PVF worker: Add seccomp restrictions (restrict networking) (#2009)

polkadot/node/core/pvf/src/prepare/worker_intf.rs

@@ -18,6 +18,7 @@
 
 use crate::{
 	metrics::Metrics,
+	security,
 	worker_intf::{
 		clear_worker_dir_path, framed_recv, framed_send, spawn_with_program_path, IdleWorker,
 		SpawnErr, WorkerDir, WorkerHandle, JOB_TIMEOUT_WALL_CLOCK_FACTOR,
@@ -126,7 +127,9 @@ pub async fn start_work(
 		pid,
 		|tmp_artifact_file, mut stream, worker_dir| async move {
 			let preparation_timeout = pvf.prep_timeout();
-			if let Err(err) = send_request(&mut stream, pvf).await {
+			let audit_log_file = security::AuditLogFile::try_open_and_seek_to_end().await;
+
+			if let Err(err) = send_request(&mut stream, pvf.clone()).await {
 				gum::warn!(
 					target: LOG_TARGET,
 					worker_pid = %pid,
@@ -150,7 +153,19 @@ pub async fn start_work(
 
 			match result {
 				// Received bytes from worker within the time limit.
-				Ok(Ok(prepare_result)) =>
+				Ok(Ok(prepare_result)) => {
+					// Check if any syscall violations occurred during the job. For now this is only
+					// informative, as we are not enforcing the seccomp policy yet.
+					for syscall in security::check_seccomp_violations_for_worker(audit_log_file, pid).await {
+						gum::error!(
+							target: LOG_TARGET,
+							worker_pid = %pid,
+							%syscall,
+							?pvf,
+							"A forbidden syscall was attempted! This is a violation of our seccomp security policy. Report an issue ASAP!"
+						);
+					}
+
 					handle_response(
 						metrics,
 						IdleWorker { stream, pid, worker_dir },
@@ -160,7 +175,8 @@ pub async fn start_work(
 						artifact_path,
 						preparation_timeout,
 					)
-					.await,
+					.await
+				},
 				Ok(Err(err)) => {
 					// Communication error within the time limit.
 					gum::warn!(
@@ -169,6 +185,21 @@ pub async fn start_work(
 						"failed to recv a prepare response: {:?}",
 						err,
 					);
+
+					// The worker died. Check if it was due to a seccomp violation.
+					//
+					// NOTE: Log, but don't change the outcome. Not all validators may have auditing
+					// enabled, so we don't want attackers to abuse a non-deterministic outcome.
+					for syscall in security::check_seccomp_violations_for_worker(audit_log_file, pid).await {
+						gum::error!(
+							target: LOG_TARGET,
+							worker_pid = %pid,
+							%syscall,
+							?pvf,
+							"A forbidden syscall was attempted! This is a violation of our seccomp security policy. Report an issue ASAP!"
+						);
+					}
+
 					Outcome::IoErr(err.to_string())
 				},
 				Err(_) => {