runc exec: use manager.AddPid

go.mod

@@ -14,7 +14,7 @@ require (
 	github.com/moby/sys/user v0.4.0
 	github.com/moby/sys/userns v0.1.0
 	github.com/mrunalp/fileutils v0.5.1
-	github.com/opencontainers/cgroups v0.0.4
+	github.com/opencontainers/cgroups v0.0.5
 	github.com/opencontainers/runtime-spec v1.2.2-0.20250818071321-383cadbf08c0
 	github.com/opencontainers/selinux v1.12.0
 	github.com/seccomp/libseccomp-golang v0.11.1

go.sum

@@ -44,8 +44,8 @@ github.com/moby/sys/userns v0.1.0 h1:tVLXkFOxVu9A64/yh59slHVv9ahO9UIev4JZusOLG/g
 github.com/moby/sys/userns v0.1.0/go.mod h1:IHUYgu/kao6N8YZlp9Cf444ySSvCmDlmzUcYfDHOl28=
 github.com/mrunalp/fileutils v0.5.1 h1:F+S7ZlNKnrwHfSwdlgNSkKo67ReVf8o9fel6C3dkm/Q=
 github.com/mrunalp/fileutils v0.5.1/go.mod h1:M1WthSahJixYnrXQl/DFQuteStB1weuxD2QJNHXfbSQ=
-github.com/opencontainers/cgroups v0.0.4 h1:XVj8P/IHVms/j+7eh8ggdkTLAxjz84ZzuFyGoE28DR4=
-github.com/opencontainers/cgroups v0.0.4/go.mod h1:s8lktyhlGUqM7OSRL5P7eAW6Wb+kWPNvt4qvVfzA5vs=
+github.com/opencontainers/cgroups v0.0.5 h1:DRITAqcOnY0uSBzIpt1RYWLjh5DPDiqUs4fY6Y0ktls=
+github.com/opencontainers/cgroups v0.0.5/go.mod h1:oWVzJsKK0gG9SCRBfTpnn16WcGEqDI8PAcpMGbqWxcs=
 github.com/opencontainers/runtime-spec v1.2.2-0.20250818071321-383cadbf08c0 h1:RLn0YfUWkiqPGtgUANvJrcjIkCHGRl3jcz/c557M28M=
 github.com/opencontainers/runtime-spec v1.2.2-0.20250818071321-383cadbf08c0/go.mod h1:jwyrGlmzljRJv/Fgzds9SsS/C5hL+LL3ko9hs6T5lQ0=
 github.com/opencontainers/selinux v1.12.0 h1:6n5JV4Cf+4y0KNXW48TLj5DwfXpvWlxXplUkdTrmPb8=

libcontainer/container_linux.go

@@ -7,7 +7,6 @@ import (
 	"io"
 	"os"
 	"os/exec"
-	"path"
 	"path/filepath"
 	"reflect"
 	"strconv"
@@ -655,40 +654,10 @@ func (c *Container) newSetnsProcess(p *Process, cmd *exec.Cmd, comm *processComm
 			bootstrapData: data,
 			container:     c,
 		},
-		cgroupPaths:     state.CgroupPaths,
 		rootlessCgroups: c.config.RootlessCgroups,
 		intelRdtPath:    state.IntelRdtPath,
 		initProcessPid:  state.InitProcessPid,
 	}
-	if len(p.SubCgroupPaths) > 0 {
-		if add, ok := p.SubCgroupPaths[""]; ok {
-			// cgroup v1: using the same path for all controllers.
-			// cgroup v2: the only possible way.
-			for k := range proc.cgroupPaths {
-				subPath := path.Join(proc.cgroupPaths[k], add)
-				if !strings.HasPrefix(subPath, proc.cgroupPaths[k]) {
-					return nil, fmt.Errorf("%s is not a sub cgroup path", add)
-				}
-				proc.cgroupPaths[k] = subPath
-			}
-			// cgroup v2: do not try to join init process's cgroup
-			// as a fallback (see (*setnsProcess).start).
-			proc.initProcessPid = 0
-		} else {
-			// Per-controller paths.
-			for ctrl, add := range p.SubCgroupPaths {
-				if val, ok := proc.cgroupPaths[ctrl]; ok {
-					subPath := path.Join(val, add)
-					if !strings.HasPrefix(subPath, val) {
-						return nil, fmt.Errorf("%s is not a sub cgroup path", add)
-					}
-					proc.cgroupPaths[ctrl] = subPath
-				} else {
-					return nil, fmt.Errorf("unknown controller %s in SubCgroupPaths", ctrl)
-				}
-			}
-		}
-	}
 	return proc, nil
 }
 

libcontainer/container_linux_test.go

@@ -32,6 +32,10 @@ func (m *mockCgroupManager) Apply(pid int) error {
 	return nil
 }
 
