HIGH Introduced in 5.1
trusted-keys Teardown UAF
CVE-2026-89763
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
KernelScan AI6.3MEDIUM
01Description
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.
02KernelScan AI Analysis
Risk summary
A race condition in the trusted keys module teardown path allows a concurrent key operation to access a freed digest array and a released TPM chip, resulting in a use-after-free. An attacker with local access and the ability to unload kernel modules (CAP_SYS_MODULE) could exploit this to achieve kernel memory corruption, potentially leading to privilege escalation or denial of service.
Vulnerability analysis
When the trusted keys module is unloaded, its cleanup function frees the TPM digest array and drops the TPM chip reference before unregistering the key type from the kernel's key subsystem. Because key type unregistration is the synchronization point that blocks new key lookups and waits for in-flight key operations to finish, performing it last leaves a window where a concurrent key creation or update can still call into TPM functions that dereference the already-freed digest array and released chip. The fix reorders the teardown so that the key type is unregistered first, ensuring no new operations can start and all in-progress ones have completed before any backend resources are released. Exploiting this requires local access with the ability to unload kernel modules (CAP_SYS_MODULE in the init namespace) and winning a race between module unload and a concurrent trusted key operation.
Lifecycle
03Fix Versions
| Branch | Introduced | Fixed in | Patch commit |
|---|---|---|---|
| 6.18 | 5.1 | 6.18.50 | 753c978f2400 |
| 7.2 | 5.1 | 7.2.4 | 2f7541afbc57 |
| mainline | 5.1 | 7.3-rc1 | 5e2d672280d9 |
| 6.12 | 5.1 | 6.12.111 | 3d67b4acbfc7 |
| cip/6.12 | 5.1 | 6.12.111-cip32 | 3d67b4acbfc7 |