fix: continue when the Mbed TLS stream cannot install the client credential

Reverses the half of #785 that failed Open when mbedtls_ssl_conf_own_cert
returned an error. That drew the line between a configuration mistake and a
resource fault; the contract draws it between our own credential and the peer's
identity, so both now report and continue.

The same fault is indistinguishable on the OpenSSL side - a failed PEM load and a
failed allocation surface as one return code - so leaving this one blocking would
have left the two adapters differing on an event neither can tell apart.

Continuing is safe: ssl_append_key_cert returns MBEDTLS_ERR_SSL_ALLOC_FAILED
before the key_cert node is appended (library/ssl_tls.c, 3.6.2), so nothing is
installed and the connection continues server-authenticated, exactly as the
OpenSSL adapter's does. ApplyTlsPolicy returns void again and leaves Open's
chain.

The severity moves with it, to the WARNING and CAT_BAD_CONFIG that
docs/error-severity.md gives a component that was built and is delivering.
Rating a resource fault BAD_CONFIG is the one cost of collapsing the two paths,
and the detail code still separates them for a handler that wants to retry one
and not the other.

docs/tls.md states the rule both adapters now share, and its client-credential
obligation covers the third failure mode rather than two. The divergence note
comes off the OpenSSL platform page, and its setup page no longer says a
half-supplied credential is rejected at Open.

Part of #782.

Author: DavidCozens

Platform/MbedTls/Source/SolidSyslogMbedTlsStream.c

@@ -36,7 +36,7 @@ static inline uint32_t MbedTlsStream_ResolveHandshakeTimeoutMs(struct SolidSyslo
 static inline struct SolidSyslogMbedTlsStream* MbedTlsStream_SelfFromBase(struct SolidSyslogStream* base);
 static inline bool MbedTlsStream_Open(struct SolidSyslogStream* base, const struct SolidSyslogAddress* addr);
 static inline bool MbedTlsStream_ApplySslConfigDefaults(struct SolidSyslogMbedTlsStream* self);
-static inline bool MbedTlsStream_ApplyTlsPolicy(struct SolidSyslogMbedTlsStream* self);
+static inline void MbedTlsStream_ApplyTlsPolicy(struct SolidSyslogMbedTlsStream* self);
 static inline bool MbedTlsStream_HasClientCredential(const struct SolidSyslogMbedTlsStreamConfig* config);
 static inline bool MbedTlsStream_HasHalfOfClientCredential(const struct SolidSyslogMbedTlsStreamConfig* config);
 static inline bool MbedTlsStream_BindContextToConfig(struct SolidSyslogMbedTlsStream* self);
@@ -133,8 +133,8 @@ static inline bool MbedTlsStream_Open(struct SolidSyslogStream* base, const stru
     bool ok = SolidSyslogStream_Open(self->Config.Transport, addr) && MbedTlsStream_ApplySslConfigDefaults(self);
     if (ok)
     {
-        ok = MbedTlsStream_ApplyTlsPolicy(self) && MbedTlsStream_BindContextToConfig(self) &&
-             MbedTlsStream_ConfigureExpectedHostname(self);
+        MbedTlsStream_ApplyTlsPolicy(self);
+        ok = MbedTlsStream_BindContextToConfig(self) && MbedTlsStream_ConfigureExpectedHostname(self);
     }
     if (ok)
     {
@@ -169,9 +169,13 @@ static inline bool MbedTlsStream_ApplySslConfigDefaults(struct SolidSyslogMbedTl
 
