app: set up acl on X11 socket

The socket is typically owned by the priv-user, and inaccessible by the target user, so just allowing access to the directory is not enough. This change fixes this oversight and add checks that will also be useful for merging #1.

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

test/sandbox/assert.go

@@ -15,6 +15,7 @@ import (
 	"errors"
 	"io/fs"
 	"log"
+	"net"
 	"os"
 	"syscall"
 )
@@ -33,6 +34,10 @@ type TestCase struct {
 	FS      *FS               `json:"fs"`
 	Mount   []*MountinfoEntry `json:"mount"`
 	Seccomp bool              `json:"seccomp"`
+
+	TrySocket      string `json:"try_socket,omitempty"`
+	SocketAbstract bool   `json:"socket_abstract,omitempty"`
+	SocketPathname bool   `json:"socket_pathname,omitempty"`
 }
 
 type T struct {
@@ -125,6 +130,47 @@ func (t *T) MustCheck(want *TestCase) {
 	} else {
 		printf("[SKIP] skipping seccomp check")
 	}
+
+	if want.TrySocket != "" {
+		abstractConn, abstractErr := net.Dial("unix", "@"+want.TrySocket)
+		pathnameConn, pathnameErr := net.Dial("unix", want.TrySocket)
+		ok := true
+
+		if abstractErr == nil {
+			if err := abstractConn.Close(); err != nil {
+				ok = false
+				log.Printf("Close: %v", err)
+			}
+		}
+		if pathnameErr == nil {
+			if err := pathnameConn.Close(); err != nil {
+				ok = false
+				log.Printf("Close: %v", err)
+			}
+		}
+
+		abstractWantErr := error(syscall.EPERM)
+		pathnameWantErr := error(syscall.ENOENT)
+		if want.SocketAbstract {
+			abstractWantErr = nil
+		}
+		if want.SocketPathname {
+			pathnameWantErr = nil
+		}
+
+		if !errors.Is(abstractErr, abstractWantErr) {
+			ok = false
+			log.Printf("abstractErr: %v, want %v", abstractErr, abstractWantErr)
+		}
+		if !errors.Is(pathnameErr, pathnameWantErr) {
+			ok = false
+			log.Printf("pathnameErr: %v, want %v", pathnameErr, pathnameWantErr)
+		}
+
+		if !ok {
+			os.Exit(1)
+		}
+	}
 }
 
 func MustCheckFilter(pid int, want string) {

test/sandbox/case/default.nix

@@ -50,6 +50,9 @@ let
         useCommonPaths
         userns
         ;
+      enablements = {
+        inherit (tc) x11;
+      };
       share = testProgram;
       packages = [ ];
       path = "${testProgram}/bin/hakurei-test";

test/sandbox/case/device.nix

@@ -25,6 +25,7 @@ in
   mapRealUid = false;
   useCommonPaths = true;
   userns = false;
+  x11 = true;
 
   # 0, PresetStrict
   expectedFilter = {
@@ -35,6 +36,7 @@ in
   want = {
     env = [
       "DBUS_SESSION_BUS_ADDRESS=unix:path=/run/user/65534/bus"
+      "DISPLAY=unix:/tmp/.X11-unix/X0"
       "HOME=/var/lib/hakurei/u0/a4"
       "PULSE_SERVER=unix:/run/user/65534/pulse/native"
       "SHELL=/run/current-system/sw/bin/bash"
@@ -161,7 +163,9 @@ in
         } null;
         devices = fs "800001ed" null null;
       } null;
-      tmp = fs "800001f8" { } null;
+      tmp = fs "800001f8" {
+        ".X11-unix" = fs "801001ff" { X0 = fs "10001fd" null null; } null;
+      } null;
       usr = fs "800001c0" { bin = fs "800001ed" { env = fs "80001ff" null null; } null; } null;
       var = fs "800001c0" {
         lib = fs "800001c0" {
@@ -231,10 +235,15 @@ in
       (ent ignore "/etc/passwd" "ro,nosuid,nodev,relatime" "tmpfs" "rootfs" "rw,uid=1000004,gid=1000004")
       (ent ignore "/etc/group" "ro,nosuid,nodev,relatime" "tmpfs" "rootfs" "rw,uid=1000004,gid=1000004")
       (ent ignore "/run/user/65534/wayland-0" "ro,nosuid,nodev,relatime" "ext4" "/dev/disk/by-label/nixos" "rw")
+      (ent "/tmp/.X11-unix" "/tmp/.X11-unix" "ro,nosuid,nodev,relatime" "ext4" "/dev/disk/by-label/nixos" "rw")
       (ent ignore "/run/user/65534/pulse/native" "ro,nosuid,nodev,relatime" "tmpfs" "tmpfs" ignore)
       (ent ignore "/run/user/65534/bus" "ro,nosuid,nodev,relatime" "ext4" "/dev/disk/by-label/nixos" "rw")
     ];
 
