[PATCH 6.18 131/212] bridge: cfm: Fix race condition in peer_mep deletion

Greg Kroah-Hartman
2026-03-23T14:09:21Z

From: Hyunwoo Kim <imv4bel@gmail.com>

[ Upstream commit 3715a00855316066cdda69d43648336367422127 ]

When a peer MEP is being deleted, cancel_delayed_work_sync() is called
on ccm_rx_dwork before freeing. However, br_cfm_frame_rx() runs in
softirq context under rcu_read_lock (without RTNL) and can re-schedule
ccm_rx_dwork via ccm_rx_timer_start() between cancel_delayed_work_sync()
returning and kfree_rcu() being called.

The following is a simple race scenario:

cpu0 cpu1

mep_delete_implementation()
cancel_delayed_work_sync(ccm_rx_dwork);
br_cfm_frame_rx()
// peer_mep still in hlist
if (peer_mep->ccm_defect)
ccm_rx_timer_start()
queue_delayed_work(ccm_rx_dwork)
hlist_del_rcu(&peer_mep->head);
kfree_rcu(peer_mep, rcu);
ccm_rx_work_expired()
// on freed peer_mep

To prevent this, cancel_delayed_work_sync() is replaced with
disable_delayed_work_sync() in both peer MEP deletion paths, so
that subsequent queue_delayed_work() calls from br_cfm_frame_rx()
are silently rejected.

The cc_peer_disable() helper retains cancel_delayed_work_sync()
because it is also used for the CC enable/disable toggle path where
the work must remain re-schedulable.

Fixes: dc32cbb3dbd7 ("bridge: cfm: Kernel space implementation of CFM. CCM frame RX added.")
Signed-off-by: Hyunwoo Kim <imv4bel@gmail.com>
Reviewed-by: Ido Schimmel <idosch@nvidia.com>
Link: https://patch.msgid.link/abBgYT5K_FI9rD1a@v4bel
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/bridge/br_cfm.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/bridge/br_cfm.c b/net/bridge/br_cfm.c
index c2c1c7d44c615..f4ca77d9b0e96 100644
--- a/net/bridge/br_cfm.c
+++ b/net/bridge/br_cfm.c
@@ -576,7 +576,7 @@ static void mep_delete_implementation(struct net_bridge *br,

/* Empty and free peer MEP list */
hlist_for_each_entry_safe(peer_mep, n_store, &mep->peer_mep_list, head) {
- cancel_delayed_work_sync(&peer_mep->ccm_rx_dwork);
+ disable_delayed_work_sync(&peer_mep->ccm_rx_dwork);
hlist_del_rcu(&peer_mep->head);
kfree_rcu(peer_mep, rcu);
}
@@ -732,7 +732,7 @@ int br_cfm_cc_peer_mep_remove(struct net_bridge *br, const u32 instance,
return -ENOENT;
}

- cc_peer_disable(peer_mep);
+ disable_delayed_work_sync(&peer_mep->ccm_rx_dwork);

hlist_del_rcu(&peer_mep->head);
kfree_rcu(peer_mep, rcu);
--
2.51.0