 /* TLS policy owned by the library - set per-ssl_config so it cannot leak
  * into the integrator's other ssl_configs (per coexistence contract). */
-static inline bool MbedTlsStream_ApplyTlsPolicy(struct SolidSyslogMbedTlsStream* self)
+/* No fault in our own credential stops delivery: the collector is the
+ * enforcement point for it, and one that requires a client certificate refuses
+ * the handshake anyway. Every failure here leaves nothing installed, so the
+ * connection continues server-authenticated rather than half-presenting a
+ * credential. */
+static inline void MbedTlsStream_ApplyTlsPolicy(struct SolidSyslogMbedTlsStream* self)
 {
-    bool ok = true;
     mbedtls_ssl_conf_authmode(&self->SslConfig, MBEDTLS_SSL_VERIFY_REQUIRED);
     /* Pin the floor at TLS 1.2 rather than inheriting MBEDTLS_SSL_PRESET_DEFAULT,
      * which can negotiate down to TLS 1.0/1.1 on permissive integrator builds.
@@ -184,15 +188,13 @@ static inline bool MbedTlsStream_ApplyTlsPolicy(struct SolidSyslogMbedTlsStream*
     mbedtls_ssl_conf_rng(&self->SslConfig, mbedtls_ctr_drbg_random, self->Config.Rng);
     if (MbedTlsStream_HasClientCredential(&self->Config))
     {
-        ok = mbedtls_ssl_conf_own_cert(&self->SslConfig, self->Config.ClientCertChain, self->Config.ClientKey) == 0;
-        if (!ok)
+        /* Only MBEDTLS_ERR_SSL_ALLOC_FAILED, which returns before the key_cert
+         * node is appended, so nothing is left half-configured. */
+        if (mbedtls_ssl_conf_own_cert(&self->SslConfig, self->Config.ClientCertChain, self->Config.ClientKey) != 0)
         {
-            /* Only MBEDTLS_ERR_SSL_ALLOC_FAILED. Failing Open rather than
-             * connecting without the certificate: a device configured for
-             * mutual TLS must not present itself as one that was not. */
             MbedTlsStream_Report(
-                SOLIDSYSLOG_SEVERITY_ERROR,
-                SOLIDSYSLOG_CAT_TLS_STREAM_INIT_FAILED,
+                SOLIDSYSLOG_SEVERITY_WARNING,
+                SOLIDSYSLOG_CAT_BAD_CONFIG,
                 SOLIDSYSLOG_MBEDTLS_STREAM_ERROR_CLIENT_CREDENTIAL_NOT_INSTALLED
             );
         }
@@ -209,7 +211,6 @@ static inline bool MbedTlsStream_ApplyTlsPolicy(struct SolidSyslogMbedTlsStream*
     {
         /* Neither supplied - server-authenticated TLS is the deliberate case. */
     }
-    return ok;
 }
 
 static inline bool MbedTlsStream_HasClientCredential(const struct SolidSyslogMbedTlsStreamConfig* config)

Tests/MbedTls/SolidSyslogMbedTlsStreamTest.cpp

@@ -888,22 +888,23 @@ TEST(SolidSyslogMbedTlsStream, OpenReportsIncompleteClientCredentialWhenClientCe
     CHECK_INCOMPLETE_CREDENTIAL_REPORTED();
 }
 
-TEST(SolidSyslogMbedTlsStream, OpenFailsAndReportsWhenClientCredentialCannotBeInstalled)
-
+TEST(SolidSyslogMbedTlsStream, OpenReportsClientCredentialNotInstalledAndStillConnects)
 {
     /* Both halves supplied, but mbedTLS cannot take them - the only documented
-     * failure is MBEDTLS_ERR_SSL_ALLOC_FAILED. Discarding it is the silent
-     * downgrade to server-authenticated TLS this stops. */
+     * failure is MBEDTLS_ERR_SSL_ALLOC_FAILED, which returns before anything is
+     * appended to the config. Nothing is presented, so the connection continues
+     * server-authenticated and the collector decides whether to accept it. */
     static mbedtls_x509_crt clientCertMarker;
     static mbedtls_pk_context clientKeyMarker;
     WireClientCredential(&clientCertMarker, &clientKeyMarker);
     MbedTlsFake_SetSslConfOwnCertReturn(MBEDTLS_ERR_SSL_ALLOC_FAILED);
 
-    CHECK_FALSE(SolidSyslogStream_Open(handle, addr));
+    CHECK_TRUE(SolidSyslogStream_Open(handle, addr));
 
-    CHECK_OPEN_UNWOUND_WITH_ERROR(
-        transport,
-        SOLIDSYSLOG_CAT_TLS_STREAM_INIT_FAILED,
+    CHECK_ERROR_REPORTED_ONCE(
+        SOLIDSYSLOG_SEVERITY_WARNING,
+        &MbedTlsStreamErrorSource,
+        SOLIDSYSLOG_CAT_BAD_CONFIG,
         SOLIDSYSLOG_MBEDTLS_STREAM_ERROR_CLIENT_CREDENTIAL_NOT_INSTALLED
     );
 }

docs/platforms/openssl/index.md

@@ -59,17 +59,6 @@ an encrypted store has to be written to a readable file before this adapter can
 use it. Tracked under
 [E39](https://github.com/cososo-ltd/solid-syslog/issues/782).
 
