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C-WCOW: SecurityPolicy and sidecar fixes #2527

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fa9158d
C-WCOW: Use go channel
MahatiC Sep 24, 2025
f4d6807
C-WCOW: Move security context dir code
MahatiC Sep 25, 2025
d7e2efe
C-WCOW: Differentiate container cmdline
MahatiC Sep 25, 2025
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15 changes: 7 additions & 8 deletions internal/gcs-sidecar/bridge.go
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Original file line number Diff line number Diff line change
Expand Up @@ -33,7 +33,7 @@ import (
type Bridge struct {
mu sync.Mutex
pendingMu sync.Mutex
pending map[sequenceID]*prot.ContainerExecuteProcessResponse
pending map[sequenceID]chan *prot.ContainerExecuteProcessResponse

hostState *Host
// List of handlers for handling different rpc message requests.
Expand Down Expand Up @@ -83,7 +83,7 @@ type request struct {
func NewBridge(shimConn io.ReadWriteCloser, inboxGCSConn io.ReadWriteCloser, initialEnforcer securitypolicy.SecurityPolicyEnforcer, logWriter io.Writer) *Bridge {
hostState := NewHost(initialEnforcer)
return &Bridge{
pending: make(map[sequenceID]*prot.ContainerExecuteProcessResponse),
pending: make(map[sequenceID]chan *prot.ContainerExecuteProcessResponse),
rpcHandlerList: make(map[prot.RPCProc]HandlerFunc),
hostState: hostState,
shimConn: shimConn,
Expand Down Expand Up @@ -449,20 +449,19 @@ func (b *Bridge) ListenAndServeShimRequests() error {
_ = sendWithContextCancel(ctx, sidecarErrChan, recverr)
return
}
// If this is a ContainerExecuteProcessResponse, notify
// If this is a ContainerExecuteProcessResponse, notify the channel
const MsgExecuteProcessResponse prot.MsgType = prot.MsgTypeResponse | prot.MsgType(prot.RPCExecuteProcess)

if header.Type == MsgExecuteProcessResponse {
logrus.Tracef("Printing after inbox exec resp")
var procResp prot.ContainerExecuteProcessResponse
if err := json.Unmarshal(message, &procResp); err != nil {
logrus.Tracef("unmarshal failed")
log.G(ctx).WithError(err).Error("failed to unmarshal the request")
return
}

b.pendingMu.Lock()
if _, exists := b.pending[header.ID]; exists {
logrus.Tracef("Header ID in pending exists")
b.pending[header.ID] = &procResp
if ch, ok := b.pending[header.ID]; ok {
ch <- &procResp
}
b.pendingMu.Unlock()
}
Expand Down
105 changes: 29 additions & 76 deletions internal/gcs-sidecar/handlers.go
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Original file line number Diff line number Diff line change
Expand Up @@ -9,7 +9,6 @@ import (
"fmt"
"os"
"path/filepath"
"strings"
"time"

"github.com/Microsoft/hcsshim/hcn"
Expand All @@ -19,15 +18,12 @@ import (
hcsschema "github.com/Microsoft/hcsshim/internal/hcs/schema2"
"github.com/Microsoft/hcsshim/internal/log"
"github.com/Microsoft/hcsshim/internal/oc"
"github.com/Microsoft/hcsshim/internal/oci"
"github.com/Microsoft/hcsshim/internal/protocol/guestrequest"
"github.com/Microsoft/hcsshim/internal/protocol/guestresource"
"github.com/Microsoft/hcsshim/internal/windevice"
"github.com/Microsoft/hcsshim/pkg/annotations"
"github.com/Microsoft/hcsshim/pkg/cimfs"
"github.com/Microsoft/hcsshim/pkg/securitypolicy"
"github.com/pkg/errors"
"golang.org/x/sys/windows"
)

const (
Expand Down Expand Up @@ -89,11 +85,19 @@ func (b *Bridge) createContainer(req *request) (err error) {
if err != nil {
return fmt.Errorf("CreateContainer operation is denied by policy: %w", err)
}

if err := b.hostState.SetupSecurityContextDir(ctx, &spec); err != nil {
return err
}
commandLine := len(spec.Process.Args) > 0
c := &Container{
id: containerID,
spec: spec,
processes: make(map[uint32]*containerProcess),
id: containerID,
spec: spec,
processes: make(map[uint32]*containerProcess),
commandLine: commandLine,
commandLineExec: false,
}

