Add support for container kernel capabilities (#716)

This patch adds two new command-line flags to specify one or
more kernel capabilities to add or remove from the workflow
containers.

The command-line flag `--container-cap-add` allows for adding
specific capabilities on the workflow containers; where as,

The command-line flag `--container-cap-drop` allows for removing
specific capabilities on the workflow containers.

This was developed to specifically be able to add `SYS_PTRACE`
to a workflow I maintain. It involves using this capability to
monitor a make build, to then build a compilation database.

Signed-off-by: Joseph Benden <joe@benden.us>

pkg/container/docker_run.go

@@ -63,7 +63,7 @@ type FileEntry struct {
 
 // Container for managing docker run containers
 type Container interface {
-	Create() common.Executor
+	Create(capAdd []string, capDrop []string) common.Executor
 	Copy(destPath string, files ...*FileEntry) common.Executor
 	CopyDir(destPath string, srcPath string, useGitIgnore bool) common.Executor
 	Pull(forcePull bool) common.Executor
@@ -100,14 +100,14 @@ func supportsContainerImagePlatform(cli *client.Client) bool {
 	return constraint.Check(sv)
 }
 
-func (cr *containerReference) Create() common.Executor {
+func (cr *containerReference) Create(capAdd []string, capDrop []string) common.Executor {
 	return common.
 		NewDebugExecutor("%sdocker create image=%s platform=%s entrypoint=%+q cmd=%+q", logPrefix, cr.input.Image, cr.input.Platform, cr.input.Entrypoint, cr.input.Cmd).
 		Then(
 			common.NewPipelineExecutor(
 				cr.connect(),
 				cr.find(),
-				cr.create(),
+				cr.create(capAdd, capDrop),
 			).IfNot(common.Dryrun),
 		)
 }
@@ -274,7 +274,7 @@ func (cr *containerReference) remove() common.Executor {
 	}
 }
 
-func (cr *containerReference) create() common.Executor {
+func (cr *containerReference) create(capAdd []string, capDrop []string) common.Executor {
 	return func(ctx context.Context) error {
 		if cr.id != "" {
 			return nil
@@ -315,6 +315,8 @@ func (cr *containerReference) create() common.Executor {
 			}
 		}
 		resp, err := cr.cli.ContainerCreate(ctx, config, &container.HostConfig{
+			CapAdd:      capAdd,
+			CapDrop:     capDrop,
 			Binds:       input.Binds,
 			Mounts:      mounts,
 			NetworkMode: container.NetworkMode(input.NetworkMode),

pkg/runner/run_context.go

@@ -148,7 +148,7 @@ func (rc *RunContext) startJobContainer() common.Executor {
 		return common.NewPipelineExecutor(
 			rc.JobContainer.Pull(rc.Config.ForcePull),
 			rc.stopJobContainer(),
-			rc.JobContainer.Create(),
+			rc.JobContainer.Create(rc.Config.ContainerCapAdd, rc.Config.ContainerCapDrop),
 			rc.JobContainer.Start(false),
 			rc.JobContainer.UpdateFromEnv("/etc/environment", &rc.Env),
 			rc.JobContainer.Exec([]string{"mkdir", "-m", "0777", "-p", ActPath}, rc.Env, "root"),

pkg/runner/runner.go

@@ -40,6 +40,8 @@ type Config struct {
 	ContainerDaemonSocket string            // Path to Docker daemon socket
 	UseGitIgnore          bool              // controls if paths in .gitignore should not be copied into container, default true
 	GitHubInstance        string            // GitHub instance to use, default "github.com"
+	ContainerCapAdd       []string          // list of kernel capabilities to add to the containers
+	ContainerCapDrop      []string          // list of kernel capabilities to remove from the containers
 }
 
 // Resolves the equivalent host path inside the container

pkg/runner/step_context.go

@@ -299,7 +299,7 @@ func (sc *StepContext) runUsesContainer() common.Executor {
 		return common.NewPipelineExecutor(
 			stepContainer.Pull(rc.Config.ForcePull),
 			stepContainer.Remove().IfBool(!rc.Config.ReuseContainers),
-			stepContainer.Create(),
+			stepContainer.Create(rc.Config.ContainerCapAdd, rc.Config.ContainerCapDrop),
 			stepContainer.Start(true),
 		).Finally(
 			stepContainer.Remove().IfBool(!rc.Config.ReuseContainers),
@@ -517,7 +517,7 @@ func (sc *StepContext) execAsDocker(ctx context.Context, action *model.Action, a
 		prepImage,
 		stepContainer.Pull(rc.Config.ForcePull),
 		stepContainer.Remove().IfBool(!rc.Config.ReuseContainers),
-		stepContainer.Create(),
+		stepContainer.Create(rc.Config.ContainerCapAdd, rc.Config.ContainerCapDrop),
 		stepContainer.Start(true),
 	).Finally(
 		stepContainer.Remove().IfBool(!rc.Config.ReuseContainers),