From 565118bf26330050ae45b26feff6185150a36d02 Mon Sep 17 00:00:00 2001
From: Italo Guerrieri <guerital@amazon.com>
Date: Wed, 29 Nov 2017 18:04:03 +0100
Subject: [PATCH] Check if tag is equal to 0

This is needed because in the syntax of Google protobuf the zero
value is not valid tag value. The specification
(https://developers.google.com/protocol-buffers/docs/proto3) says
that "The smallest tag number you can specify is 1, and the largest
is 2^29-1, or 536,870,911."
---
 protobuf-c/protobuf-c.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/protobuf-c/protobuf-c.c b/protobuf-c/protobuf-c.c
index 5debac8..7d93170 100644
--- a/protobuf-c/protobuf-c.c
+++ b/protobuf-c/protobuf-c.c
@@ -2072,6 +2072,11 @@ parse_tag_and_wiretype(size_t len,
 	unsigned shift = 4;
 	unsigned rv;
 
+	/* 0 is not a valid tag value */
+	if ((data[0] & 0xf8) == 0) {
+		return 0;
+	}
+
 	*wiretype_out = data[0] & 7;
 	if ((data[0] & 0x80) == 0) {
 		*tag_out = tag;