runsc: Make identity user mapping work for filesystem

runsc/cmd/gofer.go

@@ -17,6 +17,7 @@ package cmd
 import (
 	"context"
 	"encoding/json"
+	"encoding/binary"
 	"fmt"
 	"io"
 	"os"
@@ -64,6 +65,8 @@ var goferCaps = &specs.LinuxCapabilities{
 	Bounding:  caps,
 	Effective: caps,
 	Permitted: caps,
+	Inheritable: caps,
+	Ambient: caps,
 }
 
 var goferUdsOpenCaps = &specs.LinuxCapabilities{
@@ -818,6 +821,26 @@ func waitForFD(fd int, fdName string) error {
 	return nil
 }
 
+func waitForID(fd int, fdName string) (uint32, uint32, error) {
+	log.Debugf("Waiting on %s %d...", fdName, fd)
+	f := os.NewFile(uintptr(fd), fdName)
+	defer f.Close()
+
+	var uid uint32
+	var gid uint32
+	buf := make([]byte, 8)
+
+	if n,  err := f.Read(buf); n != 8 || err != nil {
+		e := fmt.Errorf("failed to convert to int:%v :%v", uid, err)
+		return 0, 0, e
+	}
+	uid = binary.BigEndian.Uint32(buf[0:4])
+	gid = binary.BigEndian.Uint32(buf[4:8])
+
+
+	return uid, gid, nil
+}
+
 // spawnProcMounter executes the /proc unmounter process.
 // It returns a function to wait on the proc unmounter process, which
 // should be called (via defer) in case of errors in order to clean up the
@@ -872,17 +895,22 @@ func (g *goferSyncFDs) syncUsernsForRootless() {
 //
 // Postcondition: All callers must re-exec themselves after this returns.
 func syncUsernsForRootless(fd int) {
-	if err := waitForFD(fd, "userns sync FD"); err != nil {
-		util.Fatalf("failed to sync on userns FD: %v", err)
+	var uid uint32
+	var gid uint32
+	var err error
+
+	if uid, gid, err = waitForID(fd, "userns sync FD"); err != nil {
+		util.Fatalf("failed to sync on userns FD:%v: %v %v", uid, gid, err)
 	}
 
+
 	// SETUID changes UID on the current system thread, so we have
 	// to re-execute current binary.
 	runtime.LockOSThread()
-	if _, _, errno := unix.RawSyscall(unix.SYS_SETUID, 0, 0, 0); errno != 0 {
+	if _, _, errno := unix.RawSyscall(unix.SYS_SETUID, uintptr(uid), 0, 0); errno != 0 {
 		util.Fatalf("failed to set UID: %v", errno)
 	}
-	if _, _, errno := unix.RawSyscall(unix.SYS_SETGID, 0, 0, 0); errno != 0 {
+	if _, _, errno := unix.RawSyscall(unix.SYS_SETGID, uintptr(gid), 0, 0); errno != 0 {
 		util.Fatalf("failed to set GID: %v", errno)
 	}
 }

runsc/container/container.go

@@ -1392,6 +1392,13 @@ func (c *Container) createGoferProcess(conf *config.Config, mountHints *boot.Pod
 		{Type: specs.UTSNamespace},
 	}
 
+	var gSyncFile *os.File
+	defer func() {
+		if gSyncFile != nil {
+			gSyncFile.Close()
+		}
+	}()
+
 	rootlessEUID := unix.Geteuid() != 0
 	// Setup any uid/gid mappings, and create or join the configured user
 	// namespace so the gofer's view of the filesystem aligns with the
@@ -1413,7 +1420,7 @@ func (c *Container) createGoferProcess(conf *config.Config, mountHints *boot.Pod
 		if err != nil {
 			return nil, nil, nil, nil, err
 		}
-		defer syncFile.Close()
+		gSyncFile = syncFile
 	}
 
 	// Create synchronization FD for chroot.
@@ -1459,6 +1466,13 @@ func (c *Container) createGoferProcess(conf *config.Config, mountHints *boot.Pod
 		return nil, nil, nil, nil, fmt.Errorf("creating gofer filestore files: %w", err)
 	}
 
