fix: make daemon reset conflict safe

internal/shell/shell.go

@@ -14,8 +14,6 @@ import (
 	"path/filepath"
 	"strings"
 
-	"golang.org/x/sys/unix"
-
 	"proxyctl/internal/profile"
 	"proxyctl/internal/securefs"
 	"proxyctl/internal/target"
@@ -194,41 +192,9 @@ func (a *Adapter) StartupPath() string      { return a.configuration.StartupFile
 
 // DiagnosticChecks performs no writes or command execution.
 func (a *Adapter) DiagnosticChecks(_ context.Context, _ *profile.Profile) []target.Check {
-	paths := []string{a.configuration.EnvironmentFile, a.configuration.RecoveryFile}
-	writable := true
-	var evidence []string
-	for _, path := range paths {
-		ok, detail := writablePath(path)
-		writable = writable && ok
-		evidence = append(evidence, detail)
-	}
 	return []target.Check{
 		{Name: "required commands", OK: true, Evidence: "Shell Target requires no external commands"},
-		{Name: "write authority", OK: writable, Evidence: strings.Join(evidence, "; ")},
-	}
-}
-
-func writablePath(path string) (bool, string) {
-	candidate := path
-	for {
-		info, err := os.Stat(candidate)
-		if err == nil {
-			if !info.IsDir() {
-				candidate = filepath.Dir(candidate)
-			}
-			if err := unix.Access(candidate, unix.W_OK); err != nil {
-				return false, candidate + " is not writable: " + err.Error()
-			}
-			return true, candidate + " is writable"
-		}
-		if !errors.Is(err, fs.ErrNotExist) {
-			return false, candidate + " cannot be inspected: " + err.Error()
-		}
-		parent := filepath.Dir(candidate)
-		if parent == candidate {
-			return false, path + " has no writable existing ancestor"
-		}
-		candidate = parent
+		target.ReadOnlyWriteAuthority(a.configuration.EnvironmentFile, a.configuration.RecoveryFile),
 	}
 }
 

internal/shell/shell_test.go

@@ -6,6 +6,7 @@ import (
 	"os"
 	"os/exec"
 	"path/filepath"
+	"reflect"
 	"strings"
 	"testing"
 
@@ -15,6 +16,70 @@ import (
 	"proxyctl/internal/target/targettest"
 )
 
+func TestShellDiagnosticsRejectSymlinkedPathsWithoutTouchingVictim(t *testing.T) {
+	for _, test := range []struct {
+		name string
+		path func(t *testing.T, root, victim string) string
+	}{
+		{
+			name: "final path",
+			path: func(t *testing.T, root, victim string) string {
+				t.Helper()
+				path := filepath.Join(root, "config", "shell.env")
+				if err := os.MkdirAll(filepath.Dir(path), 0o700); err != nil {
+					t.Fatal(err)
+				}
+				if err := os.Symlink(victim, path); err != nil {
+					t.Fatal(err)
+				}
+				return path
+			},
+		},
+		{
+			name: "ancestor path",
+			path: func(t *testing.T, root, victim string) string {
+				t.Helper()
+				link := filepath.Join(root, "config")
+				if err := os.Symlink(filepath.Dir(victim), link); err != nil {
+					t.Fatal(err)
+				}
+				return filepath.Join(link, filepath.Base(victim))
+			},
+		},
+	} {
+		t.Run(test.name, func(t *testing.T) {
+			root := t.TempDir()
+			victim := filepath.Join(t.TempDir(), "victim")
+			const content = "shell-diagnostic-victim"
+			if err := os.WriteFile(victim, []byte(content), 0o640); err != nil {
+				t.Fatal(err)
+			}
+			before, err := os.Stat(victim)
+			if err != nil {
+				t.Fatal(err)
+			}
+			environmentPath := test.path(t, root, victim)
+			a := shell.New(shell.Configuration{Shell: "/bin/bash", EnvironmentFile: environmentPath, RecoveryFile: filepath.Join(root, "state", "shell.json")}, nil, shell.MapEnvironment{})
+
+			checks := a.DiagnosticChecks(context.Background(), nil)
+			if len(checks) != 2 || checks[1].OK || !strings.Contains(checks[1].Evidence, "symbolic link") {
+				t.Fatalf("Shell diagnostics accepted symlink: %#v", checks)
+			}
+			after, err := os.Stat(victim)
+			if err != nil {
+				t.Fatal(err)
+			}
+			got, err := os.ReadFile(victim)
+			if err != nil {
+				t.Fatal(err)
+			}
+			if string(got) != content || !reflect.DeepEqual(before.Sys(), after.Sys()) {
+				t.Fatalf("diagnostics changed victim: before=%#v after=%#v content=%q", before, after, got)
+			}
+		})
+	}
+}
+
 func TestShellAvailabilitySupportsOnlyBashAndZsh(t *testing.T) {
 	for _, tc := range []struct {
 		shell     string