Fix several potential buffer over-read errors in JSONParser::ConsumeNumber.

base/json/json_parser.cc

Index: base/json/json_parser.cc
diff --git a/base/json/json_parser.cc b/base/json/json_parser.cc
index 50c8921d9352cccc235adea6b17e846275635c46..b94136979851cd7af114c6b25a1b980436d6daa5 100644
--- a/base/json/json_parser.cc
+++ b/base/json/json_parser.cc
@@ -680,11 +680,7 @@ std::unique_ptr<Value> JSONParser::ConsumeNumber() {
   end_index = index_;
 
   // The optional fraction part.
-  if (*pos_ == '.') {
-    if (!CanConsume(1)) {
-      ReportError(JSONReader::JSON_SYNTAX_ERROR, 1);
-      return nullptr;
-    }
+  if (CanConsume(1) && *pos_ == '.') {
     NextChar();
     if (!ReadInt(true)) {
       ReportError(JSONReader::JSON_SYNTAX_ERROR, 1);
@@ -694,10 +690,15 @@ std::unique_ptr<Value> JSONParser::ConsumeNumber() {
   }
 
   // Optional exponent part.
-  if (*pos_ == 'e' || *pos_ == 'E') {
+  if (CanConsume(1) && (*pos_ == 'e' || *pos_ == 'E')) {
     NextChar();
-    if (*pos_ == '-' || *pos_ == '+')
+    if (!CanConsume(1)) {

[dcheng, 2017/02/24 23:05:33]

In theory, we don't need 696-697, and we can fold CanConsume(1) into 699.

I think it might be a bit more confusing to read that way though, so I'm OK with
this.

[Robert Sesek, 2017/02/24 23:07:21]

Yeah, I agree that this is easier to read than folding onto 699.

+      ReportError(JSONReader::JSON_SYNTAX_ERROR, 1);
+      return nullptr;
+    }
+    if (*pos_ == '-' || *pos_ == '+') {
       NextChar();
+    }
     if (!ReadInt(true)) {
       ReportError(JSONReader::JSON_SYNTAX_ERROR, 1);
       return nullptr;