libcontainer: remove all mount logic from nsexec

go.mod

@@ -10,7 +10,7 @@ require (
 	github.com/cyphar/filepath-securejoin v0.2.4
 	github.com/docker/go-units v0.5.0
 	github.com/godbus/dbus/v5 v5.1.0
-	github.com/moby/sys/mountinfo v0.6.2
+	github.com/moby/sys/mountinfo v0.7.1
 	github.com/moby/sys/user v0.1.0
 	github.com/mrunalp/fileutils v0.5.1
 	github.com/opencontainers/runtime-spec v1.1.1-0.20230823135140-4fec88fd00a4

go.sum

@@ -26,8 +26,8 @@ github.com/google/go-cmp v0.5.9 h1:O2Tfq5qg4qc4AmwVlvv0oLiVAGB7enBSJ2x2DqQFi38=
 github.com/inconshreveable/mousetrap v1.0.0/go.mod h1:PxqpIevigyE2G7u3NXJIT2ANytuPF1OarO4DADm73n8=
 github.com/kr/pretty v0.3.1 h1:flRD4NNwYAUpkphVc1HcthR4KEIFJ65n8Mw5qdRn3LE=
 github.com/kr/text v0.2.0 h1:5Nx0Ya0ZqY2ygV366QzturHI13Jq95ApcVaJBhpS+AY=
-github.com/moby/sys/mountinfo v0.6.2 h1:BzJjoreD5BMFNmD9Rus6gdd1pLuecOFPt8wC+Vygl78=
-github.com/moby/sys/mountinfo v0.6.2/go.mod h1:IJb6JQeOklcdMU9F5xQ8ZALD+CUr5VlGpwtX+VE0rpI=
+github.com/moby/sys/mountinfo v0.7.1 h1:/tTvQaSJRr2FshkhXiIpux6fQ2Zvc4j7tAhMTStAG2g=
+github.com/moby/sys/mountinfo v0.7.1/go.mod h1:IJb6JQeOklcdMU9F5xQ8ZALD+CUr5VlGpwtX+VE0rpI=
 github.com/moby/sys/user v0.1.0 h1:WmZ93f5Ux6het5iituh9x2zAG7NFY9Aqi49jjE1PaQg=
 github.com/moby/sys/user v0.1.0/go.mod h1:fKJhFOnsCN6xZ5gSfbM6zaHGgDJMrqt9/reuj4T7MmU=
 github.com/mrunalp/fileutils v0.5.1 h1:F+S7ZlNKnrwHfSwdlgNSkKo67ReVf8o9fel6C3dkm/Q=

libcontainer/apparmor/apparmor_linux.go

@@ -26,14 +26,19 @@ func isEnabled() bool {
 }
 
 func setProcAttr(attr, value string) error {
-	// Under AppArmor you can only change your own attr, so use /proc/self/
-	// instead of /proc/<tid>/ like libapparmor does
-	attrPath := "/proc/self/attr/apparmor/" + attr
-	if _, err := os.Stat(attrPath); errors.Is(err, os.ErrNotExist) {
+	attr = utils.CleanPath(attr)
+	attrSubPath := "attr/apparmor/" + attr
+	if _, err := os.Stat("/proc/self/" + attrSubPath); errors.Is(err, os.ErrNotExist) {
 		// fall back to the old convention
-		attrPath = "/proc/self/attr/" + attr
+		attrSubPath = "attr/" + attr
 	}
 
+	// Under AppArmor you can only change your own attr, so there's no reason
+	// to not use /proc/thread-self/ (instead of /proc/<tid>/, like libapparmor
+	// does).
+	attrPath, closer := utils.ProcThreadSelf(attrSubPath)
+	defer closer()
+
 	f, err := os.OpenFile(attrPath, os.O_WRONLY, 0)
 	if err != nil {
 		return err

libcontainer/cgroups/cgroups_test.go

@@ -5,6 +5,9 @@ import (
 )
 
 func TestParseCgroups(t *testing.T) {
+	// We don't need to use /proc/thread-self here because runc always runs
+	// with every thread in the same cgroup. This lets us avoid having to do
+	// runtime.LockOSThread.
 	cgroups, err := ParseCgroupFile("/proc/self/cgroup")
 	if err != nil {
 		t.Fatal(err)

