Account for the OS returning an empty certificate chain.

net/cert/cert_verify_proc_mac.cc

Index: net/cert/cert_verify_proc_mac.cc
diff --git a/net/cert/cert_verify_proc_mac.cc b/net/cert/cert_verify_proc_mac.cc
index 388d0fc41a93b81ba84d8565bec4996fbe0b31f7..303f0aa6633d034309d6b126f53f5feb1f91c96c 100644
--- a/net/cert/cert_verify_proc_mac.cc
+++ b/net/cert/cert_verify_proc_mac.cc
@@ -176,15 +176,13 @@ OSStatus CreateTrustPolicies(const std::string& hostname,
 }
 
 // Stores the constructed certificate chain |cert_chain| and information about
-// the signature algorithms used into |*verify_result|. If the leaf cert in
-// |cert_chain| contains a weak (MD2, MD4, MD5, SHA-1) signature, stores that
-// in |*leaf_is_weak|.
+// the signature algorithms used into |*verify_result|. |cert_chain| must not be
+// empty.
 void GetCertChainInfo(CFArrayRef cert_chain,
                       CSSM_TP_APPLE_EVIDENCE_INFO* chain_info,
-                      CertVerifyResult* verify_result,
-                      bool* leaf_is_weak) {
-  *leaf_is_weak = false;
-  verify_result->verified_cert = nullptr;
+                      CertVerifyResult* verify_result) {
+  DCHECK_LT(0, CFArrayGetCount(cert_chain));
+
   verify_result->has_md2 = false;
   verify_result->has_md4 = false;
   verify_result->has_md5 = false;
@@ -232,16 +230,10 @@ void GetCertChainInfo(CFArrayRef cert_chain,
     const CSSM_OID* alg_oid = &sig_algorithm->algorithm;
     if (CSSMOIDEqual(alg_oid, &CSSMOID_MD2WithRSA)) {
       verify_result->has_md2 = true;
-      if (i == 0)
-        *leaf_is_weak = true;
     } else if (CSSMOIDEqual(alg_oid, &CSSMOID_MD4WithRSA)) {
       verify_result->has_md4 = true;
-      if (i == 0)
-        *leaf_is_weak = true;
     } else if (CSSMOIDEqual(alg_oid, &CSSMOID_MD5WithRSA)) {
       verify_result->has_md5 = true;
-      if (i == 0)
-        *leaf_is_weak = true;
     } else if (CSSMOIDEqual(alg_oid, &CSSMOID_SHA1WithRSA) ||
                CSSMOIDEqual(alg_oid, &CSSMOID_SHA1WithRSA_OIW) ||
                CSSMOIDEqual(alg_oid, &CSSMOID_SHA1WithDSA) ||
@@ -249,12 +241,12 @@ void GetCertChainInfo(CFArrayRef cert_chain,
                CSSMOIDEqual(alg_oid, &CSSMOID_SHA1WithDSA_JDK) ||
                CSSMOIDEqual(alg_oid, &CSSMOID_ECDSA_WithSHA1)) {
       verify_result->has_sha1 = true;
-      if (i == 0)
-        *leaf_is_weak = true;
     }
   }
-  if (!verified_cert)
+  if (!verified_cert) {
+    NOTREACHED();
     return;
+  }
 
   verify_result->verified_cert =
       X509Certificate::CreateFromHandle(verified_cert, verified_chain);
@@ -561,17 +553,19 @@ int CertVerifyProcMac::VerifyInternal(
     if (rv != OK)
       return rv;
 
-    CertVerifyResult temp_verify_result;
-    bool leaf_is_weak = false;
-    GetCertChainInfo(temp_chain, temp_chain_info, &temp_verify_result,
-                     &leaf_is_weak);
-
     bool untrusted = (temp_trust_result != kSecTrustResultUnspecified &&
                       temp_trust_result != kSecTrustResultProceed);
-    bool weak_chain =
-        !leaf_is_weak &&
-        (temp_verify_result.has_md2 || temp_verify_result.has_md4 ||
-         temp_verify_result.has_md5 || temp_verify_result.has_sha1);
+    bool weak_chain = false;
+    if (CFArrayGetCount(cert_array) > 0) {
+      CertVerifyResult temp_verify_result;
+      GetCertChainInfo(temp_chain, temp_chain_info, &temp_verify_result);
+      weak_chain = temp_verify_result.has_md2 || temp_verify_result.has_md4 ||
+                   temp_verify_result.has_md5 || temp_verify_result.has_sha1;
+    } else {
+      // If the chain is trusted or has recoverable errors, it cannot be empty.
+      DCHECK(untrusted);
+      DCHECK_NE(kSecTrustResultRecoverableTrustFailure, temp_trust_result);
+    }
     // Set the result to the current chain if:
     // - This is the first verification attempt. This ensures that if
     //   everything is awful (e.g. it may just be an untrusted cert), that
@@ -583,10 +577,6 @@ int CertVerifyProcMac::VerifyInternal(
     //   the old chain contained weak algorithms while the current chain only
     //   contains strong algorithms, then prefer the current chain over the
     //   old chain.
-    //
-    // Note: If the leaf certificate itself is weak, then the only
-    // consideration is whether or not there is a trusted chain. That's
-    // because no amount of path discovery will fix a weak leaf.

[Ryan Sleevi, 2015/04/23 00:30:50]

This is a bug that we _aren't_ exiting this loop after the first pass when
leaf_is_weak, so I'd rather *not* delete all this code, and instead fix that
bug.

     if (!trust_ref || (!untrusted && (candidate_untrusted ||
                                       (candidate_weak && !weak_chain)))) {
       trust_ref = temp_ref;
@@ -609,9 +599,8 @@ int CertVerifyProcMac::VerifyInternal(
   if (crl_set && !CheckRevocationWithCRLSet(completed_chain, crl_set))
     verify_result->cert_status |= CERT_STATUS_REVOKED;
 
-  bool leaf_is_weak_unused = false;
-  GetCertChainInfo(completed_chain, chain_info, verify_result,
-                   &leaf_is_weak_unused);
+  if (CFArrayGetCount(completed_chain) > 0)
+    GetCertChainInfo(completed_chain, chain_info, verify_result);
 
   // As of Security Update 2012-002/OS X 10.7.4, when an RSA key < 1024 bits
   // is encountered, CSSM returns CSSMERR_TP_VERIFY_ACTION_FAILED and adds