diff --git a/src/syscall/exec_linux.go b/src/syscall/exec_linux.go index 3aa30c73640..9bac0421248 100644 --- a/src/syscall/exec_linux.go +++ b/src/syscall/exec_linux.go @@ -33,6 +33,11 @@ type SysProcAttr struct { Cloneflags uintptr // Flags for clone calls (Linux only) UidMappings []SysProcIDMap // User ID mappings for user namespaces. GidMappings []SysProcIDMap // Group ID mappings for user namespaces. + // GidMappingsEnableSetgroups enabling setgroups syscall. + // If false, then setgroups syscall will be disabled for the child process. + // This parameter is no-op if GidMappings == nil. Otherwise for unprivileged + // users this should be set to false for mappings work. + GidMappingsEnableSetgroups bool } // Implemented in runtime package. @@ -366,6 +371,32 @@ func writeIDMappings(path string, idMap []SysProcIDMap) error { return nil } +// writeSetgroups writes to /proc/PID/setgroups "deny" if enable is false +// and "allow" if enable is true. +// This is needed since kernel 3.19, because you can't write gid_map without +// disabling setgroups() system call. +func writeSetgroups(pid int, enable bool) error { + sgf := "/proc/" + itoa(pid) + "/setgroups" + fd, err := Open(sgf, O_RDWR, 0) + if err != nil { + return err + } + + var data []byte + if enable { + data = []byte("allow") + } else { + data = []byte("deny") + } + + if _, err := Write(fd, data); err != nil { + Close(fd) + return err + } + + return Close(fd) +} + // writeUidGidMappings writes User ID and Group ID mappings for user namespaces // for a process and it is called from the parent process. func writeUidGidMappings(pid int, sys *SysProcAttr) error { @@ -377,6 +408,10 @@ func writeUidGidMappings(pid int, sys *SysProcAttr) error { } if sys.GidMappings != nil { + // If the kernel is too old to support /proc/PID/setgroups, writeSetGroups will return ENOENT; this is OK. + if err := writeSetgroups(pid, sys.GidMappingsEnableSetgroups); err != nil && err != ENOENT { + return err + } gidf := "/proc/" + itoa(pid) + "/gid_map" if err := writeIDMappings(gidf, sys.GidMappings); err != nil { return err diff --git a/src/syscall/exec_linux_test.go b/src/syscall/exec_linux_test.go new file mode 100644 index 00000000000..a39fd58c1fd --- /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") + } +}