Subject: CVE-2023-52837: nbd: fix uaf in nbd_open

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

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

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

nbd: fix uaf in nbd_open

Commit 4af5f2e03013 ("nbd: use blk_mq_alloc_disk and
blk_cleanup_disk") cleans up disk by blk_cleanup_disk() and it won't set
disk->private_data as NULL as before. UAF may be triggered in nbd_open()
if someone tries to open nbd device right after nbd_put() since nbd has
been free in nbd_dev_remove().

Fix this by implementing ->free_disk and free private data in it.

The Linux kernel CVE team has assigned CVE-2023-52837 to this issue.

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

	Issue introduced in 5.14 with commit 4af5f2e03013 and fixed in 6.1.63 with commit 4e9b3ec84dc9
	Issue introduced in 5.14 with commit 4af5f2e03013 and fixed in 6.5.12 with commit 879947f4180b
	Issue introduced in 5.14 with commit 4af5f2e03013 and fixed in 6.6.2 with commit 56bd7901b5e9
	Issue introduced in 5.14 with commit 4af5f2e03013 and fixed in 6.7 with commit 327462725b0f

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-2023-52837
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/block/nbd.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/4e9b3ec84dc97909876641dad14e0a2300d6c2a3
	https://git.kernel.org/stable/c/879947f4180bc6e83af64eb0515e0cf57fce15db
	https://git.kernel.org/stable/c/56bd7901b5e9dbc9112036ea615ebcba1565fafe
	https://git.kernel.org/stable/c/327462725b0f759f093788dfbcb2f1fd132f956b