CVE-2026-74274: cxl/region: Fill first free targets[] slot during auto-discovery

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

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

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

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

cxl/region: Fill first free targets[] slot during auto-discovery

Any invalid endpoint decoder pointer in the target array of an active
region is not allowed by cxl driver. This means cxl driver always
assumes the first p->nr_targets entries of the target array in an
auto-assembly region are valid. However, there are scenarios that could
leave NULL endpoint decoder pointer holes in the target array.

1. When cxl_cancel_auto_attach() removes an endpoint decoder from a
   target array, the target slot is set to NULL. If the removed endpoint
   decoder is not the last element in the target array, the target array
   will contain a NULL hole.

2. When a auto-assembly region removes an assigned endpoint decoder, if
   the removed endpoint decoder is not the last element in the target
   array, always remains a NULL hole in the target array.

When a NULL pointer hole exists in a region's target array, it
introduces two potential problems:
1. Access an endpoint decoder via a NULL pointer. it always trigger
   calltrace like that.
    Oops: general protection fault, probably for non-canonical address 0xdffffc0000000008: 0000 [#1] SMP KASAN PTI
    RIP: 0010:cxl_calc_interleave_pos+0x26/0x810 [cxl_core]
    Call Trace:
      <TASK>
      cxl_region_attach+0xc50/0x2140 [cxl_core]
      cxl_add_to_region+0x321/0x2330 [cxl_core]
      discover_region+0x92/0x150 [cxl_port]
      device_for_each_child+0xf3/0x170
      cxl_port_probe+0x150/0x200 [cxl_port]
      cxl_bus_probe+0x4f/0xa0 [cxl_core]
      really_probe+0x1c8/0x960
      __driver_probe_device+0x323/0x450
      driver_probe_device+0x45/0x120
      __device_attach_driver+0x15d/0x280
      bus_for_each_drv+0x10f/0x190

2. Not having enough valid endpoint decoders attached to an
   auto-assembly region. if an auto-assembly region is created with lock
   flag or assigned endpoint decoder with lock flag, which means
   assigned endpoint decoder will not be reset during detaching, they
   could re-attach to the auto-assembly region again. But cxl region
   driver relies on p->nr_targets to verify whether the required number
   of endpoint decoders has been attached, and NULL endpoint decoder
   pointers are still counted in that case.

To fix above issues, adjust cxl_region_attach_auto() logic to find the
first free target slot for endpoint decoder attachment, this ensures
NULL holes in the target array are filled, rather than adding new
endpoint decoders at the tail of the target array.

The Linux kernel CVE team has assigned CVE-2026-74274 to this issue.


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

	Issue introduced in 6.19 with commit 2230c4bdc4120417799c74326ade3123da226d54 and fixed in 7.1.5 with commit 6fde3fcdfec438ba0df26e25a8ac7c3707211799
	Issue introduced in 6.19 with commit 2230c4bdc4120417799c74326ade3123da226d54 and fixed in 7.2-rc1 with commit aa8a76711c15041ec1e42c3a74c15c2df0bd31f6

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-2026-74274
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/6fde3fcdfec438ba0df26e25a8ac7c3707211799
	https://git.kernel.org/stable/c/aa8a76711c15041ec1e42c3a74c15c2df0bd31f6