+func (m *mockCgroupManager) AddPid(_ string, _ int) error {
+	return nil
+}
+
 func (m *mockCgroupManager) Set(_ *cgroups.Resources) error {
 	return nil
 }

libcontainer/process_linux.go

@@ -6,12 +6,15 @@ import (
 	"errors"
 	"fmt"
 	"io"
+	"maps"
 	"net"
 	"os"
 	"os/exec"
+	"path"
 	"path/filepath"
 	"runtime"
 	"strconv"
+	"strings"
 	"sync"
 	"time"
 
@@ -153,7 +156,6 @@ func (p *containerProcess) wait() (*os.ProcessState, error) { //nolint:unparam
 
 type setnsProcess struct {
 	containerProcess
-	cgroupPaths     map[string]string
 	rootlessCgroups bool
 	intelRdtPath    string
 	initProcessPid  int
@@ -244,6 +246,76 @@ func (p *setnsProcess) setFinalCPUAffinity() error {
 	return nil
 }
 
+func (p *setnsProcess) addIntoCgroupV1() error {
+	if sub, ok := p.process.SubCgroupPaths[""]; ok || len(p.process.SubCgroupPaths) == 0 {
+		// Either same sub-cgroup for all paths, or no sub-cgroup.
+		err := p.manager.AddPid(sub, p.pid())
+		if err != nil && !p.rootlessCgroups {
+			return fmt.Errorf("error adding pid %d to cgroups: %w", p.pid(), err)
+		}
+		return nil
+	}
+
+	// Per-controller sub-cgroup paths. Not supported by AddPid (or systemd),
+	// so we have to calculate and check all sub-cgroup paths, and write
+	// directly to cgroupfs.
+	paths := maps.Clone(p.manager.GetPaths())
+	for ctrl, sub := range p.process.SubCgroupPaths {
+		base, ok := paths[ctrl]
+		if !ok {
+			return fmt.Errorf("unknown controller %s in SubCgroupPaths", ctrl)
+		}
+		cgPath := path.Join(base, sub)
+		if !strings.HasPrefix(cgPath, base) {
+			return fmt.Errorf("bad sub cgroup path: %s", sub)
+		}
+		paths[ctrl] = cgPath
+	}
+
+	for _, path := range paths {
+		if err := cgroups.WriteCgroupProc(path, p.pid()); err != nil && !p.rootlessCgroups {
+			return fmt.Errorf("error adding pid %d to cgroups: %w", p.pid(), err)
+		}
+	}
+
+	return nil
+}
+
+func (p *setnsProcess) addIntoCgroupV2() error {
+	sub := p.process.SubCgroupPaths[""]
+	err := p.manager.AddPid(sub, p.pid())
+	if err != nil && !p.rootlessCgroups {
+		// On cgroup v2 + nesting + domain controllers, adding to initial cgroup may fail with EBUSY.
+		// https://github.com/opencontainers/runc/issues/2356#issuecomment-621277643
+		// Try to join the cgroup of InitProcessPid, unless sub-cgroup is explicitly set.
+		if p.initProcessPid != 0 && sub == "" {
+			initProcCgroupFile := fmt.Sprintf("/proc/%d/cgroup", p.initProcessPid)
+			initCg, initCgErr := cgroups.ParseCgroupFile(initProcCgroupFile)
+			if initCgErr == nil {
+				if initCgPath, ok := initCg[""]; ok {
+					initCgDirpath := filepath.Join(fs2.UnifiedMountpoint, initCgPath)
+					logrus.Debugf("adding pid %d to cgroup failed (%v), attempting to join %s",
+						p.pid(), err, initCgDirpath)
+					// NOTE: initCgDirPath is not guaranteed to exist because we didn't pause the container.
+					err = cgroups.WriteCgroupProc(initCgDirpath, p.pid())
+				}
+			}
+		}
+		if err != nil {
+			return fmt.Errorf("error adding pid %d to cgroups: %w", p.pid(), err)
+		}
+	}
+
+	return nil
+}
+
+func (p *setnsProcess) addIntoCgroup() error {
+	if cgroups.IsCgroup2UnifiedMode() {
+		return p.addIntoCgroupV2()
+	}
+	return p.addIntoCgroupV1()
+}
+
 func (p *setnsProcess) start() (retErr error) {
 	defer p.comm.closeParent()
 
