Correctly implement magic symlinks in VFS2 procfs.

Updates #1195

PiperOrigin-RevId: 305143567

3 files changed, 33 insertions, 0 deletions

diff --git a/pkg/sentry/fsimpl/proc/task_fds.go b/pkg/sentry/fsimpl/proc/task_fds.go
index 76bfc5307..9c8656b28 100644
--- a/pkg/sentry/fsimpl/proc/task_fds.go
+++ b/pkg/sentry/fsimpl/proc/task_fds.go
@@ -196,6 +196,12 @@ func (s *fdSymlink) Readlink(ctx context.Context) (string, error) {
 	return vfsObj.PathnameWithDeleted(ctx, root, s.file.VirtualDentry())
 }
 
+func (s *fdSymlink) Getlink(ctx context.Context) (vfs.VirtualDentry, string, error) {
+	vd := s.file.VirtualDentry()
+	vd.IncRef()
+	return vd, "", nil
+}
+
 func (s *fdSymlink) DecRef() {
 	s.AtomicRefCount.DecRefWithDestructor(func() {
 		s.Destroy()
diff --git a/pkg/sentry/fsimpl/proc/task_files.go b/pkg/sentry/fsimpl/proc/task_files.go
index df0d1bcc5..88ea6a6d8 100644
--- a/pkg/sentry/fsimpl/proc/task_files.go
+++ b/pkg/sentry/fsimpl/proc/task_files.go
@@ -610,6 +610,23 @@ func (s *exeSymlink) Readlink(ctx context.Context) (string, error) {
 	return exec.PathnameWithDeleted(ctx), nil
 }
 
+// Getlink implements kernfs.Inode.Getlink.
+func (s *exeSymlink) Getlink(ctx context.Context) (vfs.VirtualDentry, string, error) {
+	if !kernel.ContextCanTrace(ctx, s.task, false) {
+		return vfs.VirtualDentry{}, "", syserror.EACCES
+	}
+
+	exec, err := s.executable()
+	if err != nil {
+		return vfs.VirtualDentry{}, "", err
+	}
+	defer exec.DecRef()
+
+	vd := exec.(*fsbridge.VFSFile).FileDescription().VirtualDentry()
+	vd.IncRef()
+	return vd, "", nil
+}
+
 func (s *exeSymlink) executable() (file fsbridge.File, err error) {
 	s.task.WithMuLocked(func(t *kernel.Task) {
 		mm := t.MemoryManager()
diff --git a/pkg/sentry/fsimpl/proc/tasks_files.go b/pkg/sentry/fsimpl/proc/tasks_files.go
index 882c1981e..4621e2de0 100644
--- a/pkg/sentry/fsimpl/proc/tasks_files.go
+++ b/pkg/sentry/fsimpl/proc/tasks_files.go
@@ -63,6 +63,11 @@ func (s *selfSymlink) Readlink(ctx context.Context) (string, error) {
 	return strconv.FormatUint(uint64(tgid), 10), nil
 }
 
+func (s *selfSymlink) Getlink(ctx context.Context) (vfs.VirtualDentry, string, error) {
+	target, err := s.Readlink(ctx)
+	return vfs.VirtualDentry{}, target, err
+}
+
 // SetStat implements Inode.SetStat not allowing inode attributes to be changed.
 func (*selfSymlink) SetStat(context.Context, *vfs.Filesystem, *auth.Credentials, vfs.SetStatOptions) error {
 	return syserror.EPERM
@@ -101,6 +106,11 @@ func (s *threadSelfSymlink) Readlink(ctx context.Context) (string, error) {
 	return fmt.Sprintf("%d/task/%d", tgid, tid), nil
 }
 
+func (s *threadSelfSymlink) Getlink(ctx context.Context) (vfs.VirtualDentry, string, error) {
+	target, err := s.Readlink(ctx)
+	return vfs.VirtualDentry{}, target, err
+}
+
 // SetStat implements Inode.SetStat not allowing inode attributes to be changed.
 func (*threadSelfSymlink) SetStat(context.Context, *vfs.Filesystem, *auth.Credentials, vfs.SetStatOptions) error {
 	return syserror.EPERM