Merge release-20210705.0-14-g275932bf0 (automated)

8 files changed, 290 insertions, 109 deletions

diff --git a/pkg/sentry/control/proc.go b/pkg/sentry/control/proc.go
index b7ee5425d..6352ea71a 100644
--- a/pkg/sentry/control/proc.go
+++ b/pkg/sentry/control/proc.go
@@ -223,7 +223,7 @@ func (proc *Proc) execAsync(args *ExecArgs) (*kernel.ThreadGroup, kernel.ThreadI
 			_ = fd.Close()
 		}
 	}()
-	ttyFile, ttyFileVFS2, err := fdimport.Import(ctx, fdTable, args.StdioIsPty, fds)
+	ttyFile, ttyFileVFS2, err := fdimport.Import(ctx, fdTable, args.StdioIsPty, args.KUID, args.KGID, fds)
 	if err != nil {
 		return nil, 0, nil, nil, err
 	}
diff --git a/pkg/sentry/fdimport/fdimport.go b/pkg/sentry/fdimport/fdimport.go
index badd5b073..f2b9630eb 100644
--- a/pkg/sentry/fdimport/fdimport.go
+++ b/pkg/sentry/fdimport/fdimport.go
@@ -24,6 +24,7 @@ import (
 	"gvisor.dev/gvisor/pkg/sentry/fs/host"
 	hostvfs2 "gvisor.dev/gvisor/pkg/sentry/fsimpl/host"
 	"gvisor.dev/gvisor/pkg/sentry/kernel"
+	"gvisor.dev/gvisor/pkg/sentry/kernel/auth"
 	"gvisor.dev/gvisor/pkg/sentry/vfs"
 )
 
@@ -31,9 +32,9 @@ import (
 // sets up TTY for the first 3 FDs in the slice representing stdin, stdout,
 // stderr. Used FDs are either closed or released. It's safe for the caller to
 // close any remaining files upon return.
-func Import(ctx context.Context, fdTable *kernel.FDTable, console bool, fds []*fd.FD) (*host.TTYFileOperations, *hostvfs2.TTYFileDescription, error) {
+func Import(ctx context.Context, fdTable *kernel.FDTable, console bool, uid auth.KUID, gid auth.KGID, fds []*fd.FD) (*host.TTYFileOperations, *hostvfs2.TTYFileDescription, error) {
 	if kernel.VFS2Enabled {
-		ttyFile, err := importVFS2(ctx, fdTable, console, fds)
+		ttyFile, err := importVFS2(ctx, fdTable, console, uid, gid, fds)
 		return nil, ttyFile, err
 	}
 	ttyFile, err := importFS(ctx, fdTable, console, fds)
@@ -89,7 +90,7 @@ func importFS(ctx context.Context, fdTable *kernel.FDTable, console bool, fds []
 	return ttyFile.FileOperations.(*host.TTYFileOperations), nil
 }
 
-func importVFS2(ctx context.Context, fdTable *kernel.FDTable, console bool, stdioFDs []*fd.FD) (*hostvfs2.TTYFileDescription, error) {
+func importVFS2(ctx context.Context, fdTable *kernel.FDTable, console bool, uid auth.KUID, gid auth.KGID, stdioFDs []*fd.FD) (*hostvfs2.TTYFileDescription, error) {
 	k := kernel.KernelFromContext(ctx)
 	if k == nil {
 		return nil, fmt.Errorf("cannot find kernel from context")
@@ -103,7 +104,13 @@ func importVFS2(ctx context.Context, fdTable *kernel.FDTable, console bool, stdi
 			// Import the file as a host TTY file.
 			if ttyFile == nil {
 				var err error
-				appFile, err = hostvfs2.ImportFD(ctx, k.HostMount(), hostFD.FD(), true /* isTTY */)
+				appFile, err = hostvfs2.NewFD(ctx, k.HostMount(), hostFD.FD(), &hostvfs2.NewFDOptions{
+					Savable:      true,
+					IsTTY:        true,
+					VirtualOwner: true,
+					UID:          uid,
+					GID:          gid,
+				})
 				if err != nil {
 					return nil, err
 				}
@@ -121,7 +128,12 @@ func importVFS2(ctx context.Context, fdTable *kernel.FDTable, console bool, stdi
 			}
 		} else {
 			var err error
-			appFile, err = hostvfs2.ImportFD(ctx, k.HostMount(), hostFD.FD(), false /* isTTY */)
+			appFile, err = hostvfs2.NewFD(ctx, k.HostMount(), hostFD.FD(), &hostvfs2.NewFDOptions{
+				Savable:      true,
+				VirtualOwner: true,
+				UID:          uid,
+				GID:          gid,
+			})
 			if err != nil {
 				return nil, err
 			}
diff --git a/pkg/sentry/fsimpl/host/host.go b/pkg/sentry/fsimpl/host/host.go
index 9998bd0c3..89aa7b3d9 100644
--- a/pkg/sentry/fsimpl/host/host.go
+++ b/pkg/sentry/fsimpl/host/host.go
@@ -42,6 +42,36 @@ import (
 	"gvisor.dev/gvisor/pkg/waiter"
 )
 
