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.

Author: Kurt-von-Laven

CHANGELOG.md

@@ -27,6 +27,8 @@ Note: Can be used with `oxsecurity/megalinter@beta` in your GitHub Action mega-l
   - Added **cli_lint_fix_arg_name** parameter to **powershell formatter** descriptor as without it, autofix does not work, by @bdovaz in [#2294](https://github.com/oxsecurity/megalinter/pull/2294)
   - Created **ProtolintLinter** class to fix the problem that returns exit code 1 when it encounters a problem to correct even though it corrects it correctly, by @bdovaz in [#2294](https://github.com/oxsecurity/megalinter/pull/2294)
   - Concatenate **--output** parameter correctly to **xmllint** linter, by @bdovaz in [#2294](https://github.com/oxsecurity/megalinter/pull/2294)
+  - Run Docker container as current user rather than root by @Kurt-von-Laven in
+  [#1975](https://github.com/oxsecurity/megalinter/issues/1975).
 
 - Documentation
   - Change **swiftlint** example that did not correctly reflect the **--fix** parameter, by @bdovaz in [#2294](https://github.com/oxsecurity/megalinter/pull/2294)

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 { getgid, getuid } = require("process");
 const which = require("which");
 const fs = require("fs-extra");
 const { MegaLinterUpgrader } = require("./upgrade");
@@ -127,6 +128,9 @@ ERROR: Docker engine has not been found on your system.
     if (options["containerName"]) {
       commandArgs.push(...["--name", options["containerName"]]);
     }
+    if (getuid && getgid) {
+      commandArgs.push(...["--user", `${getuid()}:${getgid()}`]);
+    }
     commandArgs.push(...["-v", "/var/run/docker.sock:/var/run/docker.sock:rw"]);
     commandArgs.push(...["-v", `${lintPath}:/tmp/lint:rw`]);
     if (options.fix === true) {