CVE-2026-89486: ipmi: Fix use-after-free of cmd_rcvr in _ipmi_destroy_user()

CVE-2026-89486: ipmi: Fix use-after-free of cmd_rcvr in _ipmi_destroy_user()

[Greg Kroah-Hartman]

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

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

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

ipmi: Fix use-after-free of cmd_rcvr in _ipmi_destroy_user()

Commit 9e91f8a6c868 ("ipmi:msghandler: Remove srcu for the
ipmi_interfaces list") dropped the synchronize_rcu() between unlinking
the command receivers from intf->cmd_rcvrs and freeing them, updating
only the comment that explains why the barrier is needed.

The cmd_rcvrs list is still traversed under plain RCU: find_cmd_rcvr()
walks it inside rcu_read_lock(), and handle_ipmb_get_msg_cmd() borrows
rcvr->user from that lookup within the same read-side section. Without
the grace period, _ipmi_destroy_user() can kfree() a cmd_rcvr while a
reader still holds a pointer to it, causing a use-after-free.

The rework only made srcu unnecessary for the interfaces list; the
cmd_rcvrs list still relies on plain RCU. Restore the synchronize_rcu()
before freeing the receivers.

The Linux kernel CVE team has assigned CVE-2026-89486 to this issue.


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

	Issue introduced in 6.16 with commit 9e91f8a6c8688e27f4ccce7db457da87d6458836 and fixed in 6.18.50 with commit 3088e41292fecf132f85f79af5ee4d620b9ff1b4
	Issue introduced in 6.16 with commit 9e91f8a6c8688e27f4ccce7db457da87d6458836 and fixed in 7.2.4 with commit 5dc0b2a9af95a97861c1bffaf1687a3173e395c5
	Issue introduced in 6.16 with commit 9e91f8a6c8688e27f4ccce7db457da87d6458836 and fixed in 7.3-rc1 with commit 05ec76cfbce653e07cec19b9b8b20e33449d5d87

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-2026-89486
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/3088e41292fecf132f85f79af5ee4d620b9ff1b4
	https://git.kernel.org/stable/c/5dc0b2a9af95a97861c1bffaf1687a3173e395c5
	https://git.kernel.org/stable/c/05ec76cfbce653e07cec19b9b8b20e33449d5d87