-### A half-supplied client credential stops delivery
-
-A certificate without its key, or a key without its certificate, is rejected when
-the stream opens, so nothing is delivered until the configuration is corrected.
-The contract asks for it to be reported with delivery continuing, on the grounds
-that the collector is the enforcement point for our own credential.
-
-This adapter is stricter than the contract rather than weaker, and the stricter
-behaviour is safe. Tracked as
-[#734](https://github.com/cososo-ltd/solid-syslog/issues/734).
-
 ### The cipher policy does not bind a TLS 1.3 connection
 
 The cipher list is passed to OpenSSL unchanged and pins nothing of the library's

docs/platforms/openssl/setup.md

@@ -9,15 +9,15 @@ itself, and this page is the wiring.
 ## What you need
 
 OpenSSL 3.0 or later on the include and link path, and a platform supplying the
-TCP stream underneath — the [capability matrix](../index.md) shows which fill
+TCP stream underneath - the [capability matrix](../index.md) shows which fill
 that role.
 
 ```cmake
 set(SOLIDSYSLOG_PLATFORMS "OpenSsl;<Network>")
 ```
 
 `<Network>` is whichever platform the [capability matrix](../index.md) says
-fills that role on your target — see
+fills that role on your target - see
 [naming your platforms](../../build-integration.md#cmake) for how the list is
 read.
 
@@ -48,7 +48,7 @@ struct SolidSyslogStream* transport = CreateTcpStream();
 static struct SolidSyslogOpenSslStreamConfig tlsConfig;
 tlsConfig = (struct SolidSyslogOpenSslStreamConfig) {0};
 tlsConfig.Transport = transport;
-tlsConfig.Sleep = MySleep;                    /* required — no fallback */
+tlsConfig.Sleep = MySleep;                    /* required - no fallback */
 tlsConfig.CaBundlePath = "/etc/ssl/collector-ca.pem";
 tlsConfig.ServerName = "collector.example.net";
 
@@ -57,15 +57,15 @@ struct SolidSyslogStream* tls = SolidSyslogOpenSslStream_Create(&tlsConfig);
 
 Zero-initialise the config before filling it.
 
-For mutual TLS, add the client credential — both fields or neither, since
-supplying one without the other is rejected at `Open`:
+For mutual TLS, add the client credential - both fields, since one without the
+other is reported and leaves the connection server-authenticated:
 
 ```c
 tlsConfig.ClientCertChainPath = "/etc/ssl/device-chain.pem";
 tlsConfig.ClientKeyPath       = "/etc/ssl/device-key.pem";
 ```
 
