seccomp: move out of helper

Signed-off-by: Ophestra <cat@gensokyo.uk>

seccomp/seccomp.go

@@ -0,0 +1,123 @@
+package seccomp
+
+/*
+#cgo linux pkg-config: --static libseccomp
+
+#include "seccomp-build.h"
+*/
+import "C"
+import (
+	"errors"
+	"fmt"
+	"runtime"
+	"syscall"
+)
+
+var CPrintln func(v ...any)
+
+// LibraryError represents a libseccomp error.
+type LibraryError struct {
+	Prefix  string
+	Seccomp syscall.Errno
+	Errno   error
+}
+
+func (e *LibraryError) Error() string {
+	if e.Seccomp == 0 {
+		if e.Errno == nil {
+			panic("invalid libseccomp error")
+		}
+		return fmt.Sprintf("%s: %s", e.Prefix, e.Errno)
+	}
+	if e.Errno == nil {
+		return fmt.Sprintf("%s: %s", e.Prefix, e.Seccomp)
+	}
+	return fmt.Sprintf("%s: %s (%s)", e.Prefix, e.Seccomp, e.Errno)
+}
+
+func (e *LibraryError) Is(err error) bool {
+	if e == nil {
+		return err == nil
+	}
+	if ef, ok := err.(*LibraryError); ok {
+		return *e == *ef
+	}
+	return (e.Seccomp != 0 && errors.Is(err, e.Seccomp)) ||
+		(e.Errno != nil && errors.Is(err, e.Errno))
+}
+
+var resPrefix = [...]string{
+	0: "",
+	1: "seccomp_init failed",
+	2: "seccomp_arch_add failed",
+	3: "seccomp_arch_add failed (multiarch)",
+	4: "internal libseccomp failure",
+	5: "seccomp_rule_add failed",
+	6: "seccomp_export_bpf failed",
+	7: "seccomp_load failed",
+}
+
+type SyscallOpts = C.f_syscall_opts
+
+const (
+	flagVerbose SyscallOpts = C.F_VERBOSE
+	// FlagExt are project-specific extensions.
+	FlagExt SyscallOpts = C.F_EXT
+	// FlagDenyNS denies namespace setup syscalls.
+	FlagDenyNS SyscallOpts = C.F_DENY_NS
+	// FlagDenyTTY denies faking input.
+	FlagDenyTTY SyscallOpts = C.F_DENY_TTY
+	// FlagDenyDevel denies development-related syscalls.
+	FlagDenyDevel SyscallOpts = C.F_DENY_DEVEL
+	// FlagMultiarch allows multiarch/emulation.
+	FlagMultiarch SyscallOpts = C.F_MULTIARCH
+	// FlagLinux32 sets PER_LINUX32.
+	FlagLinux32 SyscallOpts = C.F_LINUX32
+	// FlagCan allows AF_CAN.
+	FlagCan SyscallOpts = C.F_CAN
+	// FlagBluetooth allows AF_BLUETOOTH.
+	FlagBluetooth SyscallOpts = C.F_BLUETOOTH
+)
+
+func buildFilter(fd int, opts SyscallOpts) error {
+	var (
+		arch      C.uint32_t = 0
+		multiarch C.uint32_t = 0
+	)
+	switch runtime.GOARCH {
+	case "386":
+		arch = C.SCMP_ARCH_X86
+	case "amd64":
+		arch = C.SCMP_ARCH_X86_64
+		multiarch = C.SCMP_ARCH_X86
+	case "arm":
+		arch = C.SCMP_ARCH_ARM
+	case "arm64":
+		arch = C.SCMP_ARCH_AARCH64
+		multiarch = C.SCMP_ARCH_ARM
+	}
+
+	// this removes repeated transitions between C and Go execution
+	// when producing log output via F_println and CPrintln is nil
+	if CPrintln != nil {
+		opts |= flagVerbose
+	}
+
+	var ret C.int
+	res, err := C.f_build_filter(&ret, C.int(fd), arch, multiarch, opts)
+	if prefix := resPrefix[res]; prefix != "" {
+		return &LibraryError{
+			prefix,
+			-syscall.Errno(ret),
+			err,
+		}
+	}
+	return err
+}
+
+//export F_println
+func F_println(v *C.char) {
+	if CPrintln != nil {
+		CPrintln(C.GoString(v))
+	}
+}