+// These are the modes that are stored with virtualOwner.
+const virtualOwnerModes = linux.STATX_MODE | linux.STATX_UID | linux.STATX_GID
+
+// +stateify savable
+type virtualOwner struct {
+	// This field is initialized at creation time and is immutable.
+	enabled bool
+
+	// mu protects the fields below and they can be accessed using atomic memory
+	// operations.
+	mu  sync.Mutex `state:"nosave"`
+	uid uint32
+	gid uint32
+	// mode is also stored, otherwise setting the host file to `0000` could remove
+	// access to the file.
+	mode uint32
+}
+
+func (v *virtualOwner) atomicUID() uint32 {
+	return atomic.LoadUint32(&v.uid)
+}
+
+func (v *virtualOwner) atomicGID() uint32 {
+	return atomic.LoadUint32(&v.gid)
+}
+
+func (v *virtualOwner) atomicMode() uint32 {
+	return atomic.LoadUint32(&v.mode)
+}
+
 // inode implements kernfs.Inode.
 //
 // +stateify savable
@@ -98,6 +128,11 @@ type inode struct {
 	// Event queue for blocking operations.
 	queue waiter.Queue
 
+	// virtualOwner caches ownership and permission information to override the
+	// underlying file owner and permission. This is used to allow the unstrusted
+	// application to change these fields without affecting the host.
+	virtualOwner virtualOwner
+
 	// If haveBuf is non-zero, hostFD represents a pipe, and buf contains data
 	// read from the pipe from previous calls to inode.beforeSave(). haveBuf
 	// and buf are protected by bufMu. haveBuf is accessed using atomic memory
@@ -147,7 +182,7 @@ func newInode(ctx context.Context, fs *filesystem, hostFD int, savable bool, fil
 type NewFDOptions struct {
 	// If Savable is true, the host file descriptor may be saved/restored by
 	// numeric value; the sandbox API requires a corresponding host FD with the
-	// same numeric value to be provieded at time of restore.
+	// same numeric value to be provided at time of restore.
 	Savable bool
 
 	// If IsTTY is true, the file descriptor is a TTY.
@@ -157,6 +192,12 @@ type NewFDOptions struct {
 	// the new file description will inherit flags from hostFD.
 	HaveFlags bool
 	Flags     uint32
+
+	// VirtualOwner allow the host file to have owner and permissions different
+	// than the underlying host file.
+	VirtualOwner bool
+	UID          auth.KUID
+	GID          auth.KGID
 }
 
 // NewFD returns a vfs.FileDescription representing the given host file
@@ -168,8 +209,8 @@ func NewFD(ctx context.Context, mnt *vfs.Mount, hostFD int, opts *NewFDOptions)
 	}
 
 	// Retrieve metadata.
-	var s unix.Stat_t
-	if err := unix.Fstat(hostFD, &s); err != nil {
+	var stat unix.Stat_t
+	if err := unix.Fstat(hostFD, &stat); err != nil {
 		return nil, err
 	}
 
@@ -183,11 +224,19 @@ func NewFD(ctx context.Context, mnt *vfs.Mount, hostFD int, opts *NewFDOptions)
 		flags = uint32(flagsInt)
 	}
 
-	d := &kernfs.Dentry{}
-	i, err := newInode(ctx, fs, hostFD, opts.Savable, linux.FileMode(s.Mode).FileType(), opts.IsTTY)
+	fileType := linux.FileMode(stat.Mode).FileType()
+	i, err := newInode(ctx, fs, hostFD, opts.Savable, fileType, opts.IsTTY)
 	if err != nil {
 		return nil, err
 	}
+	if opts.VirtualOwner {
+		i.virtualOwner.enabled = true
+		i.virtualOwner.uid = uint32(opts.UID)
+		i.virtualOwner.gid = uint32(opts.GID)
+		i.virtualOwner.mode = stat.Mode
+	}
+
+	d := &kernfs.Dentry{}
 	d.Init(&fs.Filesystem, i)
 
 	// i.open will take a reference on d.
@@ -196,15 +245,7 @@ func NewFD(ctx context.Context, mnt *vfs.Mount, hostFD int, opts *NewFDOptions)
 	// For simplicity, fileDescription.offset is set to 0. Technically, we
 	// should only set to 0 on files that are not seekable (sockets, pipes,
 	// etc.), and use the offset from the host fd otherwise when importing.
-	return i.open(ctx, d, mnt, flags)
-}
-
-// ImportFD sets up and returns a vfs.FileDescription from a donated fd.
-func ImportFD(ctx context.Context, mnt *vfs.Mount, hostFD int, isTTY bool) (*vfs.FileDescription, error) {
-	return NewFD(ctx, mnt, hostFD, &NewFDOptions{
-		Savable: true,
-		IsTTY:   isTTY,
-	})
+	return i.open(ctx, d, mnt, fileType, flags)
 }
 
