Fix handling of csrNonce in MTRCommissioningParameters. (project-chip#42075)

* Fix handling of csrNonce in MTRCommissioningParameters.

The CSR nonce passed via CommissioningParameters was being ignored by
AutoCommisssioner, because it was just fetching a random nonce from the
OperationalCredentialsDelegate.

This fix makes it possible for an OperationalCredentialsDelegate to indicate
that the AutoCommissioner should use whatever nonce was provided via
CommissioningParameters, and uses that in MTROperationalCredentialsDelegate, so
we don't override the data from MTRCommissioningParameters.

* Apply suggestion from code review.

Co-authored-by: Karsten Sperling <[email protected]>

* Address review comment.

---------

Co-authored-by: Karsten Sperling <[email protected]>

Author: bzbarsky-apple

src/controller/AutoCommissioner.cpp

@@ -970,9 +970,17 @@ CHIP_ERROR AutoCommissioner::CommissioningStepFinished(CHIP_ERROR err, Commissio
             // reference to the operational credential delegate here
             if (mOperationalCredentialsDelegate != nullptr)
             {
-                MutableByteSpan nonce(mCSRNonce);
-                ReturnErrorOnFailure(mOperationalCredentialsDelegate->ObtainCsrNonce(nonce));
-                mParams.SetCSRNonce(ByteSpan(mCSRNonce, sizeof(mCSRNonce)));
+                uint8_t csrNonceBytes[sizeof(mCSRNonce)];
+                MutableByteSpan nonce(csrNonceBytes);
+                CHIP_ERROR csrError = mOperationalCredentialsDelegate->ObtainCsrNonce(nonce);
+                if (csrError != CHIP_ERROR_NOT_IMPLEMENTED)
+                {
+                    ReturnErrorOnFailure(csrError);
+
+                    MutableByteSpan savedCSRNonce(mCSRNonce);
+                    ReturnErrorOnFailure(CopySpanToMutableSpan(nonce, savedCSRNonce));
+                    mParams.SetCSRNonce(savedCSRNonce);
+                }
             }
             break;
         }

src/controller/OperationalCredentialsDelegate.h

@@ -81,6 +81,17 @@ class DLL_EXPORT OperationalCredentialsDelegate
      */
     virtual void SetFabricIdForNextNOCRequest(FabricId fabricId) {}
 
+    /**
+     * ObtainCsrNonce can be overridden to return CHIP_ERROR_NOT_IMPLEMENTED to
+     * indicate that whatever CSR nonce came from the CommissioningParameters
+     * should be used, or overridden to return a specific nonce that will be
+     * used instead of the one from CommissioningParameters, if AutoCommissioner
+     * is used.
+     *
+     * The default implementation of this method generates a random nonce,
+     * which will take precedence over the one from CommissioningParameters
+     * if AutoCommissioner is used.
+     */
     virtual CHIP_ERROR ObtainCsrNonce(MutableByteSpan & csrNonce)
     {
         VerifyOrReturnError(csrNonce.size() == kCSRNonceLength, CHIP_ERROR_INVALID_ARGUMENT);

src/darwin/Framework/CHIP/MTROperationalCredentialsDelegate.h

@@ -54,6 +54,8 @@ class MTROperationalCredentialsDelegate : public chip::Controller::OperationalCr
 
     void SetFabricIdForNextNOCRequest(chip::FabricId fabricId) override { mNextFabricId = fabricId; }
 
+    CHIP_ERROR ObtainCsrNonce(chip::MutableByteSpan & csrNonce) override { return CHIP_ERROR_NOT_IMPLEMENTED; }
+
     void SetDeviceID(chip::NodeId deviceId) { mDeviceBeingPaired = deviceId; }
     void ResetDeviceID() { mDeviceBeingPaired = chip::kUndefinedNodeId; }
 

src/darwin/Framework/CHIPTests/MTROperationalCertificateIssuerTests.m

@@ -28,6 +28,7 @@
 static NSString * kOnboardingPayload = @"MT:-24J0AFN00KA0648G00";
 static const uint16_t kLocalPort = 5541;
 static const uint16_t kTestVendorId = 0xFFF1u;
+static NSString * kCSRNonceStr = @"01234567890123456789012345678901"; // 32 chars
 
 // Singleton controller we use.
 static MTRDeviceController * sController = nil;
@@ -53,9 +54,12 @@ - (void)controller:(MTRDeviceController *)controller commissioningSessionEstabli
 {
     XCTAssertEqual(error.code, 0);
 
+    __auto_type * params = [[MTRCommissioningParameters alloc] init];
+    params.csrNonce = [kCSRNonceStr dataUsingEncoding:NSUTF8StringEncoding];
+
     NSError * commissionError = nil;
     [sController commissionNodeWithID:@(kDeviceId)
-                  commissioningParams:[[MTRCommissioningParameters alloc] init]
+                  commissioningParams:params
                                 error:&commissionError];
     XCTAssertNil(commissionError);
 
@@ -97,6 +101,8 @@ - (void)issueOperationalCertificateForRequest:(MTROperationalCSRInfo *)csrInfo
     XCTAssertNotNil(attestationInfo);
     XCTAssertEqual(controller, sController);
 
+    XCTAssertEqualObjects(csrInfo.csrNonce, [kCSRNonceStr dataUsingEncoding:NSUTF8StringEncoding]);
+
     __auto_type * csrInfoCopy = [[MTROperationalCSRInfo alloc] initWithCSRElementsTLV:csrInfo.csrElementsTLV
                                                                  attestationSignature:csrInfo.attestationSignature];
     XCTAssertEqualObjects(csrInfoCopy.csr, csrInfo.csr);