Fix: Check for errors in FUSE Readlink response.

The `fuse.Conn.Call` method can return a `fuse.Response` containing an error,
which needs to be checked via `res.Error()` before accessing the response data.

Reported-by: syzbot+5e1585f8a22c6e82884b@syzkaller.appspotmail.com
Co-authored-by: Lucas Manning <lucasmanning@google.com>
PiperOrigin-RevId: 824748103

Author: 2 people

pkg/sentry/fsimpl/fuse/inode.go

@@ -601,6 +601,9 @@ func (i *inode) Readlink(ctx context.Context, mnt *vfs.Mount) (string, error) {
 		if err != nil {
 			return "", err
 		}
+		if err := res.Error(); err != nil {
+			return "", err
+		}
 		i.link = string(res.data[res.hdr.SizeBytes():])
 		if !mnt.Options().ReadOnly {
 			i.attrTime = ktime.ZeroTime