net: followup to codereview for cl/7096014

net/base/asn1_util.cc

Index: net/base/asn1_util.cc
diff --git a/net/base/asn1_util.cc b/net/base/asn1_util.cc
index ee25d41be8cb22cb58aca4e406c34b3485f24029..a1e8637f8706a95f0aacdc8ad295e6f785322952 100644
--- a/net/base/asn1_util.cc
+++ b/net/base/asn1_util.cc
@@ -14,11 +14,32 @@ bool ParseElement(base::StringPiece* in,
                   unsigned *out_header_len) {
   const uint8* data = reinterpret_cast<const uint8*>(in->data());
 
+  // We don't support kAny and kOptional at the same time.
+  if ((tag_value & kAny) && (tag_value & kOptional))
+    return false;
+
+  if (in->empty() && (tag_value & kOptional)) {
+    if (out_header_len)
+      *out_header_len = 0;
+    if (out)
+      *out = base::StringPiece();
+    return true;
+  }
+
   if (in->size() < 2)
     return false;
 
-  if (tag_value != kAny && static_cast<unsigned char>(data[0]) != tag_value)
+  if (tag_value != kAny &&
+      static_cast<unsigned char>(data[0]) != (tag_value & 0xff)) {
+    if (tag_value & kOptional) {
+      if (out_header_len)
+        *out_header_len = 0;
+      if (out)
+        *out = base::StringPiece();
+      return true;
+    }
     return false;
+  }
 
   size_t len = 0;
   if ((data[1] & 0x80) == 0) {
@@ -71,9 +92,9 @@ bool GetElement(base::StringPiece* in,
   return true;
 }
 
-// SeekToSPKI changes |cert| so that it points to a suffix of the original
-// value where the suffix begins at the start of the ASN.1 SubjectPublicKeyInfo
-// value.
+// SeekToSPKI changes |cert| so that it points to a suffix of the
+// TBSCertificate where the suffix begins at the start of the ASN.1
+// SubjectPublicKeyInfo value.
 static bool SeekToSPKI(base::StringPiece* cert) {
   // From RFC 5280, section 4.1
   //    Certificate  ::=  SEQUENCE  {
@@ -94,14 +115,19 @@ static bool SeekToSPKI(base::StringPiece* cert) {
   if (!GetElement(cert, kSEQUENCE, &certificate))
     return false;
 
+  // We don't allow junk after the certificate.
+  if (!cert->empty())
+    return false;
+
   base::StringPiece tbs_certificate;
   if (!GetElement(&certificate, kSEQUENCE, &tbs_certificate))
     return false;
 
-  // The version is optional, so a failure to parse it is fine.
-  GetElement(&tbs_certificate,
-             kCompound | kContextSpecific | 0,
-             NULL);
+  if (!GetElement(&tbs_certificate,
+                  kOptional | kConstructed | kContextSpecific | 0,
+                  NULL)) {
+    return false;
+  }
 
   // serialNumber
   if (!GetElement(&tbs_certificate, kINTEGER, NULL))
@@ -134,6 +160,7 @@ bool ExtractSPKIFromDERCert(base::StringPiece cert,
 bool ExtractCRLURLsFromDERCert(base::StringPiece cert,
                                std::vector<base::StringPiece>* urls_out) {
   urls_out->clear();
+  std::vector<base::StringPiece> tmp_urls_out;
 
   if (!SeekToSPKI(&cert))
     return false;
@@ -150,17 +177,21 @@ bool ExtractCRLURLsFromDERCert(base::StringPiece cert,
   if (!GetElement(&cert, kSEQUENCE, NULL))
     return false;
   // issuerUniqueID
-  GetElement(&cert, kCompound | kContextSpecific | 1, NULL);
+  if (!GetElement(&cert, kOptional | kConstructed | kContextSpecific | 1, NULL))
+    return false;
   // subjectUniqueID
-  GetElement(&cert, kCompound | kContextSpecific | 2, NULL);
+  if (!GetElement(&cert, kOptional | kConstructed | kContextSpecific | 2, NULL))
+    return false;
 
   base::StringPiece extensions_seq;
-  if (!GetElement(&cert, kCompound | kContextSpecific | 3,
+  if (!GetElement(&cert, kOptional | kConstructed | kContextSpecific | 3,
                   &extensions_seq)) {
-    // If there are no extensions, then there are no CRL URLs.
-    return true;
+    return false;
   }
 
+  if (extensions_seq.empty())
+    return true;
+
   // Extensions  ::=  SEQUENCE SIZE (1..MAX) OF Extension
   // Extension   ::=  SEQUENCE  {
   //      extnID      OBJECT IDENTIFIER,
@@ -218,7 +249,7 @@ bool ExtractCRLURLsFromDERCert(base::StringPiece cert,
         return false;
 
       base::StringPiece name;
-      if (!GetElement(&distrib_point, kContextSpecific | kCompound | 0,
+      if (!GetElement(&distrib_point, kContextSpecific | kConstructed | 0,
                       &name)) {
         // If it doesn't contain a name then we skip it.
         continue;
@@ -231,7 +262,8 @@ bool ExtractCRLURLsFromDERCert(base::StringPiece cert,
         continue;
       }
 
-      if (GetElement(&distrib_point, kContextSpecific | kCompound | 2, NULL)) {
+      if (GetElement(&distrib_point,
+                     kContextSpecific | kConstructed | 2, NULL)) {
         // If it contains a alternative issuer, then we skip it.
         continue;
       }
@@ -240,8 +272,10 @@ bool ExtractCRLURLsFromDERCert(base::StringPiece cert,
       //   fullName                [0]     GeneralNames,
       //   nameRelativeToCRLIssuer [1]     RelativeDistinguishedName }
       base::StringPiece general_names;
-      if (!GetElement(&name, kContextSpecific | kCompound | 0, &general_names))
+      if (!GetElement(&name,
+                      kContextSpecific | kConstructed | 0, &general_names)) {
         continue;
+      }
 
       // GeneralNames ::= SEQUENCE SIZE (1..MAX) OF GeneralName
       // GeneralName ::= CHOICE {
@@ -251,7 +285,7 @@ bool ExtractCRLURLsFromDERCert(base::StringPiece cert,
       while (general_names.size() > 0) {
         base::StringPiece url;
         if (GetElement(&general_names, kContextSpecific | 6, &url)) {
-          urls_out->push_back(url);
+          tmp_urls_out.push_back(url);
         } else {
           if (!GetElement(&general_names, kAny, NULL))
             return false;
@@ -260,6 +294,7 @@ bool ExtractCRLURLsFromDERCert(base::StringPiece cert,
     }
   }
 
+  urls_out->swap(tmp_urls_out);
   return true;
 }