CVE-2026-64044: ovpn: respect peer refcount in CMD_NEW_PEER error path

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

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

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

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

ovpn: respect peer refcount in CMD_NEW_PEER error path

ovpn_nl_peer_new_doit()'s error path calls ovpn_peer_release() directly
rather than ovpn_peer_put(), bypassing the kref. The accompanying
comment ("peer was not yet hashed, thus it is not used in any context")
holds for UDP but not for TCP.

For UDP, the ovpn_socket union uses the .ovpn arm and never points back
at a peer; UDP encap_recv looks up peers via the not-yet-populated
hashtables, so the new peer is unreachable until ovpn_peer_add()
publishes it.

For TCP, ovpn_socket_new() sets ovpn_sock->peer and
ovpn_tcp_socket_attach() publishes ovpn_sock via rcu_assign_sk_user_data().
>From that moment until ovpn_socket_release() detaches in the error path,
the TCP fd is fully wired: userspace recvmsg / sendmsg / close / poll
on the fd, as well as the strparser-driven ovpn_tcp_rcv() path, can
reach the peer through sk_user_data -> ovpn_sock->peer and bump its
refcount via ovpn_peer_hold().

ovpn_tcp_socket_wait_finish() (called inside ovpn_socket_release())
drains strparser and the tx work, but does not synchronize with
userspace syscall callers that already hold a peer reference. If
ovpn_nl_peer_modify() or ovpn_peer_add() returns an error while such
a caller is in flight - notably an ovpn_tcp_recvmsg() blocked in
__skb_recv_datagram() on peer->tcp.user_queue - the direct
ovpn_peer_release() destroys the peer while the caller still holds
the reference, and the eventual ovpn_peer_put() from that caller
operates on freed memory.

Replace the direct destructor call with ovpn_peer_put() so the kref
correctly defers destruction until the last reference is dropped.
In the common case where no concurrent user is present, behaviour is
unchanged: the kref hits zero immediately and ovpn_peer_release_kref()
runs the same destructor.

With this conversion ovpn_peer_release() has no callers outside peer.c
- ovpn_peer_release_kref() in the same translation unit is the only
remaining user - so make it static and drop its declaration from
peer.h.

The Linux kernel CVE team has assigned CVE-2026-64044 to this issue.


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

	Issue introduced in 6.16 with commit 11851cbd60ea1e5abbd97619d69845ead99303d6 and fixed in 6.18.34 with commit 8298834912d76dbc82c12b6b4ab7590ed2bb8ae5
	Issue introduced in 6.16 with commit 11851cbd60ea1e5abbd97619d69845ead99303d6 and fixed in 7.0.11 with commit 0c3ef71879c0264de6c42463031d9e057da87840
	Issue introduced in 6.16 with commit 11851cbd60ea1e5abbd97619d69845ead99303d6 and fixed in 7.1 with commit 1fef6614673ff0846d30acdeeaf3cf98bb5f6116

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-2026-64044
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/ovpn/netlink.c
	drivers/net/ovpn/peer.c
	drivers/net/ovpn/peer.h


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/8298834912d76dbc82c12b6b4ab7590ed2bb8ae5
	https://git.kernel.org/stable/c/0c3ef71879c0264de6c42463031d9e057da87840
	https://git.kernel.org/stable/c/1fef6614673ff0846d30acdeeaf3cf98bb5f6116