cmd/hsu: return hsurc id

The uid format is stable, this value is what caller has to obtain through hsu.

Closes #14.

Signed-off-by: Ophestra <cat@gensokyo.uk>

cmd/hsu/main.go

@@ -15,7 +15,7 @@ import (
 const (
 	hsuConfFile = "/etc/hsurc"
 	envShim     = "HAKUREI_SHIM"
-	envAID      = "HAKUREI_APP_ID"
+	envIdentity = "HAKUREI_IDENTITY"
 	envGroups   = "HAKUREI_GROUPS"
 
 	PR_SET_NO_NEW_PRIVS = 0x26
@@ -48,8 +48,8 @@ func main() {
 	}
 
 	// uid = 1000000 +
-	//   fid * 10000 +
-	//           aid
+	//    id * 10000 +
+	//      identity
 	uid := 1000000
 
 	// refuse to run if hsurc is not protected correctly
@@ -62,29 +62,25 @@ func main() {
 	}
 
 	// authenticate before accepting user input
+	var id int
 	if f, err := os.Open(hsuConfFile); err != nil {
 		log.Fatal(err)
-	} else if fid, ok := mustParseConfig(f, puid); !ok {
+	} else if v, ok := mustParseConfig(f, puid); !ok {
 		log.Fatalf("uid %d is not in the hsurc file", puid)
 	} else {
-		uid += fid * 10000
+		id = v
+		if err = f.Close(); err != nil {
+			log.Fatal(err)
 		}
 
-	// allowed aid range 0 to 9999
-	if as, ok := os.LookupEnv(envAID); !ok {
-		log.Fatal("HAKUREI_APP_ID not set")
-	} else if aid, err := parseUint32Fast(as); err != nil || aid < 0 || aid > 9999 {
-		log.Fatal("invalid aid")
-	} else {
-		uid += aid
+		uid += id * 10000
 	}
 
 	// pass through setup fd to shim
 	var shimSetupFd string
 	if s, ok := os.LookupEnv(envShim); !ok {
-		// hakurei requests target uid
-		// print resolved uid and exit
-		fmt.Print(uid)
+		// hakurei requests hsurc user id
+		fmt.Print(id)
 		os.Exit(0)
 	} else if len(s) != 1 || s[0] > '9' || s[0] < '3' {
 		log.Fatal("HAKUREI_SHIM holds an invalid value")
@@ -92,6 +88,15 @@ func main() {
 		shimSetupFd = s
 	}
 
+	// allowed identity range 0 to 9999
+	if as, ok := os.LookupEnv(envIdentity); !ok {
+		log.Fatal("HAKUREI_IDENTITY not set")
+	} else if identity, err := parseUint32Fast(as); err != nil || identity < 0 || identity > 9999 {
+		log.Fatal("invalid identity")
+	} else {
+		uid += identity
+	}
+
 	// supplementary groups
 	var suppGroups, suppCurrent []int
 

internal/app/process.go

@@ -255,7 +255,7 @@ func (seal *outcome) main() {
 			// passed through to shim by hsu
 			shimEnv + "=" + strconv.Itoa(fd),
 			// interpreted by hsu
-			"HAKUREI_APP_ID=" + seal.user.identity.String(),
+			"HAKUREI_IDENTITY=" + seal.user.identity.String(),
 		}
 	}
 

internal/sys/hsu.go

@@ -17,49 +17,22 @@ import (
 
 // Hsu caches responses from cmd/hsu.
 type Hsu struct {
-	uidOnce sync.Once
-	uidCopy map[int]struct {
-		uid int
-		err error
-	}
-	uidMu sync.RWMutex
+	idOnce sync.Once
+	idErr  error
+	id     int
 }
 
 var ErrHsuAccess = errors.New("current user is not in the hsurc file")
 
 func (h *Hsu) Uid(identity int) (int, error) {
-	h.uidOnce.Do(func() {
-		h.uidCopy = make(map[int]struct {
-			uid int
-			err error
-		})
-	})
-
-	{
-		h.uidMu.RLock()
-		u, ok := h.uidCopy[identity]
-		h.uidMu.RUnlock()
-		if ok {
-			return u.uid, u.err
-		}
-	}
-
-	h.uidMu.Lock()
-	defer h.uidMu.Unlock()
-
-	u := struct {
-		uid int
-		err error
-	}{}
-	defer func() { h.uidCopy[identity] = u }()
-
-	u.uid = -1
+	h.idOnce.Do(func() {
+		h.id = -1
 		hsuPath := internal.MustHsuPath()
 
 		cmd := exec.Command(hsuPath)
 		cmd.Path = hsuPath
 		cmd.Stderr = os.Stderr // pass through fatal messages
-	cmd.Env = []string{"HAKUREI_APP_ID=" + strconv.Itoa(identity)}
+		cmd.Env = make([]string, 0)
 		cmd.Dir = container.FHSRoot
 		var (
 			p         []byte
@@ -67,19 +40,25 @@ func (h *Hsu) Uid(identity int) (int, error) {
 		)
 
 		const step = "obtain uid from hsu"
-	if p, u.err = cmd.Output(); u.err == nil {
-		u.uid, u.err = strconv.Atoi(string(p))
-		if u.err != nil {
-			u.err = &hst.AppError{Step: step, Err: u.err, Msg: "invalid uid string from hsu"}
+		if p, h.idErr = cmd.Output(); h.idErr == nil {
+			h.id, h.idErr = strconv.Atoi(string(p))
+			if h.idErr != nil {
+				h.idErr = &hst.AppError{Step: step, Err: h.idErr, Msg: "invalid uid string from hsu"}
 			}
-	} else if errors.As(u.err, &exitError) && exitError != nil && exitError.ExitCode() == 1 {
+		} else if errors.As(h.idErr, &exitError) && exitError != nil && exitError.ExitCode() == 1 {
 			// hsu prints an error message in this case
-		u.err = &hst.AppError{Step: step, Err: ErrHsuAccess}
-	} else if os.IsNotExist(u.err) {
-		u.err = &hst.AppError{Step: step, Err: os.ErrNotExist,
+			h.idErr = &hst.AppError{Step: step, Err: ErrHsuAccess}
+		} else if os.IsNotExist(h.idErr) {
+			h.idErr = &hst.AppError{Step: step, Err: os.ErrNotExist,
 				Msg: fmt.Sprintf("the setuid helper is missing: %s", hsuPath)}
 		}
-	return u.uid, u.err
+	})
+
+	uid := -1
+	if h.id >= 0 {
+		uid = 1000000 + h.id*10000 + identity
+	}
+	return uid, h.idErr
 }
 
 // MustUid calls [State.Uid] and terminates on error.