 // filesystemType implements vfs.FilesystemType.
@@ -270,7 +311,7 @@ func (fs *filesystem) MountOptions() string {
 // CheckPermissions implements kernfs.Inode.CheckPermissions.
 func (i *inode) CheckPermissions(ctx context.Context, creds *auth.Credentials, ats vfs.AccessTypes) error {
 	var s unix.Stat_t
-	if err := unix.Fstat(i.hostFD, &s); err != nil {
+	if err := i.stat(&s); err != nil {
 		return err
 	}
 	return vfs.GenericCheckPermissions(creds, ats, linux.FileMode(s.Mode), auth.KUID(s.Uid), auth.KGID(s.Gid))
@@ -279,7 +320,7 @@ func (i *inode) CheckPermissions(ctx context.Context, creds *auth.Credentials, a
 // Mode implements kernfs.Inode.Mode.
 func (i *inode) Mode() linux.FileMode {
 	var s unix.Stat_t
-	if err := unix.Fstat(i.hostFD, &s); err != nil {
+	if err := i.stat(&s); err != nil {
 		// Retrieving the mode from the host fd using fstat(2) should not fail.
 		// If the syscall does not succeed, something is fundamentally wrong.
 		panic(fmt.Sprintf("failed to retrieve mode from host fd %d: %v", i.hostFD, err))
@@ -306,7 +347,7 @@ func (i *inode) Stat(ctx context.Context, vfsfs *vfs.Filesystem, opts vfs.StatOp
 		// Fallback to fstat(2), if statx(2) is not supported on the host.
 		//
 		// TODO(b/151263641): Remove fallback.
-		return i.fstat(fs)
+		return i.statxFromStat(fs)
 	}
 	if err != nil {
 		return linux.Statx{}, err
@@ -330,19 +371,35 @@ func (i *inode) Stat(ctx context.Context, vfsfs *vfs.Filesystem, opts vfs.StatOp
 	// device numbers.
 	ls.Mask |= s.Mask & linux.STATX_ALL
 	if s.Mask&linux.STATX_TYPE != 0 {
-		ls.Mode |= s.Mode & linux.S_IFMT
+		if i.virtualOwner.enabled {
+			ls.Mode |= uint16(i.virtualOwner.atomicMode()) & linux.S_IFMT
+		} else {
+			ls.Mode |= s.Mode & linux.S_IFMT
+		}
 	}
 	if s.Mask&linux.STATX_MODE != 0 {
-		ls.Mode |= s.Mode &^ linux.S_IFMT
+		if i.virtualOwner.enabled {
+			ls.Mode |= uint16(i.virtualOwner.atomicMode()) &^ linux.S_IFMT
+		} else {
+			ls.Mode |= s.Mode &^ linux.S_IFMT
+		}
 	}
 	if s.Mask&linux.STATX_NLINK != 0 {
 		ls.Nlink = s.Nlink
 	}
 	if s.Mask&linux.STATX_UID != 0 {
-		ls.UID = s.Uid
+		if i.virtualOwner.enabled {
+			ls.UID = i.virtualOwner.atomicUID()
+		} else {
+			ls.UID = s.Uid
+		}
 	}
 	if s.Mask&linux.STATX_GID != 0 {
-		ls.GID = s.Gid
+		if i.virtualOwner.enabled {
+			ls.GID = i.virtualOwner.atomicGID()
+		} else {
+			ls.GID = s.Gid
+		}
 	}
 	if s.Mask&linux.STATX_ATIME != 0 {
 		ls.Atime = unixToLinuxStatxTimestamp(s.Atime)
@@ -366,7 +423,7 @@ func (i *inode) Stat(ctx context.Context, vfsfs *vfs.Filesystem, opts vfs.StatOp
 	return ls, nil
 }
 
-// fstat is a best-effort fallback for inode.Stat() if the host does not
+// statxFromStat is a best-effort fallback for inode.Stat() if the host does not
 // support statx(2).
 //
 // We ignore the mask and sync flags in opts and simply supply
@@ -374,9 +431,9 @@ func (i *inode) Stat(ctx context.Context, vfsfs *vfs.Filesystem, opts vfs.StatOp
 // of a mask or sync flags. fstat(2) does not provide any metadata
 // equivalent to Statx.Attributes, Statx.AttributesMask, or Statx.Btime, so
 // those fields remain empty.
-func (i *inode) fstat(fs *filesystem) (linux.Statx, error) {
+func (i *inode) statxFromStat(fs *filesystem) (linux.Statx, error) {
 	var s unix.Stat_t
-	if err := unix.Fstat(i.hostFD, &s); err != nil {
+	if err := i.stat(&s); err != nil {
 		return linux.Statx{}, err
 	}
 
@@ -400,7 +457,21 @@ func (i *inode) fstat(fs *filesystem) (linux.Statx, error) {
 	}, nil
 }
 
