[PATCH net] net: udp_tunnel: fix memory leak in udp_tunnel_nic_unregister()
From: Eric Dumazet <edumazet@google.com>
Date: 2026-07-24 09:11:39
Subsystem:
networking [general], the rest · Maintainers:
"David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Linus Torvalds
syzbot reported a memory leak [1] in the UDP tunnel NIC offload code.
When device registration fails (e.g. in register_netdevice()), netdev core
unwinds by sending a single NETDEV_UNREGISTER notification. If work was queued
during NETDEV_REGISTER (utn->work_pending is set), udp_tunnel_nic_unregister()
returns early:
if (utn->work_pending)
return;
Because failed registrations do not enter netdev_wait_allrefs_any(), no
subsequent NETDEV_UNREGISTER rebroadcast will ever occur. As a result, the
struct udp_tunnel_nic allocated in udp_tunnel_nic_alloc() is leaked
permanently.
Fix this by removing the early return. Instead, synchronously cancel any
pending work with cancel_delayed_work_sync() before freeing @utn.
To be able to call cancel_delayed_work_sync() while holding RTNL (the work also
needs RTNL), switch udp_tunnel_nic_device_sync_work() to rtnl_trylock(). If RTNL
is contended, requeue the work with a 1 jiffy delay (via queue_delayed_work())
to prevent high CPU contention while waiting for RTNL lock.
The utn->work_pending bookkeeping is no longer needed and is removed, as
the workqueue core already tracks the pending/running state of the work.
[1]
BUG: memory leak
unreferenced object 0xffff888127d5f840 (size 96):
comm "syz-executor", pid 5806, jiffies 4294942188
backtrace (crc 99fdb6c8):
__kmalloc_noprof+0x3bf/0x550
udp_tunnel_nic_alloc net/ipv4/udp_tunnel_nic.c:756 [inline]
udp_tunnel_nic_register net/ipv4/udp_tunnel_nic.c:833 [inline]
udp_tunnel_nic_netdevice_event+0x804/0xab0 net/ipv4/udp_tunnel_nic.c:931
notifier_call_chain+0x59/0x160 kernel/notifier.c:85
call_netdevice_notifiers_info+0x7d/0xb0 net/core/dev.c:2250
register_netdevice+0xc10/0xeb0 net/core/dev.c:11478
Fixes: cc4e3835eff4 ("udp_tunnel: add central NIC RX port offload infrastructure")
Reported-by: syzbot+eca845fb8c18dd6b44c1@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/netdev/6a632b15.dde6c935.cf6c8.0011.GAE@google.com/T/#u (local)
Signed-off-by: Eric Dumazet <edumazet@google.com>
---
net/ipv4/udp_tunnel_nic.c | 32 +++++++++++++++++---------------
1 file changed, 17 insertions(+), 15 deletions(-)
diff --git a/net/ipv4/udp_tunnel_nic.c b/net/ipv4/udp_tunnel_nic.c
index 3b32a0afa9798d3c416d9ae570e6d529f70e6697..53a1a9c1f8bff01674481e8d88238f2af61d8bb1 100644
--- a/net/ipv4/udp_tunnel_nic.c
+++ b/net/ipv4/udp_tunnel_nic.c@@ -32,13 +32,12 @@ struct udp_tunnel_nic_table_entry { * @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 * @n_tables: number of tables under @entries * @missed: bitmap of tables which overflown * @entries: table of tables of ports currently offloaded */ struct udp_tunnel_nic { - struct work_struct work; + struct delayed_work work; struct net_device *dev;
@@ -46,7 +45,6 @@ struct udp_tunnel_nic { u8 need_sync:1; u8 need_replay:1; - u8 work_pending:1; unsigned int n_tables; unsigned long missed;
@@ -301,11 +299,10 @@ __udp_tunnel_nic_device_sync(struct net_device *dev, struct udp_tunnel_nic *utn) static void udp_tunnel_nic_device_sync(struct net_device *dev, struct udp_tunnel_nic *utn) { - if (!utn->need_sync || utn->work_pending) + if (!utn->need_sync) return; - queue_work(udp_tunnel_nic_workqueue, &utn->work); - utn->work_pending = 1; + queue_delayed_work(udp_tunnel_nic_workqueue, &utn->work, 0); } static bool
@@ -731,12 +728,17 @@ udp_tunnel_nic_replay(struct net_device *dev, struct udp_tunnel_nic *utn) static void udp_tunnel_nic_device_sync_work(struct work_struct *work) { struct udp_tunnel_nic *utn = - container_of(work, struct udp_tunnel_nic, work); + container_of(work, struct udp_tunnel_nic, work.work); - rtnl_lock(); + /* We cannot block on RTNL here, otherwise we would deadlock with + * udp_tunnel_nic_unregister() calling cancel_delayed_work_sync() + * while holding RTNL. Requeue with 1 jiffy delay if RTNL is contended. + */ + if (!rtnl_trylock()) { + queue_delayed_work(udp_tunnel_nic_workqueue, &utn->work, 1); + return; + } mutex_lock(&utn->lock); - - utn->work_pending = 0; __udp_tunnel_nic_device_sync(utn->dev, utn); if (utn->need_replay)
@@ -757,7 +759,7 @@ udp_tunnel_nic_alloc(const struct udp_tunnel_nic_info *info, if (!utn) return NULL; utn->n_tables = n_tables; - INIT_WORK(&utn->work, udp_tunnel_nic_device_sync_work); + INIT_DELAYED_WORK(&utn->work, udp_tunnel_nic_device_sync_work); mutex_init(&utn->lock); for (i = 0; i < n_tables; i++) {
@@ -901,11 +903,11 @@ 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. + /* Make sure no work is running or queued before freeing @utn. + * The work handler uses rtnl_trylock(), so it will not deadlock + * against the RTNL we are holding here. */ - if (utn->work_pending) - return; + cancel_delayed_work_sync(&utn->work); udp_tunnel_nic_free(utn); release_dev:
--
2.55.0.229.g6434b31f56-goog