Avoid hang during discovery in projects with symlink loops

Specific combinations of symlinks can cause infinite recursion loops during project discovery. This is avoided by
limiting the depth of symlink follows to a reasonable number.

Author: per1234

internal/project/project.go

@@ -18,6 +18,7 @@ package project
 
 import (
 	"fmt"
+	"os"
 
 	"github.com/arduino/arduino-lint/internal/configuration"
 	"github.com/arduino/arduino-lint/internal/project/library"
@@ -87,7 +88,7 @@ func findProjects(targetPath *paths.Path) ([]Type, error) {
 	} else {
 		if configuration.SuperprojectTypeFilter() == projecttype.All || configuration.Recursive() {
 			// Project discovery and/or type detection is required.
-			foundParentProjects = findProjectsUnderPath(targetPath, configuration.SuperprojectTypeFilter(), configuration.Recursive())
+			foundParentProjects = findProjectsUnderPath(targetPath, configuration.SuperprojectTypeFilter(), configuration.Recursive(), 0)
 		} else {
 			// Project was explicitly defined by user.
 			foundParentProjects = append(foundParentProjects,
@@ -115,7 +116,7 @@ func findProjects(targetPath *paths.Path) ([]Type, error) {
 }
 
 // findProjectsUnderPath finds projects of the given type under the given path. It returns a slice containing the definitions of all found projects.
-func findProjectsUnderPath(targetPath *paths.Path, projectTypeFilter projecttype.Type, recursive bool) []Type {
+func findProjectsUnderPath(targetPath *paths.Path, projectTypeFilter projecttype.Type, recursive bool, symlinkDepth int) []Type {
 	var foundProjects []Type
 
 	isProject, foundProjectType := isProject(targetPath, projectTypeFilter)
@@ -133,12 +134,23 @@ func findProjectsUnderPath(targetPath *paths.Path, projectTypeFilter projecttype
 		return foundProjects
 	}
 
-	if recursive {
+	if recursive && symlinkDepth < 10 {
 		// targetPath was not a project, so search the subfolders.
 		directoryListing, _ := targetPath.ReadDir()
 		directoryListing.FilterDirs()
 		for _, potentialProjectDirectory := range directoryListing {
-			foundProjects = append(foundProjects, findProjectsUnderPath(potentialProjectDirectory, projectTypeFilter, recursive)...)
+			// It is possible for a combination of symlinks to parent paths to cause project discovery to get stuck in
+			// an endless loop of recursion. This is avoided by keeping count of the depth of symlinks and discontinuing
+			// recursion when it exceeds reason.
+			pathStat, err := os.Lstat(potentialProjectDirectory.String())
+			if err != nil {
+				panic(err)
+			}
+			if pathStat.Mode()&os.ModeSymlink != 0 {
+				symlinkDepth++
+			}
+
+			foundProjects = append(foundProjects, findProjectsUnderPath(potentialProjectDirectory, projectTypeFilter, recursive, symlinkDepth)...)
 		}
 	}
 
@@ -184,7 +196,7 @@ func findSubprojects(superproject Type, apexSuperprojectType projecttype.Type) [
 			directoryListing.FilterDirs()
 
 			for _, subprojectPath := range directoryListing {
-				immediateSubprojects = append(immediateSubprojects, findProjectsUnderPath(subprojectPath, subProjectType, searchPathsRecursively)...)
+				immediateSubprojects = append(immediateSubprojects, findProjectsUnderPath(subprojectPath, subProjectType, searchPathsRecursively, 0)...)
 			}
 		}
 	}