linux: add /sys/fs/cgroup if /sys is a bind mount

if /sys is bind mounted from the host then also add an explicit mount
for /sys/fs/cgroup so that 'ro' is honored.

Signed-off-by: Giuseppe Scrivano <gscrivan@redhat.com>

pkg/specgen/generate/oci_linux.go

@@ -107,11 +107,19 @@ func SpecGenToOCI(ctx context.Context, s *specgen.SpecGenerator, rt *libpod.Runt
 		}
 		sysMnt := spec.Mount{
 			Destination: "/sys",
-			Type:        "bind", // should we use a constant for this, like createconfig?
+			Type:        "bind",
 			Source:      "/sys",
 			Options:     []string{"rprivate", "nosuid", "noexec", "nodev", r, "rbind"},
 		}
 		g.AddMount(sysMnt)
+		g.RemoveMount("/sys/fs/cgroup")
+		sysFsCgroupMnt := spec.Mount{
+			Destination: "/sys/fs/cgroup",
+			Type:        "bind",
+			Source:      "/sys/fs/cgroup",
+			Options:     []string{"rprivate", "nosuid", "noexec", "nodev", r, "rbind"},
+		}
+		g.AddMount(sysFsCgroupMnt)
 		if !s.Privileged && isRootless {
 			g.AddLinuxMaskedPaths("/sys/kernel")
 		}

test/system/030-run.bats

@@ -974,4 +974,9 @@ EOF
     run_podman 125 create --name "$randomname/" $IMAGE
 }
 
+@test "podman run --net=host --cgroupns=host with read only cgroupfs" {
+    # verify that the last /sys/fs/cgroup mount is read-only
+    run_podman run --net=host --cgroupns=host --rm $IMAGE sh -c "grep ' / /sys/fs/cgroup ' /proc/self/mountinfo | tail -n 1 | grep '/sys/fs/cgroup ro'"
+}
+
 # vim: filetype=sh