CVE-2026-52994: vsock/virtio: fix MSG_ZEROCOPY pinned-pages accounting

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

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

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

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

vsock/virtio: fix MSG_ZEROCOPY pinned-pages accounting

virtio_transport_init_zcopy_skb() uses iter->count as the size argument
for msg_zerocopy_realloc(), which in turn passes it to
mm_account_pinned_pages() for RLIMIT_MEMLOCK accounting. However, this
function is called after virtio_transport_fill_skb() has already consumed
the iterator via __zerocopy_sg_from_iter(), so on the last skb, iter->count
will be 0, skipping the RLIMIT_MEMLOCK enforcement.

Pass pkt_len (the total bytes being sent) as an explicit parameter to
virtio_transport_init_zcopy_skb() instead of reading the already-consumed
iter->count.

This matches TCP and UDP, which both call msg_zerocopy_realloc() with
the original message size.

The Linux kernel CVE team has assigned CVE-2026-52994 to this issue.


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

	Issue introduced in 6.7 with commit 581512a6dc939ef122e49336626ae159f3b8a345 and fixed in 6.18.33 with commit 6af1736b5810bc8a4a43a8518530113f5a757dc1
	Issue introduced in 6.7 with commit 581512a6dc939ef122e49336626ae159f3b8a345 and fixed in 7.0.10 with commit d0117950075f0a9d5944980784c719d8ebcd4bff
	Issue introduced in 6.7 with commit 581512a6dc939ef122e49336626ae159f3b8a345 and fixed in 7.1 with commit 1cb36e252211506f51095fe7ced8286cc77b4c80

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-2026-52994
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/6af1736b5810bc8a4a43a8518530113f5a757dc1
	https://git.kernel.org/stable/c/d0117950075f0a9d5944980784c719d8ebcd4bff
	https://git.kernel.org/stable/c/1cb36e252211506f51095fe7ced8286cc77b4c80