+func (i *inode) stat(stat *unix.Stat_t) error {
+	if err := unix.Fstat(i.hostFD, stat); err != nil {
+		return err
+	}
+	if i.virtualOwner.enabled {
+		stat.Uid = i.virtualOwner.atomicUID()
+		stat.Gid = i.virtualOwner.atomicGID()
+		stat.Mode = i.virtualOwner.atomicMode()
+	}
+	return nil
+}
+
 // SetStat implements kernfs.Inode.SetStat.
+//
+// +checklocksignore
 func (i *inode) SetStat(ctx context.Context, fs *vfs.Filesystem, creds *auth.Credentials, opts vfs.SetStatOptions) error {
 	s := &opts.Stat
 
@@ -408,11 +479,22 @@ func (i *inode) SetStat(ctx context.Context, fs *vfs.Filesystem, creds *auth.Cre
 	if m == 0 {
 		return nil
 	}
-	if m&^(linux.STATX_MODE|linux.STATX_SIZE|linux.STATX_ATIME|linux.STATX_MTIME) != 0 {
+	supportedModes := uint32(linux.STATX_MODE | linux.STATX_SIZE | linux.STATX_ATIME | linux.STATX_MTIME)
+	if i.virtualOwner.enabled {
+		if m&virtualOwnerModes != 0 {
+			// Take lock if any of the virtual owner fields will be updated.
+			i.virtualOwner.mu.Lock()
+			defer i.virtualOwner.mu.Unlock()
+		}
+
+		supportedModes |= virtualOwnerModes
+	}
+	if m&^supportedModes != 0 {
 		return linuxerr.EPERM
 	}
+
 	var hostStat unix.Stat_t
-	if err := unix.Fstat(i.hostFD, &hostStat); err != nil {
+	if err := i.stat(&hostStat); err != nil {
 		return err
 	}
 	if err := vfs.CheckSetStat(ctx, creds, &opts, linux.FileMode(hostStat.Mode), auth.KUID(hostStat.Uid), auth.KGID(hostStat.Gid)); err != nil {
@@ -420,8 +502,12 @@ func (i *inode) SetStat(ctx context.Context, fs *vfs.Filesystem, creds *auth.Cre
 	}
 
 	if m&linux.STATX_MODE != 0 {
-		if err := unix.Fchmod(i.hostFD, uint32(s.Mode)); err != nil {
-			return err
+		if i.virtualOwner.enabled {
+			i.virtualOwner.mode = uint32(opts.Stat.Mode)
+		} else {
+			if err := unix.Fchmod(i.hostFD, uint32(s.Mode)); err != nil {
+				return err
+			}
 		}
 	}
 	if m&linux.STATX_SIZE != 0 {
@@ -449,6 +535,14 @@ func (i *inode) SetStat(ctx context.Context, fs *vfs.Filesystem, creds *auth.Cre
 			return err
 		}
 	}
+	if i.virtualOwner.enabled {
+		if m&linux.STATX_UID != 0 {
+			i.virtualOwner.uid = opts.Stat.UID
+		}
+		if m&linux.STATX_GID != 0 {
+			i.virtualOwner.gid = opts.Stat.GID
+		}
+	}
 	return nil
 }
 
@@ -473,16 +567,15 @@ func (i *inode) Open(ctx context.Context, rp *vfs.ResolvingPath, d *kernfs.Dentr
 	if i.Mode().FileType() == linux.S_IFSOCK {
 		return nil, linuxerr.ENXIO
 	}
-	return i.open(ctx, d, rp.Mount(), opts.Flags)
-}
-
-func (i *inode) open(ctx context.Context, d *kernfs.Dentry, mnt *vfs.Mount, flags uint32) (*vfs.FileDescription, error) {
-	var s unix.Stat_t
-	if err := unix.Fstat(i.hostFD, &s); err != nil {
+	var stat unix.Stat_t
+	if err := i.stat(&stat); err != nil {
 		return nil, err
 	}
-	fileType := s.Mode & linux.FileTypeMask
+	fileType := linux.FileMode(stat.Mode).FileType()
+	return i.open(ctx, d, rp.Mount(), fileType, opts.Flags)
+}
 
+func (i *inode) open(ctx context.Context, d *kernfs.Dentry, mnt *vfs.Mount, fileType linux.FileMode, flags uint32) (*vfs.FileDescription, error) {
 	// Constrain flags to a subset we can handle.
 	//
 	// TODO(gvisor.dev/issue/2601): Support O_NONBLOCK by adding RWF_NOWAIT to pread/pwrite calls.
diff --git a/pkg/sentry/fsimpl/host/host_state_autogen.go b/pkg/sentry/fsimpl/host/host_state_autogen.go
index 47253a87e..607474165 100644
--- a/pkg/sentry/fsimpl/host/host_state_autogen.go
+++ b/pkg/sentry/fsimpl/host/host_state_autogen.go
@@ -30,6 +30,40 @@ func (r *ConnectedEndpointRefs) StateLoad(stateSourceObject state.Source) {
 	stateSourceObject.AfterLoad(r.afterLoad)
 }
 
