From 91821d6b920b821a5c8e15421b775ed1a28c0091 Mon Sep 17 00:00:00 2001
From: Roy Tam <roytam@gmail.com>
Date: Tue, 10 Dec 2019 10:53:09 +0800
Subject: [PATCH] partly imported from tenfourfox: #578: M1579060 M1586176

---
 security/pkix/lib/pkixcert.cpp | 19 +++++++------------
 security/pkix/lib/pkixder.h    | 11 +++++++++++
 2 files changed, 18 insertions(+), 12 deletions(-)

diff --git a/security/pkix/lib/pkixcert.cpp b/security/pkix/lib/pkixcert.cpp
index ffa58fd3b5..79ee12dba4 100644
--- a/security/pkix/lib/pkixcert.cpp
+++ b/security/pkix/lib/pkixcert.cpp
@@ -105,29 +105,24 @@ BackCert::Init()
     return rv;
   }
 
-  static const uint8_t CSC = der::CONTEXT_SPECIFIC | der::CONSTRUCTED;
-
   // According to RFC 5280, all fields below this line are forbidden for
   // certificate versions less than v3.  However, for compatibility reasons,
   // we parse v1/v2 certificates in the same way as v3 certificates.  So if
   // these fields appear in a v1 certificate, they will be used.
 
   // Ignore issuerUniqueID if present.
-  if (tbsCertificate.Peek(CSC | 1)) {
-    rv = der::ExpectTagAndSkipValue(tbsCertificate, CSC | 1);
-    if (rv != Success) {
-      return rv;
-    }
+  rv = der::SkipOptionalImplicitPrimitiveTag(tbsCertificate, 1);
+  if (rv != Success) {
+    return rv;
   }
 
   // Ignore subjectUniqueID if present.
-  if (tbsCertificate.Peek(CSC | 2)) {
-    rv = der::ExpectTagAndSkipValue(tbsCertificate, CSC | 2);
-    if (rv != Success) {
-      return rv;
-    }
+  rv = der::SkipOptionalImplicitPrimitiveTag(tbsCertificate, 2);
+  if (rv != Success) {
+    return rv;
   }
 
+  static const uint8_t CSC = der::CONTEXT_SPECIFIC | der::CONSTRUCTED;
   rv = der::OptionalExtensions(
          tbsCertificate, CSC | 3,
          [this](Reader& extnID, const Input& extnValue, bool critical,
diff --git a/security/pkix/lib/pkixder.h b/security/pkix/lib/pkixder.h
index a17114bcb9..71691a35e2 100644
--- a/security/pkix/lib/pkixder.h
+++ b/security/pkix/lib/pkixder.h
@@ -123,6 +123,17 @@ ExpectTagAndSkipValue(Reader& input, uint8_t tag)
   return ExpectTagAndGetValue(input, tag, ignoredValue);
 }
 
+// This skips IMPLICIT OPTIONAL tags that are "primitive" (not constructed),
+// given the number in the class of the tag (i.e. the number in the brackets in
+// `issuerUniqueID  [1]  IMPLICIT UniqueIdentifier OPTIONAL`).
+inline Result SkipOptionalImplicitPrimitiveTag(Reader& input,
+                                               uint8_t numberInClass) {
+  if (input.Peek(CONTEXT_SPECIFIC | numberInClass)) {
+    return ExpectTagAndSkipValue(input, CONTEXT_SPECIFIC | numberInClass);
+  }
+  return Success;
+}
+
 // Like ExpectTagAndGetValue, except the output Input will contain the
 // encoded tag and length along with the value.
 inline Result