CVE-2026-68415: xfrm: clear mode callbacks after failed mode setup

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

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

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

xfrm: clear mode callbacks after failed mode setup

xfrm_state_gc_task can run long after a failed IPTFS state setup. In the
reproduced case, __xfrm_init_state() cached x->mode_cbs, IPTFS setup
returned -ENOMEM before publishing mode_data, and the temporary module
reference from xfrm_get_mode_cbs() was dropped immediately. The dead state
then kept x->mode_cbs until deferred GC ran after xfrm_iptfs had been
unloaded.

Clear x->mode_cbs when mode init or clone fails before publishing
mode_data. Those states never installed mode-specific state or the
long-term IPTFS module pin, so deferred GC has nothing mode-specific to
destroy and must not retain a callback table pointer past the temporary
lookup reference.

The buggy scenario involves two paths, with each column showing the order
within that path:

failed setup path:
1. cache x->mode_cbs
2. mode setup fails before mode_data
3. drop the temporary module ref
4. dead state keeps x->mode_cbs cached

GC/unload path:
1. xfrm_state_put() queues GC work
2. xfrm_iptfs unloads later
3. xfrm_state_gc_task runs
4. GC dereferences stale x->mode_cbs

This also covers the failed clone path where clone_state() returns before
publishing mode_data.

Validation reproduced this kernel report:
Kernel panic - not syncing: Fatal exception
CONFIG_FAULT_INJECTION_STACKTRACE_FILTER=y
failslab_stacktrace_filter matched xfrm_iptfs frames
ack_error=-12
FAULT_INJECTION: forcing a failure
BUG: unable to handle page fault
Workqueue: events xfrm_state_gc_task
RIP: xfrm_state_gc_task+0x142/0x650
Modules linked in: esp4_offload xfrm_user [last unloaded: xfrm_iptfs]
Kernel panic - not syncing: Fatal exception

The Linux kernel CVE team has assigned CVE-2026-68415 to this issue.


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

	Issue introduced in 6.14 with commit 4b3faf610cc63bfac972711635eafbca5e7d7117 and fixed in 6.18.42 with commit 9845a35986a658816f7752f7ebd7c455a4c7dfdf
	Issue introduced in 6.14 with commit 4b3faf610cc63bfac972711635eafbca5e7d7117 and fixed in 7.1.6 with commit c37a079230128a5237f45fb4e181bc069a5c2955
	Issue introduced in 6.14 with commit 4b3faf610cc63bfac972711635eafbca5e7d7117 and fixed in 7.2-rc4 with commit 2538bd3cd1ff5af655908469544ac7b7ae259386

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-2026-68415
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:
	net/xfrm/xfrm_state.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/9845a35986a658816f7752f7ebd7c455a4c7dfdf
	https://git.kernel.org/stable/c/c37a079230128a5237f45fb4e181bc069a5c2955
	https://git.kernel.org/stable/c/2538bd3cd1ff5af655908469544ac7b7ae259386