fix: memory leak

Fix a memory leak due to out of bounds access at _jsonb_escape()

Closes #3
Co-authored-by: Aníbal Portero Hermida <anibal.portero@pantacor.com>

Author: lcsmuller

json-build.h

@@ -371,7 +371,10 @@ _jsonb_escape(
         }
     }
 
-    if (*pos + len + extra_bytes > bufsize) return JSONB_ERROR_NOMEM;
+    if (*pos + len + extra_bytes > bufsize) {
+        *buf = '\0';
+        return JSONB_ERROR_NOMEM;
+    }
 
     if (esc_buf) {
         *pos += len + extra_bytes;
@@ -400,7 +403,7 @@ jsonb_key(jsonb *b, char buf[], size_t bufsize, const char key[], size_t len)
     case JSONB_OBJECT_KEY_OR_CLOSE: {
         enum jsonbcode ret;
         BUFFER_COPY_CHAR(b, '"', pos, buf, bufsize);
-        ret = _jsonb_escape(&pos, buf + b->pos, bufsize, key, len);
+        ret = _jsonb_escape(&pos, buf + b->pos, bufsize - b->pos, key, len);
         if (ret != JSONB_OK) return ret;
         BUFFER_COPY(b, "\":", 2, pos, buf, bufsize);
         STACK_HEAD(b, JSONB_OBJECT_VALUE);
@@ -551,7 +554,7 @@ jsonb_string(
         return JSONB_ERROR_INPUT;
     }
     BUFFER_COPY_CHAR(b, '"', pos, buf, bufsize);
-    ret = _jsonb_escape(&pos, buf + b->pos, bufsize, str, len);
+    ret = _jsonb_escape(&pos, buf + b->pos, bufsize - b->pos, str, len);
     if (ret != JSONB_OK) return ret;
     BUFFER_COPY_CHAR(b, '"', pos, buf, bufsize);
     STACK_HEAD(b, next_state);

test/test.c

@@ -228,6 +228,27 @@ check_string_escaping(void)
     PASS();
 }
 
+TEST
+check_string_escaping_bounds(void)
+{
+    const char str[] = "\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n";
+    char buf[(sizeof("{}") - 1)
+             + 4 * ((sizeof("\"\"") - 1) + (sizeof(str) - 1))];
+    jsonb b;
+
+    jsonb_init(&b);
+    jsonb_object(&b, buf, sizeof(buf));
+    ASSERT_EQm(buf, JSONB_OK,
+               jsonb_key(&b, buf, sizeof(buf), str, sizeof(str) - 1));
+    ASSERT_EQm(buf, JSONB_OK,
+               jsonb_string(&b, buf, sizeof(buf), str, sizeof(str) - 1));
+    ASSERT_EQm(buf, JSONB_ERROR_NOMEM,
+               jsonb_key(&b, buf, sizeof(buf), str, sizeof(str) - 1));
+    fprintf(stderr, "%s", buf);
+
+    PASS();
+}
+
 TEST
 check_string_streaming(void)
 {
@@ -307,6 +328,7 @@ check_string_streaming(void)
 SUITE(string)
 {
     RUN_TEST(check_string_escaping);
+    RUN_TEST(check_string_escaping_bounds);
     RUN_TEST(check_string_streaming);
 }