Subject: CVE-2021-47459: can: j1939: j1939_netdev_start(): fix UAF for rx_kref of j1939_priv

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

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

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

can: j1939: j1939_netdev_start(): fix UAF for rx_kref of j1939_priv

It will trigger UAF for rx_kref of j1939_priv as following.

        cpu0                                    cpu1
j1939_sk_bind(socket0, ndev0, ...)
j1939_netdev_start
                                        j1939_sk_bind(socket1, ndev0, ...)
                                        j1939_netdev_start
j1939_priv_set
                                        j1939_priv_get_by_ndev_locked
j1939_jsk_add
.....
j1939_netdev_stop
kref_put_lock(&priv->rx_kref, ...)
                                        kref_get(&priv->rx_kref, ...)
                                        REFCOUNT_WARN("addition on 0;...")

====================================================
refcount_t: addition on 0; use-after-free.
WARNING: CPU: 1 PID: 20874 at lib/refcount.c:25 refcount_warn_saturate+0x169/0x1e0
RIP: 0010:refcount_warn_saturate+0x169/0x1e0
Call Trace:
 j1939_netdev_start+0x68b/0x920
 j1939_sk_bind+0x426/0xeb0
 ? security_socket_bind+0x83/0xb0

The rx_kref's kref_get() and kref_put() should use j1939_netdev_lock to
protect.

The Linux kernel CVE team has assigned CVE-2021-47459 to this issue.

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

	Issue introduced in 5.4 with commit 9d71dd0c7009 and fixed in 5.4.156 with commit a0e47d2833b4
	Issue introduced in 5.4 with commit 9d71dd0c7009 and fixed in 5.10.76 with commit 864e77771a24
	Issue introduced in 5.4 with commit 9d71dd0c7009 and fixed in 5.14.15 with commit 6e8811707e2d
	Issue introduced in 5.4 with commit 9d71dd0c7009 and fixed in 5.15 with commit d9d52a3ebd28

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-2021-47459
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/can/j1939/main.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/a0e47d2833b4f65e6c799f28c6b636d36b8b936d
	https://git.kernel.org/stable/c/864e77771a24c877aaf53aee019f78619cbcd668
	https://git.kernel.org/stable/c/6e8811707e2df0c6ba920f0cad3a3bca7b42132f
	https://git.kernel.org/stable/c/d9d52a3ebd284882f5562c88e55991add5d01586