+	if rootlessEUID {
+                chrootSyncSandEnd.Close()
+                if err := sandbox.SendIDToSandbox(gSyncFile, c.Spec); err != nil {
+                        return nil, nil, nil, nil,  err
+		}
+	}
+
 	return sandEnds, goferFilestores, devSandEnd, mountsSand, nil
 }
 

runsc/sandbox/sandbox.go

@@ -17,6 +17,7 @@ package sandbox
 
 import (
 	"context"
+	"encoding/binary"
 	"encoding/json"
 	"errors"
 	"fmt"
@@ -1030,6 +1031,13 @@ func (s *Sandbox) createSandboxProcess(conf *config.Config, args *Args, startSyn
 	// configured.
 	rootlessEUID := unix.Geteuid() != 0
 	setUserMappings := false
+	var gSyncFile *os.File
+        defer func() {
+                if gSyncFile != nil {
+                        gSyncFile.Close()
+                }
+        }()
+
 	if conf.Network == config.NetworkHost || conf.DirectFS {
 		if userns, ok := specutils.GetNS(specs.UserNamespace, args.Spec); ok {
 			log.Infof("Sandbox will be started in container's user namespace: %+v", userns)
@@ -1039,7 +1047,7 @@ func (s *Sandbox) createSandboxProcess(conf *config.Config, args *Args, startSyn
 				if err != nil {
 					return err
 				}
-				defer syncFile.Close()
+				gSyncFile = syncFile
 				setUserMappings = true
 			} else {
 				specutils.SetUIDGIDMappings(cmd, args.Spec)
@@ -1284,6 +1292,9 @@ func (s *Sandbox) createSandboxProcess(conf *config.Config, args *Args, startSyn
 		if err := SetUserMappings(args.Spec, cmd.Process.Pid); err != nil {
 			return err
 		}
+		if err := SendIDToSandbox(gSyncFile, args.Spec); err != nil {
+			return err
+		}
 	}
 
 	s.child = true
@@ -1293,6 +1304,60 @@ func (s *Sandbox) createSandboxProcess(conf *config.Config, args *Args, startSyn
 	return nil
 }
 
+// Send the UID & GID to the sandbox and gofer process
+// This UID & GID is the ID for container init process
+func SendIDToSandbox(syncFile *os.File, spec *specs.Spec) error {
+
+	specUID := uint32(spec.Process.User.UID)
+	specGID := uint32(spec.Process.User.GID)
+
+	euid := uint32(os.Geteuid())
+	egid := uint32(os.Getegid())
+
+	var cuid uint32
+	var cgid uint32
+	var uidFound, gidFound bool
+
+	// Find which container UID & GID the host user map to
+	for _, idMap := range spec.Linux.UIDMappings {
+		if euid >= idMap.HostID && euid < idMap.Size + idMap.HostID {
+			cuid = euid - idMap.HostID + idMap.ContainerID
+			uidFound = true
+			break
+		}
+	}
+
+	for _, idMap := range spec.Linux.GIDMappings {
+                if egid >= idMap.HostID && euid < idMap.Size + idMap.HostID  {
+                        cgid = egid - idMap.HostID + idMap.ContainerID
+			gidFound = true
+                        break
+                }
+        }
+
+	if !uidFound || !gidFound {
+		return fmt.Errorf("current host uid(%d) or gid(%d) has no mapping in container", euid, egid)
+	}
+
+	// Make sure the specified UID & GID is the same as the host user map to
+	if cuid != specUID {
+		return fmt.Errorf("host uid %d can't map to container uid %d, expected %d", euid, specUID, cuid)
+	}
+
+	if cgid != specGID {
+		return fmt.Errorf("host gid %d can't map to container gid %d, expected %d", egid, specGID, cgid)
+	}
+
+	buf := make([]byte, 8)
+	binary.BigEndian.PutUint32(buf[0:4], cuid)
+	binary.BigEndian.PutUint32(buf[4:8], cgid)
+	if _, err := syncFile.Write(buf); err != nil {
+		return fmt.Errorf("write uid&gid to sandbox error: %w", err)
+	}
+
+	return nil
+}
+
 // Wait waits for the containerized process to exit, and returns its WaitStatus.
 func (s *Sandbox) Wait(cid string) (unix.WaitStatus, error) {
 	log.Debugf("Waiting for container %q in sandbox %q", cid, s.ID)