syscall: add GidMappingsEnableSetgroups to Linux SysProcAttr
Linux 3.19 made a change in the handling of setgroups and the 'gid_map' file to
address a security issue.
The upshot of the 3.19 changes is that in order to update the 'gid_maps' file,
use of the setgroups() system call in this user namespace must first be disabled
by writing "deny" to one of the /proc/PID/setgroups files for this namespace.
Also added tests for remapping uid_map and gid_map inside new user
namespace.
Fixes #10626
Change-Id: I4d2539acbab741a37092d277e10f31fc39a8feb7
Reviewed-on: https://go-review.googlesource.com/10670
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
diff --git a/src/syscall/exec_linux_test.go b/src/syscall/exec_linux_test.go
new file mode 100644
index 0000000..a39fd58
--- /dev/null
+++ b/src/syscall/exec_linux_test.go
@@ -0,0 +1,84 @@
+// Copyright 2015 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// +build linux
+
+package syscall_test
+
+import (
+ "os"
+ "os/exec"
+ "strings"
+ "syscall"
+ "testing"
+)
+
+func whoamiCmd(t *testing.T, uid int, setgroups bool) *exec.Cmd {
+ if _, err := os.Stat("/proc/self/ns/user"); err != nil {
+ if os.IsNotExist(err) {
+ t.Skip("kernel doesn't support user namespaces")
+ }
+ t.Fatalf("Failed to stat /proc/self/ns/user: %v", err)
+ }
+ cmd := exec.Command("whoami")
+ cmd.SysProcAttr = &syscall.SysProcAttr{
+ Cloneflags: syscall.CLONE_NEWUSER,
+ UidMappings: []syscall.SysProcIDMap{
+ {ContainerID: 0, HostID: uid, Size: 1},
+ },
+ GidMappings: []syscall.SysProcIDMap{
+ {ContainerID: 0, HostID: uid, Size: 1},
+ },
+ GidMappingsEnableSetgroups: setgroups,
+ }
+ return cmd
+}
+
+func testNEWUSERRemap(t *testing.T, uid int, setgroups bool) {
+ cmd := whoamiCmd(t, uid, setgroups)
+ out, err := cmd.CombinedOutput()
+ if err != nil {
+ t.Fatalf("Cmd failed with err %v, output: %s", err, out)
+ }
+ sout := strings.TrimSpace(string(out))
+ want := "root"
+ if sout != want {
+ t.Fatalf("whoami = %q; want %q", out, want)
+ }
+}
+
+func TestCloneNEWUSERAndRemapRootDisableSetgroups(t *testing.T) {
+ if os.Getuid() != 0 {
+ t.Skip("skipping root only test")
+ }
+ testNEWUSERRemap(t, 0, false)
+}
+
+func TestCloneNEWUSERAndRemapRootEnableSetgroups(t *testing.T) {
+ if os.Getuid() != 0 {
+ t.Skip("skipping root only test")
+ }
+ testNEWUSERRemap(t, 0, false)
+}
+
+func TestCloneNEWUSERAndRemapNoRootDisableSetgroups(t *testing.T) {
+ if os.Getuid() == 0 {
+ t.Skip("skipping unprivileged user only test")
+ }
+ testNEWUSERRemap(t, os.Getuid(), false)
+}
+
+func TestCloneNEWUSERAndRemapNoRootSetgroupsEnableSetgroups(t *testing.T) {
+ if os.Getuid() == 0 {
+ t.Skip("skipping unprivileged user only test")
+ }
+ cmd := whoamiCmd(t, os.Getuid(), true)
+ err := cmd.Run()
+ if err == nil {
+ t.Skip("probably old kernel without security fix")
+ }
+ if !strings.Contains(err.Error(), "operation not permitted") {
+ t.Fatalf("Unprivileged gid_map rewriting with GidMappingsEnableSetgroups must fail")
+ }
+}