     seccomp = true;
+
+    try_socket = "/tmp/.X11-unix/X0";
+    socket_abstract = true;
+    socket_pathname = true;
   };
 }

test/sandbox/case/mapuid.nix

@@ -34,6 +34,7 @@ in
   mapRealUid = true;
   useCommonPaths = true;
   userns = false;
+  x11 = false;
 
   # 0, PresetStrict
   expectedFilter = {
@@ -266,5 +267,9 @@ in
     ];
 
     seccomp = true;
+
+    try_socket = "/tmp/.X11-unix/X0";
+    socket_abstract = true;
+    socket_pathname = false;
   };
 }

test/sandbox/case/pdlike.nix

@@ -34,6 +34,7 @@ in
   mapRealUid = false;
   useCommonPaths = false;
   userns = true;
+  x11 = false;
 
   # 0, PresetExt | PresetDenyDevel
   expectedFilter = {
@@ -261,5 +262,9 @@ in
     ];
 
     seccomp = true;
+
+    try_socket = "/tmp/.X11-unix/X0";
+    socket_abstract = true;
+    socket_pathname = false;
   };
 }

test/sandbox/case/preset.nix

@@ -34,6 +34,7 @@ in
   mapRealUid = false;
   useCommonPaths = false;
   userns = false;
+  x11 = false;
 
   # 0, PresetStrict
   expectedFilter = {
@@ -259,5 +260,9 @@ in
     ];
 
     seccomp = true;
+
+    try_socket = "/tmp/.X11-unix/X0";
+    socket_abstract = true;
+    socket_pathname = false;
   };
 }

test/sandbox/case/tty.nix

@@ -34,6 +34,7 @@ in
   mapRealUid = false;
   useCommonPaths = true;
   userns = false;
+  x11 = true;
 
   # 0, PresetExt | PresetDenyNS | PresetDenyDevel
   expectedFilter = {
@@ -44,6 +45,7 @@ in
   want = {
     env = [
       "DBUS_SESSION_BUS_ADDRESS=unix:path=/run/user/65534/bus"
+      "DISPLAY=unix:/tmp/.X11-unix/X0"
       "HOME=/var/lib/hakurei/u0/a2"
       "PULSE_SERVER=unix:/run/user/65534/pulse/native"
       "SHELL=/run/current-system/sw/bin/bash"
@@ -188,7 +190,9 @@ in
         } null;
         devices = fs "800001ed" null null;
       } null;
-      tmp = fs "800001f8" { } null;
+      tmp = fs "800001f8" {
+        ".X11-unix" = fs "801001ff" { X0 = fs "10001fd" null null; } null;
+      } null;
       usr = fs "800001c0" { bin = fs "800001ed" { env = fs "80001ff" null null; } null; } null;
       var = fs "800001c0" {
         lib = fs "800001c0" {
@@ -263,10 +267,15 @@ in
       (ent ignore "/etc/passwd" "ro,nosuid,nodev,relatime" "tmpfs" "rootfs" "rw,uid=1000002,gid=1000002")
       (ent ignore "/etc/group" "ro,nosuid,nodev,relatime" "tmpfs" "rootfs" "rw,uid=1000002,gid=1000002")
       (ent ignore "/run/user/65534/wayland-0" "ro,nosuid,nodev,relatime" "ext4" "/dev/disk/by-label/nixos" "rw")
+      (ent "/tmp/.X11-unix" "/tmp/.X11-unix" "ro,nosuid,nodev,relatime" "ext4" "/dev/disk/by-label/nixos" "rw")
       (ent ignore "/run/user/65534/pulse/native" "ro,nosuid,nodev,relatime" "tmpfs" "tmpfs" ignore)
       (ent ignore "/run/user/65534/bus" "ro,nosuid,nodev,relatime" "ext4" "/dev/disk/by-label/nixos" "rw")
     ];
 
     seccomp = true;
+
+    try_socket = "/tmp/.X11-unix/X0";
+    socket_abstract = true;
+    socket_pathname = true;
   };
 }