CVE-2026-80934: wifi: mt76: mt7996: fix TX DMA mapping leak for AddBA req frames

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

From: Greg Kroah-Hartman <gregkh@kernel.org>

Description
===========

In the Linux kernel, the following vulnerability has been resolved:

wifi: mt76: mt7996: fix TX DMA mapping leak for AddBA req frames

mt7996/mt7992 hand the firmware a HW MAC-TXP for AddBA req action frames
(MT_TXD7_MAC_TXD, set in mt7996_mac_write_txwi_80211()), but are otherwise
FW-TXP devices. On tx free mt76_connac_txp_skb_unmap() therefore decodes
the per-frame txp as a struct mt76_connac_fw_txp. For a MAC-TXP the
fw_txp.nbuf byte aliases the AddBA TID word (MT_TXP1_TID_ADDBA), which is
always zero, so the unmap loop runs zero times and the skb DMA mapping in
buf[1] is never unmapped. buf[1].skip_unmap is set unconditionally, so the
generic DMA-ring cleanup skips it as well.

Each AddBA req therefore leaks one TX DMA mapping, roughly one per
(re)association. With WED enabled these mappings are bounced through the
WED swiotlb pool, so under continuous client reconnect churn the pool is
exhausted after ~1-2 days, after which DMA mapping fails for WED, the WiFi
MCU and other on-SoC consumers.

Keep the deferred (token release) unmap that the design relies on, and add
an mt7996-specific txp unmap that inspects MT_TXD7_MAC_TXD and unmaps
buf[1] from the MAC-TXP layout for those frames, delegating to
mt76_connac_txp_skb_unmap() otherwise.

The Linux kernel CVE team has assigned CVE-2026-80934 to this issue.


Affected and fixed versions
===========================

	Issue introduced in 6.18 with commit cb6ebbdffef2a888b95f121637cd1fad473919c6 and fixed in 6.18.50 with commit 01f2e0da8548f82d704b65b513026cfedc5f8962
	Issue introduced in 6.18 with commit cb6ebbdffef2a888b95f121637cd1fad473919c6 and fixed in 7.2.4 with commit b754d3a6d44c53d9853eba374d8a7ef279a9d00a
	Issue introduced in 6.18 with commit cb6ebbdffef2a888b95f121637cd1fad473919c6 and fixed in 7.3-rc1 with commit deaa2e3656937fbbe312f0ee2616c756c6e2511f
	Issue introduced in 6.17.8 with commit 91a5a48702e948e45df01a4f2fd54a0b0d0d6efb

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2026-80934
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	drivers/net/wireless/mediatek/mt76/mt7996/mac.c


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/01f2e0da8548f82d704b65b513026cfedc5f8962
	https://git.kernel.org/stable/c/b754d3a6d44c53d9853eba374d8a7ef279a9d00a
	https://git.kernel.org/stable/c/deaa2e3656937fbbe312f0ee2616c756c6e2511f