kcer_nss_fuzzer: Skip certs that NSS doesn’t consider valid

The RunImportCertFromBytesUseValidCert method tries to import a
valid certificate and checks that it succeeds. Filter out
certificates that NSS doesn’t consider valid.

Fixed: b:415855133
Change-Id: I32ae3f72fc4bfa1b3f5c6542bac2bbf93ab08850
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6518956
Auto-Submit: Michael Ershov <miersh@google.com>
Commit-Queue: Andreea Costinas <acostinas@google.com>
Reviewed-by: Andreea Costinas <acostinas@google.com>
Cr-Commit-Position: refs/heads/main@{#1456830}

chromeos/ash/components/kcer/kcer_nss/kcer_nss_fuzzer.cc

@@ -883,6 +883,12 @@ void KcerFuzzer::RunImportCertFromBytesUseValidCert() {
   if (!cert) {
     return;
   }
+  net::ScopedCERTCertificate nss_cert =
+      net::x509_util::CreateCERTCertificateFromX509Certificate(cert.get());
+  if (!nss_cert) {
+    // NSS doesn't consider the cert valid.
+    return;
+  }
 
   base::span<const uint8_t> cert_data = GetCertData(cert);
   CertDer cert_der(std::vector<uint8_t>(cert_data.begin(), cert_data.end()));