Add ExportBPFMem

Also, add a test for ExportBPF and ExportBPFMem.

Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>

seccomp.go

@@ -27,6 +27,9 @@ import (
 int seccomp_precompute(scmp_filter_ctx ctx) {
 	return -EOPNOTSUPP;
 }
+int seccomp_export_bpf_mem(const scmp_filter_ctx ctx, void *buf, size_t *len)  {
+	return -EOPNOTSUPP;
+}
 #endif
 */
 import "C"
@@ -1242,6 +1245,30 @@ func (f *ScmpFilter) ExportBPF(file *os.File) error {
 	return nil
 }
 
+// ExportBPFMem is similar to [ExportBPF], except the data is written into
+// a memory and returned as []byte.
+func (f *ScmpFilter) ExportBPFMem() ([]byte, error) {
+	f.lock.Lock()
+	defer f.lock.Unlock()
+
+	if !f.valid {
+		return nil, errBadFilter
+	}
+
+	var len C.size_t
+	// Get the size required.
+	if retCode := C.seccomp_export_bpf_mem(f.filterCtx, unsafe.Pointer(nil), &len); retCode < 0 {
+		return nil, errRc(retCode)
+	}
+	// Get the data.
+	buf := make([]byte, int(len))
+	if retCode := C.seccomp_export_bpf_mem(f.filterCtx, unsafe.Pointer(&buf[0]), &len); retCode < 0 {
+		return nil, errRc(retCode)
+	}
+
+	return buf, nil
+}
+
 // Userspace Notification API
 
 // GetNotifFd returns the userspace notification file descriptor associated with the given

seccomp_test.go

@@ -3,8 +3,10 @@
 package seccomp
 
 import (
+	"bytes"
 	"errors"
 	"fmt"
+	"io"
 	"os"
 	"os/exec"
 	"strings"
@@ -773,6 +775,64 @@ func subprocessCreateActKillProcessFilter(t *testing.T) {
 	}
 }
 
+func TestExportBPF(t *testing.T) {
+	execInSubprocess(t, subprocessExportBPF)
+}
+
+func subprocessExportBPF(t *testing.T) {
+	filter, err := NewFilter(ActAllow)
+	if err != nil {
+		t.Fatalf("Error creating filter: %s", err)
+	}
+	defer filter.Release()
+
+	call, err := GetSyscallFromName("getpid")
+	if err != nil {
+		t.Fatalf("Error getting syscall number of getpid: %s", err)
+	}
+
+	err = filter.AddRule(call, ActErrno.SetReturnCode(42))
+	if err != nil {
+		t.Fatalf("Error adding rule: %s", err)
+	}
+
+	file, err := os.Create(t.TempDir() + "/bpf")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer file.Close()
+
+	err = filter.ExportBPF(file)
+	if err != nil {
+		t.Fatalf("ExportBPF: %v", err)
+	}
+
+	if _, err := file.Seek(0, io.SeekStart); err != nil {
+		t.Fatal(err)
+	}
+	contents, err := io.ReadAll(file)
+	if err != nil {
+		t.Fatal(err)
+	}
+	t.Logf("ExportBPF: size %d", len(contents))
+
+	expErr := error(nil)
+	// ExportBPFMem needs seccomp 2.6.0.
+	if checkAPI(t.Name(), 0, 2, 6, 0) != nil {
+		expErr = syscall.EOPNOTSUPP
+	}
+	contentsMem, err := filter.ExportBPFMem()
+	if err != expErr {
+		t.Errorf("ExportBPFMem: want %v, got %v", expErr, err)
+	}
+	if err == nil {
+		t.Logf("ExportBPFMem: size %d", len(contents))
+		if !bytes.Equal(contents, contentsMem) {
+			t.Errorf("Got different data from ExportBPF and ExportBPFMem (%v != %v)", contents, contentsMem)
+		}
+	}
+}
+
 //
 // Seccomp notification tests
 //