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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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34 changes: 33 additions & 1 deletion pkg/cdi/container-edits.go
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Original file line number Diff line number Diff line change
Expand Up @@ -114,9 +114,18 @@ func (e *ContainerEdits) Apply(spec *oci.Spec) error {
}

if len(e.Mounts) > 0 {
var (
uids []oci.LinuxIDMapping
gids []oci.LinuxIDMapping
)

if specHasUserNamespace(spec) {
uids = cloneIDMappings(spec.Linux.UIDMappings)
gids = cloneIDMappings(spec.Linux.GIDMappings)
}
for _, m := range e.Mounts {
specgen.RemoveMount(m.ContainerPath)
specgen.AddMount((&Mount{m}).toOCI())
specgen.AddMount((&Mount{m}).toOCI(withMountIDMappings(uids, gids)))
}
sortMounts(&specgen)
}
Expand Down Expand Up @@ -389,3 +398,26 @@ 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
}

// cloneIDMappings clones a slice of OCI LinuxIDMappings.
func cloneIDMappings(mappings []oci.LinuxIDMapping) []oci.LinuxIDMapping {
if mappings == nil {
return nil
}
clone := make([]oci.LinuxIDMapping, len(mappings))
copy(clone, mappings)
return clone
}
97 changes: 97 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 @@ -687,6 +687,103 @@ 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",
},
},
},
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",
UIDMappings: []oci.LinuxIDMapping{
{
ContainerID: 0,
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@elezar elezar Oct 20, 2025

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When is ContainerID non-zero?

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@klihub klihub Oct 20, 2025

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Do you mean in practice ? In principle, one could set up arbitrary mappings with multiple ranges which is possible, but in practice I think you'll only see a single range and starting (in the container) with 0, because that's what this is primarily used for. But from the OCI Spec point of view, nothing dictates any range or sub-range to start (in the container) at 0.

HostID: 1000,
Size: 999,
},
},
GIDMappings: []oci.LinuxIDMapping{
{
ContainerID: 0,
HostID: 2000,
Size: 777,
},
},
},
},
},
},
} {
t.Run(tc.name, func(t *testing.T) {
edits := ContainerEdits{tc.edits}
Expand Down
23 changes: 21 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 +30,33 @@ func (h *Hook) toOCI() spec.Hook {
}
}

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

// withMountIDMappings adds UID and GID mappings for the given mount.
func withMountIDMappings(uid, gid []spec.LinuxIDMapping) ociMountOption {
return func(m *spec.Mount) {
if uid != nil {
m.UIDMappings = uid
}
if gid != nil {
m.GIDMappings = gid
}
}
}

// 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