CVE-2026-89763: KEYS: trusted: Fix TPM teardown ordering

CVE-2026-89763: KEYS: trusted: Fix TPM teardown ordering

[Greg Kroah-Hartman]

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

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

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

KEYS: trusted: Fix TPM teardown ordering

trusted_tpm_exit() drops the TPM chip reference and frees the digest
array before unregistering the trusted key type. key_type_lookup()
holds key_types_sem for reading until the key operation finishes, while
unregister_key_type() takes it for writing. It therefore provides the
synchronization point that must precede backend teardown.

The current order permits this interleaving:

  CPU 0                              CPU 1
  trusted_tpm_exit()                 key_type_lookup("trusted")
    put_device(&chip->dev)             trusted_tpm_seal()
    kfree(digests)                       pcrlock()
    unregister_key_type()                  tpm_pcr_extend(..., digests)

CPU 1 can consequently dereference the freed digest array. The chip can
also be released before callbacks stop using it.

KASAN reported:

  BUG: KASAN: slab-use-after-free in tpm_pcr_extend+0x1f0/0x200
  Read of size 2 at addr ffff88810872d000 by task poc/89
  Call Trace:
    tpm_pcr_extend+0x1f0/0x200
    pcrlock+0x42/0x70 [trusted]
    trusted_tpm_seal+0x1b6/0x570 [trusted]
    trusted_instantiate+0x293/0x340 [trusted]
    __key_instantiate_and_link+0xb2/0x2b0
    __key_create_or_update+0x61e/0xb50
    __do_sys_add_key+0x1b8/0x310
  Allocated by task 88:
    __kmalloc_noprof+0x1a7/0x490
    do_one_initcall+0xa1/0x390
    do_init_module+0x2df/0x840
  Freed by task 90:
    kfree+0x131/0x3c0
    trusted_tpm_exit+0x59/0xa0 [trusted]
    __do_sys_delete_module+0x346/0x510

Move unregister_key_type() before releasing either resource. This stops
new lookups and waits for in-flight key operations to finish before the
backend state is destroyed.

The Linux kernel CVE team has assigned CVE-2026-89763 to this issue.


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

	Issue introduced in 5.1 with commit 0b6cf6b97b7ef1fa3c7fefab0cac897a1c4a3400 and fixed in 6.18.50 with commit 753c978f2400f9783eb524842a975d3ac950d511
	Issue introduced in 5.1 with commit 0b6cf6b97b7ef1fa3c7fefab0cac897a1c4a3400 and fixed in 7.2.4 with commit 2f7541afbc57fe9d26769a22c31d8ce8790c9a19
	Issue introduced in 5.1 with commit 0b6cf6b97b7ef1fa3c7fefab0cac897a1c4a3400 and fixed in 7.3-rc1 with commit 5e2d672280d97d83de43031d93761b12dadd7b8a

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-2026-89763
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:
	security/keys/trusted-keys/trusted_tpm1.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/753c978f2400f9783eb524842a975d3ac950d511
	https://git.kernel.org/stable/c/2f7541afbc57fe9d26769a22c31d8ce8790c9a19
	https://git.kernel.org/stable/c/5e2d672280d97d83de43031d93761b12dadd7b8a