ci: add lint to forbid the usage of os.Create

os.Create is shorthand for open(O_CREAT|O_TRUNC) *without* O_EXCL, which
is incredibly unsafe for us to do when interacting with a container
rootfs (especially before pivot_root) as an attacker could swap the
target path with a symlink that points to the host filesystem, causing
us to delete the contents of or create host files.

We did have a similar bug in CVE-2024-45310, but in that case we
(luckily) didn't have O_TRUNC set which avoided the worst possible case.
However, os.Create does set O_TRUNC and we were using it in scenarios
that may have been exploitable.

Because of how easy it us for us to accidentally introduce this kind of
bug, we should simply not allow the usage of os.Create in our entire
codebase.

Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>

libcontainer/criu_linux.go

@@ -1077,7 +1077,7 @@ func (c *Container) criuNotifications(resp *criurpc.CriuResp, process *Process,
 	logrus.Debugf("notify: %s\n", script)
 	switch script {
 	case "post-dump":
-		f, err := os.Create(filepath.Join(c.stateDir, "checkpoint"))
+		f, err := os.Create(filepath.Join(c.stateDir, "checkpoint")) //nolint:forbidigo // this is a host-side operation in a runc-controlled directory
 		if err != nil {
 			return err
 		}