CVE-2026-81005: ipmi: si: Fix NULL pointer dereference after failed registration

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

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

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

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

ipmi: si: Fix NULL pointer dereference after failed registration

try_smi_init() allocates new_smi->si_sm and later calls
ipmi_register_smi_mod(), which maps to ipmi_add_smi().

During ipmi_add_smi(), the upper IPMI message handler obtains the
initial BMC device information through __bmc_get_device_id(). This can
fail if the BMC does not return a successful response to the Get Device
ID command.

When the BMC returns a nonzero completion code, the device-id helper
retries the command and eventually returns -EIO if the device ID still
cannot be fetched.

On this failure path, ipmi_add_smi() logs "Unable to get the device id"
and goes to out_err_started, where it invokes the lower driver's
shutdown callback. try_smi_init() then logs the returned registration
failure:

 ipmi_si IPI0001:00: IPMI message handler: Unable to get the device id: -5
 ipmi_si IPI0001:00: Unable to register device: error -5

For ipmi_si, the shutdown callback is shutdown_smi(), which cleans up
the SI state machine data, frees smi_info->si_sm, and sets
smi_info->si_sm and smi_info->intf to NULL.

However, intf->in_shutdown is not set on this failed-registration
rollback path. Therefore, the asynchronous redo_bmc_reg work item can
still retry BMC device-id probing after the lower driver has already
cleared its SI state machine data. In the observed case, that retry path
reached start_next_msg(), which passed the NULL smi_info->si_sm pointer
to the selected KCS state machine handler:

BUG: unable to handle kernel NULL pointer dereference at 0000000000000000
Workqueue: events redo_bmc_reg [ipmi_msghandler]
RIP: start_kcs_transaction+0x2c/0x190 [ipmi_si]
Call Trace:
 start_next_msg+0x50/0x80 [ipmi_si]
 check_start_timer_thread.part.9+0x3b/0x50 [ipmi_si]
 sender+0x69/0x80 [ipmi_si]
 i_ipmi_request+0x2ac/0x9d0 [ipmi_msghandler]
 __get_device_id.isra.29+0xaa/0x180 [ipmi_msghandler]
 __bmc_get_device_id+0xef/0x950 [ipmi_msghandler]
 redo_bmc_reg+0x52/0x60 [ipmi_msghandler]
 process_one_work+0x1a7/0x360

Set intf->in_shutdown on the out_err_started path before invoking the
lower driver's shutdown callback. This prevents later redo_bmc_reg
retries from using an interface whose lower driver state has been
cleaned up, and applies the same shutdown state to other IPMI interfaces
as well.

The Linux kernel CVE team has assigned CVE-2026-81005 to this issue.


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

	Issue introduced in 4.19 with commit 2512e40e48d21d8bac09f7e91d2c3ceb2d3b50b2 and fixed in 6.12.109 with commit d4be659a3e56f4eb16039ab8a1162efea086a714
	Issue introduced in 4.19 with commit 2512e40e48d21d8bac09f7e91d2c3ceb2d3b50b2 and fixed in 6.18.50 with commit 53af3a8bae0a93c1342e1b5519812203332aca8e
	Issue introduced in 4.19 with commit 2512e40e48d21d8bac09f7e91d2c3ceb2d3b50b2 and fixed in 7.2.4 with commit 8ada17dd4c4ffd6b94621e735d77eda196ce118f
	Issue introduced in 4.19 with commit 2512e40e48d21d8bac09f7e91d2c3ceb2d3b50b2 and fixed in 7.3-rc1 with commit 6d920a75df9a83ab096b3cde7a643b656e4fdfeb
	Issue introduced in 4.18.10 with commit 288bd736c8a027040fc261c86a87b65e7bc3f6fa

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-2026-81005
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/char/ipmi/ipmi_msghandler.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/d4be659a3e56f4eb16039ab8a1162efea086a714
	https://git.kernel.org/stable/c/53af3a8bae0a93c1342e1b5519812203332aca8e
	https://git.kernel.org/stable/c/8ada17dd4c4ffd6b94621e735d77eda196ce118f
	https://git.kernel.org/stable/c/6d920a75df9a83ab096b3cde7a643b656e4fdfeb