libcontainer/cgroups/file.go

@@ -136,13 +136,14 @@ func openFile(dir, file string, flags int) (*os.File, error) {
 		//
 		// TODO: if such usage will ever be common, amend this
 		// to reopen cgroupFd and retry openat2.
-		fdStr := strconv.Itoa(cgroupFd)
-		fdDest, _ := os.Readlink("/proc/self/fd/" + fdStr)
+		fdPath, closer := utils.ProcThreadSelf("fd/" + strconv.Itoa(cgroupFd))
+		defer closer()
+		fdDest, _ := os.Readlink(fdPath)
 		if fdDest != cgroupfsDir {
 			// Wrap the error so it is clear that cgroupFd
 			// is opened to an unexpected/wrong directory.
-			err = fmt.Errorf("cgroupFd %s unexpectedly opened to %s != %s: %w",
-				fdStr, fdDest, cgroupfsDir, err)
+			err = fmt.Errorf("cgroupFd %d unexpectedly opened to %s != %s: %w",
+				cgroupFd, fdDest, cgroupfsDir, err)
 		}
 		return nil, err
 	}

libcontainer/cgroups/fs2/defaultpath.go

@@ -55,6 +55,9 @@ func _defaultDirPath(root, cgPath, cgParent, cgName string) (string, error) {
 		return filepath.Join(root, innerPath), nil
 	}
 
+	// we don't need to use /proc/thread-self here because runc always runs
+	// with every thread in the same cgroup. This lets us avoid having to do
+	// runtime.LockOSThread.
 	ownCgroup, err := parseCgroupFile("/proc/self/cgroup")
 	if err != nil {
 		return "", err

libcontainer/cgroups/v1_utils.go

@@ -99,11 +99,12 @@ func tryDefaultPath(cgroupPath, subsystem string) string {
 // expensive), so it is assumed that cgroup mounts are not being changed.
 func readCgroupMountinfo() ([]*mountinfo.Info, error) {
 	readMountinfoOnce.Do(func() {
+		// mountinfo.GetMounts uses /proc/thread-self, so we can use it without
+		// issues.
 		cgroupMountinfo, readMountinfoErr = mountinfo.GetMounts(
 			mountinfo.FSTypeFilter("cgroup"),
 		)
 	})
-
 	return cgroupMountinfo, readMountinfoErr
 }
 
@@ -196,6 +197,9 @@ func getCgroupMountsV1(all bool) ([]Mount, error) {
 		return nil, err
 	}
 
+	// We don't need to use /proc/thread-self here because runc always runs
+	// with every thread in the same cgroup. This lets us avoid having to do
+	// runtime.LockOSThread.
 	allSubsystems, err := ParseCgroupFile("/proc/self/cgroup")
 	if err != nil {
 		return nil, err
@@ -214,6 +218,10 @@ func GetOwnCgroup(subsystem string) (string, error) {
 	if IsCgroup2UnifiedMode() {
 		return "", errUnified
 	}
+
+	// We don't need to use /proc/thread-self here because runc always runs
+	// with every thread in the same cgroup. This lets us avoid having to do
+	// runtime.LockOSThread.
 	cgroups, err := ParseCgroupFile("/proc/self/cgroup")
 	if err != nil {
 		return "", err

libcontainer/configs/mount.go

@@ -3,5 +3,5 @@ package configs
 const (
 	// EXT_COPYUP is a directive to copy up the contents of a directory when
 	// a tmpfs is mounted over it.
-	EXT_COPYUP = 1 << iota //nolint:golint // ignore "don't use ALL_CAPS" warning
+	EXT_COPYUP = 1 << iota //nolint:golint,revive // ignore "don't use ALL_CAPS" warning
 )

libcontainer/configs/mount_linux.go

@@ -2,6 +2,24 @@ package configs
 
 import "golang.org/x/sys/unix"
 
+type MountIDMapping struct {
+	// Recursive indicates if the mapping needs to be recursive.
+	Recursive bool `json:"recursive"`
+
+	// UserNSPath is a path to a user namespace that indicates the necessary
+	// id-mappings for MOUNT_ATTR_IDMAP. If set to non-"", UIDMappings and
+	// GIDMappings must be set to nil.
+	UserNSPath string `json:"userns_path,omitempty"`
+
+	// UIDMappings is the uid mapping set for this mount, to be used with
+	// MOUNT_ATTR_IDMAP.
+	UIDMappings []IDMap `json:"uid_mappings,omitempty"`
+
+	// GIDMappings is the gid mapping set for this mount, to be used with
+	// MOUNT_ATTR_IDMAP.
+	GIDMappings []IDMap `json:"gid_mappings,omitempty"`
+}
+
 type Mount struct {
 	// Source path for the mount.
 	Source string `json:"source"`
@@ -34,23 +52,15 @@ type Mount struct {
 	// Extensions are additional flags that are specific to runc.
 	Extensions int `json:"extensions"`
 