-Then the sender, unchanged from the plain-TCP case — it sees a Stream and does
+Then the sender, unchanged from the plain-TCP case - it sees a Stream and does
 not know or care that it is a TLS one:
 
 ```c
@@ -85,5 +85,5 @@ created.
 
 Failures report through the error handler rather than silently. Install one
 before you start, and read [error severity](../../error-severity.md) for what
-each level is telling you — a `CRITICAL` at create time means the stream fell
+each level is telling you - a `CRITICAL` at create time means the stream fell
 back to the Null object, and nothing will be delivered.

docs/tls.md

@@ -211,7 +211,7 @@ Where the key must not be in application memory at all, that is a property of th
 credential source rather than of the window: a source backed by a secure element
 or a hardware key store never hands the key over in the first place.
 
-### Report a partially configured client credential
+### Report a client credential that will not be presented
 
 Mutual TLS is all-or-nothing: a certificate without its key, or a key without its
 certificate, is a configuration error and is reported as one. It is never
@@ -225,10 +225,19 @@ it is reported at the same point. Left to the handshake, it comes back as a
 rejection from the collector, which sends the integrator looking at the collector
 for a fault that is on the device.
 
-Delivery continues. The receiver is the enforcement point for our credential - a
-collector that requires a client certificate will refuse the handshake, and one
-that does not was never going to check. Blocking here would deny the audit trail
-without changing what the collector decides.
+A credential the TLS library will not take is reported on the same terms: a file
+that does not load, memory it cannot allocate. The cause differs and the reports
+distinguish it where the library does, but the consequence is the one that
+matters - what the integrator configured is not in force.
+
+Delivery continues in every one of those cases. The receiver is the enforcement
+point for our credential - a collector that requires a client certificate will
+refuse the handshake, and one that does not was never going to check. Blocking
+here would deny the audit trail without changing what the collector decides.
+
+The rule stops at our own credential, and the line is the one drawn under
+*Delivery is preferred to silence*: a fault in the material we present never
+stops delivery, and a failed check on the peer always does.
 
 ### Permit the cryptographic level to be chosen
 

misra_suppressions.txt

@@ -59,7 +59,7 @@ misra-c2012-11.3:Platform/MbedTls/Source/SolidSyslogMbedTlsHmacSha256Policy.c:83
 misra-c2012-11.3:Platform/MbedTls/Source/SolidSyslogMbedTlsAesGcmPolicy.c:85
 misra-c2012-11.3:Platform/OpenSsl/Source/SolidSyslogOpenSslAesGcmPolicy.c:89
 misra-c2012-11.3:Platform/OpenSsl/Source/SolidSyslogOpenSslHmacSha256Policy.c:84
-misra-c2012-11.3:Platform/OpenSsl/Source/SolidSyslogOpenSslStream.c:93
+misra-c2012-11.3:Platform/OpenSsl/Source/SolidSyslogOpenSslStream.c:99
 misra-c2012-11.3:Platform/Posix/Source/SolidSyslogPosixAddress.c:18
 misra-c2012-11.3:Platform/Posix/Source/SolidSyslogPosixAddressPrivate.h:27
 misra-c2012-11.3:Platform/Posix/Source/SolidSyslogPosixAddressPrivate.h:32
@@ -86,8 +86,8 @@ misra-c2012-11.5:Platform/LwipRaw/Source/SolidSyslogLwipRawDnsResolver.c:158
 misra-c2012-11.5:Platform/LwipRaw/Source/SolidSyslogLwipRawDnsResolver.c:220
 misra-c2012-11.5:Platform/LwipRaw/Source/SolidSyslogLwipRawTcpStream.c:151
 misra-c2012-11.5:Platform/LwipRaw/Source/SolidSyslogLwipRawTcpStream.c:159
-misra-c2012-11.5:Platform/MbedTls/Source/SolidSyslogMbedTlsStream.c:344
-misra-c2012-11.5:Platform/MbedTls/Source/SolidSyslogMbedTlsStream.c:356
+misra-c2012-11.5:Platform/MbedTls/Source/SolidSyslogMbedTlsStream.c:345
+misra-c2012-11.5:Platform/MbedTls/Source/SolidSyslogMbedTlsStream.c:357
 
 # D.003 — Rule 5.7: repeating struct tags (no-typedef-struct convention)
 # See docs/misra-deviations.md#d003
@@ -196,8 +196,8 @@ misra-c2012-8.9:Core/Source/SolidSyslogFileBlockDevice.c:24
 
 # D.013 — Rule 11.5: void* <-> a byte pointer at third-party byte-buffer API boundaries
 # See docs/misra-deviations.md#d013
-misra-c2012-11.5:Platform/MbedTls/Source/SolidSyslogMbedTlsStream.c:381
-misra-c2012-11.5:Platform/MbedTls/Source/SolidSyslogMbedTlsStream.c:399
+misra-c2012-11.5:Platform/MbedTls/Source/SolidSyslogMbedTlsStream.c:382
+misra-c2012-11.5:Platform/MbedTls/Source/SolidSyslogMbedTlsStream.c:400
 misra-c2012-11.5:Platform/Windows/Source/SolidSyslogWinsockDatagram.c:146
 misra-c2012-11.5:Platform/Windows/Source/SolidSyslogWinsockTcpStream.c:358
 misra-c2012-11.5:Platform/Windows/Source/SolidSyslogWinsockTcpStream.c:378