Fix bad cast of malformed https rdata

Another case of the apparently poor job I did adding in the malformed
vairant of HttpsRecordRdata.  ServiceFormHttpsRecordRdata::IsEqual() did
not check if the input was malformed before casting to service form. Fix
is to check before casting, and also to use the AsServiceForm() helper
instead of a raw cast, as the helper has the CHECKs designed to make
bugs like this obvious.

Fixed: 1146873
Change-Id: I5222a09c9c032bc163ca1beebf4bf1e0504ccad6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2526931
Commit-Queue: Eric Orth <ericorth@chromium.org>
Commit-Queue: Dan McArdle <dmcardle@chromium.org>
Auto-Submit: Eric Orth <ericorth@chromium.org>
Reviewed-by: Dan McArdle <dmcardle@chromium.org>
Cr-Commit-Position: refs/heads/master@{#825500}

net/dns/https_record_rdata.cc

@@ -240,8 +240,7 @@ bool AliasFormHttpsRecordRdata::IsEqual(const HttpsRecordRdata* other) const {
   if (!other->IsAlias())
     return false;
 
-  const AliasFormHttpsRecordRdata* alias =
-      static_cast<const AliasFormHttpsRecordRdata*>(other);
+  const AliasFormHttpsRecordRdata* alias = other->AsAliasForm();
   return alias_name_ == alias->alias_name_;
 }
 
@@ -295,11 +294,10 @@ ServiceFormHttpsRecordRdata::~ServiceFormHttpsRecordRdata() = default;
 bool ServiceFormHttpsRecordRdata::IsEqual(const HttpsRecordRdata* other) const {
   DCHECK(other);
 
-  if (other->IsAlias())
+  if (other->IsAlias() || other->IsMalformed())
     return false;
 
-  const ServiceFormHttpsRecordRdata* service =
-      static_cast<const ServiceFormHttpsRecordRdata*>(other);
+  const ServiceFormHttpsRecordRdata* service = other->AsServiceForm();
   return priority_ == service->priority_ &&
          service_name_ == service->service_name_ &&
          mandatory_keys_ == service->mandatory_keys_ &&

net/dns/https_record_rdata_unittest.cc

@@ -156,5 +156,47 @@ TEST(HttpsRecordRdataTest, RejectCorruptRdata) {
   EXPECT_TRUE(rdata->IsMalformed());
 }
 
+TEST(HttpsRecordRdataTest, AliasIsEqualRejectsWrongType) {
+  AliasFormHttpsRecordRdata alias("alias.name.test");
+  ServiceFormHttpsRecordRdata service(
+      1u /* priority */, "service.name.test", {} /* mandatory_keys */,
+      {} /* alpn_ids */, true /* default_alpn */, base::nullopt /* port */,
+      {} /* ipv4_hint */, "" /* ech_config */, {} /* ipv6_hint */,
+      {} /* unparsed_params */);
+  MalformedHttpsRecordRdata malformed;
+
+  EXPECT_TRUE(alias.IsEqual(&alias));
+  EXPECT_FALSE(alias.IsEqual(&service));
+  EXPECT_FALSE(alias.IsEqual(&malformed));
+}
+
+TEST(HttpsRecordRdataTest, ServiceIsEqualRejectsWrongType) {
+  AliasFormHttpsRecordRdata alias("alias.name.test");
+  ServiceFormHttpsRecordRdata service(
+      1u /* priority */, "service.name.test", {} /* mandatory_keys */,
+      {} /* alpn_ids */, true /* default_alpn */, base::nullopt /* port */,
+      {} /* ipv4_hint */, "" /* ech_config */, {} /* ipv6_hint */,
+      {} /* unparsed_params */);
+  MalformedHttpsRecordRdata malformed;
+
+  EXPECT_FALSE(service.IsEqual(&alias));
+  EXPECT_TRUE(service.IsEqual(&service));
+  EXPECT_FALSE(service.IsEqual(&malformed));
+}
+
+TEST(HttpsRecordRdataTest, MalformedIsEqualRejectsWrongType) {
+  AliasFormHttpsRecordRdata alias("alias.name.test");
+  ServiceFormHttpsRecordRdata service(
+      1u /* priority */, "service.name.test", {} /* mandatory_keys */,
+      {} /* alpn_ids */, true /* default_alpn */, base::nullopt /* port */,
+      {} /* ipv4_hint */, "" /* ech_config */, {} /* ipv6_hint */,
+      {} /* unparsed_params */);
+  MalformedHttpsRecordRdata malformed;
+
+  EXPECT_FALSE(malformed.IsEqual(&alias));
+  EXPECT_FALSE(malformed.IsEqual(&service));
+  EXPECT_TRUE(malformed.IsEqual(&malformed));
+}
+
 }  // namespace
 }  // namespace net