internal/apply/user.go

@@ -7,6 +7,7 @@ import (
 	osuser "os/user"
 	"path/filepath"
 	"strconv"
+	"strings"
 
 	"github.com/novox/mesh-host/internal/declaration"
 	"github.com/novox/mesh-host/internal/system"
@@ -97,18 +98,9 @@ func own(path, owner string) error {
 	if owner == "" {
 		return nil
 	}
-	found, err := osuser.Lookup(owner)
+	uid, gid, err := idsOf(owner)
 	if err != nil {
-		return fmt.Errorf("%s should belong to %q and this machine has no such user: %w",
-			path, owner, err)
-	}
-	uid, err := strconv.Atoi(found.Uid)
-	if err != nil {
-		return err
-	}
-	gid, err := strconv.Atoi(found.Gid)
-	if err != nil {
-		return err
+		return fmt.Errorf("%s should belong to %q: %w", path, owner, err)
 	}
 	if err := os.Chown(path, uid, gid); err != nil {
 		return fmt.Errorf("cannot give %s to %q: %w", path, owner, err)
@@ -116,12 +108,54 @@ func own(path, owner string) error {
 	return nil
 }
 
+// idsOf resolves an owner to a uid and gid: a name this machine knows, or numbers it does not.
+//
+// **Numbers, because a container's user is a number the machine has never heard of.** A directory
+// a module mounts into its container belongs to whoever runs inside — grafana's 472, redis's 999,
+// www-data's 33 — and none of those has a row in this machine's passwd, so there is no name to
+// look up and none to create. Refusing them looked principled and meant every module whose
+// container drops privileges could not own its own data: the store's config was unreadable to
+// the store, and the forge could not traverse into the directory that held its files.
+//
+// "uid:gid" and bare "uid" are numeric; anything else is a name, resolved as before.
+func idsOf(owner string) (int, int, error) {
+	user, group, both := strings.Cut(owner, ":")
+	if uid, err := strconv.Atoi(user); err == nil {
+		gid := uid
+		if both {
+			g, err := strconv.Atoi(group)
+			if err != nil {
+				return 0, 0, fmt.Errorf(
+					"%q reads as a uid with a group that is not a gid", owner)
+			}
+			gid = g
+		}
+		return uid, gid, nil
+	}
+	if both {
+		return 0, 0, fmt.Errorf("%q mixes a name with a colon; a name stands alone", owner)
+	}
+	found, err := osuser.Lookup(owner)
+	if err != nil {
+		return 0, 0, fmt.Errorf("this machine has no such user: %w", err)
+	}
+	uid, err := strconv.Atoi(found.Uid)
+	if err != nil {
+		return 0, 0, err
+	}
+	gid, err := strconv.Atoi(found.Gid)
+	if err != nil {
+		return 0, 0, err
+	}
+	return uid, gid, nil
+}
+
 // ownedBy reports whether a path already belongs to a user, so applying twice changes nothing.
 func ownedBy(path, owner string) (bool, error) {
 	if owner == "" {
 		return true, nil
 	}
-	found, err := osuser.Lookup(owner)
+	wantUID, wantGID, err := idsOf(owner)
 	if err != nil {
 		return false, nil
 	}
@@ -133,7 +167,7 @@ func ownedBy(path, owner string) (bool, error) {
 	if !ok {
 		return false, nil
 	}
-	return strconv.Itoa(uid) == found.Uid && strconv.Itoa(gid) == found.Gid, nil
+	return uid == wantUID && gid == wantGID, nil
 }
 
 // ownAll gives a whole tree to a user, for an archive that was unpacked into it.

internal/apply/user_numeric_test.go

@@ -0,0 +1,34 @@
+package apply
+
+import "testing"
+
+// A container's user is a number the machine has never heard of — grafana's 472, redis's 999 —
+// so an owner must be expressible without a passwd row. Refusing numerics looked principled and
+// meant every module whose container drops privileges could not own its own data.
+func TestAnOwnerMayBeANumberTheMachineDoesNotKnow(t *testing.T) {
+	for owner, want := range map[string][2]int{
+		"472:472":     {472, 472},
+		"1000:1000":   {1000, 1000},
+		"999":         {999, 999},
+		"10001:10001": {10001, 10001},
+		"33:0":        {33, 0},
+	} {
+		uid, gid, err := idsOf(owner)
+		if err != nil {
+			t.Errorf("%q refused: %v", owner, err)
+			continue
+		}
+		if uid != want[0] || gid != want[1] {
+			t.Errorf("%q resolved to %d:%d, wanted %d:%d", owner, uid, gid, want[0], want[1])
+		}
+	}
+	if _, _, err := idsOf("no-such-user-exists-here"); err == nil {
+		t.Error("a name this machine does not know was accepted")
+	}
+	if _, _, err := idsOf("root:something"); err == nil {
+		t.Error("a name with a colon was accepted; a name stands alone")
+	}
+	if uid, gid, err := idsOf("root"); err != nil || uid != 0 || gid != 0 {
+		t.Errorf("root resolved to %d:%d (%v); names must still work", uid, gid, err)
+	}
+}