🐛 fixed a bug parsing BSON strings #1320

include/nlohmann/detail/input/binary_reader.hpp

@@ -186,12 +186,18 @@ class binary_reader
     @param[in, out] result  A reference to the string variable where the read
                             string is to be stored.
     @tparam NumberType The type of the length @a len
-    @pre len > 0
+    @pre len >= 1
     @return `true` if the string was successfully parsed
     */
     template<typename NumberType>
     bool get_bson_string(const NumberType len, string_t& result)
     {
+        if (JSON_UNLIKELY(len < 1))
+        {
+            auto last_token = get_token_string();
+            return sax->parse_error(chars_read, last_token, parse_error::create(112, chars_read, exception_message(input_format_t::bson, "string length must be at least 1, is " + std::to_string(len), "string")));
+        }
+
         return get_string(input_format_t::bson, len - static_cast<NumberType>(1), result) and get() != std::char_traits<char>::eof();
     }
 

single_include/nlohmann/json.hpp

@@ -6532,6 +6532,12 @@ class binary_reader
     template<typename NumberType>
     bool get_bson_string(const NumberType len, string_t& result)
     {
+        if (JSON_UNLIKELY(len < 1))
+        {
+            auto last_token = get_token_string();
+            return sax->parse_error(chars_read, last_token, parse_error::create(112, chars_read, exception_message(input_format_t::bson, "string length must be at least 1, is " + std::to_string(len), "string")));
+        }
+
         return get_string(input_format_t::bson, len - static_cast<NumberType>(1), result) and get() != std::char_traits<char>::eof();
     }
 

test/src/unit-bson.cpp

@@ -100,6 +100,20 @@ TEST_CASE("BSON")
         CHECK_THROWS_WITH(json::to_bson(j), "[json.exception.out_of_range.409] BSON key cannot contain code point U+0000 (at byte 2)");
     }
 
+    SECTION("string length must be at least 1")
+    {
+        // from https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=11175
+        std::vector<uint8_t> v =
+        {
+            0x20, 0x20, 0x20, 0x20,
+            0x02,
+            0x00,
+            0x00, 0x00, 0x00, 0x80
+        };
+        CHECK_THROWS_AS(json::from_bson(v), json::parse_error&);
+        CHECK_THROWS_WITH(json::from_bson(v), "[json.exception.parse_error.112] parse error at byte 10: syntax error while parsing BSON string: string length must be at least 1, is -2147483648");
+    }
+
     SECTION("objects")
     {
         SECTION("empty object")