CVE-2026-74325wifi: mt76: use kfree_rcu for offchannel link in mt76_put_vif_phy_link

Official description

In the Linux kernel, the following vulnerability has been resolved: wifi: mt76: use kfree_rcu for offchannel link in mt76_put_vif_phy_link 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).

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/c7a83899203ed36696a2d35ddd03c0f522874a63
• https://git.kernel.org/stable/c/50e700ac0edce72dee5c3a9755865d9423696ac7
• https://git.kernel.org/stable/c/7fae097aa9a56c30febf539d72ef3773165d3aa3