Rewrite cJSON_Minify, fixing buffer overflows, fixes #338

Also first tests for cJSON_Minify.
Thanks @bigric3 for reporting

cJSON.c

@@ -151,6 +151,9 @@ static void * CJSON_CDECL internal_realloc(void *pointer, size_t size)
 #define internal_realloc realloc
 #endif
 
+/* strlen of character literals resolved at compile time */
+#define static_strlen(string_literal) (sizeof(string_literal) - sizeof(""))
+
 static internal_hooks global_hooks = { internal_malloc, internal_free, internal_realloc };
 
 static unsigned char* cJSON_strdup(const unsigned char* string, const internal_hooks * const hooks)
@@ -2637,69 +2640,94 @@ CJSON_PUBLIC(cJSON *) cJSON_Duplicate(const cJSON *item, cJSON_bool recurse)
     return NULL;
 }
 
-CJSON_PUBLIC(void) cJSON_Minify(char *json)
+static void skip_oneline_comment(char **input)
 {
-    unsigned char *into = (unsigned char*)json;
+    *input += static_strlen("//");
 
-    if (json == NULL)
+    for (; (*input)[0] != '\0'; ++(*input))
     {
-        return;
+        if ((*input)[0] == '\n') {
+            *input += static_strlen("\n");
+            return;
+        }
     }
+}
+
+static void skip_multiline_comment(char **input)
+{
+    *input += static_strlen("/*");
 
-    while (*json)
+    for (; (*input)[0] != '\0'; ++(*input))
     {
-        if (*json == ' ')
+        if (((*input)[0] == '*') && ((*input)[1] == '/'))
         {
-            json++;
+            *input += static_strlen("*/");
+            return;
         }
-        else if (*json == '\t')
-        {
-            /* Whitespace characters. */
-            json++;
-        }
-        else if (*json == '\r')
-        {
-            json++;
-        }
-        else if (*json=='\n')
-        {
-            json++;
-        }
-        else if ((*json == '/') && (json[1] == '/'))
-        {
-            /* double-slash comments, to end of line. */
-            while (*json && (*json != '\n'))
-            {
-                json++;
-            }
+    }
+}
+
+static void minify_string(char **input, char **output) {
+    (*output)[0] = (*input)[0];
+    *input += static_strlen("\"");
+    *output += static_strlen("\"");
+
+
+    for (; (*input)[0] != '\0'; ++(*input), ++(*output)) {
+        (*output)[0] = (*input)[0];
+
+        if ((*input)[0] == '\"') {
+            (*output)[0] = '\"';
+            *input += static_strlen("\"");
+            *output += static_strlen("\"");
+            return;
+        } else if (((*input)[0] == '\\') && ((*input)[1] == '\"')) {
+            (*output)[1] = (*input)[1];
+            *input += static_strlen("\"");
+            *output += static_strlen("\"");
         }
-        else if ((*json == '/') && (json[1] == '*'))
+    }
+}
+
+CJSON_PUBLIC(void) cJSON_Minify(char *json)
+{
+    char *into = json;
+
+    if (json == NULL)
+    {
+        return;
+    }
+
+    while (json[0] != '\0')
+    {
+        switch (json[0])
         {
-            /* multiline comments. */
-            while (*json && !((*json == '*') && (json[1] == '/')))
-            {
+            case ' ':
+            case '\t':
+            case '\r':
+            case '\n':
                 json++;
-            }
-            json += 2;
-        }
-        else if (*json == '\"')
-        {
-            /* string literals, which are \" sensitive. */
-            *into++ = (unsigned char)*json++;
-            while (*json && (*json != '\"'))
-            {
-                if (*json == '\\')
+                break;
+
+            case '/':
+                if (json[1] == '/')
                 {
-                    *into++ = (unsigned char)*json++;
+                    skip_oneline_comment(&json);
                 }
-                *into++ = (unsigned char)*json++;
-            }
-            *into++ = (unsigned char)*json++;
-        }
-        else
-        {
-            /* All other characters. */
-            *into++ = (unsigned char)*json++;
+                else if (json[1] == '*')
+                {
+                    skip_multiline_comment(&json);
+                }
+                break;
+
+            case '\"':
+                minify_string(&json, (char**)&into);
+                break;
+
+            default:
+                into[0] = json[0];
+                json++;
+                into++;
         }
     }
 

tests/CMakeLists.txt

@@ -57,6 +57,7 @@ if(ENABLE_CJSON_TEST)
         compare_tests
         cjson_add
         readme_examples
+        minify_tests
     )
 
     option(ENABLE_VALGRIND OFF "Enable the valgrind memory checker for the tests.")