@@ -277,28 +349,8 @@ func (p *setnsProcess) start() (retErr error) {
 	if err := p.execSetns(); err != nil {
 		return fmt.Errorf("error executing setns process: %w", err)
 	}
-	for _, path := range p.cgroupPaths {
-		if err := cgroups.WriteCgroupProc(path, p.pid()); err != nil && !p.rootlessCgroups {
-			// On cgroup v2 + nesting + domain controllers, WriteCgroupProc may fail with EBUSY.
-			// https://github.com/opencontainers/runc/issues/2356#issuecomment-621277643
-			// Try to join the cgroup of InitProcessPid.
-			if cgroups.IsCgroup2UnifiedMode() && p.initProcessPid != 0 {
-				initProcCgroupFile := fmt.Sprintf("/proc/%d/cgroup", p.initProcessPid)
-				initCg, initCgErr := cgroups.ParseCgroupFile(initProcCgroupFile)
-				if initCgErr == nil {
-					if initCgPath, ok := initCg[""]; ok {
-						initCgDirpath := filepath.Join(fs2.UnifiedMountpoint, initCgPath)
-						logrus.Debugf("adding pid %d to cgroups %v failed (%v), attempting to join %q (obtained from %s)",
-							p.pid(), p.cgroupPaths, err, initCg, initCgDirpath)
-						// NOTE: initCgDirPath is not guaranteed to exist because we didn't pause the container.
-						err = cgroups.WriteCgroupProc(initCgDirpath, p.pid())
-					}
-				}
-			}
-			if err != nil {
-				return fmt.Errorf("error adding pid %d to cgroups: %w", p.pid(), err)
-			}
-		}
+	if err := p.addIntoCgroup(); err != nil {
+		return err
 	}
 	// Set final CPU affinity right after the process is moved into container's cgroup.
 	if err := p.setFinalCPUAffinity(); err != nil {

script/setup_rootless.sh

@@ -12,4 +12,4 @@ ssh-keygen -t ecdsa -N "" -f "$HOME/.ssh/rootless.key"
 sudo mkdir -p -m 0700 /home/rootless/.ssh
 sudo cp "$HOME/.ssh/rootless.key" /home/rootless/.ssh/id_ecdsa
 sudo cp "$HOME/.ssh/rootless.key.pub" /home/rootless/.ssh/authorized_keys
-sudo chown -R rootless.rootless /home/rootless
+sudo chown -R rootless:rootless /home/rootless

tests/integration/exec.bats

@@ -226,17 +226,17 @@ function check_exec_debug() {
 	# Check we can't join parent cgroup.
 	runc exec --cgroup ".." test_busybox cat /proc/self/cgroup
 	[ "$status" -ne 0 ]
-	[[ "$output" == *" .. is not a sub cgroup path"* ]]
+	[[ "$output" == *"bad sub cgroup path"* ]]
 
 	# Check we can't join non-existing subcgroup.
 	runc exec --cgroup nonexistent test_busybox cat /proc/self/cgroup
 	[ "$status" -ne 0 ]
-	[[ "$output" == *" adding pid "*"/nonexistent/cgroup.procs: no such file "* ]]
+	[[ "$output" == *" adding pid "*"o such file or directory"* ]]
 
 	# Check we can't join non-existing subcgroup (for a particular controller).
 	runc exec --cgroup cpu:nonexistent test_busybox cat /proc/self/cgroup
 	[ "$status" -ne 0 ]
-	[[ "$output" == *" adding pid "*"/nonexistent/cgroup.procs: no such file "* ]]
+	[[ "$output" == *" adding pid "*"o such file or directory"* ]]
 
 	# Check we can't specify non-existent controller.
 	runc exec --cgroup whaaat:/ test_busybox true
@@ -277,12 +277,12 @@ function check_exec_debug() {
 	# Check we can't join parent cgroup.
 	runc exec --cgroup ".." test_busybox cat /proc/self/cgroup
 	[ "$status" -ne 0 ]
-	[[ "$output" == *" .. is not a sub cgroup path"* ]]
+	[[ "$output" == *"bad sub cgroup path"* ]]
 
 	# Check we can't join non-existing subcgroup.
 	runc exec --cgroup nonexistent test_busybox cat /proc/self/cgroup
 	[ "$status" -ne 0 ]
-	[[ "$output" == *" adding pid "*"/nonexistent/cgroup.procs: no such file "* ]]
+	[[ "$output" == *" adding pid "*"o such file or directory"* ]]
 
 	# Check we can join top-level cgroup (implicit).
 	runc exec test_busybox grep '^0::/$' /proc/self/cgroup
@@ -318,7 +318,7 @@ function check_exec_debug() {
 	# Check that --cgroup / disables the init cgroup fallback.
 	runc exec --cgroup / test_busybox true
 	[ "$status" -ne 0 ]
-	[[ "$output" == *" adding pid "*" to cgroups"*"/cgroup.procs: device or resource busy"* ]]
+	[[ "$output" == *" adding pid "*" to cgroups"*"evice or resource busy"* ]]
 
 	# Check that explicit --cgroup foobar works.
 	runc exec --cgroup foobar test_busybox grep '^0::/foobar$' /proc/self/cgroup