fix: avoid nil pointer dereference in shellAction

The shellAction function was calling cmd.Flags() directly multiple times
throughout the function instead of using the flags variable that was already
captured at the beginning (line 72).

In certain execution paths, cmd.Flags() could return nil, causing a panic:
  panic: runtime error: invalid memory address or nil pointer dereference
  [signal SIGSEGV: segmentation violation code=0x2 addr=0x98 pc=0x...]

This fix changes three locations to consistently use the flags variable:
- Line 164: workDir flag access
- Line 200: shell flag access
- Line 211: preserve-env flag access

Additionally, adds a nil check for inst.Config before accessing it to
prevent similar panics and provide clearer error messages when instances
have configuration errors.

Signed-off-by: Christian Stewart <[email protected]>

Author: paralin

cmd/limactl/shell.go

@@ -94,6 +94,12 @@ func shellAction(cmd *cobra.Command, args []string) error {
 		}
 		return err
 	}
+	if inst.Config == nil {
+		if len(inst.Errors) > 0 {
+			return fmt.Errorf("instance %q has configuration errors: %w", instName, errors.Join(inst.Errors...))
+		}
+		return fmt.Errorf("instance %q has no configuration", instName)
+	}
 	if inst.Status == limatype.StatusStopped {
 		startNow, err := flags.GetBool("start")
 		if err != nil {
@@ -155,14 +161,14 @@ func shellAction(cmd *cobra.Command, args []string) error {
 	// changeDirCmd := "cd workDir || exit 1"                  if workDir != ""
 	//              := "cd hostCurrentDir || cd hostHomeDir"   if workDir == ""
 	var changeDirCmd string
-	workDir, err := cmd.Flags().GetString("workdir")
+	workDir, err := flags.GetString("workdir")
 	if err != nil {
 		return err
 	}
 	if workDir != "" {
 		changeDirCmd = fmt.Sprintf("cd %s || exit 1", shellescape.Quote(workDir))
 		// FIXME: check whether y.Mounts contains the home, not just len > 0
-	} else if len(inst.Config.Mounts) > 0 || inst.VMType == limatype.WSL2 {
+	} else if inst.Config != nil && (len(inst.Config.Mounts) > 0 || inst.VMType == limatype.WSL2) {
 		hostCurrentDir, err := os.Getwd()
 		if err == nil && runtime.GOOS == "windows" {
 			hostCurrentDir, err = mountDirFromWindowsDir(ctx, inst, hostCurrentDir)
@@ -191,7 +197,7 @@ func shellAction(cmd *cobra.Command, args []string) error {
 	}
 	logrus.Debugf("changeDirCmd=%q", changeDirCmd)
 
-	shell, err := cmd.Flags().GetString("shell")
+	shell, err := flags.GetString("shell")
 	if err != nil {
 		return err
 	}
@@ -202,7 +208,7 @@ func shellAction(cmd *cobra.Command, args []string) error {
 	}
 	// Handle environment variable propagation
 	var envPrefix string
-	preserveEnv, err := cmd.Flags().GetBool("preserve-env")
+	preserveEnv, err := flags.GetBool("preserve-env")
 	if err != nil {
 		return err
 	}