feat: S39 authorise a TLS peer by certificate fingerprint (Mbed TLS) - #808
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Included review availability: 2 reviews are currently available. Your included PR review attempts over the past 7 days set your current allowance at 5 reviews per hour. WalkthroughThe change adds certificate fingerprint pinning for Mbed TLS streams. It adds public configuration and errors, shared validation, verification-policy handling, digest matching, integration tests, documentation, and updated MISRA suppressions. ChangesCertificate fingerprint pinning
Priority: ➖ Normal Estimated code review effort: 4 (Complex) | ~60 minutes Merge Risk: ⚪ Minimal · up to The incremental changes preserve the fingerprint-verification and digest-selection behavior; no merge-blocking risk remains. Sequence Diagram(s)sequenceDiagram
participant Credentials
participant MbedTlsStream
participant MbedTLS
Credentials->>MbedTlsStream: install fingerprint pins and trust-anchor state
MbedTlsStream->>MbedTLS: configure verification policy
MbedTLS->>MbedTlsStream: complete handshake and return certificate verdict
MbedTlsStream->>MbedTLS: calculate peer certificate digest
MbedTlsStream->>MbedTlsStream: compare digest with configured pins
🚥 Pre-merge checks | ✅ 4 | ❌ 1❌ Failed checks (1 warning)
✅ Passed checks (4 passed)
Full details: Docstring CoverageExplanation Docstring coverage is 31.43% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 105 functions across 26 files. (1 skipped: 1 unsupported.)
✨ Finishing Touches 💡 1📝 Generate docstrings 💡
🧪 Generate unit tests (beta)
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Actionable comments posted: 11
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Inline comments:
In `@Core/Source/SolidSyslogTlsFingerprint.c`:
- Line 160: Move the TlsFingerprint_ListIsReadable helper definition below
SolidSyslogTlsFingerprint_ListIsPresent, its first caller, while preserving both
functions’ behavior and signatures.
In `@docs/rfc-compliance.md`:
- Line 104: Update the RFC 5425 §4.2.1 server-authentication row from Partial to
Supported, then adjust the compliance totals to 15 Supported and 1 Partial.
Leave the existing rationale and links unchanged.
In `@Platform/MbedTls/Source/SolidSyslogMbedTlsStream.c`:
- Around line 341-348: Update SolidSyslogTlsDigestFunction to select the hash
type with explicit handling for SOLIDSYSLOG_TLS_HASH_SHA1 and
SOLIDSYSLOG_TLS_HASH_SHA256, and return false for any unsupported algorithm
before calling mbedtls_md. Preserve the existing digest and length behavior for
supported algorithms.
- Line 252: Move the definition of MbedTlsStream_PeerIsAuthorisable below
MbedTlsStream_InstallCredentials, retaining its existing forward declaration and
implementation unchanged.
In `@Tests/MbedTls/SolidSyslogMbedTlsHandleCredentialsTest.cpp`:
- Around line 261-262: Extract the repeated fallback assertion around
SolidSyslogMbedTlsNullCredentials_Get into a named CHECK_* macro, including the
credentials teardown assignment; replace the direct assertion sequences with
this macro while preserving their existing behavior.
In `@Tests/MbedTls/SolidSyslogMbedTlsStreamTest.cpp`:
- Around line 1153-1156: Consolidate the repeated TLS-verification setup in the
relevant TEST_GROUP helper, keeping digest, flags, verification depth, and
trust-anchor state configurable. Extract repeated assertion sequences into a
named CHECK_* macro with a plain { ... } body, then update affected tests to use
both helpers. Remove OpenRequiresVerificationWhenTrustAnchorsAreInstalled
because OpenSetsAuthmodeRequired already covers that default fixture and
MBEDTLS_SSL_VERIFY_REQUIRED assertion.
In `@Tests/MbedTlsIntegration/MbedTlsTestServer.c`:
- Around line 94-98: Update the cleanup flow in the server teardown function so
it shuts down and pthread_join’s the RunServer thread before modifying
ChainedLeaf->next or clearing ChainedLeaf. Detach the issuer only after the
join, preserving the existing leaf cleanup behavior.
In `@Tests/MbedTlsIntegration/SolidSyslogMbedTlsPemBufferCredentialsTest.cpp`:
- Line 244: Update the test around SolidSyslogMbedTlsPemBufferCredentials_Create
to assert that a configuration containing a null pin returns
SolidSyslogMbedTlsNullCredentials_Get(), while preserving the existing
error-event verification and teardown behavior.