+func (v *virtualOwner) StateTypeName() string {
+	return "pkg/sentry/fsimpl/host.virtualOwner"
+}
+
+func (v *virtualOwner) StateFields() []string {
+	return []string{
+		"enabled",
+		"uid",
+		"gid",
+		"mode",
+	}
+}
+
+func (v *virtualOwner) beforeSave() {}
+
+// +checklocksignore
+func (v *virtualOwner) StateSave(stateSinkObject state.Sink) {
+	v.beforeSave()
+	stateSinkObject.Save(0, &v.enabled)
+	stateSinkObject.Save(1, &v.uid)
+	stateSinkObject.Save(2, &v.gid)
+	stateSinkObject.Save(3, &v.mode)
+}
+
+func (v *virtualOwner) afterLoad() {}
+
+// +checklocksignore
+func (v *virtualOwner) StateLoad(stateSourceObject state.Source) {
+	stateSourceObject.Load(0, &v.enabled)
+	stateSourceObject.Load(1, &v.uid)
+	stateSourceObject.Load(2, &v.gid)
+	stateSourceObject.Load(3, &v.mode)
+}
+
 func (i *inode) StateTypeName() string {
 	return "pkg/sentry/fsimpl/host.inode"
 }
@@ -51,6 +85,7 @@ func (i *inode) StateFields() []string {
 		"isTTY",
 		"savable",
 		"queue",
+		"virtualOwner",
 		"haveBuf",
 		"buf",
 	}
@@ -74,8 +109,9 @@ func (i *inode) StateSave(stateSinkObject state.Sink) {
 	stateSinkObject.Save(12, &i.isTTY)
 	stateSinkObject.Save(13, &i.savable)
 	stateSinkObject.Save(14, &i.queue)
-	stateSinkObject.Save(15, &i.haveBuf)
-	stateSinkObject.Save(16, &i.buf)
+	stateSinkObject.Save(15, &i.virtualOwner)
+	stateSinkObject.Save(16, &i.haveBuf)
+	stateSinkObject.Save(17, &i.buf)
 }
 
 // +checklocksignore
@@ -95,8 +131,9 @@ func (i *inode) StateLoad(stateSourceObject state.Source) {
 	stateSourceObject.Load(12, &i.isTTY)
 	stateSourceObject.Load(13, &i.savable)
 	stateSourceObject.Load(14, &i.queue)
-	stateSourceObject.Load(15, &i.haveBuf)
-	stateSourceObject.Load(16, &i.buf)
+	stateSourceObject.Load(15, &i.virtualOwner)
+	stateSourceObject.Load(16, &i.haveBuf)
+	stateSourceObject.Load(17, &i.buf)
 	stateSourceObject.AfterLoad(i.afterLoad)
 }
 
@@ -279,6 +316,7 @@ func (t *TTYFileDescription) StateLoad(stateSourceObject state.Source) {
 
 func init() {
 	state.Register((*ConnectedEndpointRefs)(nil))
+	state.Register((*virtualOwner)(nil))
 	state.Register((*inode)(nil))
 	state.Register((*filesystemType)(nil))
 	state.Register((*filesystem)(nil))
diff --git a/runsc/boot/loader.go b/runsc/boot/loader.go
index 165fb2ebb..5bfb15971 100644
--- a/runsc/boot/loader.go
+++ b/runsc/boot/loader.go
@@ -715,7 +715,7 @@ func (l *Loader) startContainer(spec *specs.Spec, conf *config.Config, cid strin
 			return fmt.Errorf("using TTY, stdios not expected: %d", l)
 		}
 		if ep.hostTTY == nil {
-			return fmt.Errorf("terminal enabled but no TTY provided (--console-socket possibly passed)")
+			return fmt.Errorf("terminal enabled but no TTY provided. Did you set --console-socket on create?")
 		}
 		info.stdioFDs = []*fd.FD{ep.hostTTY, ep.hostTTY, ep.hostTTY}
 		ep.hostTTY = nil
@@ -734,7 +734,7 @@ func (l *Loader) startContainer(spec *specs.Spec, conf *config.Config, cid strin
 func (l *Loader) createContainerProcess(root bool, cid string, info *containerInfo) (*kernel.ThreadGroup, *host.TTYFileOperations, *hostvfs2.TTYFileDescription, error) {
 	// Create the FD map, which will set stdin, stdout, and stderr.
 	ctx := info.procArgs.NewContext(l.k)
-	fdTable, ttyFile, ttyFileVFS2, err := createFDTable(ctx, info.spec.Process.Terminal, info.stdioFDs)
+	fdTable, ttyFile, ttyFileVFS2, err := createFDTable(ctx, info.spec.Process.Terminal, info.stdioFDs, info.spec.Process.User)
 	if err != nil {
 		return nil, nil, nil, fmt.Errorf("importing fds: %w", err)
 	}
@@ -980,7 +980,7 @@ func (l *Loader) executeAsync(args *control.ExecArgs) (kernel.ThreadID, error) {
 		tty:     ttyFile,
 		ttyVFS2: ttyFileVFS2,
 	}
-	log.Debugf("updated processes: %s", l.processes)
+	log.Debugf("updated processes: %v", l.processes)
 
