linux-cve-announce - CVE-2026-23069: vsock/virtio: fix potential underflow in virtio_transport_get

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Message-ID: <2026020417-CVE-2026-23069-d026@gregkh>
Date: Wed,  4 Feb 2026 17:14:28 +0100
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...nel.org>
Subject: CVE-2026-23069: vsock/virtio: fix potential underflow in virtio_transport_get_credit()

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

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

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

vsock/virtio: fix potential underflow in virtio_transport_get_credit()

The credit calculation in virtio_transport_get_credit() uses unsigned
arithmetic:

  ret = vvs->peer_buf_alloc - (vvs->tx_cnt - vvs->peer_fwd_cnt);

If the peer shrinks its advertised buffer (peer_buf_alloc) while bytes
are in flight, the subtraction can underflow and produce a large
positive value, potentially allowing more data to be queued than the
peer can handle.

Reuse virtio_transport_has_space() which already handles this case and
add a comment to make it clear why we are doing that.

[Stefano: use virtio_transport_has_space() instead of duplicating the code]
[Stefano: tweak the commit message]

The Linux kernel CVE team has assigned CVE-2026-23069 to this issue.


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

	Issue introduced in 4.8 with commit 06a8fc78367d070720af960dcecec917d3ae5f3b and fixed in 6.6.122 with commit 02f9af192b98d15883c70dd41ac76d1b0217c899
	Issue introduced in 4.8 with commit 06a8fc78367d070720af960dcecec917d3ae5f3b and fixed in 6.12.68 with commit d05bc313788f0684b27f0f5b60c52a844669b542
	Issue introduced in 4.8 with commit 06a8fc78367d070720af960dcecec917d3ae5f3b and fixed in 6.18.8 with commit ec0f1b3da8061be3173d1c39faaf9504f91942c3
	Issue introduced in 4.8 with commit 06a8fc78367d070720af960dcecec917d3ae5f3b and fixed in 6.19-rc7 with commit 3ef3d52a1a9860d094395c7a3e593f3aa26ff012

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-2026-23069
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/vmw_vsock/virtio_transport_common.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/02f9af192b98d15883c70dd41ac76d1b0217c899
	https://git.kernel.org/stable/c/d05bc313788f0684b27f0f5b60c52a844669b542
	https://git.kernel.org/stable/c/ec0f1b3da8061be3173d1c39faaf9504f91942c3
	https://git.kernel.org/stable/c/3ef3d52a1a9860d094395c7a3e593f3aa26ff012