Update restrictions for better handling of mounts

This also cleans up some of the left over restriction paths code from
before.
Docker-DCO-1.1-Signed-off-by: Michael Crosby <michael@crosbymichael.com> (github: crosbymichael)

Author: crosbymichael

mount/init.go

@@ -123,15 +123,12 @@ func newSystemMounts(rootfs, mountLabel string, mounts libcontainer.Mounts) []mo
 	systemMounts := []mount{
 		{source: "proc", path: filepath.Join(rootfs, "proc"), device: "proc", flags: defaultMountFlags},
 		{source: "sysfs", path: filepath.Join(rootfs, "sys"), device: "sysfs", 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)},
 	}
 
 	if len(mounts.OfType("devtmpfs")) == 1 {
 		systemMounts = append(systemMounts, mount{source: "tmpfs", path: filepath.Join(rootfs, "dev"), device: "tmpfs", flags: syscall.MS_NOSUID | syscall.MS_STRICTATIME, data: label.FormatMountLabel("mode=755", mountLabel)})
 	}
-	systemMounts = append(systemMounts,
-		mount{source: "shm", path: filepath.Join(rootfs, "dev", "shm"), device: "tmpfs", flags: defaultMountFlags, data: label.FormatMountLabel("mode=1777,size=65536k", mountLabel)},
-		mount{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)},
-	)
-
 	return systemMounts
 }

nsinit/init.go

@@ -72,8 +72,8 @@ func Init(container *libcontainer.Container, uncleanRootfs, consolePath string,
 
 	runtime.LockOSThread()
 
-	if restrictionPath := container.Context["restriction_path"]; restrictionPath != "" {
-		if err := restrict.Restrict("/", restrictionPath); err != nil {
+	if container.Context["restrictions"] != "" {
+		if err := restrict.Restrict(); err != nil {
 			return err
 		}
 	}

security/restrict/restrict.go

@@ -11,67 +11,42 @@ import (
 	"github.com/dotcloud/docker/pkg/system"
 )
 
-// "restrictions" are container paths (files, directories, whatever) that have to be masked.
-// maskPath is a "safe" path to be mounted over maskedPath. It can take two special values:
-// - if it is "", then nothing is mounted;
-// - if it is "EMPTY", then an empty directory is mounted instead.
-// If remountRO is true then the maskedPath is remounted read-only (regardless of whether a maskPath was used).
-type restriction struct {
-	maskedPath string
-	maskPath   string
-	remountRO  bool
-}
-
-var restrictions = []restriction{
-	{"/proc", "", true},
-	{"/sys", "", true},
-	{"/proc/kcore", "/dev/null", false},
-}
-
 // This has to be called while the container still has CAP_SYS_ADMIN (to be able to perform mounts).
 // However, afterwards, CAP_SYS_ADMIN should be dropped (otherwise the user will be able to revert those changes).
-// "empty" should be the path to an empty directory.
-func Restrict(rootfs, empty string) error {
-	for _, restriction := range restrictions {
-		dest := filepath.Join(rootfs, restriction.maskedPath)
-		if restriction.maskPath != "" {
-			var source string
-			if restriction.maskPath == "EMPTY" {
-				source = empty
-			} else {
-				source = filepath.Join(rootfs, restriction.maskPath)
-			}
-			if err := system.Mount(source, dest, "", syscall.MS_BIND, ""); err != nil {
-				return fmt.Errorf("unable to bind-mount %s over %s: %s", source, dest, err)
-			}
-		}
-		if restriction.remountRO {
-			if err := system.Mount("", dest, "", syscall.MS_REMOUNT|syscall.MS_RDONLY, ""); err != nil {
-				return fmt.Errorf("unable to remount %s readonly: %s", dest, err)
-			}
+func Restrict() error {
+	// remount proc and sys as readonly
+	for _, dest := range []string{"proc", "sys"} {
+		if err := system.Mount("", dest, "", syscall.MS_REMOUNT|syscall.MS_RDONLY, ""); err != nil {
+			return fmt.Errorf("unable to remount %s readonly: %s", dest, err)
 		}
 	}
 
+	if err := system.Mount("/proc/kcore", "/dev/null", "", syscall.MS_BIND, ""); err != nil {
+		return fmt.Errorf("unable to bind-mount /dev/null over /proc/kcore")
+	}
+
 	// This weird trick will allow us to mount /proc read-only, while being able to use AppArmor.
 	// This is because apparently, loading an AppArmor profile requires write access to /proc/1/attr.
 	// So we do another mount of procfs, ensure it's write-able, and bind-mount a subset of it.
-	tmpProcPath := filepath.Join(rootfs, ".proc")
-	if err := os.Mkdir(tmpProcPath, 0700); err != nil {
-		return fmt.Errorf("unable to create temporary proc mountpoint %s: %s", tmpProcPath, err)
+	var (
+		rwAttrPath = filepath.Join(".proc", "1", "attr")
+		roAttrPath = filepath.Join("proc", "1", "attr")
+	)
+
+	if err := os.Mkdir(".proc", 0700); err != nil {
+		return fmt.Errorf("unable to create temporary proc mountpoint .proc: %s", err)
 	}
-	if err := system.Mount("proc", tmpProcPath, "proc", 0, ""); err != nil {
+	if err := system.Mount("proc", ".proc", "proc", 0, ""); err != nil {
 		return fmt.Errorf("unable to mount proc on temporary proc mountpoint: %s", err)
 	}
-	if err := system.Mount("proc", tmpProcPath, "", syscall.MS_REMOUNT, ""); err != nil {
+	if err := system.Mount("proc", ".proc", "", syscall.MS_REMOUNT, ""); err != nil {
 		return fmt.Errorf("unable to remount proc read-write: %s", err)
 	}
-	rwAttrPath := filepath.Join(rootfs, ".proc", "1", "attr")
-	roAttrPath := filepath.Join(rootfs, "proc", "1", "attr")
 	if err := system.Mount(rwAttrPath, roAttrPath, "", syscall.MS_BIND, ""); err != nil {
 		return fmt.Errorf("unable to bind-mount %s on %s: %s", rwAttrPath, roAttrPath, err)
 	}
-	if err := system.Unmount(tmpProcPath, 0); err != nil {
+	if err := system.Unmount(".proc", 0); err != nil {
 		return fmt.Errorf("unable to unmount temporary proc filesystem: %s", err)
 	}
-	return nil
+	return os.RemoveAll(".proc")
 }

security/restrict/unsupported.go

@@ -4,6 +4,6 @@ package restrict
 
 import "fmt"
 
-func Restrict(rootfs, empty string) error {
+func Restrict() error {
 	return fmt.Errorf("not supported")
 }