CVE-2026-68409: wifi: mac80211: defer link RX stats percpu free to RCU

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

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

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

wifi: mac80211: defer link RX stats percpu free to RCU

sta_remove_link() frees a removed MLO link's RX stats percpu buffer right
away, but defers only the link container to RCU:

	sta_info_free_link(&alloc->info);
	kfree_rcu(alloc, rcu_head);

The RX fast path reads link_sta under rcu_read_lock and writes the percpu
stats. A reader that resolved link_sta before the removal keeps the
pointer. The container stays alive from the kfree_rcu, so the read still
works. But the percpu block it points to is already freed. This needs
uses_rss. That is when pcpu_rx_stats exists.

The full STA teardown frees the deflink stats only after
synchronize_net(). The link removal path had no such barrier. The race is
hard to win in practice, but the free should still wait for RCU.

Free the link together with its data from a single RCU callback, so the
percpu block is reclaimed only after readers drain.

The Linux kernel CVE team has assigned CVE-2026-68409 to this issue.


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

	Issue introduced in 6.0 with commit c71420db653aba30a234d1e4cf86dde376e604fa and fixed in 6.18.42 with commit 2aa1789880fa5e41049b0f6a74a4fc2fa1997610
	Issue introduced in 6.0 with commit c71420db653aba30a234d1e4cf86dde376e604fa and fixed in 7.1.6 with commit a03fceae0c65b31ce31840dac5e26684ceecb65b
	Issue introduced in 6.0 with commit c71420db653aba30a234d1e4cf86dde376e604fa and fixed in 7.2-rc4 with commit aa2eb62525188269cdd402a583b9a8ed94657ff0

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-2026-68409
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:
	net/mac80211/sta_info.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/2aa1789880fa5e41049b0f6a74a4fc2fa1997610
	https://git.kernel.org/stable/c/a03fceae0c65b31ce31840dac5e26684ceecb65b
	https://git.kernel.org/stable/c/aa2eb62525188269cdd402a583b9a8ed94657ff0