diff --git a/cgroups/utils.go b/cgroups/utils.go index 111c8714..0d19b3ea 100644 --- a/cgroups/utils.go +++ b/cgroups/utils.go @@ -2,6 +2,7 @@ package cgroups import ( "bufio" + "fmt" "io" "os" "path/filepath" @@ -30,6 +31,80 @@ func FindCgroupMountpoint(subsystem string) (string, error) { return "", ErrNotFound } +type Mount struct { + Mountpoint string + Subsystems []string +} + +func (m Mount) GetThisCgroupDir() (string, error) { + if len(m.Subsystems) == 0 { + return "", fmt.Errorf("no subsystem for mount") + } + + return GetThisCgroupDir(m.Subsystems[0]) +} + +func GetCgroupMounts() ([]Mount, error) { + mounts, err := mount.GetMounts() + if err != nil { + return nil, err + } + + all, err := GetAllSubsystems() + if err != nil { + return nil, err + } + + allMap := make(map[string]bool) + for _, s := range all { + allMap[s] = true + } + + res := []Mount{} + for _, mount := range mounts { + if mount.Fstype == "cgroup" { + m := Mount{Mountpoint: mount.Mountpoint} + + for _, opt := range strings.Split(mount.VfsOpts, ",") { + if strings.HasPrefix(opt, "name=") { + m.Subsystems = append(m.Subsystems, opt) + } + if allMap[opt] { + m.Subsystems = append(m.Subsystems, opt) + } + } + res = append(res, m) + } + } + return res, nil +} + +// Returns all the cgroup subsystems supported by the kernel +func GetAllSubsystems() ([]string, error) { + f, err := os.Open("/proc/cgroups") + if err != nil { + return nil, err + } + defer f.Close() + + subsystems := []string{} + + s := bufio.NewScanner(f) + for s.Scan() { + if err := s.Err(); err != nil { + return nil, err + } + text := s.Text() + if text[0] != '#' { + parts := strings.Fields(text) + if len(parts) > 4 && parts[3] != "0" { + subsystems = append(subsystems, parts[0]) + } + } + } + return subsystems, nil +} + // Returns the relative path to the cgroup docker is running in. func GetThisCgroupDir(subsystem string) (string, error) { f, err := os.Open("/proc/self/cgroup") diff --git a/mount/init.go b/mount/init.go index 4e913ad1..e61d3c3b 100644 --- a/mount/init.go +++ b/mount/init.go @@ -6,9 +6,11 @@ import ( "fmt" "os" "path/filepath" + "strings" "syscall" "github.com/docker/libcontainer" + "github.com/docker/libcontainer/cgroups" "github.com/docker/libcontainer/label" "github.com/docker/libcontainer/mount/nodes" "github.com/dotcloud/docker/pkg/symlink" @@ -92,6 +94,69 @@ func mountSystem(rootfs string, container *libcontainer.Container) error { return fmt.Errorf("mounting %s into %s %s", m.source, m.path, err) } } + + // Mount all cgroup subsystems into the container, read-only. Create symlinks for each + // subsystem if any subsystems are merged + cgroupMounts, err := cgroups.GetCgroupMounts() + if err != nil { + return err + } + + cgroupsDir := filepath.Join(rootfs, "/sys/fs/cgroup") + + for _, m := range cgroupMounts { + dir := filepath.Base(m.Mountpoint) + mountpoint := filepath.Join(cgroupsDir, dir) + + if err := os.MkdirAll(mountpoint, 0755); err != nil && !os.IsExist(err) { + return fmt.Errorf("mkdirall %s %s", mountpoint, err) + } + + // Bind-mount the cgroup to /sys/fs/cgroup with the same name as the outer mount + if err := system.Mount(m.Mountpoint, mountpoint, "bind", uintptr(syscall.MS_BIND|defaultMountFlags), ""); err != nil { + return fmt.Errorf("mounting %s into %s %s", m.Mountpoint, mountpoint, err) + } + // Make it read-only + if err := system.Mount(mountpoint, mountpoint, "bind", uintptr(syscall.MS_BIND|syscall.MS_REMOUNT|syscall.MS_RDONLY|defaultMountFlags), ""); err != nil { + return fmt.Errorf("remounting %s into %s %s", mountpoint, mountpoint, err) + } + + hasName := false + for _, subsys := range m.Subsystems { + isName := strings.HasPrefix(subsys, "name=") + canonicalName := subsys + if isName { + hasName = true + canonicalName = subsys[5:] + } + + // For the merged case dir will be something like "cpu,cpuacct", so + // we make symlinks for all the pure subsystem names "cpu -> cpu,cpuacct", etc + if canonicalName != dir { + if err := os.Symlink(dir, filepath.Join(cgroupsDir, canonicalName)); err != nil { + return fmt.Errorf("creating cgroup symlink for %s: %s", dir, err) + } + } + } + + // For named cgroups, such as name=systemd we mount a read-write subset at the + // current cgroup path. This lets e.g. systemd work inside a container, as it can create subcgroups inside the + // current cgroup, while not being able to do anything dangerous in the real cgroups + if hasName { + cgroupPath, _ := m.GetThisCgroupDir() + if cgroupPath != "" && cgroupPath != "/" { + if err := system.Mount(filepath.Join(m.Mountpoint, cgroupPath), filepath.Join(mountpoint, cgroupPath), "bind", uintptr(syscall.MS_BIND|defaultMountFlags), ""); err != nil { + return fmt.Errorf("mounting %s into %s %s", filepath.Join(m.Mountpoint, cgroupPath), filepath.Join(mountpoint, cgroupPath), err) + } + } + } + } + + // Make /sys/fs/cgroup read-only + if err := system.Mount(cgroupsDir, cgroupsDir, "bind", uintptr(syscall.MS_REMOUNT|syscall.MS_RDONLY|defaultMountFlags), ""); err != nil { + return fmt.Errorf("remounting %s read-only %s", cgroupsDir, err) + } + return nil } @@ -193,6 +258,7 @@ func newSystemMounts(rootfs, mountLabel string, mounts libcontainer.Mounts) []mo {source: "proc", path: filepath.Join(rootfs, "proc"), device: "proc", flags: defaultMountFlags}, {source: "sysfs", path: filepath.Join(rootfs, "sys"), device: "sysfs", flags: defaultMountFlags}, {source: "tmpfs", path: filepath.Join(rootfs, "dev"), device: "tmpfs", flags: syscall.MS_NOSUID | syscall.MS_STRICTATIME, data: label.FormatMountLabel("mode=755", mountLabel)}, + {source: "tmpfs", path: filepath.Join(rootfs, "sys/fs/cgroup"), device: "tmpfs", flags: defaultMountFlags}, {source: "shm", path: filepath.Join(rootfs, "dev", "shm"), device: "tmpfs", flags: defaultMountFlags, data: label.FormatMountLabel("mode=1777,size=65536k", mountLabel)}, {source: "devpts", path: filepath.Join(rootfs, "dev", "pts"), device: "devpts", flags: syscall.MS_NOSUID | syscall.MS_NOEXEC, data: label.FormatMountLabel("newinstance,ptmxmode=0666,mode=620,gid=5", mountLabel)}, }