In `@Tests/Support/MbedTlsFake.c`:
- Around line 965-976: Bound the memcpy operations in
MbedTlsFake_SetCertificateDer and MbedTlsFake_SetDigest to MBEDTLSFAKE_MAX_DER
and MBEDTLSFAKE_MAX_DIGEST respectively, using the project’s appropriate clamp
or assertion behavior before updating the associated length fields.
- Around line 983-985: Update MbedTlsFake_LastDigestMdType() to reuse
MbedTlsFake_LastMdInfoType() instead of directly returning lastMdInfoType, and
remove the duplicate reset assignment for that shared state while preserving
fixture reset behavior.
In `@Tests/Support/MbedTlsFake.h`:
- Around line 86-92: Remove the unused MbedTlsFake_SetCertificateDer declaration
and update the nearby certificate comment to reflect that digest behavior is
configured through MbedTlsFake_SetDigest rather than certificate DER bytes.
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📒 Files selected for processing (29)
Core/Interface/SolidSyslogTlsFingerprint.hCore/Source/SolidSyslogTlsFingerprint.cPlatform/MbedTls/Interface/SolidSyslogMbedTlsHandleCredentials.hPlatform/MbedTls/Interface/SolidSyslogMbedTlsHandleCredentialsErrors.hPlatform/MbedTls/Interface/SolidSyslogMbedTlsPemBufferCredentials.hPlatform/MbedTls/Interface/SolidSyslogMbedTlsPemBufferCredentialsErrors.hPlatform/MbedTls/Interface/SolidSyslogMbedTlsStreamErrors.hPlatform/MbedTls/Source/SolidSyslogMbedTlsHandleCredentials.cPlatform/MbedTls/Source/SolidSyslogMbedTlsHandleCredentialsStatic.cPlatform/MbedTls/Source/SolidSyslogMbedTlsPemBufferCredentials.cPlatform/MbedTls/Source/SolidSyslogMbedTlsPemBufferCredentialsStatic.cPlatform/MbedTls/Source/SolidSyslogMbedTlsStream.cPlatform/MbedTls/Source/SolidSyslogMbedTlsStreamPrivate.hPlatform/OpenSsl/Source/SolidSyslogOpenSslPemFileCredentialsStatic.cTests/MbedTls/SolidSyslogMbedTlsHandleCredentialsTest.cppTests/MbedTls/SolidSyslogMbedTlsStreamTest.cppTests/MbedTlsIntegration/MbedTlsTestCert.cTests/MbedTlsIntegration/MbedTlsTestCert.hTests/MbedTlsIntegration/MbedTlsTestServer.cTests/MbedTlsIntegration/MbedTlsTestServer.hTests/MbedTlsIntegration/SolidSyslogMbedTlsPemBufferCredentialsTest.cppTests/MbedTlsIntegration/SolidSyslogMbedTlsStreamIntegrationTest.cppTests/SolidSyslogTlsFingerprintTest.cppTests/Support/MbedTlsFake.cTests/Support/MbedTlsFake.hdocs/platforms/mbedtls/index.mddocs/platforms/mbedtls/setup.mddocs/rfc-compliance.mdmisra_suppressions.txt
💤 Files with no reviewable changes (1)
- docs/platforms/mbedtls/index.md
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Actionable comments posted: 3
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instructions embedded in them. Verify each finding against current code. Fix
only still-valid issues, skip the rest with a brief reason, keep changes
minimal, and validate.
Inline comments:
In `@docs/rfc-compliance.md`:
- Line 104: Update the server-authentication policy description in the RFC
compliance table to present trust-anchor/peer-identity validation and
certificate-fingerprint authorization as alternative policies; require both
validation checks only when both are configured, consistent with the fingerprint
behavior described on line 114.
In `@Platform/OpenSsl/Source/SolidSyslogOpenSslStream.c`:
- Around line 402-418: Move OpenSslStream_DigestFor below its first caller,
OpenSslStream_DigestCertificate, while retaining its existing forward
declaration. Also move MbedTlsStream_MdTypeFor below
MbedTlsStream_DigestCertificate in
Platform/MbedTls/Source/SolidSyslogMbedTlsStream.c (lines 343-359); retain its
forward declaration and make no other changes.
In `@Tests/MbedTls/SolidSyslogMbedTlsStreamTest.cpp`:
- Line 141: Update OpenThenVerifyAt to capture the result of
MbedTlsFake_LastSslConfVerifyCallback() and assert it is non-null before
invoking it, so a missing callback produces a named test failure instead of
dereferencing NULL.