log.G(ctx).Tracef("Adding ContainerID: %v", containerID)
if err := b.hostState.AddContainer(req.ctx, containerID, c); err != nil {
log.G(ctx).Tracef("Container exists in the map.")
Expand All @@ -104,49 +108,6 @@ func (b *Bridge) createContainer(req *request) (err error) {
b.hostState.RemoveContainer(ctx, containerID)
}
}(err)
// Write security policy, signed UVM reference and host AMD certificate to
// container's rootfs, so that application and sidecar containers can have
// access to it. The security policy is required by containers which need to
// extract init-time claims found in the security policy. The directory path
// containing the files is exposed via UVM_SECURITY_CONTEXT_DIR env var.
// It may be an error to have a security policy but not expose it to the
// container as in that case it can never be checked as correct by a verifier.
if oci.ParseAnnotationsBool(ctx, spec.Annotations, annotations.WCOWSecurityPolicyEnv, true) {
encodedPolicy := b.hostState.securityPolicyEnforcer.EncodedSecurityPolicy()
hostAMDCert := spec.Annotations[annotations.WCOWHostAMDCertificate]
if len(encodedPolicy) > 0 || len(hostAMDCert) > 0 || len(b.hostState.uvmReferenceInfo) > 0 {
// Use os.MkdirTemp to make sure that the directory is unique.
securityContextDir, err := os.MkdirTemp(spec.Root.Path, securitypolicy.SecurityContextDirTemplate)
if err != nil {
return fmt.Errorf("failed to create security context directory: %w", err)
}
// Make sure that files inside directory are readable
if err := os.Chmod(securityContextDir, 0755); err != nil {
return fmt.Errorf("failed to chmod security context directory: %w", err)
}

if len(encodedPolicy) > 0 {
if err := writeFileInDir(securityContextDir, securitypolicy.PolicyFilename, []byte(encodedPolicy), 0777); err != nil {
return fmt.Errorf("failed to write security policy: %w", err)
}
}
if len(b.hostState.uvmReferenceInfo) > 0 {
if err := writeFileInDir(securityContextDir, securitypolicy.ReferenceInfoFilename, []byte(b.hostState.uvmReferenceInfo), 0777); err != nil {
return fmt.Errorf("failed to write UVM reference info: %w", err)
}
}

if len(hostAMDCert) > 0 {
if err := writeFileInDir(securityContextDir, securitypolicy.HostAMDCertFilename, []byte(hostAMDCert), 0777); err != nil {
return fmt.Errorf("failed to write host AMD certificate: %w", err)
}
}

containerCtxDir := fmt.Sprintf("/%s", filepath.Base(securityContextDir))
secCtxEnv := fmt.Sprintf("UVM_SECURITY_CONTEXT_DIR=%s", containerCtxDir)
spec.Process.Env = append(spec.Process.Env, secCtxEnv)
}
}

// Strip the spec field
hostedSystemBytes, err := json.Marshal(cwcowHostedSystem)
Expand Down Expand Up @@ -265,15 +226,6 @@ func (b *Bridge) shutdownForced(req *request) (err error) {
return nil
}

// escapeArgs makes a Windows-style escaped command line from a set of arguments.
func escapeArgs(args []string) string {
escapedArgs := make([]string, len(args))
for i, a := range args {
escapedArgs[i] = windows.EscapeArg(a)
}
return strings.Join(escapedArgs, " ")
}

func (b *Bridge) executeProcess(req *request) (err error) {
_, span := oc.StartSpan(req.ctx, "sidecar::executeProcess")
defer span.End()
Expand Down Expand Up @@ -313,15 +265,19 @@ func (b *Bridge) executeProcess(req *request) (err error) {
return fmt.Errorf("failed to get created container: %w", err)
}

// if this is an exec of Container command line, then it's already enforced
// during container creation, hence skip it here
containerCommandLine := escapeArgs(c.spec.Process.Args)
if processParams.CommandLine != containerCommandLine {
c.processesMutex.Lock()
isCreateExec := c.commandLine && !c.commandLineExec
if isCreateExec {
// if this is an exec of Container command line, then it's already enforced
// during container creation, hence skip it here
c.commandLineExec = true
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@anmaxvl anmaxvl Nov 12, 2025 •
edited
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is this basically "init process started" indicator? or rather "init process start attempted"

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@anmaxvl anmaxvl Nov 12, 2025

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also, is the assumption that no out of order exec requests will come?

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@MahatiC MahatiC Nov 12, 2025

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Requests are handled sequentially by gcs-sidecar. Also, isInitExec is a misnomer as it has nothing to do with init, I have changed the variable name. This is specifically to differentiate the exec at start container vs other exec processes.


}
c.processesMutex.Unlock()
if !isCreateExec {
user := securitypolicy.IDName{
Name: processParams.User,
}

log.G(req.ctx).Tracef("Enforcing policy on exec in container")
_, _, _, err = b.hostState.securityPolicyEnforcer.
EnforceExecInContainerPolicyV2(
Expand All @@ -339,9 +295,10 @@ func (b *Bridge) executeProcess(req *request) (err error) {
}
headerID := req.header.ID

// initiate process ID
// initiate exec process response channel
procRespCh := make(chan *prot.ContainerExecuteProcessResponse, 1)
b.pendingMu.Lock()
b.pending[headerID] = nil // nil means not yet received
b.pending[headerID] = procRespCh
b.pendingMu.Unlock()

defer func() {
Expand All @@ -354,13 +311,8 @@ func (b *Bridge) executeProcess(req *request) (err error) {
b.forwardRequestToGcs(req)

