Run Docker container as current user (#1975)

Previously, mega-linter-runner ran the MegaLinter Docker image as root.
Users whose files became owned by root as a consequence of this
behavior will need to chown them to be owned by the appropriate user.
This change only affects POSIX platforms, because process.getuid and
process.getgid are only available there.

CHANGELOG.md

@@ -8,6 +8,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 
 Note: Can be used with `oxsecurity/megalinter@beta` in your GitHub Action mega-linter.yml file, or with `oxsecurity/megalinter:beta` docker image
 
+- Run Docker container as current user rather than root ([#1975](https://github.com/oxsecurity/megalinter/issues/1975))
 - Remove default npm-groovy-lint extra arguments ([#1872](https://github.com/oxsecurity/megalinter/issues/1872))
 
 - Linter versions upgrades

mega-linter-runner/lib/runner.js

@@ -4,6 +4,7 @@ const optionsDefinition = require("./options");
 const { spawnSync } = require("child_process");
 const c = require("chalk");
 const path = require("path");
+const process = require("process");
 const which = require("which");
 const fs = require("fs-extra");
 const { MegaLinterUpgrader } = require("./upgrade");
@@ -127,6 +128,11 @@ ERROR: Docker engine has not been found on your system.
     if (options["containerName"]) {
       commandArgs.push(...["--name", options["containerName"]]);
     }
+    if (process.getuid && process.getgid) {
+      commandArgs.push(
+        ...["--user", `${process.getuid()}:${process.getgid()}`]
+      );
+    }
     commandArgs.push(...["-v", "/var/run/docker.sock:/var/run/docker.sock:rw"]);
     commandArgs.push(...["-v", `${lintPath}:/tmp/lint:rw`]);
     if (options.fix === true) {