sandbox/seccomp: resolve rules natively

This enables loading syscall filter policies from external cross-platform config files.

This also removes a significant amount of C code.

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

1 files changed, 183 insertions, 0 deletions

diff --git a/sandbox/seccomp/libseccomp.go b/sandbox/seccomp/libseccomp.go
new file mode 100644
index 00000000..58ae8599
--- /dev/null
+++ b/sandbox/seccomp/libseccomp.go
@@ -0,0 +1,183 @@
+package seccomp
+
+/*
+#cgo linux pkg-config: --static libseccomp
+
+#include <libseccomp-helper.h>
+*/
+import "C"
+import (
+	"errors"
+	"fmt"
+	"runtime"
+	"syscall"
+	"unsafe"
+)
+
+var (
+	ErrInvalidRules = errors.New("invalid native rules slice")
+)
+
+// 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))
+}
+
+// A NativeRule specifies an arch-specific action taken by seccomp under certain conditions.
+type NativeRule struct {
+	// Syscall is the arch-dependent syscall number to act against.
+	Syscall C.int
+	// Errno is the errno value to return when the condition is satisfied.
+	Errno C.int
+	// Arg is the optional struct scmp_arg_cmp passed to libseccomp.
+	Arg *ScmpArgCmp
+}
+
+type PrepareFlag = C.hakurei_prepare_flag
+
+const (
+	// AllowMultiarch allows multiarch/emulation.
+	AllowMultiarch PrepareFlag = C.HAKUREI_PREPARE_MULTIARCH
+	// AllowCAN allows AF_CAN.
+	AllowCAN PrepareFlag = C.HAKUREI_PREPARE_CAN
+	// AllowBluetooth allows AF_BLUETOOTH.
+	AllowBluetooth PrepareFlag = C.HAKUREI_PREPARE_BLUETOOTH
+)
+
+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",
+}
+
+// Prepare streams filter contents to fd, or installs it to the current process if fd < 0.
+func Prepare(fd int, rules []NativeRule, flags PrepareFlag) error {
+	if len(rules) == 0 {
+		return ErrInvalidRules
+	}
+
+	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
+	}
+
+	var ret C.int
+
+	rulesPinner := new(runtime.Pinner)
+	for i := range rules {
+		rule := &rules[i]
+		rulesPinner.Pin(rule)
+		if rule.Arg != nil {
+			rulesPinner.Pin(rule.Arg)
+		}
+	}
+	res, err := C.hakurei_prepare_filter(
+		&ret, C.int(fd),
+		arch, multiarch,
+		(*C.struct_hakurei_syscall_rule)(unsafe.Pointer(&rules[0])),
+		C.size_t(len(rules)),
+		flags,
+	)
+	rulesPinner.Unpin()
+
+	if prefix := resPrefix[res]; prefix != "" {
+		return &LibraryError{
+			prefix,
+			-syscall.Errno(ret),
+			err,
+		}
+	}
+	return err
+}
+
+// ScmpCompare is the equivalent of scmp_compare;
+// Comparison operators
+type ScmpCompare = C.enum_scmp_compare
+
+const (
+	_SCMP_CMP_MIN = C._SCMP_CMP_MIN
+
+	// not equal
+	SCMP_CMP_NE = C.SCMP_CMP_NE
+	// less than
+	SCMP_CMP_LT = C.SCMP_CMP_LT
+	// less than or equal
+	SCMP_CMP_LE = C.SCMP_CMP_LE
+	// equal
+	SCMP_CMP_EQ = C.SCMP_CMP_EQ
+	// greater than or equal
+	SCMP_CMP_GE = C.SCMP_CMP_GE
+	// greater than
+	SCMP_CMP_GT = C.SCMP_CMP_GT
+	// masked equality
+	SCMP_CMP_MASKED_EQ = C.SCMP_CMP_MASKED_EQ
+
+	_SCMP_CMP_MAX = C._SCMP_CMP_MAX
+)
+
+// ScmpDatum is the equivalent of scmp_datum_t;
+// Argument datum
+type ScmpDatum uint64
+
+// ScmpArgCmp is the equivalent of struct scmp_arg_cmp;
+// Argument / Value comparison definition
+type ScmpArgCmp struct {
+	// argument number, starting at 0
+	arg C.uint
+	// the comparison op, e.g. SCMP_CMP_*
+	op ScmpCompare
+
+	datum_a, datum_b ScmpDatum
+}
+
+// only used for testing
+func syscallResolveName(s string) (trap int) {
+	v := C.CString(s)
+	trap = int(C.seccomp_syscall_resolve_name(v))
+	C.free(unsafe.Pointer(v))
+
+	return
+}