Bug 2516608 (CVE-2026-72151)

Summary: CVE-2026-72151 kernel: tpm: tpm2-sessions: wait for async KPP completion in tpm_buf_append_salt
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
Severity: medium Docs Contact:
Priority: medium    
Version: unspecifiedCC: rhel-process-autobot, watson-tool-maintainers
Target Milestone: ---Keywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in the Linux kernel's Trusted Platform Module (TPM2) session handling. Specifically, the `tpm_buf_append_salt()` function does not properly manage asynchronous cryptographic key operations. This oversight can lead to a use-after-free vulnerability, where the system attempts to access memory that has already been released. This issue can be automatically triggered during routine system operations, potentially allowing a local attacker to cause a system crash or, in some scenarios, escalate their privileges.
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Description OSIDB Bzimport 2026-08-15 06:21:40 UTC 
In the Linux kernel, the following vulnerability has been resolved:

tpm: tpm2-sessions: wait for async KPP completion in tpm_buf_append_salt

tpm_buf_append_salt() in drivers/char/tpm/tpm2-sessions.c calls
crypto_kpp_generate_public_key() and crypto_kpp_compute_shared_secret()
without installing a completion callback, discards both return values,
and immediately frees the kpp_request via kpp_request_free(). When the
resolved ecdh-nist-p256 KPP backend is asynchronous (atmel-ecc, HPRE,
keembay-ocs), either operation returns -EINPROGRESS and the deferred
completion worker dereferences the freed request.

The path fires automatically from the hwrng_fillfn kernel thread via
tpm_get_random -> tpm2_get_random -> tpm2_start_auth_session ->
tpm_buf_append_salt on every entropy poll, without any userland action.

Install crypto_req_done as the completion callback, wrap both KPP
operations in crypto_wait_req(), and propagate errors to the caller.
The wait is a no-op for synchronous backends.
Comment 1 Keith Grant 2026-08-18 12:59:40 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2026081534-CVE-2026-72151-db64@gregkh/T