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fix(runtime): bind-mount file secrets to target paths in Apple container runtime #172

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fix(runtime): bind-mount file secrets to target paths in Apple container runtime #172

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73a1a3f
fix(runtime): bind-mount file secrets to target paths in Apple contai…
ryancee Apr 19, 2026
68a1bfc
fix(runtime): clarify MetadataInterception comment for Apple runtime
ryancee Apr 19, 2026
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22 changes: 12 additions & 10 deletions pkg/runtime/apple_container.go
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Original file line number Diff line number Diff line change
Expand Up @@ -18,9 +18,7 @@ import (
"context"
"encoding/json"
"fmt"
"os"
"os/exec"
"path/filepath"
"strings"
"time"

Expand Down Expand Up @@ -48,11 +46,14 @@ func (r *AppleContainerRuntime) ExecUser() string {

func (r *AppleContainerRuntime) Run(ctx context.Context, config RunConfig) (string, error) {
// Stage file, variable, and secret-map secrets before building args
var secretMountSpecs []string
if config.HomeDir != "" && len(config.ResolvedSecrets) > 0 {
containerHome := util.GetHomeDir(config.UnixUsername)
if _, err := writeFileSecrets(config.HomeDir, containerHome, config.ResolvedSecrets); err != nil {
mounts, err := writeFileSecrets(config.HomeDir, containerHome, config.ResolvedSecrets)
if err != nil {
return "", fmt.Errorf("failed to stage file secrets: %w", err)
}
secretMountSpecs = mounts
if err := writeVariableSecrets(config.HomeDir, config.ResolvedSecrets); err != nil {
return "", fmt.Errorf("failed to write variable secrets: %w", err)
}
Expand All @@ -66,6 +67,10 @@ func (r *AppleContainerRuntime) Run(ctx context.Context, config RunConfig) (stri
config.Env = append(config.Env, telemetryGCPCredentialsEnvVar+"="+credPath)
}

// Apple container runtime does not support Linux capabilities (--cap-add).
// Metadata interception relies on GCE_METADATA_HOST env var instead of iptables.
config.MetadataInterception = false

@gemini-code-assist gemini-code-assist Bot Apr 19, 2026

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medium

The comment mentions that metadata interception relies on the GCE_METADATA_HOST environment variable instead of iptables. However, the code only disables MetadataInterception (to avoid the unsupported --cap-add NET_ADMIN flag) but does not appear to set the GCE_METADATA_HOST variable. If the runtime is expected to provide this alternative interception mechanism, consider injecting the environment variable into config.Env here.

@ryancee ryancee Apr 19, 2026

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Good catch. GCE_METADATA_HOST and GCE_METADATA_ROOT are already injected into the agent env by the broker (runtimebroker/start_context.go) when in assign/block metadata modes — no need to set them here. The original comment was just misleading. Updated it in 68a1bfc to accurately describe the trade-off: iptables interception is unavailable on Apple, so only apps honouring the standard env vars will reach the scion metadata server; apps that hardcode metadata.google.internal won't be intercepted.


args, err := buildCommonRunArgs(config)
if err != nil {
return "", err
Expand Down Expand Up @@ -109,13 +114,10 @@ func (r *AppleContainerRuntime) Run(ctx context.Context, config RunConfig) (stri
// Skip the original 'run', '-d', and '-i' from buildCommonRunArgs (indices 0, 1, 2)
newArgs = append(newArgs, args[3:]...)

// Insert secrets staging directory volume before the image so it is treated
// as a container flag rather than an argument to the container command.
if config.HomeDir != "" && len(config.ResolvedSecrets) > 0 {
secretsDir := filepath.Join(filepath.Dir(config.HomeDir), "secrets")
if _, err := os.Stat(secretsDir); err == nil {
newArgs = insertVolumeFlags(newArgs, config.Image, []string{secretsDir + ":/run/scion-secrets:ro"})
}
// Insert file secret bind-mounts before the image so they are treated as
// container flags rather than arguments to the container command.
if len(secretMountSpecs) > 0 {
newArgs = insertVolumeFlags(newArgs, config.Image, secretMountSpecs)
}

WriteRuntimeDebugFile(config, r.Command, newArgs)
Expand Down