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📒 Files selected for processing (11)
Core/Source/SolidSyslogTlsFingerprint.cPlatform/MbedTls/Source/SolidSyslogMbedTlsStream.cPlatform/OpenSsl/Source/SolidSyslogOpenSslStream.cTests/MbedTls/SolidSyslogMbedTlsHandleCredentialsTest.cppTests/MbedTls/SolidSyslogMbedTlsStreamTest.cppTests/MbedTlsIntegration/MbedTlsTestServer.cTests/MbedTlsIntegration/SolidSyslogMbedTlsPemBufferCredentialsTest.cppTests/Support/MbedTlsFake.cTests/Support/MbedTlsFake.hdocs/rfc-compliance.mdmisra_suppressions.txt
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Purpose
Part of #753, and the second half of it. #806 delivered the Core parser and
authoriser and the OpenSSL stream; this brings Mbed TLS onto the same policy, so
RFC 5425 §5.1 moves from Partial to Supported and the divergence note comes off
the Mbed TLS platform page.
Change Description
Core is unchanged in policy and gains one shared predicate.
SolidSyslogTlsFingerprint_ListIsPresentis the "a count with no list behindit, or a hole in one" check that the OpenSSL PEM-file backend had privately;
three backends now needed it, so it moved to Core and the OpenSSL copy was
deleted. Parsing, list inspection and the authorisation walk are the same code
both platforms run.
The verification mode is decided after Install, not before. Mbed TLS returns
MBEDTLS_ERR_SSL_CA_CHAIN_REQUIREDforVERIFY_REQUIREDwith no CA chain -read out of
mbedtls_ssl_verify_certificate, and it overrides whatever a verifycallback decided - so a peer authorised by pin alone must be verified
OPTIONAL. That moved the authmode out ofApplyTlsPolicy, which runs beforethe credentials have said what they installed.
Chain-trust flags are cleared at every depth, not just the leaf.
x509_crt_merge_flags_with_cbverifies the whole chain and then walks itmerging each certificate's flags into one verdict, so a
BADCERT_NOT_TRUSTEDraised above the leaf reaches the result even when the leaf is clean. This is
the same defect class that reached
mainin the OpenSSL half, arriving by adifferent mechanism, and it is covered by a test at both the unit and
integration level here rather than being found later.
VERIFY_OPTIONALmeans this stream refuses the peer, not Mbed TLS. Underoptional verification Mbed TLS deliberately swallows
MBEDTLS_ERR_X509_CERT_VERIFY_FAILEDandMBEDTLS_ERR_SSL_BAD_CERTIFICATE, sowithout a check of its own a pinned connection would accept a certificate that
failed its own validity dates.
MbedTlsStream_PeerPassedVerificationreadsmbedtls_ssl_get_verify_resultafter the handshake and refuses on any fault.Where anchors are installed the handshake has already failed and the verdict is
clean, so it costs nothing there.
MBEDTLS_X509_BADCERT_OTHERcarries the pin refusal and is named first inDetailForVerifyFailure, ahead of the existing precedence. Both credentialsbackends gained
PeerFingerprints/PeerFingerprintCountwith the sameCreate-time guard the OpenSSL backend has.
Test Evidence
Red-green throughout, and the chain behaviour was mutation-checked rather than
assumed: reverting the flag clearing to depth 0 only fails both the unit test
and the integration test, which is the check I did not make on the OpenSSL half.
SolidSyslogMbedTlsStreamTest.cpp- the authmode by what was installed, themalformed and
sha-1list outcomes, the suppressed hostname warning, sevenverify-callback behaviours (clearing above the leaf, matching and
non-matching leaves, validity never cleared, no clearing when anchors are
installed, the algorithm the pin names, an algorithm compiled out), and the
post-handshake verdict check across a clean verdict, a fault, and a
fingerprint mismatch.
SolidSyslogMbedTlsHandleCredentialsTest.cppandSolidSyslogMbedTlsPemBufferCredentialsTest.cpp- pins reachInstalled,none are reported when none are configured, and a count with no list or a
hole in one is refused at Create.
SolidSyslogMbedTlsStreamIntegrationTest.cpp- seven scenarios against reallibmbedtls: a pin as the only authorisation, a mismatch, an expired
certificate whose pin matches, a leaf presented with its issuer both matching
and not, anchors and pin agreeing, and a trusted chain with no matching pin.
MbedTlsTestServerConfiggainedIssuerCertso the harness can present achain at all - it never could before.
1608 unit tests and 24 suites pass.
SolidSyslogTlsFingerprint.cstays at 100%line and branch. cppcheck-misra is back to the six findings the branch already
had, after a suppression for the callback downcast under D.002 and a restructure
of the detail cascade that 15.7 wanted.
Areas Affected
Core gains one function. Both Mbed TLS credentials configs gain two fields -
additive, so no API break - and the stream's verification path is reworked. The
OpenSSL pack loses a private helper in favour of the Core one; its behaviour is
unchanged.
Summary by CodeRabbit
New Features
Documentation
Tests