 	return tgid, nil
 }
@@ -1024,7 +1024,7 @@ func (l *Loader) waitPID(tgid kernel.ThreadID, cid string, waitStatus *uint32) e
 
 		l.mu.Lock()
 		delete(l.processes, eid)
-		log.Debugf("updated processes (removal): %s", l.processes)
+		log.Debugf("updated processes (removal): %v", l.processes)
 		l.mu.Unlock()
 		return nil
 	}
@@ -1092,7 +1092,7 @@ func newRootNetworkNamespace(conf *config.Config, clock tcpip.Clock, uniqueID st
 		return inet.NewRootNamespace(s, creator), nil
 
 	default:
-		panic(fmt.Sprintf("invalid network configuration: %d", conf.Network))
+		panic(fmt.Sprintf("invalid network configuration: %v", conf.Network))
 	}
 
 }
@@ -1212,7 +1212,7 @@ func (l *Loader) signal(cid string, pid, signo int32, mode SignalDeliveryMode) e
 		return nil
 
 	default:
-		panic(fmt.Sprintf("unknown signal delivery mode %s", mode))
+		panic(fmt.Sprintf("unknown signal delivery mode %v", mode))
 	}
 }
 
@@ -1337,14 +1337,14 @@ func (l *Loader) ttyFromIDLocked(key execID) (*host.TTYFileOperations, *hostvfs2
 	return ep.tty, ep.ttyVFS2, nil
 }
 
-func createFDTable(ctx context.Context, console bool, stdioFDs []*fd.FD) (*kernel.FDTable, *host.TTYFileOperations, *hostvfs2.TTYFileDescription, error) {
+func createFDTable(ctx context.Context, console bool, stdioFDs []*fd.FD, user specs.User) (*kernel.FDTable, *host.TTYFileOperations, *hostvfs2.TTYFileDescription, error) {
 	if len(stdioFDs) != 3 {
 		return nil, nil, nil, fmt.Errorf("stdioFDs should contain exactly 3 FDs (stdin, stdout, and stderr), but %d FDs received", len(stdioFDs))
 	}
 
 	k := kernel.KernelFromContext(ctx)
 	fdTable := k.NewFDTable()
-	ttyFile, ttyFileVFS2, err := fdimport.Import(ctx, fdTable, console, stdioFDs)
+	ttyFile, ttyFileVFS2, err := fdimport.Import(ctx, fdTable, console, auth.KUID(user.UID), auth.KGID(user.GID), stdioFDs)
 	if err != nil {
 		fdTable.DecRef(ctx)
 		return nil, nil, nil, err
diff --git a/runsc/cmd/exec.go b/runsc/cmd/exec.go
index 242d474b8..2139fdf53 100644
--- a/runsc/cmd/exec.go
+++ b/runsc/cmd/exec.go
@@ -146,12 +146,12 @@ func (ex *Exec) Execute(_ context.Context, f *flag.FlagSet, args ...interface{})
 	if ex.detach {
 		return ex.execChildAndWait(waitStatus)
 	}
-	return ex.exec(c, e, waitStatus)
+	return ex.exec(conf, c, e, waitStatus)
 }
 
-func (ex *Exec) exec(c *container.Container, e *control.ExecArgs, waitStatus *unix.WaitStatus) subcommands.ExitStatus {
+func (ex *Exec) exec(conf *config.Config, c *container.Container, e *control.ExecArgs, waitStatus *unix.WaitStatus) subcommands.ExitStatus {
 	// Start the new process and get its pid.
-	pid, err := c.Execute(e)
+	pid, err := c.Execute(conf, e)
 	if err != nil {
 		return Errorf("executing processes for container: %v", err)
 	}
diff --git a/runsc/container/container.go b/runsc/container/container.go
index b789bc7da..213fbc771 100644
--- a/runsc/container/container.go
+++ b/runsc/container/container.go
@@ -310,7 +310,7 @@ func New(conf *config.Config, args Args) (*Container, error) {
 			defer tty.Close()
 		}
 
-		if err := c.Sandbox.CreateContainer(c.ID, tty); err != nil {
+		if err := c.Sandbox.CreateContainer(conf, c.ID, tty); err != nil {
 			return nil, err
 		}
 	}
@@ -480,13 +480,13 @@ func Run(conf *config.Config, args Args) (unix.WaitStatus, error) {
 
 // Execute runs the specified command in the container. It returns the PID of
 // the newly created process.
-func (c *Container) Execute(args *control.ExecArgs) (int32, error) {
+func (c *Container) Execute(conf *config.Config, args *control.ExecArgs) (int32, error) {
 	log.Debugf("Execute in container, cid: %s, args: %+v", c.ID, args)
 	if err := c.requireStatus("execute in", Created, Running); err != nil {
 		return 0, err
 	}
 	args.ContainerID = c.ID
-	return c.Sandbox.Execute(args)
+	return c.Sandbox.Execute(conf, args)
 }
 
