Limit prehook executable paths to the prehooks dir

app/connect.go

@@ -167,9 +167,14 @@ func (a *App) Connect(connectStr string) (success bool) {
 	a.dialing = url
 	a.websocketHub.UpdateStatus()
 
-	if exec := url.Params.Get("prehook"); exec != "" {
-		if err := prehook.Verify(exec); err != nil {
-			log.Printf("prehook invalid: %s", err)
+	prehookScript := prehook.Script{
+		Dir:  a.options.PrehooksPath,
+		File: url.Params.Get("prehook"),
+		Args: url.Params["prehook-arg"],
+	}
+	if prehookScript.File != "" {
+		if err := prehookScript.VerifyFile(); err != nil {
+			log.Printf("invalid prehook: %s", err)
 			return
 		}
 	}
@@ -192,19 +197,15 @@ func (a *App) Connect(connectStr string) (success bool) {
 		return
 	}
 
-	if exec := url.Params.Get("prehook"); exec != "" {
+	if prehookScript.File != "" {
 		log.Println("Running prehook...")
-		script := prehook.Script{
-			File: exec,
-			Args: url.Params["prehook-arg"],
-			Env: append([]string{
-				buildinfo.AppName + "_DIAL_URL=" + connectStr,
-				buildinfo.AppName + "_REMOTE_ADDR=" + conn.RemoteAddr().String(),
-				buildinfo.AppName + "_LOCAL_ADDR=" + conn.LocalAddr().String(),
-			}, append(os.Environ(), a.Env()...)...),
-		}
+		prehookScript.Env = append([]string{
+			buildinfo.AppName + "_DIAL_URL=" + connectStr,
+			buildinfo.AppName + "_REMOTE_ADDR=" + conn.RemoteAddr().String(),
+			buildinfo.AppName + "_LOCAL_ADDR=" + conn.LocalAddr().String(),
+		}, append(os.Environ(), a.Env()...)...)
 		conn = prehook.Wrap(conn)
-		if err := script.Execute(ctx, conn); err != nil {
+		if err := prehookScript.Execute(ctx, conn); err != nil {
 			conn.Close()
 			log.Printf("Prehook script failed: %s", err)
 			return

cli/connect.go

@@ -50,7 +50,7 @@ params:
   ?freq=        Sets QSY frequency (ardop and ax25 only)
   ?host=        Overrides the host part of the path. Useful for serial-tnc to specify e.g. /dev/ttyS0.
   ?prehook=     Sets an executable middleware to run before the connection is handed over to the B2F protocol.
-                 The executable must be given as full path, or a file located in $PATH or {CONFIG_DIR}/prehooks/.
+                 The executable must be located in {CONFIG_DIR}/prehooks/.
 		 Received packets are forwarded to STDIN. Data written to STDOUT forwarded to the remote node.
 		 Additional arguments can be passed with one or more &prehook-arg=.
 		 Environment variables describing the dialed connection are provided.

internal/prehook/prehook.go

@@ -12,9 +12,11 @@ import (
 	"net"
 	"os"
 	"os/exec"
+	"path/filepath"
 	"time"
 
 	"github.com/la5nta/pat/internal/debug"
+	"github.com/la5nta/pat/internal/directories"
 	"golang.org/x/sync/errgroup"
 )
 
@@ -22,6 +24,7 @@ var ErrConnNotWrapped = errors.New("connection not wrapped for prehook")
 
 type Script struct {
 	File string
+	Dir  string
 	Args []string
 	Env  []string
 }
@@ -41,13 +44,31 @@ type Conn struct {
 	br *bufio.Reader
 }
 
-// Verify returns nil if the given script file is found and valid.
-func Verify(file string) error {
-	_, err := exec.LookPath(file)
-	if errors.Is(err, exec.ErrDot) {
-		err = nil
+// VerifyFile returns nil if the given script file is found and valid.
+func (s Script) VerifyFile() error {
+	p, err := s.Path()
+	if err != nil {
+		return err
 	}
-	return err
+	info, err := os.Stat(p)
+	if err != nil {
+		return err
+	}
+	if info.IsDir() {
+		return fmt.Errorf("%s: is a directory", s.File)
+	}
+	if _, err := exec.LookPath(p); err != nil {
+		return err
+	}
+	return nil
+}
+
+func (s Script) Path() (string, error) {
+	p := filepath.Join(s.Dir, s.File)
+	if !directories.IsInPath(s.Dir, p) {
+		return "", fmt.Errorf("%s: escapes base path", p)
+	}
+	return p, nil
 }
 
 // Wrap returns a wrapped connection with the ability to execute a prehook.
@@ -67,7 +88,11 @@ func (p *Conn) Read(b []byte) (int, error) { return p.br.Read(b) }
 // Execute executes the prehook script, returning nil if the process
 // terminated successfully (exit code 0).
 func (p *Conn) Execute(ctx context.Context, script Script) error {
-	cmd := exec.CommandContext(ctx, script.File, script.Args...)
+	name, err := script.Path()
+	if err != nil {
+		return err
+	}
+	cmd := exec.CommandContext(ctx, name, script.Args...)
 	cmd.Env = script.Env
 	cmd.Stderr = os.Stderr
 	cmd.Stdout = p.Conn