4/udp_tunnel_nic.c b/net/ipv4/udp_tunnel_nic.c
index 9944ed923ddfd10f9adf6ad788c0740daeaf2adb..939d6f656bb71814718bc3bf84be665adad27e4b
100644
--- a/net/ipv4/udp_tunnel_nic.c
+++ b/net/ipv4/udp_tunnel_nic.c
@@ -30,9 +30,7 @@ struct udp_tunnel_nic_table_entry {
* @work: async work for talking to hardware from process context
* @dev: netdev pointer
* @lock: protects all fields
- * @need_sync: at least one port start changed
- * @need_replay: space was freed, we need a replay of all ports
- * @work_pending: @work is currently scheduled
+ * @flags: sync, replay, pending flags
* @n_tables: number of tables under @entries
* @missed: bitmap of tables which overflown
* @entries: table of tables of ports currently offloaded
@@ -44,9 +42,10 @@ struct udp_tunnel_nic {
struct mutex lock;
- u8 need_sync:1;
- u8 need_replay:1;
- u8 work_pending:1;
+ unsigned long flags;
+#define UDP_TUNNEL_NIC_NEED_SYNC 0
+#define UDP_TUNNEL_NIC_NEED_REPLAY 1
+#define UDP_TUNNEL_NIC_WORK_PENDING 2
unsigned int n_tables;
unsigned long missed;
@@ -116,7 +115,7 @@ udp_tunnel_nic_entry_queue(struct udp_tunnel_nic *utn,
unsigned int flag)
{
entry->flags |= flag;
- utn->need_sync = 1;
+ set_bit(UDP_TUNNEL_NIC_NEED_SYNC, &utn->flags);
}
static void
@@ -283,7 +282,7 @@ udp_tunnel_nic_device_sync_by_table(struct net_device *dev,
static void
__udp_tunnel_nic_device_sync(struct net_device *dev, struct
udp_tunnel_nic *utn)
{
- if (!utn->need_sync)
+ if (!test_bit(UDP_TUNNEL_NIC_NEED_SYNC, &utn->flags))
return;
if (dev->udp_tunnel_nic_info->sync_table)
@@ -291,21 +290,24 @@ __udp_tunnel_nic_device_sync(struct net_device
*dev, struct udp_tunnel_nic *utn)
else
udp_tunnel_nic_device_sync_by_port(dev, utn);
- utn->need_sync = 0;
+ clear_bit(UDP_TUNNEL_NIC_NEED_SYNC, &utn->flags);
/* Can't replay directly here, in case we come from the tunnel driver's
* notification - trying to replay may deadlock inside tunnel driver.
*/
- utn->need_replay = udp_tunnel_nic_should_replay(dev, utn);
+ if (udp_tunnel_nic_should_replay(dev, utn))
+ set_bit(UDP_TUNNEL_NIC_NEED_REPLAY, &utn->flags);
+ else
+ clear_bit(UDP_TUNNEL_NIC_NEED_REPLAY, &utn->flags);
}
static void
udp_tunnel_nic_device_sync(struct net_device *dev, struct udp_tunnel_nic *utn)
{
- if (!utn->need_sync)
+ if (!test_bit(UDP_TUNNEL_NIC_NEED_SYNC, &utn->flags))
return;
+ set_bit(UDP_TUNNEL_NIC_WORK_PENDING, &utn->flags);
queue_work(udp_tunnel_nic_workqueue, &utn->work);
- utn->work_pending = 1;
}
static bool
@@ -348,7 +350,7 @@ udp_tunnel_nic_has_collision(struct net_device
*dev, struct udp_tunnel_nic *utn,
if (!udp_tunnel_nic_entry_is_free(entry) &&
entry->port == ti->port &&
entry->type != ti->type) {
- __set_bit(i, &utn->missed);
+ set_bit(i, &utn->missed);
return true;
}
}
@@ -483,7 +485,7 @@ udp_tunnel_nic_add_new(struct net_device *dev,
struct udp_tunnel_nic *utn,
* are no devices currently which have multiple tables accepting
* the same tunnel type, and false positives are okay.
*/
- __set_bit(i, &utn->missed);
+ set_bit(i, &utn->missed);
}
return false;
@@ -552,7 +554,7 @@ static void __udp_tunnel_nic_reset_ntf(struct
net_device *dev)
mutex_lock(&utn->lock);
- utn->need_sync = false;
+ clear_bit(UDP_TUNNEL_NIC_NEED_SYNC, &utn->flags);
for (i = 0; i < utn->n_tables; i++)
for (j = 0; j < info->tables[i].n_entries; j++) {
struct udp_tunnel_nic_table_entry *entry;
@@ -696,8 +698,8 @@ udp_tunnel_nic_flush(struct net_device *dev,
struct udp_tunnel_nic *utn)
for (i = 0; i < utn->n_tables; i++)
memset(utn->entries[i], 0, array_size(info->tables[i].n_entries,
sizeof(**utn->entries)));
- WARN_ON(utn->need_sync);
- utn->need_replay = 0;
+ WARN_ON(test_bit(UDP_TUNNEL_NIC_NEED_SYNC, &utn->flags));
+ clear_bit(UDP_TUNNEL_NIC_NEED_REPLAY, &utn->flags);
}
static void
@@ -713,8 +715,8 @@ udp_tunnel_nic_replay(struct net_device *dev,
struct udp_tunnel_nic *utn)
for (i = 0; i < utn->n_tables; i++)
for (j = 0; j < info->tables[i].n_entries; j++)
udp_tunnel_nic_entry_freeze_used(&utn->entries[i][j]);
- utn->missed = 0;
- utn->need_replay = 0;
+ bitmap_zero(&utn->missed, UDP_TUNNEL_NIC_MAX_TABLES);
+ clear_bit(UDP_TUNNEL_NIC_NEED_REPLAY, &utn->flags);
if (!info->shared) {
udp_tunnel_get_rx_info(dev);
@@ -736,10 +738,10 @@ static void
udp_tunnel_nic_device_sync_work(struct work_struct *work)
rtnl_lock();
mutex_lock(&utn->lock);
- utn->work_pending = 0;
+ clear_bit(UDP_TUNNEL_NIC_WORK_PENDING, &utn->flags);
__udp_tunnel_nic_device_sync(utn->dev, utn);
- if (utn->need_replay)
+ if (test_bit(UDP_TUNNEL_NIC_NEED_REPLAY, &utn->flags))
udp_tunnel_nic_replay(utn->dev, utn);
mutex_unlock(&utn->lock);
@@ -866,6 +868,11 @@ udp_tunnel_nic_unregister(struct net_device *dev,
struct udp_tunnel_nic *utn)
udp_tunnel_nic_lock(dev);
+ if (test_bit(UDP_TUNNEL_NIC_WORK_PENDING, &utn->flags)) {
+ udp_tunnel_nic_unlock(dev);
+ return;
+ }
+
/* For a shared table remove this dev from the list of sharing devices
* and if there are other devices just detach.
*/
@@ -901,12 +908,6 @@ udp_tunnel_nic_unregister(struct net_device *dev,
struct udp_tunnel_nic *utn)
udp_tunnel_nic_flush(dev, utn);
udp_tunnel_nic_unlock(dev);
- /* Wait for the work to be done using the state, netdev core will
- * retry unregister until we give up our reference on this device.
- */
- if (utn->work_pending)
- return;
-
udp_tunnel_nic_free(utn);
release_dev:
dev->udp_tunnel_nic = NULL;