 // Event returns events for the container.
@@ -910,6 +910,9 @@ func (c *Container) createGoferProcess(spec *specs.Spec, conf *config.Config, bu
 	binPath := specutils.ExePath
 	cmd := exec.Command(binPath, args...)
 	cmd.ExtraFiles = goferEnds
+
+	// Set Args[0] to make easier to spot the gofer process. Otherwise it's
+	// shown as `exe`.
 	cmd.Args[0] = "runsc-gofer"
 
 	if attached {
diff --git a/runsc/sandbox/sandbox.go b/runsc/sandbox/sandbox.go
index 9dea7c4d2..95b5d9615 100644
--- a/runsc/sandbox/sandbox.go
+++ b/runsc/sandbox/sandbox.go
@@ -65,6 +65,11 @@ type Sandbox struct {
 	// is not running.
 	Pid int `json:"pid"`
 
+	// UID is the user ID in the parent namespace that the sandbox is running as.
+	UID int `json:"uid"`
+	// GID is the group ID in the parent namespace that the sandbox is running as.
+	GID int `json:"gid"`
+
 	// Cgroup has the cgroup configuration for the sandbox.
 	Cgroup *cgroup.Cgroup `json:"cgroup"`
 
@@ -176,18 +181,22 @@ func New(conf *config.Config, args *Args) (*Sandbox, error) {
 }
 
 // CreateContainer creates a non-root container inside the sandbox.
-func (s *Sandbox) CreateContainer(cid string, tty *os.File) error {
+func (s *Sandbox) CreateContainer(conf *config.Config, cid string, tty *os.File) error {
 	log.Debugf("Create non-root container %q in sandbox %q, PID: %d", cid, s.ID, s.Pid)
-	sandboxConn, err := s.sandboxConnect()
-	if err != nil {
-		return fmt.Errorf("couldn't connect to sandbox: %v", err)
-	}
-	defer sandboxConn.Close()
 
 	var files []*os.File
 	if tty != nil {
 		files = []*os.File{tty}
 	}
+	if err := s.configureStdios(conf, files); err != nil {
+		return err
+	}
+
+	sandboxConn, err := s.sandboxConnect()
+	if err != nil {
+		return fmt.Errorf("couldn't connect to sandbox: %v", err)
+	}
+	defer sandboxConn.Close()
 
 	args := boot.CreateArgs{
 		CID:         cid,
@@ -225,6 +234,11 @@ func (s *Sandbox) StartRoot(spec *specs.Spec, conf *config.Config) error {
 // StartContainer starts running a non-root container inside the sandbox.
 func (s *Sandbox) StartContainer(spec *specs.Spec, conf *config.Config, cid string, stdios, goferFiles []*os.File) error {
 	log.Debugf("Start non-root container %q in sandbox %q, PID: %d", cid, s.ID, s.Pid)
+
+	if err := s.configureStdios(conf, stdios); err != nil {
+		return err
+	}
+
 	sandboxConn, err := s.sandboxConnect()
 	if err != nil {
 		return fmt.Errorf("couldn't connect to sandbox: %v", err)
@@ -318,8 +332,13 @@ func (s *Sandbox) NewCGroup() (*cgroup.Cgroup, error) {
 
 // Execute runs the specified command in the container. It returns the PID of
 // the newly created process.
-func (s *Sandbox) Execute(args *control.ExecArgs) (int32, error) {
+func (s *Sandbox) Execute(conf *config.Config, args *control.ExecArgs) (int32, error) {
 	log.Debugf("Executing new process in container %q in sandbox %q", args.ContainerID, s.ID)
+
+	if err := s.configureStdios(conf, args.Files); err != nil {
+		return 0, err
+	}
+
 	conn, err := s.sandboxConnect()
 	if err != nil {
 		return 0, s.connError(err)
@@ -505,6 +524,7 @@ func (s *Sandbox) createSandboxProcess(conf *config.Config, args *Args, startSyn
 	cmd.Stdin = nil
 	cmd.Stdout = nil
 	cmd.Stderr = nil
+	var stdios [3]*os.File
 
 	// If the console control socket file is provided, then create a new
 	// pty master/replica pair and set the TTY on the sandbox process.
@@ -525,11 +545,9 @@ func (s *Sandbox) createSandboxProcess(conf *config.Config, args *Args, startSyn
 		cmd.SysProcAttr.Ctty = nextFD
 
 		// Pass the tty as all stdio fds to sandbox.
-		for i := 0; i < 3; i++ {
-			cmd.ExtraFiles = append(cmd.ExtraFiles, tty)
-			cmd.Args = append(cmd.Args, "--stdio-fds="+strconv.Itoa(nextFD))
-			nextFD++
-		}
+		stdios[0] = tty
+		stdios[1] = tty
+		stdios[2] = tty
 
 		if conf.Debug {
 			// If debugging, send the boot process stdio to the
@@ -541,11 +559,9 @@ func (s *Sandbox) createSandboxProcess(conf *config.Config, args *Args, startSyn
 	} else {
 		// If not using a console, pass our current stdio as the
 		// container stdio via flags.
-		for _, f := range []*os.File{os.Stdin, os.Stdout, os.Stderr} {
-			cmd.ExtraFiles = append(cmd.ExtraFiles, f)
-			cmd.Args = append(cmd.Args, "--stdio-fds="+strconv.Itoa(nextFD))
-			nextFD++
-		}
+		stdios[0] = os.Stdin
+		stdios[1] = os.Stdout
+		stdios[2] = os.Stderr
 
 		if conf.Debug {
 			// If debugging, send the boot process stdio to the
@@ -595,6 +611,10 @@ func (s *Sandbox) createSandboxProcess(conf *config.Config, args *Args, startSyn
 		nss = append(nss, specs.LinuxNamespace{Type: specs.NetworkNamespace})
 	}
 