// fetch the process ID from response
deadline := time.Now().Add(5 * time.Second)
for time.Now().Before(deadline) {
log.G(req.ctx).Tracef("waiting for exec resp")
b.pendingMu.Lock()
resp := b.pending[headerID]
b.pendingMu.Unlock()

select {
case resp := <-procRespCh:
// capture the Process details, so that we can later enforce
// on the allowed signals on the Process
if resp != nil {
Expand All @@ -374,10 +326,11 @@ func (b *Bridge) executeProcess(req *request) (err error) {
}
return nil
}
time.Sleep(10 * time.Millisecond) // backoff
// Channel closed or received nil, treat as error
return errors.New("received nil exec response")
case <-time.After(5 * time.Second):
return errors.New("timed out waiting for exec response")
}

return errors.Wrap(err, "timedout waiting for exec response")
}
return nil
}
Expand Down
61 changes: 56 additions & 5 deletions internal/gcs-sidecar/host.go
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Original file line number Diff line number Diff line change
Expand Up @@ -20,10 +20,12 @@ import (
hcsschema "github.com/Microsoft/hcsshim/internal/hcs/schema2"
"github.com/Microsoft/hcsshim/internal/log"
"github.com/Microsoft/hcsshim/internal/logfields"
oci "github.com/Microsoft/hcsshim/internal/oci"
"github.com/Microsoft/hcsshim/internal/protocol/guestresource"
"github.com/Microsoft/hcsshim/internal/pspdriver"
"github.com/Microsoft/hcsshim/pkg/annotations"
"github.com/Microsoft/hcsshim/pkg/securitypolicy"
oci "github.com/opencontainers/runtime-spec/specs-go"
specs "github.com/opencontainers/runtime-spec/specs-go"
"github.com/pkg/errors"
"github.com/sirupsen/logrus"
)
Expand All @@ -40,10 +42,12 @@ type Host struct {
}

type Container struct {
id string
spec oci.Spec
processesMutex sync.Mutex
processes map[uint32]*containerProcess
id string
spec specs.Spec
processesMutex sync.Mutex
processes map[uint32]*containerProcess
commandLine bool
commandLineExec bool
}

// Process is a struct that defines the lifetime and operations associated with
Expand All @@ -63,6 +67,53 @@ func NewHost(initialEnforcer securitypolicy.SecurityPolicyEnforcer) *Host {
}
}

// Write security policy, signed UVM reference and host AMD certificate to
// container's rootfs, so that application and sidecar containers can have
// access to it. The security policy is required by containers which need to
// extract init-time claims found in the security policy. The directory path
// containing the files is exposed via UVM_SECURITY_CONTEXT_DIR env var.
// It may be an error to have a security policy but not expose it to the
// container as in that case it can never be checked as correct by a verifier.
func (h *Host) SetupSecurityContextDir(ctx context.Context, spec *specs.Spec) error {
if oci.ParseAnnotationsBool(ctx, spec.Annotations, annotations.WCOWSecurityPolicyEnv, true) {
encodedPolicy := h.securityPolicyEnforcer.EncodedSecurityPolicy()
hostAMDCert := spec.Annotations[annotations.WCOWHostAMDCertificate]
if len(encodedPolicy) > 0 || len(hostAMDCert) > 0 || len(h.uvmReferenceInfo) > 0 {
// Use os.MkdirTemp to make sure that the directory is unique.
securityContextDir, err := os.MkdirTemp(spec.Root.Path, securitypolicy.SecurityContextDirTemplate)
if err != nil {
return fmt.Errorf("failed to create security context directory: %w", err)
}
// Make sure that files inside directory are readable
if err := os.Chmod(securityContextDir, 0755); err != nil {
return fmt.Errorf("failed to chmod security context directory: %w", err)
}

if len(encodedPolicy) > 0 {
if err := writeFileInDir(securityContextDir, securitypolicy.PolicyFilename, []byte(encodedPolicy), 0777); err != nil {
return fmt.Errorf("failed to write security policy: %w", err)
}
}
if len(h.uvmReferenceInfo) > 0 {
if err := writeFileInDir(securityContextDir, securitypolicy.ReferenceInfoFilename, []byte(h.uvmReferenceInfo), 0777); err != nil {
return fmt.Errorf("failed to write UVM reference info: %w", err)
}
}

if len(hostAMDCert) > 0 {
if err := writeFileInDir(securityContextDir, securitypolicy.HostAMDCertFilename, []byte(hostAMDCert), 0777); err != nil {
return fmt.Errorf("failed to write host AMD certificate: %w", err)
}
}

containerCtxDir := fmt.Sprintf("/%s", filepath.Base(securityContextDir))
secCtxEnv := fmt.Sprintf("UVM_SECURITY_CONTEXT_DIR=%s", containerCtxDir)
spec.Process.Env = append(spec.Process.Env, secCtxEnv)
}
}
return nil
}

// InjectFragment extends current security policy with additional constraints
// from the incoming fragment. Note that it is base64 encoded over the bridge/
//
Expand Down