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wifi: mt76: use kfree_rcu for offchannel link in mt76_put_vif_phy_link

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mt76_put_vif_phy_link() frees the offchannel mlink with plain kfree()
after rcu_assign_pointer(NULL). However, rcu_assign_pointer only prevents
future RCU readers from obtaining the pointer -- it does not wait for
existing readers that already hold it via rcu_dereference.

The TX datapath (e.g. mt7996_mac_write_txwi) dereferences mlink->wcid
and mlink->idx under rcu_read_lock. If a TX softirq obtained the pointer
via rcu_dereference just before the NULL assignment, it will dereference
freed memory after the kfree.

struct mt76_vif_link already contains an rcu_head field that is unused at
this free site -- a developer oversight, since the adjacent
kfree_rcu_mightsleep call for rx_sc in the same function shows the
pattern was understood.

Replace kfree(mlink) with kfree_rcu(mlink, rcu_head).

Fixes: a8f424c1287c ("wifi: mt76: add multi-radio remain_on_channel functions")
Signed-off-by: Rajat Gupta <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Felix Fietkau <[email protected]>
This commit is contained in:
Rajat Gupta
2026-05-27 13:20:44 +02:00
committed by Felix Fietkau
parent 0753cf183d
commit fe0555feb3
1 changed files with 1 additions and 1 deletions
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channel.c
+1 -1
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@@ -307,7 +307,7 @@ void mt76_put_vif_phy_link(struct mt76_phy *phy, struct ieee80211_vif *vif,
rcu_assign_pointer(mvif->offchannel_link, NULL);
dev->drv->vif_link_remove(phy, vif, &vif->bss_conf, mlink);
kfree(mlink);
kfree_rcu(mlink, rcu_head);
}
void mt76_roc_complete(struct mt76_phy *phy)