Subject: CVE-2023-52849: cxl/mem: Fix shutdown order

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

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

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

cxl/mem: Fix shutdown order

Ira reports that removing cxl_mock_mem causes a crash with the following
trace:

 BUG: kernel NULL pointer dereference, address: 0000000000000044
 [..]
 RIP: 0010:cxl_region_decode_reset+0x7f/0x180 [cxl_core]
 [..]
 Call Trace:
  <TASK>
  cxl_region_detach+0xe8/0x210 [cxl_core]
  cxl_decoder_kill_region+0x27/0x40 [cxl_core]
  cxld_unregister+0x29/0x40 [cxl_core]
  devres_release_all+0xb8/0x110
  device_unbind_cleanup+0xe/0x70
  device_release_driver_internal+0x1d2/0x210
  bus_remove_device+0xd7/0x150
  device_del+0x155/0x3e0
  device_unregister+0x13/0x60
  devm_release_action+0x4d/0x90
  ? __pfx_unregister_port+0x10/0x10 [cxl_core]
  delete_endpoint+0x121/0x130 [cxl_core]
  devres_release_all+0xb8/0x110
  device_unbind_cleanup+0xe/0x70
  device_release_driver_internal+0x1d2/0x210
  bus_remove_device+0xd7/0x150
  device_del+0x155/0x3e0
  ? lock_release+0x142/0x290
  cdev_device_del+0x15/0x50
  cxl_memdev_unregister+0x54/0x70 [cxl_core]

This crash is due to the clearing out the cxl_memdev's driver context
(@cxlds) before the subsystem is done with it. This is ultimately due to
the region(s), that this memdev is a member, being torn down and expecting
to be able to de-reference @cxlds, like here:

static int cxl_region_decode_reset(struct cxl_region *cxlr, int count)
...
                if (cxlds->rcd)
                        goto endpoint_reset;
...

Fix it by keeping the driver context valid until memdev-device
unregistration, and subsequently the entire stack of related
dependencies, unwinds.

The Linux kernel CVE team has assigned CVE-2023-52849 to this issue.

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

	Issue introduced in 5.15 with commit 9cc238c7a526 and fixed in 5.15.139 with commit 20bd0198bebd
	Issue introduced in 5.15 with commit 9cc238c7a526 and fixed in 6.1.63 with commit 7c7371b41a14
	Issue introduced in 5.15 with commit 9cc238c7a526 and fixed in 6.5.12 with commit cad22a757029
	Issue introduced in 5.15 with commit 9cc238c7a526 and fixed in 6.6.2 with commit 0ca074f7d788
	Issue introduced in 5.15 with commit 9cc238c7a526 and fixed in 6.7 with commit 88d3917f82ed
	Issue introduced in 5.14.8 with commit 964a98344922

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-2023-52849
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/cxl/core/memdev.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/20bd0198bebdd706bd4614b3933ef70d7c19618f
	https://git.kernel.org/stable/c/7c7371b41a14e86f53e7dbe5baa7b1d3e0ab324b
	https://git.kernel.org/stable/c/cad22a757029c3a1985c221a2d4a6491ad4035ae
	https://git.kernel.org/stable/c/0ca074f7d788627a4e0b047ca5fbdb5fc567220c
	https://git.kernel.org/stable/c/88d3917f82ed4215a2154432c26de1480a61b209