CVE-2026-64207: net/sched: dualpi2: fix GSO backlog accounting

CVE-2026-64207: net/sched: dualpi2: fix GSO backlog accounting

[Greg Kroah-Hartman]

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

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

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

net/sched: dualpi2: fix GSO backlog accounting

When DualPI2 splits a GSO skb into N segments, it propagates N
additional packets to its parent before returning NET_XMIT_SUCCESS.
The parent then accounts for the original skb once more, leaving its
qlen one larger than the number of packets actually queued.

With QFQ as the parent, after all real packets are dequeued, QFQ still
has a non-zero qlen while its in-service aggregate has no active
classes. qfq_choose_next_agg() returns NULL and qfq_dequeue() passes
the result to qfq_peek_skb(), causing a NULL pointer dereference.

Follow the same pattern used by tbf_segment() and taprio: count only
successfully queued segments, propagate the difference between the
original skb and those segments, and return NET_XMIT_SUCCESS whenever
at least one segment was queued.

The Linux kernel CVE team has assigned CVE-2026-64207 to this issue.


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

	Issue introduced in 6.17 with commit 8f9516daedd67097a0c6e463fcb7a42b5ee9d477 and fixed in 6.18.39 with commit c4b70c1512b8f9f33f23c2c8196dfd1210207681
	Issue introduced in 6.17 with commit 8f9516daedd67097a0c6e463fcb7a42b5ee9d477 and fixed in 7.1.4 with commit 806586e33891066487db1f002be3d455cda6b516
	Issue introduced in 6.17 with commit 8f9516daedd67097a0c6e463fcb7a42b5ee9d477 and fixed in 7.2-rc1 with commit 05ed733b65ab977dd931e7f7ac0f62fdb81205c2

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-2026-64207
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/sched/sch_dualpi2.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/c4b70c1512b8f9f33f23c2c8196dfd1210207681
	https://git.kernel.org/stable/c/806586e33891066487db1f002be3d455cda6b516
	https://git.kernel.org/stable/c/05ed733b65ab977dd931e7f7ac0f62fdb81205c2