shim: Create pid-file with 0644 permissions

Fixes ae70213

In ae70213 the WritePidFile and WriteAddress functions were
changed to use AtomicFile instead of os.CreateFile. However,
AtomicFile creates a temporary file and then changes its permissions
with os.Chmod which alters the previously observed behavior of
os.CreateFile which takes the system's umask into account.

This means that on Linux-based systems these files suddenly
became world writable (containerd#9363). The address file has since been
removed, but pid-file was still created as world writable. This
commit explicitly requests 0644 permissions as even on systems
without default umask of 0022 there is no reason to have these
two files world writable.

Signed-off-by: Jaroslav Jindrak <[email protected]>

runtime/v2/shim/util.go

@@ -126,7 +126,7 @@ func WritePidFile(path string, pid int) error {
 	if err != nil {
 		return err
 	}
-	f, err := atomicfile.New(path, 0o666)
+	f, err := atomicfile.New(path, 0o644)
 	if err != nil {
 		return err
 	}