CVE-2026-68416: mtd: fix double free and WARN_ON in add_mtd_device() error paths

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

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

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

mtd: fix double free and WARN_ON in add_mtd_device() error paths

When device_register() or mtd_nvmem_add() fails inside
add_mtd_device() for a partition, the error handling triggers
mtd_release() via put_device() or device_unregister(). mtd_release()
calls release_mtd_partition() which frees the mtd_info structure.
However, callers such as mtd_add_partition() and add_mtd_partitions()
also call free_partition() in their error paths, resulting in a double
free.

Additionally, release_mtd_partition() hits WARN_ON(!list_empty(
&mtd->part.node)) because the partition node is still linked in the
parent's partitions list when the release callback fires from the
add_mtd_device() error path.

Fix this by overriding dev->type and dev->release before put_device()
in the error paths, so that device_release() invokes a no-op function
instead of mtd_release(). For the mtd_nvmem_add() failure case,
device_unregister() is replaced with device_del() to separate the
device removal from the final kobject reference drop, allowing the
override to take effect before put_device() is called.

The callers' error paths (list_del + free_partition) remain the sole
owners of mtd_info lifetime on add_mtd_device() failure, which is the
expected contract.

The normal partition teardown path is not affected: del_mtd_device()
goes through kref_put() -> mtd_device_release() -> device_unregister()
with dev->type still set to &mtd_devtype, so mtd_release() ->
release_mtd_partition() continues to work correctly for the regular
removal case.

The Linux kernel CVE team has assigned CVE-2026-68416 to this issue.


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

	Issue introduced in 6.6 with commit 19bfa9ebebb5ec0695def57eb1d80de7e9cab369 and fixed in 6.6.148 with commit ffe21a3545b439e7b11578a701c22a847c149561
	Issue introduced in 6.6 with commit 19bfa9ebebb5ec0695def57eb1d80de7e9cab369 and fixed in 6.12.101 with commit e1e96aca1bdf391e2f49531c270ffc134e5b49a5
	Issue introduced in 6.6 with commit 19bfa9ebebb5ec0695def57eb1d80de7e9cab369 and fixed in 6.18.42 with commit f98ae09c727dcf34f745c875661c64b642e4abfa
	Issue introduced in 6.6 with commit 19bfa9ebebb5ec0695def57eb1d80de7e9cab369 and fixed in 7.1.6 with commit 820f983d641937a787e841ee4b93501f69f5683e
	Issue introduced in 6.6 with commit 19bfa9ebebb5ec0695def57eb1d80de7e9cab369 and fixed in 7.2-rc4 with commit 9d4af746af8ce27eefc2338b2feaa1e01f28b6c3

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-2026-68416
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/mtd/mtdcore.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/ffe21a3545b439e7b11578a701c22a847c149561
	https://git.kernel.org/stable/c/e1e96aca1bdf391e2f49531c270ffc134e5b49a5
	https://git.kernel.org/stable/c/f98ae09c727dcf34f745c875661c64b642e4abfa
	https://git.kernel.org/stable/c/820f983d641937a787e841ee4b93501f69f5683e
	https://git.kernel.org/stable/c/9d4af746af8ce27eefc2338b2feaa1e01f28b6c3