Plumb VFS2 inside the Sentry

- Added fsbridge package with interface that can be used to open
  and read from VFS1 and VFS2 files.
- Converted ELF loader to use fsbridge
- Added VFS2 types to FSContext
- Added vfs.MountNamespace to ThreadGroup

Updates #1623

PiperOrigin-RevId: 295183950

1 files changed, 28 insertions, 0 deletions

diff --git a/pkg/sentry/strace/strace.go b/pkg/sentry/strace/strace.go
index a796b2396..46cb2a1cc 100644
--- a/pkg/sentry/strace/strace.go
+++ b/pkg/sentry/strace/strace.go
@@ -141,6 +141,10 @@ func path(t *kernel.Task, addr usermem.Addr) string {
 }
 
 func fd(t *kernel.Task, fd int32) string {
+	if kernel.VFS2Enabled {
+		return fdVFS2(t, fd)
+	}
+
 	root := t.FSContext().RootDirectory()
 	if root != nil {
 		defer root.DecRef()
@@ -169,6 +173,30 @@ func fd(t *kernel.Task, fd int32) string {
 	return fmt.Sprintf("%#x %s", fd, name)
 }
 
+func fdVFS2(t *kernel.Task, fd int32) string {
+	root := t.FSContext().RootDirectoryVFS2()
+	defer root.DecRef()
+
+	vfsObj := root.Mount().Filesystem().VirtualFilesystem()
+	if fd == linux.AT_FDCWD {
+		wd := t.FSContext().WorkingDirectoryVFS2()
+		defer wd.DecRef()
+
+		name, _ := vfsObj.PathnameWithDeleted(t, root, wd)
+		return fmt.Sprintf("AT_FDCWD %s", name)
+	}
+
+	file := t.GetFileVFS2(fd)
+	if file == nil {
+		// Cast FD to uint64 to avoid printing negative hex.
+		return fmt.Sprintf("%#x (bad FD)", uint64(fd))
+	}
+	defer file.DecRef()
+
+	name, _ := vfsObj.PathnameWithDeleted(t, root, file.VirtualDentry())
+	return fmt.Sprintf("%#x %s", fd, name)
+}
+
 func fdpair(t *kernel.Task, addr usermem.Addr) string {
 	var fds [2]int32
 	_, err := t.CopyIn(addr, &fds)