tests/minify_tests.c

@@ -0,0 +1,167 @@
+/*
+  Copyright (c) 2009-2019 Dave Gamble and cJSON contributors
+
+  Permission is hereby granted, free of charge, to any person obtaining a copy
+  of this software and associated documentation files (the "Software"), to deal
+  in the Software without restriction, including without limitation the rights
+  to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+  copies of the Software, and to permit persons to whom the Software is
+  furnished to do so, subject to the following conditions:
+
+  The above copyright notice and this permission notice shall be included in
+  all copies or substantial portions of the Software.
+
+  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+  AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+  OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+  THE SOFTWARE.
+*/
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include "unity/examples/unity_config.h"
+#include "unity/src/unity.h"
+#include "common.h"
+
+
+static void cjson_minify_should_not_overflow_buffer(void)
+{
+    char unclosed_multiline_comment[] = "/* bla";
+    char pending_escape[] = "\"\\";
+
+    cJSON_Minify(unclosed_multiline_comment);
+    TEST_ASSERT_EQUAL_STRING("", unclosed_multiline_comment);
+
+    cJSON_Minify(pending_escape);
+    TEST_ASSERT_EQUAL_STRING("\"\\", pending_escape);
+}
+
+static void cjson_minify_should_remove_single_line_comments(void)
+{
+    const char to_minify[] = "{// this is {} \"some kind\" of [] comment /*, don't you see\n}";
+
+    char* minified = (char*) malloc(sizeof(to_minify));
+    TEST_ASSERT_NOT_NULL(minified);
+    strcpy(minified, to_minify);
+
+    cJSON_Minify(minified);
+    TEST_ASSERT_EQUAL_STRING("{}", minified);
+
+    free(minified);
+}
+
+static void cjson_minify_should_remove_spaces(void)
+{
+    const char to_minify[] = "{ \"key\":\ttrue\r\n    }";
+
+    char* minified = (char*) malloc(sizeof(to_minify));
+    TEST_ASSERT_NOT_NULL(minified);
+    strcpy(minified, to_minify);
+
+    cJSON_Minify(minified);
+    TEST_ASSERT_EQUAL_STRING("{\"key\":true}", minified);
+
+    free(minified);
+}
+
+static void cjson_minify_should_remove_multiline_comments(void)
+{
+    const char to_minify[] = "{/* this is\n a /* multi\n //line \n {comment \"\\\" */}";
+
+    char* minified = (char*) malloc(sizeof(to_minify));
+    TEST_ASSERT_NOT_NULL(minified);
+    strcpy(minified, to_minify);
+
+    cJSON_Minify(minified);
+    TEST_ASSERT_EQUAL_STRING("{}", minified);
+
+    free(minified);
+}
+
+static void cjson_minify_should_not_modify_strings(void)
+{
+    const char to_minify[] = "\"this is a string \\\" \\t bla\"";
+
+    char* minified = (char*) malloc(sizeof(to_minify));
+    TEST_ASSERT_NOT_NULL(minified);
+    strcpy(minified, to_minify);
+
+    cJSON_Minify(minified);
+    TEST_ASSERT_EQUAL_STRING(to_minify, minified);
+
+    free(minified);
+}
+
+static void cjson_minify_should_minify_json(void) {
+    const char to_minify[] =
+            "{\n"
+            "    \"glossary\": { // comment\n"
+            "        \"title\": \"example glossary\",\n"
+            "  /* multi\n"
+            " line */\n"
+            "		\"GlossDiv\": {\n"
+            "            \"title\": \"S\",\n"
+            "			\"GlossList\": {\n"
+            "                \"GlossEntry\": {\n"
+            "                    \"ID\": \"SGML\",\n"
+            "					\"SortAs\": \"SGML\",\n"
+            "					\"Acronym\": \"SGML\",\n"
+            "					\"Abbrev\": \"ISO 8879:1986\",\n"
+            "					\"GlossDef\": {\n"
+            "						\"GlossSeeAlso\": [\"GML\", \"XML\"]\n"
+            "                    },\n"
+            "					\"GlossSee\": \"markup\"\n"
+            "                }\n"
+            "            }\n"
+            "        }\n"
+            "    }\n"
+            "}";
+    const char* minified =
+            "{"
+            "\"glossary\":{"
+            "\"title\":\"example glossary\","
+            "\"GlossDiv\":{"
+            "\"title\":\"S\","
+            "\"GlossList\":{"
+            "\"GlossEntry\":{"
+            "\"ID\":\"SGML\","
+            "\"SortAs\":\"SGML\","
+            "\"Acronym\":\"SGML\","
+            "\"Abbrev\":\"ISO 8879:1986\","
+            "\"GlossDef\":{"
+            "\"GlossSeeAlso\":[\"GML\",\"XML\"]"
+            "},"
+            "\"GlossSee\":\"markup\""
+            "}"
+            "}"
+            "}"
+            "}"
+            "}";
+
+    char *buffer = (char*) malloc(sizeof(to_minify));
+    strcpy(buffer, to_minify);
+
+    cJSON_Minify(buffer);
+    TEST_ASSERT_EQUAL_STRING(minified, buffer);
+
+    free(buffer);
+}
+
+int CJSON_CDECL main(void)
+{
+    UNITY_BEGIN();
+
+    RUN_TEST(cjson_minify_should_not_overflow_buffer);
+    RUN_TEST(cjson_minify_should_minify_json);
+    RUN_TEST(cjson_minify_should_remove_single_line_comments);
+    RUN_TEST(cjson_minify_should_remove_multiline_comments);
+    RUN_TEST(cjson_minify_should_remove_spaces);
+    RUN_TEST(cjson_minify_should_not_modify_strings);
+
+    return UNITY_END();
+}