Ssl socket - fix broken certificate verification

On iOS QSslConfiguration always has an empty list of system CA certificates.
Calling SecTrustSetAnchorCertificatesOnly(.., TRUE) on iOS  results in
SecTrustEvaluate failing to verify a valid certificate, since there
are no 'anchors' at all. We can use SecTrustSetAnchorCerificatesOnly(.. TRUE)
on macOS only, where we do extract/copy system certificates using
SecTrustSettingsCopyCertificates and save them in a QSslConfiguration's
list.

Task-number: QTBUG-61053
Change-Id: I70d4e46273d78414baaac8531273def707c3eebc
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>
Reviewed-by: Timur Pocheptsov <timur.pocheptsov@qt.io>

1 files changed, 25 insertions, 2 deletions

diff --git a/src/network/ssl/qsslsocket_mac.cpp b/src/network/ssl/qsslsocket_mac.cpp
index fec5fbefc0..78aceadb81 100644
--- a/src/network/ssl/qsslsocket_mac.cpp
+++ b/src/network/ssl/qsslsocket_mac.cpp
@@ -1222,9 +1222,32 @@ bool QSslSocketBackendPrivate::verifyPeerTrust()
         QCFType<SecCertificateRef> certRef = SecCertificateCreateWithData(NULL, certData);
         CFArrayAppendValue(certArray, certRef);
     }
+
     SecTrustSetAnchorCertificates(trust, certArray);
-    // Secure Transport should use anchors only from our QSslConfiguration:
-    SecTrustSetAnchorCertificatesOnly(trust, true);
+
+    // By default SecTrustEvaluate uses both CA certificates provided in
+    // QSslConfiguration and the ones from the system database. This behavior can
+    // be unexpected if a user's code tries to limit the trusted CAs to those
+    // explicitly set in QSslConfiguration.
+    // Since on macOS we initialize the default QSslConfiguration copying the
+    // system CA certificates (using SecTrustSettingsCopyCertificates) we can
+    // call SecTrustSetAnchorCertificatesOnly(trust, true) to force SecTrustEvaluate
+    // to use anchors only from our QSslConfiguration.
+    // Unfortunately, SecTrustSettingsCopyCertificates is not available on iOS
+    // and the default QSslConfiguration always has an empty list of system CA
+    // certificates. This leaves no way to provide client code with access to the
+    // actual system CA certificate list (which most use-cases need) other than
+    // by letting SecTrustEvaluate fall through to the system list; so, in this case
+    // (even though the client code may have provided its own certs), we retain
+    // the default behavior.
+
+#ifdef Q_OS_MACOS
+    const bool anchorsFromConfigurationOnly = true;
+#else
+    const bool anchorsFromConfigurationOnly = false;
+#endif
+
+    SecTrustSetAnchorCertificatesOnly(trust, anchorsFromConfigurationOnly);
 
     SecTrustResultType trustResult = kSecTrustResultInvalid;
     SecTrustEvaluate(trust, &trustResult);