Subject: CVE-2023-52792: cxl/region: Do not try to cleanup after cxl_region_setup_targets() fails

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

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

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

cxl/region: Do not try to cleanup after cxl_region_setup_targets() fails

Commit 5e42bcbc3fef ("cxl/region: decrement ->nr_targets on error in
cxl_region_attach()") tried to avoid 'eiw' initialization errors when
->nr_targets exceeded 16, by just decrementing ->nr_targets when
cxl_region_setup_targets() failed.

Commit 86987c766276 ("cxl/region: Cleanup target list on attach error")
extended that cleanup to also clear cxled->pos and p->targets[pos]. The
initialization error was incidentally fixed separately by:
Commit 8d4285425714 ("cxl/region: Fix port setup uninitialized variable
warnings") which was merged a few days after 5e42bcbc3fef.

But now the original cleanup when cxl_region_setup_targets() fails
prevents endpoint and switch decoder resources from being reused:

1) the cleanup does not set the decoder's region to NULL, which results
   in future dpa_size_store() calls returning -EBUSY
2) the decoder is not properly freed, which results in future commit
   errors associated with the upstream switch

Now that the initialization errors were fixed separately, the proper
cleanup for this case is to just return immediately. Then the resources
associated with this target get cleanup up as normal when the failed
region is deleted.

The ->nr_targets decrement in the error case also helped prevent
a p->targets[] array overflow, so add a new check to prevent against
that overflow.

Tested by trying to create an invalid region for a 2 switch * 2 endpoint
topology, and then following up with creating a valid region.

The Linux kernel CVE team has assigned CVE-2023-52792 to this issue.

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

	Issue introduced in 6.0 with commit 5e42bcbc3fef and fixed in 6.1.64 with commit 90db4c1d5eba
	Issue introduced in 6.0 with commit 5e42bcbc3fef and fixed in 6.5.13 with commit 9090c5537c93
	Issue introduced in 6.0 with commit 5e42bcbc3fef and fixed in 6.6.3 with commit 07ffcd8ec79c
	Issue introduced in 6.0 with commit 5e42bcbc3fef and fixed in 6.7 with commit 0718588c7aaa

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-2023-52792
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/region.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/90db4c1d5ebaf574d3c3065c055977982c378a83
	https://git.kernel.org/stable/c/9090c5537c93cd0811ab7bfbd925b57addfffb60
	https://git.kernel.org/stable/c/07ffcd8ec79cf7383e1e45815f4842fd357991c2
	https://git.kernel.org/stable/c/0718588c7aaa7a1510b4de972370535b61dddd0d