Stack overflow in `ParseAttrValue` with nested tensors

@@ -38,6 +38,9 @@ namespace {
 // Do not construct large tensors to compute their hash or compare for equality.
 constexpr int kMaxAttrValueTensorByteSize = 32 * 1024 * 1024;  // 32mb
 
+// Limit nesting of tensors to 100 deep to prevent memory overflow.
+constexpr int kMaxTensorNestDepth = 100;
+
 // Return the size of the tensor represented by this TensorProto. If shape is
 // not fully defined return -1.
 int64 TensorByteSize(const TensorProto& t) {
@@ -224,6 +227,54 @@ string SummarizeFunc(const NameAttrList& func) {
   return strings::StrCat(func.name(), "[", absl::StrJoin(entries, ", "), "]");
 }
 
+bool ParseAttrValueHelper_TensorNestsUnderLimit(int limit, string to_parse) {
+  int nests = 0;
+  int maxed_out = to_parse.length();
+  int open_curly = to_parse.find('{');
+  int open_bracket = to_parse.find('<');
+  int close_curly = to_parse.find('}');
+  int close_bracket = to_parse.find('>');
+  if (open_curly == -1) {
+    open_curly = maxed_out;
+  }
+  if (open_bracket == -1) {
+    open_bracket = maxed_out;
+  }
+  int min = std::min(open_curly, open_bracket);
+  do {
+    if (open_curly == maxed_out && open_bracket == maxed_out) {
+      return true;
+    }
+    if (min == open_curly) {
+      nests += 1;
+      open_curly = to_parse.find('{', open_curly + 1);
+      if (open_curly == -1) {
+        open_curly = maxed_out;
+      }
+    } else if (min == open_bracket) {
+      nests += 1;
+      open_bracket = to_parse.find('<', open_bracket + 1);
+      if (open_bracket == -1) {
+        open_bracket = maxed_out;
+      }
+    } else if (min == close_curly) {
+      nests -= 1;
+      close_curly = to_parse.find('}', close_curly + 1);
+      if (close_curly == -1) {
+        close_curly = maxed_out;
+      }
+    } else if (min == close_bracket) {
+      nests -= 1;
+      close_bracket = to_parse.find('>', close_bracket + 1);
+      if (close_bracket == -1) {
+        close_bracket = maxed_out;
+      }
+    }
+    min = std::min({open_curly, open_bracket, close_curly, close_bracket});
+  } while (nests < 100);
+  return false;
+}
+
 }  // namespace
 
 string SummarizeAttrValue(const AttrValue& attr_value) {
@@ -448,7 +499,12 @@ bool ParseAttrValue(StringPiece type, StringPiece text, AttrValue* out) {
   } else {
     to_parse = strings::StrCat(field_name, ": ", text);
   }
-
+  if (field_name == "tensor") {
+    if (!ParseAttrValueHelper_TensorNestsUnderLimit(kMaxTensorNestDepth,
+                                                    to_parse)) {
+      return false;
+    }
+  }
   return ProtoParseFromString(to_parse, out);
 }