+	// These are set to the uid/gid that the sandbox process will use.
+	s.UID = os.Getuid()
+	s.GID = os.Getgid()
+
 	// User namespace depends on the network type. Host network requires to run
 	// inside the user namespace specified in the spec or the current namespace
 	// if none is configured.
@@ -636,51 +656,49 @@ func (s *Sandbox) createSandboxProcess(conf *config.Config, args *Args, startSyn
 			const nobody = 65534
 			if conf.Rootless {
 				log.Infof("Rootless mode: sandbox will run as nobody inside user namespace, mapped to the current user, uid: %d, gid: %d", os.Getuid(), os.Getgid())
-				cmd.SysProcAttr.UidMappings = []syscall.SysProcIDMap{
-					{
-						ContainerID: nobody,
-						HostID:      os.Getuid(),
-						Size:        1,
-					},
-				}
-				cmd.SysProcAttr.GidMappings = []syscall.SysProcIDMap{
-					{
-						ContainerID: nobody,
-						HostID:      os.Getgid(),
-						Size:        1,
-					},
-				}
-
 			} else {
 				// Map nobody in the new namespace to nobody in the parent namespace.
-				//
-				// A sandbox process will construct an empty
-				// root for itself, so it has to have
-				// CAP_SYS_ADMIN and CAP_SYS_CHROOT capabilities.
-				cmd.SysProcAttr.UidMappings = []syscall.SysProcIDMap{
-					{
-						ContainerID: nobody,
-						HostID:      nobody,
-						Size:        1,
-					},
-				}
-				cmd.SysProcAttr.GidMappings = []syscall.SysProcIDMap{
-					{
-						ContainerID: nobody,
-						HostID:      nobody,
-						Size:        1,
-					},
-				}
+				s.UID = nobody
+				s.GID = nobody
 			}
 
 			// Set credentials to run as user and group nobody.
 			cmd.SysProcAttr.Credential = &syscall.Credential{Uid: nobody, Gid: nobody}
+			cmd.SysProcAttr.UidMappings = []syscall.SysProcIDMap{
+				{
+					ContainerID: nobody,
+					HostID:      s.UID,
+					Size:        1,
+				},
+			}
+			cmd.SysProcAttr.GidMappings = []syscall.SysProcIDMap{
+				{
+					ContainerID: nobody,
+					HostID:      s.GID,
+					Size:        1,
+				},
+			}
+
+			// A sandbox process will construct an empty root for itself, so it has
+			// to have CAP_SYS_ADMIN and CAP_SYS_CHROOT capabilities.
 			cmd.SysProcAttr.AmbientCaps = append(cmd.SysProcAttr.AmbientCaps, uintptr(capability.CAP_SYS_ADMIN), uintptr(capability.CAP_SYS_CHROOT))
+
 		} else {
 			return fmt.Errorf("can't run sandbox process as user nobody since we don't have CAP_SETUID or CAP_SETGID")
 		}
 	}
 
+	if err := s.configureStdios(conf, stdios[:]); err != nil {
+		return fmt.Errorf("configuring stdios: %w", err)
+	}
+	for _, file := range stdios {
+		cmd.ExtraFiles = append(cmd.ExtraFiles, file)
+		cmd.Args = append(cmd.Args, "--stdio-fds="+strconv.Itoa(nextFD))
+		nextFD++
+	}
+
+	// Set Args[0] to make easier to spot the sandbox process. Otherwise it's
+	// shown as `exe`.
 	cmd.Args[0] = "runsc-sandbox"
 
 	if s.Cgroup != nil {
@@ -1167,6 +1185,23 @@ func (s *Sandbox) waitForStopped() error {
 	return backoff.Retry(op, b)
 }
 
+// configureStdios change stdios ownership to give access to the sandbox
+// process. This may be skipped depending on the configuration.
+func (s *Sandbox) configureStdios(conf *config.Config, stdios []*os.File) error {
+	if conf.Rootless || conf.TestOnlyAllowRunAsCurrentUserWithoutChroot {
+		// Cannot change ownership without CAP_CHOWN.
+		return nil
+	}
+
+	for _, file := range stdios {
+		log.Debugf("Changing %q ownership to %d/%d", file.Name(), s.UID, s.GID)
+		if err := file.Chown(s.UID, s.GID); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
 // deviceFileForPlatform opens the device file for the given platform. If the
 // platform does not need a device file, then nil is returned.
 func deviceFileForPlatform(name string) (*os.File, error) {