seccomp: skip redundant rules

libcontainer/seccomp/config.go

@@ -56,9 +56,7 @@ func ConvertStringToOperator(in string) (configs.Operator, error) {
 }
 
 // ConvertStringToAction converts a string into a Seccomp rule match action.
-// Actions use the names they are assigned in Libseccomp's header, though some
-// (notable, SCMP_ACT_TRACE) are not available in this implementation and will
-// return errors.
+// Actions use the names they are assigned in Libseccomp's header.
 // Attempting to convert a string that is not a valid action results in an
 // error.
 func ConvertStringToAction(in string) (configs.Action, error) {

libcontainer/seccomp/seccomp_linux.go

@@ -6,11 +6,12 @@ import (
 	"errors"
 	"fmt"
 
-	"github.com/opencontainers/runc/libcontainer/configs"
-	"github.com/opencontainers/runc/libcontainer/seccomp/patchbpf"
-
 	libseccomp "github.com/seccomp/libseccomp-golang"
+	"github.com/sirupsen/logrus"
 	"golang.org/x/sys/unix"
+
+	"github.com/opencontainers/runc/libcontainer/configs"
+	"github.com/opencontainers/runc/libcontainer/seccomp/patchbpf"
 )
 
 var (
@@ -67,7 +68,7 @@ func InitSeccomp(config *configs.Seccomp) error {
 		if call == nil {
 			return errors.New("encountered nil syscall while initializing Seccomp")
 		}
-		if err := matchCall(filter, call); err != nil {
+		if err := matchCall(filter, call, defaultAction); err != nil {
 			return err
 		}
 	}
@@ -142,7 +143,7 @@ func getCondition(arg *configs.Arg) (libseccomp.ScmpCondition, error) {
 }
 
 // Add a rule to match a single syscall
-func matchCall(filter *libseccomp.ScmpFilter, call *configs.Syscall) error {
+func matchCall(filter *libseccomp.ScmpFilter, call *configs.Syscall, defAct libseccomp.ScmpAction) error {
 	if call == nil || filter == nil {
 		return errors.New("cannot use nil as syscall to block")
 	}
@@ -151,17 +152,23 @@ func matchCall(filter *libseccomp.ScmpFilter, call *configs.Syscall) error {
 		return errors.New("empty string is not a valid syscall")
 	}
 
-	// If we can't resolve the syscall, assume it's not supported on this kernel
-	// Ignore it, don't error out
-	callNum, err := libseccomp.GetSyscallFromName(call.Name)
+	// Convert the call's action to the libseccomp equivalent
+	callAct, err := getAction(call.Action, call.ErrnoRet)
 	if err != nil {
+		return fmt.Errorf("action in seccomp profile is invalid: %w", err)
+	}
+	if callAct == defAct {
+		// This rule is redundant, silently skip it
+		// to avoid error from AddRule.
 		return nil
 	}
 
-	// Convert the call's action to the libseccomp equivalent
-	callAct, err := getAction(call.Action, call.ErrnoRet)
+	// If we can't resolve the syscall, assume it is not supported
+	// by this kernel. Warn about it, don't error out.
+	callNum, err := libseccomp.GetSyscallFromName(call.Name)
 	if err != nil {
-		return fmt.Errorf("action in seccomp profile is invalid: %w", err)
+		logrus.Debugf("unknown seccomp syscall %q ignored", call.Name)
+		return nil
 	}
 
 	// Unconditional match - just add the rule

tests/integration/start_hello.bats

@@ -76,3 +76,15 @@ function teardown() {
 	runc run test_hello
 	[ "$status" -eq 0 ]
 }
+
+@test "runc run [redundant seccomp rules]" {
+	update_config '	  .linux.seccomp = {
+				"defaultAction": "SCMP_ACT_ALLOW",
+				"syscalls": [{
+					"names": ["bdflush"],
+					"action": "SCMP_ACT_ALLOW",
+				}]
+			    }'
+	runc run test_hello
+	[ "$status" -eq 0 ]
+}