hst: optionally cover /run/ early

This works around awkward root permissions.

Signed-off-by: Ophestra <cat@gensokyo.uk>

hst/container.go

@@ -69,6 +69,8 @@ const (
 	// FDevice mount /dev/ from the init mount namespace as is in the container
 	// mount namespace.
 	FDevice
+	// FCoverRun covers /run/ in the container mount namespace early.
+	FCoverRun
 
 	// FShareRuntime shares XDG_RUNTIME_DIR between containers under the same identity.
 	FShareRuntime
@@ -101,6 +103,8 @@ func (flags Flags) String() string {
 		return "mapuid"
 	case FDevice:
 		return "device"
+	case FCoverRun:
+		return "cover_run"
 	case FShareRuntime:
 		return "runtime"
 	case FShareTmpdir:
@@ -196,6 +200,8 @@ type containerConfigJSON = struct {
 
 	// Corresponds to [FDevice].
 	Device bool `json:"device,omitempty"`
+	// Corresponds to [FCoverRun].
+	CoverRun bool `json:"cover_run,omitempty"`
 
 	// Corresponds to [FShareRuntime].
 	ShareRuntime bool `json:"share_runtime,omitempty"`
@@ -219,6 +225,7 @@ func (c *ContainerConfig) MarshalJSON() ([]byte, error) {
 		Multiarch:     c.Flags&FMultiarch != 0,
 		MapRealUID:    c.Flags&FMapRealUID != 0,
 		Device:        c.Flags&FDevice != 0,
+		CoverRun:      c.Flags&FCoverRun != 0,
 		ShareRuntime:  c.Flags&FShareRuntime != 0,
 		ShareTmpdir:   c.Flags&FShareTmpdir != 0,
 	})
@@ -262,6 +269,9 @@ func (c *ContainerConfig) UnmarshalJSON(data []byte) error {
 	if v.Device {
 		c.Flags |= FDevice
 	}
+	if v.CoverRun {
+		c.Flags |= FCoverRun
+	}
 	if v.ShareRuntime {
 		c.Flags |= FShareRuntime
 	}

hst/container_test.go

@@ -21,8 +21,8 @@ func TestFlagsString(t *testing.T) {
 	}{
 		{"none", 0, "none"},
 		{"none high", hst.FAll + 1, "none"},
-		{"all", hst.FAll, "multiarch, compat, devel, userns, net, abstract, tty, mapuid, device, runtime, tmpdir"},
-		{"all high", math.MaxUint, "multiarch, compat, devel, userns, net, abstract, tty, mapuid, device, runtime, tmpdir"},
+		{"all", hst.FAll, "multiarch, compat, devel, userns, net, abstract, tty, mapuid, device, cover_run, runtime, tmpdir"},
+		{"all high", math.MaxUint, "multiarch, compat, devel, userns, net, abstract, tty, mapuid, device, cover_run, runtime, tmpdir"},
 	}
 	for _, tc := range testCases {
 		t.Run(tc.name, func(t *testing.T) {
@@ -53,7 +53,7 @@ func TestContainerConfig(t *testing.T) {
 		{"hostnet hostabstract mapuid", &hst.ContainerConfig{Flags: hst.FHostNet | hst.FHostAbstract | hst.FMapRealUID},
 			`{"env":null,"filesystem":null,"shell":null,"home":null,"args":null,"host_net":true,"host_abstract":true,"map_real_uid":true}`},
 		{"all", &hst.ContainerConfig{Flags: hst.FAll},
-			`{"env":null,"filesystem":null,"shell":null,"home":null,"args":null,"seccomp_compat":true,"devel":true,"userns":true,"host_net":true,"host_abstract":true,"tty":true,"multiarch":true,"map_real_uid":true,"device":true,"share_runtime":true,"share_tmpdir":true}`},
+			`{"env":null,"filesystem":null,"shell":null,"home":null,"args":null,"seccomp_compat":true,"devel":true,"userns":true,"host_net":true,"host_abstract":true,"tty":true,"multiarch":true,"map_real_uid":true,"device":true,"cover_run":true,"share_runtime":true,"share_tmpdir":true}`},
 	}
 
 	for _, tc := range testCases {

hst/hst_test.go

@@ -245,6 +245,7 @@ func TestTemplate(t *testing.T) {
 		"multiarch": true,
 		"map_real_uid": true,
 		"device": true,
+		"cover_run": true,
 		"share_runtime": true,
 		"share_tmpdir": true
 	}