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cdi: inject mount UID/GID mappings if user NS is in use. #288

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cdi: inject mount UID/GID mappings if user NS is in use. #288

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22 changes: 21 additions & 1 deletion pkg/cdi/container-edits.go
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Original file line number Diff line number Diff line change
Expand Up @@ -123,8 +123,15 @@ func (e *ContainerEdits) Apply(spec *oci.Spec) error {

if len(e.Mounts) > 0 {
for _, m := range e.Mounts {
mnt := &Mount{m}

specgen.RemoveMount(m.ContainerPath)
specgen.AddMount((&Mount{m}).toOCI())

if !specHasUserNamespace(spec) {
specgen.AddMount(mnt.toOCI())
} else {
specgen.AddMount(mnt.toOCI(withIDMapForBindMount()))
}
}
sortMounts(&specgen)
}
Expand Down Expand Up @@ -465,3 +472,16 @@ func (m orderedMounts) Swap(i, j int) {
func (m orderedMounts) parts(i int) int {
return strings.Count(filepath.Clean(m[i].Destination), string(os.PathSeparator))
}

// specHasUserNamespace returns true if the OCI Spec has a Linux UserNamespace.
func specHasUserNamespace(spec *oci.Spec) bool {
if spec == nil || spec.Linux == nil {
return false
}
for _, ns := range spec.Linux.Namespaces {
if ns.Type == oci.UserNamespace {
return true
}
}
return false
}
98 changes: 98 additions & 0 deletions pkg/cdi/container-edits_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -800,6 +800,104 @@ func TestApplyContainerEdits(t *testing.T) {
},
},
},
{
name: "mount added to container with Linux user namespace and uid/gid mappings",
spec: &oci.Spec{
Linux: &oci.Linux{
UIDMappings: []oci.LinuxIDMapping{
{
ContainerID: 0,
HostID: 1000,
Size: 999,
},
},
GIDMappings: []oci.LinuxIDMapping{
{
ContainerID: 0,
HostID: 2000,
Size: 777,
},
},
Namespaces: []oci.LinuxNamespace{
{
Type: oci.UserNamespace,
Path: "/foo/bar",
},
},
},
Mounts: []oci.Mount{
{
Source: "/some/host/path1",
Destination: "/dest/path/c",
},
{
Source: "/some/host/path2",
Destination: "/dest/path/b",
},
},
},
edits: &cdi.ContainerEdits{
Mounts: []*cdi.Mount{
{
HostPath: "/some/host/path3",
ContainerPath: "/dest/path/a",
Type: "bind",
},
{
HostPath: "/some/host/path4",
ContainerPath: "/dest/path/d",
Type: "bind",
Options: []string{"rbind"},
},
},
},
result: &oci.Spec{
Linux: &oci.Linux{
UIDMappings: []oci.LinuxIDMapping{
{
ContainerID: 0,
HostID: 1000,
Size: 999,
},
},
GIDMappings: []oci.LinuxIDMapping{
{
ContainerID: 0,
HostID: 2000,
Size: 777,
},
},
Namespaces: []oci.LinuxNamespace{
{
Type: oci.UserNamespace,
Path: "/foo/bar",
},
},
},
Mounts: []oci.Mount{
{
Source: "/some/host/path1",
Destination: "/dest/path/c",
},
{
Source: "/some/host/path2",
Destination: "/dest/path/b",
},
{
Source: "/some/host/path3",
Destination: "/dest/path/a",
Type: "bind",
Options: []string{"idmap"},
},
{
Source: "/some/host/path4",
Destination: "/dest/path/d",
Type: "bind",
Options: []string{"rbind", "ridmap"},
},
},
},
},
} {
t.Run(tc.name, func(t *testing.T) {
edits := ContainerEdits{tc.edits}
Expand Down
36 changes: 34 additions & 2 deletions pkg/cdi/oci.go
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Original file line number Diff line number Diff line change
Expand Up @@ -30,14 +30,46 @@ func (h *Hook) toOCI() spec.Hook {
}
}

// Additional OCI mount option to apply to injected mounts.
type ociMountOption func(*spec.Mount)

// withIDMapForBindMount adds any necessary ID mapping options for a bind mount.
func withIDMapForBindMount() ociMountOption {
return func(m *spec.Mount) {
option := ""
if m.Type == "bind" {
option = "idmap"
}

for _, o := range m.Options {
switch o {
case "idmap", "ridmap":
return
case "bind":
option = "idmap"
case "rbind":
option = "ridmap"
Comment on lines +49 to +51
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@elezar elezar Dec 11, 2025

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One thing here. The option that is applied depends on the ordering of the options. Should there be a difference?

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@klihub klihub Dec 11, 2025

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No. You shouldn't use both options, but neither runc nor crun will flag it an error if you do... if I read the code correctly. Also (again IIRTCC), they will behave differently. runc will interpret it as an rbind while crun will interpreting it according to whichever was specified last. So I think there is no obviously correct behavior for that corner case us here. If I can choose the less questionable one, I'd say I prefer a 'last option wins' approach.

}
}

if option != "" {
m.Options = append(m.Options, option)
}
}
}

// toOCI returns the opencontainers runtime Spec Mount for this Mount.
func (m *Mount) toOCI() spec.Mount {
return spec.Mount{
func (m *Mount) toOCI(options ...ociMountOption) spec.Mount {
om := spec.Mount{
Source: m.HostPath,
Destination: m.ContainerPath,
Options: m.Options,
Type: m.Type,
}
for _, o := range options {
o(&om)
}
return om
}

// toOCI returns the opencontainers runtime Spec LinuxDevice for this DeviceNode.
Expand Down