-	// UIDMappings is used to changing file user owners w/o calling chown.
-	// Note that, the underlying filesystem should support this feature to be
-	// used.
-	// Every mount point could have its own mapping.
-	UIDMappings []IDMap `json:"uid_mappings,omitempty"`
-
-	// GIDMappings is used to changing file group owners w/o calling chown.
-	// Note that, the underlying filesystem should support this feature to be
-	// used.
-	// Every mount point could have its own mapping.
-	GIDMappings []IDMap `json:"gid_mappings,omitempty"`
+	// Mapping is the MOUNT_ATTR_IDMAP configuration for the mount. If non-nil,
+	// the mount is configured to use MOUNT_ATTR_IDMAP-style id mappings.
+	IDMapping *MountIDMapping `json:"id_mapping,omitempty"`
 }
 
 func (m *Mount) IsBind() bool {
 	return m.Flags&unix.MS_BIND != 0
 }
 
 func (m *Mount) IsIDMapped() bool {
-	return len(m.UIDMappings) > 0 || len(m.GIDMappings) > 0
+	return m.IDMapping != nil
 }

libcontainer/configs/namespaces_linux.go

@@ -59,6 +59,9 @@ func IsNamespaceSupported(ns NamespaceType) bool {
 	if nsFile == "" {
 		return false
 	}
+	// We don't need to use /proc/thread-self here because the list of
+	// namespace types is unrelated to the thread. This lets us avoid having to
+	// do runtime.LockOSThread.
 	_, err := os.Stat("/proc/self/ns/" + nsFile)
 	// a namespace is supported if it exists and we have permissions to read it
 	supported = err == nil

libcontainer/configs/validate/validator.go

@@ -309,29 +309,32 @@ func checkBindOptions(m *configs.Mount) error {
 }
 
 func checkIDMapMounts(config *configs.Config, m *configs.Mount) error {
+	// Make sure MOUNT_ATTR_IDMAP is not set on any of our mounts. This
+	// attribute is handled differently to all other attributes (through
+	// m.IDMapping), so make sure we never store it in the actual config. This
+	// really shouldn't ever happen.
+	if m.RecAttr != nil && (m.RecAttr.Attr_set|m.RecAttr.Attr_clr)&unix.MOUNT_ATTR_IDMAP != 0 {
+		return errors.New("mount configuration cannot contain recAttr for MOUNT_ATTR_IDMAP")
+	}
 	if !m.IsIDMapped() {
 		return nil
 	}
-
 	if !m.IsBind() {
-		return fmt.Errorf("gidMappings/uidMappings is supported only for mounts with the option 'bind'")
+		return errors.New("id-mapped mounts are only supported for bind-mounts")
 	}
 	if config.RootlessEUID {
-		return fmt.Errorf("gidMappings/uidMappings is not supported when runc is being launched with EUID != 0, needs CAP_SYS_ADMIN on the runc parent's user namespace")
-	}
-	if len(config.UIDMappings) == 0 || len(config.GIDMappings) == 0 {
-		return fmt.Errorf("not yet supported to use gidMappings/uidMappings in a mount without also using a user namespace")
-	}
-	if !sameMapping(config.UIDMappings, m.UIDMappings) {
-		return fmt.Errorf("not yet supported for the mount uidMappings to be different than user namespace uidMapping")
-	}
-	if !sameMapping(config.GIDMappings, m.GIDMappings) {
-		return fmt.Errorf("not yet supported for the mount gidMappings to be different than user namespace gidMapping")
+		return errors.New("id-mapped mounts are not supported for rootless containers")
 	}
-	if !filepath.IsAbs(m.Source) {
-		return fmt.Errorf("mount source not absolute")
+	if m.IDMapping.UserNSPath == "" {
+		if len(m.IDMapping.UIDMappings) == 0 || len(m.IDMapping.GIDMappings) == 0 {
+			return errors.New("id-mapped mounts must have both uid and gid mappings specified")
+		}
+	} else {
+		if m.IDMapping.UIDMappings != nil || m.IDMapping.GIDMappings != nil {
+			// should never happen
+			return errors.New("[internal error] id-mapped mounts cannot have both userns_path and uid and gid mappings specified")
+		}
 	}
-
 	return nil
 }
 
@@ -356,27 +359,6 @@ func mountsStrict(config *configs.Config) error {
 	return nil
 }
 
-// sameMapping checks if the mappings are the same. If the mappings are the same
-// but in different order, it returns false.
-func sameMapping(a, b []configs.IDMap) bool {
-	if len(a) != len(b) {
-		return false
-	}
-
-	for i := range a {
-		if a[i].ContainerID != b[i].ContainerID {
-			return false
-		}
-		if a[i].HostID != b[i].HostID {
-			return false
-		}
-		if a[i].Size != b[i].Size {
-			return false
-		}
-	}
-	return true
-}
-
 func isHostNetNS(path string) (bool, error) {
 	const currentProcessNetns = "/proc/self/ns/net"