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bridge: cfm: Fix race condition in peer_mep deletion

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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: dc32cbb3db ("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>
This commit is contained in:
Hyunwoo Kim
2026-03-11 03:18:09 +09:00
committed by Jakub Kicinski
parent e5b31d988a
commit 3715a00855
1 changed files with 2 additions and 2 deletions
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4
net/bridge/br_cfm.c
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@@ -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);