CVE-2026-68194: wifi: mt76: mt7921: drop TXRX_NOTIFY on non-mmio buses

From: Greg Kroah-Hartman <[email protected]>

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

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

wifi: mt76: mt7921: drop TXRX_NOTIFY on non-mmio buses

PKT_TYPE_TXRX_NOTIFY is an mmio-only event, but mt7921_rx_check() and
mt7921_queue_rx_skb() dispatch it to mt7921_mac_tx_free() on every bus.
mt7921_mac_tx_free() cleans the DMA tx queues with
mt76_queue_tx_cleanup(), which calls queue_ops->tx_cleanup(). Only the
mmio queue ops implement that callback; on USB and SDIO it is NULL, so
a TXRX_NOTIFY there calls a NULL pointer in the RX worker:

  BUG: kernel NULL pointer dereference, address: 0000000000000000
  RIP: 0010:0x0
  Call Trace:
   mt7921_mac_tx_free+0x64/0x310 [mt7921_common]
   mt7921_rx_check+0x5f/0xf0 [mt7921_common]
   mt76u_rx_worker+0x1b9/0x620 [mt76_usb]

Drop the event on non-mmio buses via mt76_is_mmio(), as in
commit 5683e1488aa9 ("wifi: mt76: connac: do not check WED status for
non-mmio devices").

The Linux kernel CVE team has assigned CVE-2026-68194 to this issue.


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

	Issue introduced in 5.16 with commit 48fab5bbef4092d925ab3214773ad12e68807223 and fixed in 6.6.148 with commit ef2ee5f820c3ef87643b51e960c20b4a14d8336b
	Issue introduced in 5.16 with commit 48fab5bbef4092d925ab3214773ad12e68807223 and fixed in 6.12.101 with commit ecf995b828191829ba4a87169bccabcbeb5c9c32
	Issue introduced in 5.16 with commit 48fab5bbef4092d925ab3214773ad12e68807223 and fixed in 6.18.42 with commit 263816e92e8d66c81c98ccab2b5d2191ed08ec71
	Issue introduced in 5.16 with commit 48fab5bbef4092d925ab3214773ad12e68807223 and fixed in 7.1.6 with commit 24475d2ddc8d8dfd82f4d2be0d951401f86911a6
	Issue introduced in 5.16 with commit 48fab5bbef4092d925ab3214773ad12e68807223 and fixed in 7.2-rc5 with commit da4082e91acabc1498611ed8ccc53f0610baefc6

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-2026-68194
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/mt7921/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/ef2ee5f820c3ef87643b51e960c20b4a14d8336b
	https://git.kernel.org/stable/c/ecf995b828191829ba4a87169bccabcbeb5c9c32
	https://git.kernel.org/stable/c/263816e92e8d66c81c98ccab2b5d2191ed08ec71
	https://git.kernel.org/stable/c/24475d2ddc8d8dfd82f4d2be0d951401f86911a6
	https://git.kernel.org/stable/c/da4082e91acabc1498611ed8ccc53f0610baefc6